LIBRARY OF 1685-1056 AN INTRODUCTION TO ENTOMOLOGY AN INTRODUCTION TO ENTOMOLOGY BY JOHN HENRY COMSTOCK PROFESSOR OF ENTOMOLOGY AND GENERAL INVERTEBRATE ZOOLOGY, EMERITUS, IN CORNELL UNIVERSITY FIRST COMPLETE EDITION THIRD EDITION OF PART I ITHACA, N. Y. THE COMSTOCK PUBLISHING CO. 1920 COPYRIGHT 1920 BY THE COMSTOCK PUBLISHING CO. COPYRIGHT 1924 BY J. H. COMSTOCK PRESS OF W. F. HUMPHREY. GENEVA. N. Y. PRINTED IN U. S. A. TO MY OLD STUDENTS "WHOSE YOUTHFUL ENTHUSIASM WAS A CONSTANT INSPIRATION DURING THE LONG PERIOD OF MY SERVICE AS A TEACHER THIS EFFORT TO CONTINUE TO AID THEM IS AFFECTIONATELY INSCRIBED PREFACE IT IS now nearly thirty years since "A Manual for the Study of Insects," in the preparation of which I was aided by Mrs. Corn- stock, was published. The great advances in the science of ento- mology during this period have made a revision of that work desirable- In the revision of the "Manual" so many changes and additions have been foimd necessary that the result is a book differing greatly from the original work; for this reason, it is published imder a different title. The title selected is that of an earlier work, an "Introduction to Entomology" published in 1888 and long out of print. Part I of the present volume was published separately in 19 19, in order that it might be available for the use of classes in insect mor- phology and also that an opportunity might be offered for the sugges- tion of desirable changes to be made before the incorporation of it in the completed work. Such suggestions have been received, with the result that some very important changes have been made in the text. In the preparation of this work I have received much help from my colleagues in the entomological department of Cornell University, for which I wish to make grateful acknowledgment, and especially to Dr. J. G. Needham for aid in the study of win-g-venation, to Dr. O. A. Johannsen for help in the preparation of the chapter on tfee Diptera, to Dr. W. T. M. Forbes for help in the preparation of the chapter on the Lepidoptera, to Dr. J. C. Bradley for help in the prep- aration of the chapter on the H\TTLenoptera, and to Dr. J. T. Llovd for the use of his figures of the cases of caddice worms. From the published works of Professors Herrick, Crosby and Slingerland, Crosby and Leonard, Sanderson, and Matheson I have gleaned much information; references to these and to the more im- portant of the other sources from which material has been drawn are indicated in the text and in the bibliography at the end of the volimie. References to the bibliography are made in the text by citing the name of the author and the year in which the paper quoted was published. The wood cuts used in the text were engraved from nature by Mrs. Anna B. Comstock for our joint work, "A Manual for the Study of Insects." The other original figures and the copies of published figures were drawn by Miss Anna C. Stryke, Miss Ellen Edmonsor, Miss Mary McKeel, Mr. Albert Force, Mrs. Louise Nash, and Miss E. L. Keyes. I am deeply indebted to each of these artists for the painstaking care shown in their work. As an aid to the pronunciation of the technical terms used and of the Latin names of insects, the accented sjdlable is marked with a sign indicating the quahty of the vowel according to the English sj-s- tem of pronouncing Latin. Two objects have been kept constantly in mind in the preparation of this book: first, to aid the student in laying a firm fotmdation for his entomological studies; and second, to make available, so far as possible in the limited space of a handbook, a knowledge of the varied phenomena of the insect world. It is hoped that those who use this book will find delight in acquiring a more intimate acquaintance with these phenomena. John Henry Comstock Entomological Department Cornell University August ig24 TABLE OF CONTENTS PART I. THE STRUCTURE AND METAMORPHOSIS OF INSECTS CHAPTER I Pages The Characteristics of Insects and Their Near Relatives i Phylum Arthropoda i List of the classes of the Arthropoda 2 Table of the classes of the Arthropoda 3 Class Onychophora 4 Class Crustacea 6 • Class Palaeostracha 8 Class Arachnida 9 Class Pycnogonida 10 Class Tardigrada 12 Class Pentastomida 14 Class Diplopoda 15 Class Pauropoda 14 Class Chilopoda 28 Class Symphyla 23 Class Myrientomata 26 Class Hexapoda 20 CHAPTER II The External Anatomy of Insects 29 I. the structure of THE body- WALL a. The three layers of the body- wall 29 The hypodermis 29 The trichogens 30 The cuticula 30 Chitin 30 Chitinized and non-chitinized cuticula 30 The epidermis and the dermis 31 The basement membrane 31 h. The external apophyses of the cuticula 31 The cuticular nodules 3^ The fixed hairs ^ 3^ The spines 32 c. The appendages of the cuticula 32 The spurs 32 TABLE OF CONTENTS The setae ,2 The taxonomic value of setae ,^ A classification of setae ■,■, (1) The clothing hairs ^3 (2) The glandular hairs -jj (3) The sense-hairs jj The segmentation of the body ,4 The body-segments, somites or metameres ^4 The transverse conjunctiva 34 The segmentation of the appendages 34 The divisions of a body-segment 34 The tergum, the pleura, and the sternum , 34 The lateral conjunctivae 35 The sclerites 35 The sutures 35 The median sutures 35 The pilif erous tubercles of larvae 35 The homologizing of sclerites 35 The regions of the body 36 2. THE HEAD The corneas of the eyes 36 The corneas of the compound eyes 36 The corneas of the ocelli 37 The areas of the surface of the head 37 The front 37 The clypeus ^',8 The labrum 38 The epicranium 38 The vertex 39 The occiput 39 The genae 39 The postgenae 39 The gula 39 The ocular sclerites 39 The antennal sclerites 39 The trochantin of the mandible 40 The maxillary pleurites 40 The cervical sclerites 40 The appendages of the head 40 The antennae 40 The mouth-parts 42 The labrum 42 The mandibles 42 The maxillalae 42 The maxillae : ; 42 The labium or second maxillae 45 TABLE OF CONTENTS xi The epipharynx 46 The hypopharynx 47 d. The segments of the head 47 3. THE THORAX a. The segments of the thorax 48 The prothorax, mesothorax, and metathorax 48 The alitrunk 49 The propodeum or the median segment 49 h. The sclerites of a thoracic segment 49 The sclerites of a tergum 49 The notum 49 The postnotum or the postscutellum 50 The divisions of the notum 50 The patagia 50 The parapsides 5^ The sclerites of the pleura 51 The episternum 51 The epimerum 5^ The preepisternum 51 The paraptera 5^ The spiracles 52 The peritremes 52 The acetabula 52 The sclerites of a sternum 52 c. The articular sclerites of the appendages 53 The articular sclerites of the legs 53 The trochantin 53 The antecoxal piece 54 The second antecoxal piece 54 The articular sclerites of the wings 54 The tegula 54 The axillaries 54 d. The appendages of the thorax 55 The legs 56 The coxa 56 The styli 56 The trochanter 57 The femur 57 The tibia 57 The tarsus 57 The wings 58 The different types of wings 59 The margins of wings 60 The angles of wings 60 The axillary cord 60 The axillary membrane 60 The alula 60 The axillary excision 61 TABLE OF CONTENTS The posterior lobe 6i The methods of uniting the two wings of each side 6i The hamuli 6i The frenulum and the frenulum hook 6i The jugum 6i Thefibula 62 The hypothetical type of the primitive wing- venation 62 Longitudinal veins and cross- veins 64 The principal wing- veins .- 64 The chief branches of the wing- veins 64 The veins of the anal area 65 The reduction of the number of the wing- veins 65 Serial veins 67 The increase of the number of the wing- veins 68 The accessory veins 68 The intercalary veins 69 The adventitious veins 70 The anastomosis of veins 70 The named cross-veins 71 The arculus 72 Theterminologyof the cells of the wing 72 The corrugations of the wings 73 Convex and concave veins 73 The furrows of the wing 73 The bullae 74 The ambient vein 74 The humeral veins 74 The pterostigma or stigma 74 The epiplurae 74 The discal cell and the discal vein 74 The anal area and the preanal area of the wing 75 4. THE ABDOMEN 75 a. The segments of the abdomen 75 b. The appendages of the abdomen 7^ The styli or vestigial legs of certain Thysanura 76 The collophore of the Collembola 76 The spring of the Collembola 76 ThegenitaUa 7^ The cerci 77 The median caudal filament 7^ The prolegs of larvae 7^ 5. THE MUSIC AND THE MUSICAL ORGANS OF INSECTS 78 a. Sounds produced by striking objects outside of the body 79 b. The music of flight 80 TABLE OF CONTENTS . xiii c. Stridulating organs of the rasping type 8i The stridulating organs of the Locustidae 82 The stridulating organs of the Gryllidae and the Tettigoniidie 83 Rasping organs of other than orthopterous insects ; . 87 d. The musical organs of a cicada 89 e. The spiracular musical organs 91 /. The acute buzzing of flies and bees 91 g. Musical notation of the songs of insects 92 h. Insect choruses ^3 CHAPTER III The Internal Anatomy of Insects 94 I. THE HYPODERMAL STRUCTURES. The internal skeleton Sources of the internal skeleton . 95 Chitinized tendons 95 Invaginations ofthe body- wall or apodemes 95 The tentorium 06 The posterior arms of the tentorium 96 The anterior arms of the tentorium 97 The dorsal arms of the tentorium 97 The frontal plate of the tentorium 97 The endothorax 97 The pragmas 97 The lateral apodemes 98 The furcae 98 b. The hypodermal glands 98 The molting-fluid glands 99 Glands connected with setse 99 Venomous setas and spines 100 Androconia 100 The specific scent-glands of females 100 Tenent hairs 1 00 The osmeteria 1 01 Glands opening on the surface of the body 102 Wax-glands 102 Froth-glands of spittle insects 102 Stink-glands 102 The cephalic silk-glands 103 The salivary glands ' 104 2. THE MUSCLES. 104 3. THE ALIMENTARY CANAL AND ITS APPENDAGES I07 The more general features 107 The principal divisions 108 Imperforate intestines in the larvae of certain insects 1 08 TABLE OF CONTENTS b. The fore-intestine I09 The layers of the fore-intestine 109 The intima log The epithelium 109 The basement membrane 109 The longitudinal muscles 109 The cirailar muscles 109 The peritoneal membrane 109 The regions of the fore-intestine 109 The pharynx 109 The oesophagus i to The crop 110 The proventriculus no The oesophageal valve 1 1 1 c. The mid-intestine in The layers of the mid-intestine in The epithelium 112 Theperitrophic membrane 112 d. The hind-intestine 112 The layers of the hind-intestine 112 The regions of the hind-intestine lip, The Malpighian vessels 113 The Malpighian vessels as silk-glands 113 The caecum 113 The anus '. 113 4. THE RESPIRATORY SYSTEM 1 13 a. The open or holopneustic type of respiratory organs 114 1. The spiracles 114 The position of the spiracles 114 The number of spiracles 114 Terms indicating the distribution of the spiracles 115 The structure of spiracles 116 The closing apparatus of the tracheae 116 2. The trachecB 116 The structure of the tracheae 117 J. The tracheoles 118 4. The air-sacs 118 5. Modifications of the open type of respiratory organs 119 b. The closed or apneustic type of respiratory organs 119 I. The Tracheal gills 119 2. Respiration of parasites 120 J. The blood-gills 120 TABLE OF CONTENTS xv 5. THE CIRCULATORY SYSTEM 121 The general features of the circulatory system 121 The heart 121 The pulsations of the heart 122 The aorta 122 The circulation of the blood 122 Accessory circulatory organs 122 6. THE BLOOD 122 7. THE ADIPOSE TISSUE I23 8. THE NERVOUS SYSTEM I23 a. The central nervous system 123 b. The oesophageal sympathetic nervous system 125 c. The ventral sympathetic nervous system 127 d. The peripheral sensory nervous system 128 9. GENERALIZATIONS REGARDING THE SENSE-ORGANS OF INSECTS. . 129 A classification of the sense-organs 129 The caticular part of the sense-organs 130 10. THE ORGANS OF TOUCH I3I II. THE ORGANS OF TASTE AND SMELL I32 12. THE ORGANS OF SIGHT I34 o. The general features 134 The two types of eyes 134 The distinction between ocelli and compound eyes 134 The absence of compound eyes in most of the Apterygota 135 The absence of compound eyes in larvae 135 b. The ocelli 135 The primary ocelli 135 The adaptive ocelli 136 The structure of a visual cell 137 The structure of a primary ocellus 137 Ocelli of Ephemerida 139 c. The compound eyes 139 The physiology of compound eyes 141 The theory of mosaic vision 141 Day-eyes 142- Night-eyes 143- Eyes with double function I43. Divided eyes 144- The tapetum 144- TABLE OF CONTENTS 13. THE Or^CANS 01" IIEARI.NG I_|^- a. The general features j ,- The tympana i , - The chordotonal organs i ,- The scolopale and the scolopophore j ,5 The integumental and the subintegumental scolopophores 146 The structure of a scolopophore j_,5 The structure of a scolopale i , y The simpler forms of chordotonal organs 14-- The chordotonal ligament i ly i. The chordotonal organs of larvs , 148 c. The chordotonal organs of the Looustidas 148 d. The chordotonal organs of the Tettigoniidee and of the Gryllidae. . 149 The trachea of the leg 1 50 The spaces of the leg 151 The supra-tympanal or subgenual organ 151 The intermediate organ 1 52 Siebold's organ or the crista acustica 1 52 e. Johnston's organ 152 14. SENSE-OKGANS OF UNKNOWN FUNCTIONS The sense-domes or the olfactory pores 154 15. THE REPRODUCTIVE ORGANS The general features 156 Secondary sexual characters 157 The reproductive organs of the female 157 The general features of the ovary 157 The wall of an ovarian tube 158 The zones of an ovarian tube 158 The contents of an ovarian tube 158 The egg-follicles 158 The functions of the follicular epithelium 1 59 The ligament of the ovary 1 59 The oviduct 159 The egg-calyx 1 59 The vagina 1 59 The spermatheca , . 1 59 The bursa copulatrix i59 The coUeterial glands 160 The reproductive organs of the male 160 The general features of the testes 160 The structure of a testicular follicle 161 The spermatophores 162 Other structures 162 TABLE OF CONTENTS xvii l6. THE SUSPENSORIA OF THE VISCERA The dorsal diaphragm 162 The ventral diaphragm 163 The thread-like suspensoria of the viscera 163 17. SUPPLEMENTARY DEFINITIONS The oenocytes 163 The pericardial cells 164 The phagocytic organs 164 The light-organs 165 CHAPTER IV The Metamorphosis of Insects 166 i. the external characteristics of the metamorphosis of insects c. The egg 166 The shape of the egg 167 The sculpture of the shell 167 The microphyle 167 The number of eggs produced by insects 168 Modes of laying eggs 168 Duration of the egg-state 170 b. The hatching of young insects 171 The hatching spines 171 c. The molting of insects 171 General features of the molting of insects 171 The molting fluid 172 The number of postembryonic molts 172 Stadia 172 Instars 172 Head measurements of larvae 173 The reproduction of lost limbs 173 d. Development without metamorphosis 174 The Ametabola 174 e. Gradual metamorphosis 175 The Paurometabola 176 The term nymph 176 Deviations fi om the usual type 176 The Saltitorial Orthoptera 177 The Cicadas • 177 The Coccidge , 177 The Aleyrodidae 177 The Aphididae 177 The Thysanoptera 177 f. Incomplete metamorphosis 178 The Hemimetabola 179 The term naiad 179 Deviations from the usual type 1 80 The Odonata 180 The Ephemerida 180 i TABLE OF CONTENTS g. Complete metamorphosis i8o The Holometabola l8o The term larva i8o Theadapth'e characteristics of larvae iSi The different types of larvae 183 The prepupa 185 The pupa 186 The chrysalis 186 Active pupae 187 The cremaster 187 The cocoon 188 Modes of escape from the cocoon , . 188 The puparium 190 Modes of escape from the puparium 190 The different types of pups 190 The imago 191 h. Hyper metamorphosis 191 i. Viviparous insects 191 \^iviparity with parthenogenetic reproduction 192 Viviparity with sexual reproduction 193 j. Neoteinia I94 2. THE DEVELOPMENT OF APPENDAGES I94 a. The development of wings I95 Thedevelopmentof the wings of nymphs and naiads 195 The development of the wings in insects with a complete meta- morphosis 195 b. The development of legs I97 The development of the legs of nymphs and naiads 198 The development of the legs in insects with a complete meta- morphosis 198 c. The development of antennae I99 d. The development of mouth-parts 200 e. The development of the gential appendages 201 3. the development of the head in the muscid^ 202 4. the transformation of the internal organs 2o4 Bibliography ' 206 Index 213 TABLE OF CONTENTS PART II. THE CLASSIFICATION AND THE LIFE-HISTORIES OF INSECTS Chapter V. — The sub-classes and the orders of the class Hexapoda . 2og Chapter VI. — Order Thysanura 2 20 Chapter VII.— Order Collembola 225 Chapter VIII. — Order Orthoptera 230 Chapter IX. — Order Zoraptera 270 Chapter X. — Order Isoptera 273 Chapter XL — Order Neuroptera 281 Chapter XII. — Order Ephemerida 308 Chapter XIII. — Order Odonata 314 Chapter XIV. — Order Plecoptera 325 Chapter XV. — Order Corrodentia 331 Chapter XVI.— Order Mallophaga 335 Chapter XVII. — Order Embiidina 338 Chapter XVIII. — Order Thysanoptera 341 Chapter XIX. — Order Anoplura 347 Chapter XX. — Order Hemiptera 350 Chapter XXI. — Order Homoptera 394 Chapter XXII. — Order Dermaptera 460 Chapter XXIII. — Order Coleoptera 464 Chapter XXIV. — Order Strepsiptera 546 Chapter XXV. — Order Mecoptera 550 Chapter XXVI. — Order Trichoptera 555- Chapter XXVII. — Order Lepidoptera 571 Chapter XXVIIL— Order Diptera 773 Chapter XXIX. — Order Siphonaptera 877 Chapter XXX. — Order Hymenoptera S84 BibHography 991 PART I THE STRUCTURE AND METAMORPHOSIS OF INSECTS CHAPTER I THE CHARACTERISTICS OF INSECTS AND OF THEIR NEAR RELATIVES Phylum ARTHROPODA The Arthropods If an insect, a scorpion, a centipede, or a lobster be examined, the body will be found to be composed of a series of more or less similar rings or segments joined together; and some of these seg- ments will be found to bear jointed legs (Fig. i ) . All animals possess- ing these characteristics are classed together as the Arthropoda, one of the chief divisions or phyla of the animal kingdom. A similar segmented form of body is found among worms; but these are distinguished from the Arthropoda by the absence of legs. It should be remembered that many animals commonly called worms, as the tomato-worm, the cabbage-worm, and others, are not true 1' ^r^ I worms, but are the larvae of insects (Fig. 2). ■f ^^/ '^^^ angle-worm is the most familiar example of a. true worm. In the case of certain arthropods the dis- tinctive characteristics of the phylum are not evident from a cursory examination. This may be due to a very generalized condi- tion, as perhaps is true of Peripatns; but in Fig. I. — An arthropod, most instances it is due to a secondary modifi- cation of forni, the result of adaptation to Thus the segmentation of the body may be special modes of life. 2. — A larva of an insect. (1) AN INTRODUCTION TO ENTOMOLOGY % Fig. obscured, as in spiders and in mites (Fig. 3); or the jointed append- ages may be absent, as in the larvae of flies (Fig. 4), of bees, and of many other insects. In all of these cases, however, a careful study of the structure of the animal, or of its complete life-history, or of other animals that are evidently closely allied to it removes any doubt regarding its being an arthropod. \ ^;|' The phylum i^ithropoda is the largest of the phyla of the WT^^ animal kingdom, including many more known species than all the other phyla taken together. This vast assemblage of animals in- cludes forms differing widely in structure, all agreeing, however, in the possession of the essential characteristics of the Arthropoda. Several distinct types of arthropods are recognized; and those of each type are grouped together as a class. The number of distinct classes that should be recog- nized, and the relation of these classes to each other are matters regarding which there are still differences of opinion; we must have much more knowledge than we now possess before we can speak with any degree of certainty regarding them. Each of the classes envmerated below is regarded by all as a distinct group of animals ; but in some cases there may be a question whether the group should be given ^^^^^^^'^• the rank of a distinct class or not. The order in which the classes are discussed in this chapter is indicated in the following list. 3. — A mite, an arthropod in which the segmentation of the body is obscured. The southern cattle-tick, Boophilus anntdatiis. LIST OF THE CLASSES OF THE ARTHROPODA THE MOST PRIMITIVE ARTHROPODS Class Onychophora, page 4 THE AQUATIC SERIES Class Crustacea, page 6 Class Palffiostracha, page 8 AN OFFSHOOT OF THE AQUATIC SERIES, Class Arachnida, page 9 SECONDARILY AERIAL CHARACTERISTICS OF INSECTS AND THEIR RELATIVES 3 IV. DEGENERATE ARTHROPODS OF DOUBTFUL POSITION Class Pychnogonida, page lo Class Tardigrada, page 1 2 Class Pentastomida, page 14 V, THE PRIMARILY AERIAL SERIES Class Onychophora (See above) Class Diplopoda, page 1 5 Class Pauropoda, page 18 Class Chilopoda, page 20 Class Symphyla, page 23 Class Myrientomata, page 24 Class Hexapoda, page 26 TABLE OF CLASSES OF THE ARTHROPODA A. Worm-like animals, with an unsegmented body, but with many, unjointedlegs Onychophora A A. Body more or less distinctly segmented except in a few degen- erate forms. B. With two pairs of antennse and at least five pairs of legs; respiration aquatic Crustacea BB. Without or apparently without antennae. C. With well-developed aquatic respiratory organs. Pal^ostracha CC. With well-developed aerial respiratory organs or with- out distinct respiratory organs. D. With well-developed aerial respiratory organs. E. Body not resembling that of the Thysanura in form. Arachnida EE. Body resembling that of the Thysanura in form (Family Eosentomidae) Myrientomata DD. Without distinct respiratory organs. E. With distinctly segmented legs. F. Body resembling that of the Thysanura in form, but without antennae, and with three pairs of thoracic legs and three pairs of vestigial abdominal legs (Family Acerentomidas) Myrientomata FF. With four or five pairs of ambulatory legs; abdomen vestigial Pychnogonida EE. Legs not distinctly segmented. F. With four pairs of legs in the adult instar. Tardigrada 4 AN INTRODUCTION TO ENTOMOLOGY FF. Lar\'a with two pairs of legs, adult without legs Pentastomida BBB. With one pair, and only one, of feeler-like antennae. Respiration aerial. C. With more than three pairs of legs, and without wings. D. With two pairs of legs on some of the body-segments. DiPLOPODA DD . With only one pair of legs on each segment of the body. E. Antennae branched Pauropoda EE. Antennse not branched. F. Head without a Y-shaped epicranial suture. Tarsi of legs with a single claw each. Opening of the reproductive organs near the caudal end of the bod}^ Chilopoda FF. Head with a Y-shaped epicranial suture, as in insects. Tarsi of legs with two claws each. Opening of the reproductive organs near the head. Symphyla CC. With only three pairs of legs, and usually with wings in the adult state Hexapoda Class ONYCHOPHORA The fienus Peripatus oj authors The members of this class are air-breathing animals, with a nearly cylindrical, unsegmented body, which is furnished with many pairs of unjointed legs. The reproductive organs open near the hind end of the body. The class Onychophora occupies the position of a CDnnecting link between the Arthropoda and the phylum Annulata or worms ; and is therefore of the highest interest to students of systematic zoolog}'. All known members of this class have been included until recently in a single genus Peripatus; but now the fifty or more known species are distributed among nearly a dozen genera. The body (Fig. 5) is nearly cylindrical, cat- fff^^T^^^^^^lS^^'^^Ty^:^ in ^- € .„-J2'^'^^''^^ form, but is un- ^ % ^ Y segmented ex- ternally. It is r'ig- 5-—Peripatoides novcB-zealandica. furnished With many pairs cf legs, the number of which varies in different species. The legs have a ringed appearance, but are not distinctly jointed. CHARACTERISTICS OF INSECTS AND THEIR RELATIVES 5 The head bears a pair of ringed antennae (Fig. 6) ; behind thes3 on the sides of the head, there is a pair of short appendages teTnsd oral papillse. The mouth opening is surrounded by a row of lobes which constitute the Hps, and between these in the anterior part of the mouth-cavity there is an obtuse pro- jection, which bears a row of chitinous points. Within the mouth cavity there are two pairs of hooked plates, which have been termed the mandibles, the two plates of each side being regarded as a single mandible. Although the body is unsegmented externally, internally there are evi- dences of a metameric arrangement of parts. The ventral nerve cords, which at first sight appear to be without ganglia, are enlarged opposite each pair of legs, and these enlargments are regarded as rudimentary ganglia, pig. 6.— Ventral view of the head We can, therefore speak of each sec- and first pair of legs of Peri- ,. p 1 1 1- , paloides; a, antenna; o, oral tion of a body correspondmg to a papilla. pair of appendages as a segment. The metameric condition is farther indicated by the fact that most of these segments contain each a pair of nephridia; each nephridium opening at the base of a leg. The respiratory organs are short tracheae, which are rareiy b"anched, and in which the tasnidia appear to be rudimentary.* In some species, the spiracles are distributed irregularly; in others, they are in longitudinal rows. The sexes are distinct. The reproductive organs open near the hind end of the body, either between the last or the next to the last pair of legs. The various species are found in damp situations, under the bark of rotten stumps, under stones or other objects on the ground. They have been found in Africa, in Australia, in South America, and in the West Indies. Their relationship to the Arthropoda is shown by the presence of paired appendages, one, or perhaps two, pairs of which are modified as jaws; the presence of tracheae which are found nowhere else except *IL is quite possible that the "short tracheae" described by writers on the structure of these animals are tracheoles. See the account of the distinguishing features of trache;E and tracheoles m Chapter III. AN INTRODUCTION TO ENTOMOLOGY ■in the Arthropoda; the presence of paired ostia in the wall of the heart; and the presence of a vascular body cavity and pericardium. They resemble the Annulata in having a pair of nephridia in most of the segments of the body corresponding to the pairs of legs, and in having ciha in the generative tracts. An extended monograph of the Onychophora v/as published by Bouvier {'o$-o-j). Class CRUSTACEA The Crustaceans The members of this class are aquatic arthropods, which breathe by true gills. They have two pairs of antennoe and at least five pairs of legs. The position of the openings of the reproductive organs varies greatly; but as a rule they are situated far forward. The most familiar examples of the Crustacea are the cray- fishes, the lobsters, the shrimps, and the crabs. Cray-fishes (Fig. 7) abound in our brooks, and are often improperly called crabs. The lobsters, the shrimps, and the true crabs live in salt water. Excepting Lhnulus, the sole hving representative of the class described next, the Crus- tacea are distinguished from all other arthro- pods by their mode of respiration, being the only ones that breathe by true gills. Many in- sects live in water and are furnished with gill- like organs; but these are either tracheal gills or blood-gills, organs which differ essentially in struc- ^. ^ ■,.,. ^ Fig. 8. — Minute crustaceans ture from true gills, as Cypridopsis, c, Cyclops. Fig. 7. — A cray-fish. Daphnia; CHARACTERISTICS OF INSECTS AND THEIR RELATIVES V described later. The Crustacea also differ from other Arthropoda in having two pairs of antennae. Rudiments of two pairs of antennge have been observed in the embryos of many other arthropods ; but in these cases one or the other of the two pairs of antennae fail to develop. The examples of crustaceans named above are the more con- spicuous members of the class; but many other smaller forms abound both in the sea and in fresh water. Some of the more minute fresh- water forms are almost sure to occur in any fresh-water aquarium. In Figure 8 are repre- sented three of these greatly enlarged. The minute crustaceans form an important element in the food of fishes. Some crustaceans live in damp places on land, and are often found by collectors of insects; those most often ob- served are the sow-bugs (Oniscoida), which fre- quently occur about water-soaked wood. Figure 9 represents one of these. As there are several, most excellent text books devoted to the Crustacea, it is unnecessary to discuss farther this class in this place. Fig. 9. — A sow-bug, Cylisticus convexus (From Richardson after Sars). AN INTRODUCTION TO ENTOMOLOGY Class PALiEOSTRACHA The King-crabs or Horseshoe-crabs The members of this class are aquatic arthropods, which resemble the Crustacea in that they breathe by true gills, but in other respects are closely allied to the Arachnida. They are apparently without antenncB, the appendages hom- ologous to antenncB being not feeler-like. The reproductive organs open near the base of the abdomen. The class Palseostracha is composed almost entirely of extinct f orm.s, there being living representatives of only a single order, the Xiphosura, and this order is nearly extinct; for of it there re- mains only the genus Ltmrdus, represented by only five known species. I The members of this genus are known as king- crabs or horseshoe-crabs ; the former name is sug- gested by the great size of some of the species; the latter, by shape of the cephalothorax (Fig. lo). The king-crabs are marine; they are found on our Atlantic Coast from Maine to Florida, in the West Indies, and on the eastern shores of Asia. They are found in from two to six fathoms of water on sandy and muddy shores ; they burrow a short distance in the sand or mud and feed chiefly on worms. The single species of our coast is Lmtulus polyphemiis. Fig. 10. — A horseshoe Packard) . cralj, Limulus (After the CHARACTERISTICS OF INSECTS AND THEIR RELATIVES 9 Class ARACHNIDA Scorpions, Harvestmen, Spiders, Mites, and others The members of this class are air-breathing arthropods, in which the head and thorax are usually grown together, forming a cephalothorax, which have four pairs of legs, and which apparently have no antenncB. The reproductive organs open near the base of the abdomen. Fig. II b Fig. II. — Arachnids: a, a scorpion; h, a harvestman. c, a spider; d, an itch-mite, from below and from above. The Arachnida abound wherever insects occur, and are often mistaken for insects. But they can be easily distinguished by the characters given above, even in those cases where an exception occurs to some one of them. The more important of the exceptions are the following : in one order, the Solpugida, the head is distinct from the 10 AN INTRODUCTION TO ENTOMOLOGY thorax ; as a rule the young of mites have only six legs, but a fourth pair is added during growth ; and in the gall-mites there are only four legs. The Arachnida are air-breathing; but it is believed that they have been evc'lved from aquatic progenitors. Two forms of respira- tory organs exist in this class : first, book-lungs ; and second, tubular trachea. Some members of it possess only one of these types; but the greater number of spiders possess both. A striking characteristic of the Arachnida, which, however, is also possessed by the Palaeostracha, is the absence of true jaws. In other arthropods one or more pairs of appendages are jaw-like in form and are used exclusively as jaws; but in the Arachnida the prey is crushed either by the modified antennas alone or by these organs and other more or less leg-like appendages. The arachnids suck the blood of their victims by means of a sucking stomach; they crush their prey, but do not masticate it so as to swallow the solid parts. In the Arachnida there exist only simple eyes. The reproductive organs open near the base of the abdomen on the ventral side. In this respect the Arachnida resemble Limulus, the millipedes, and the Crustacea, and differ from the centipedes and insects. Among the more familiar representatives of this class are the scorpions (Fig. ii, a), the harvestmen (Fig. ii, h), the spiders (Fig. II, c), and the mites (Fig. ii, d). As the writer has devoted a separate volume (Comstock, '12) to the Arachnida, it will not be discussed farther in this place. Class PYCNOGONIDA The Pycnogonids The members oj this class are marine arachnid-like arthropods, in which the cephalothorax bears typically seven pairs of jointed appen- dages, but in a few fcrms there are eight pairs, and in some the anterior two or three pairs are absent; and in which the abdomen is reduced to a legless, unsegmented condition. They possess a circulatory system, but no evident respiratory organs. The reproductive organs open through the second segment of the legs; the number of legs bearing these opening varies from one to five pairs. The Pycnogonida or pycnogonids are marine animals, which bear a superficial resemblance to spiders (Fig. 12). Some of them are found under stones, near the low water line, on sea shores; but they CHARACTERISTICS OF INSECTS AND THEIR RELATIVES 11 are more abundant in deep water. Some are found attached to sea- anemones, upon which they probably prey; others are found climbing Fig. 12. — A pycnogonid, Nymphon hispidum: r, chelophore; p, palpus; 0, ovigerous legs; /, /, I, I, ambulatory legs; ab, abdo- men (After Hoeck). over sea-weeds and Hydroids; and sometim.es they are dredged in great numibers from deep water. They possess a suctorial proboscis. In none of the appendages are the basal segments modified into organs for crushing the prey. The cephalothorax comprises almost the entire body ; the abdomen being reduced to a mere vestige, without appendages, and with no external indication of segmentation. But the presence of two pairs of abdominal ganglia indicates that originally the abdomen consisted of more than one segment. There are typically seven pairs of appendages; but a few forms possess eight pairs ; and in some the first two or three pairs are absent. The appendages, when all are present, consist of a pair of chelophores, each of which when well-developed consists of one or two basal seg- ments and a chelate "hand;" the palpi, which are supposed to be tactile, and which have from five to ten joints when well-developed; the ovigerous legs, which are so-called because in the males they are used for holding the mass of eggs beneath the body; and the ambula- tory legs, of which there are usually four pairs, but a few forms possess a fifth pair. The ambulatory legs consist each of eight segments and a terminal claw. The only organs of special sense that have been found in these animals are the eyes. These are absent or at least very poorly 12 AN INTRODUCTION TO ENTOMOLOGY developed in some forms, especially those that are found in very deep water, i. e. below four or five hundred fathoms. When well-developed they are simple, and consist of two pairs, situated on a tubercle, on the head or the first compound segment of the body, the segment that bears the first four pairs of appendages. The reproductive organs open in the second segment of the legs. In some these openings occur only in the last pair of legs ; in others, in all of the ambulatory legs. Very little is known regarding the habits of these animals. The most interesting features that have been observed is perhaps the fact that the males carry the eggs in a mass, held beneath the body by the third pair of appendages, the ovigerous legs, and also carrv^ the young for a time. As to the systematic position of the class Pycnogonida, very little can be said. These animals are doubtless arthropods, and they are commonly placed near the Arachnida. Class TARDIGRADA The Tardigrades cr Bear Animalcules The members oj this class are very minute segmented animals, with four pairs of legs, but without antennce or mouth-appendages, and without special circulatory or respiratory organs; the reproductive organs open into the intestine. The Tardigrada or tardigrades are microscopic animals, measuring from one seventy-fifth to one twenty-fifth of an inch in length. They are somewhat mite-like in appearance; but are very different from mites in structure (Fig. 13 and 14). The head bears neither antennae nor mouth-appendages. The four pairs of legs are short, un jointed, and are distributed along the entire length of the body, the fourth pair being at the cau- dal end. Each leg is termin- ated by claws, which differ in number and form in different genera. The more striking features of the internal structure of Fig, 13. — A tardigrade (After Doyere). ^, ■ ^ ■ ^^ -u c ^ ^ fa V J ^ these animals is the absence of special circulatory and respiratory organs; the presence of a pair of chitinous teeth, either in the oral cavity or a short distance back of CHARACTERISTICS OF INSECTS AND THEIR RELATIVES 13 it ; the presence of Malpighian tubules ; the unpaired condition of the reproductive organs of both sexes ; and the fact that these organs open into the intestine. The central nervous system consists of a brain, a suboesophageal ganglion, and a ventral chain of four ganglia, connected by widely separated connectives. The tardigrades are very abundant, and are very widely dis- tributed. Some live in fresh water, a few are marine, but m^st of them live in damp places, and especially on the roots of moss, gro ,ving in gutters, on roofs or trees, or in ditches. Bvit although they are common, their minute size and retiring habits result in their being rarely seen except by those who are seeking them. Many of them have the power of withstanding desiccation for a long period. This has been demonstrated artificially by placing them on a microscopic slide and allowing the mositure to evaporate slowly. The body shrinks, its skin becomes wrinkled, and finally it assumes the appearance of a grain of sand in which no parts can be distinguished. In this state they can remain, it is said, for years; after which, if water be added, the body swells, assumes its normal form, and after a time, the creatures resume their activities. T-, J. ,1 , ^. .. . Fi.s;. 14.— A tardigrade (After Kegardmg the systematic position of Dovere). this class of animals nothing definite can be stated beyond the fact that they are doubtless arthropods. Their relationship to the other classes of arthropods has been masked by degenerative modifications. They are placed here near the e'.id of the series of classes of arthropods, merely as a matter of convenience, in what may be termed, an appendix to the arthropod series, which includes animals of doubtful relationships. 14 AN INTRODUCTION TO ENTOMOLOGY Class PENTASTOMIDA The Pentastomids or Linguatulids The members of this class are degenerate, worm-like, parasitic arthropods, which in the adult state have no appendages, except two pairs of hooks near the mouth; the larvce have two pairs of short legs. These animals possess neither circulatory nor respiratory organs. The reproductive organs of the male open a short distance behind the mouth; those of the female near the caudal end of the body. The Pentastomida or pentastomids are worm-like creatures, whose form has been greatly modified by their parasitic life. The adults bear little resemblance to any other arthropods. Representatives of three genera are known. These are Lingudtula in which the body is fluke-like in form (Fig. 15) and superficially annulated; Porocephahts, in which the body is cylindrical (Fig. 16) and ringed; and Re ighdrdia, which is devoid of annulations, and with poorly developed hooks and a mouth-armature. The arthropodan nature of these animals is indicated by the form of the larvae, which although greatly degenerate, are less so than the adults, having two pairs of legs (Fig. 17). Fig. 15. — A pentasto- mici, Linguatula tccnioides, female at the time of copula- tion: h, hooks; oe, oesophagus, rs, re- ceplaaila seminis, one of which is still empty; i, intestine; 07', ovary; fa, vagina (From Lang after Leuckart). Fig. 16. — A pentastomid, Porocephalus annulatus; a, ventral view of head, greatly enlarged; h, ventral view of animal, slightly enlarged (After Shipley). Fig. 17 — A pentastomid, larva of Porocephalus proboscideus, seen from below, highly magnified: i, boring anterior end; 2, first pair of chitinous procespes seen be- tween the forks of the second pair; 3, ventral nerve ganglion; 4, ali- mentary canal; 5, mouth; 6 and 7, gland cells (From Shipley after Stiles). CHARACTERISTICS OF INSECTS AND THEIR RELATIVES 15 Like many of the parasitic worms, these animals, in some cases at least, pass their larval life in one host, and complete their development in another of a different species ; some larvae being found in the bodies of herbivorous animals and the adults in predacious animals that feed on these herbivorous hosts. The systematic position of the pentastomids is very uncertain. They have been considered by some writers to be allied to the mites. But it seems better to merely place them in this appendix to the arthropod series until more is known of their relationships. Class DIPLOPODA The Millipedes or Diplopods The members of this class are air-breathing arthropods in which the head is distinct, and the remaining segments oj the body form a continuous region. The greater number of the body-segments are so grouped that each apparent segment bears two pairs of legs. The antennce are short and very similar to the legs. The openings of the reproductive organs are paired, and situated behind the second pair of legs. Vig. 1 8. — A millipede, Spiroholus marginalus. The Diplopoda and the three following classes were formerly grouped together as a single class, the Myridpoda. But this grouping has been abandoned, because it has been found that the Chilopoda are more closely allied to the insects than they are to the Diplopoda; and the Pauropoda and Symphyla are both very distinct from the Diplo- poda on the one hand and the Chilopoda on the other. Owing to the very general and long continued use of the term Myriapoda, the student who wishes to look up the literature on these four classes should consult the references under this older name. The most distinctive feature of the millipedes is that which sug- gested the name Diplopoda for the class, the fact that throughout the greater part of the length of the body there appears to be two pairs of legs borne by each segment (Fig i8). This apparent doubling of the appendages is due to a grouping of the segments in pairs and either a consolidation of the two terga of 16 AN INTRODUCTION TO ENTOMOLOGY each pair or the non-development of one of them; which of these alternatives is the case has not been definitely determined. It is clear, however, that there has been a grouping of the seg- ments in pairs in the region where the appendages are doubled, for corresponding with each tergum there are two sterna and two pairs of spiracles. A few of the anterior body segments, usually three or four in number, and sometimes one or two of the caudal segments remain single. Frequently one of the anterior single segments is legless, but the particular segment that lacks legs differs in the different families. The head, which is as distinct as is the head of insects, bears the antennae, the eyes, and the mouth -parts. The antennse are short, and usually consist each of seven segments. The eyes are usually represented by a group of ocelli on each side of the head; but the ocelli vary greatly in number, and are sometimes absent. The mouth-parts consist of an P upper lip or lahrum; a pair of mandibles; and a pair of jaws, which are united at the base, forming a large plate, which is known as the gnathochildrium. In the genus Polyxenus there is a pair of lobes between t the mandibles and the gnathochilarium, which have been named the maxUlulcB. (paragnatha?). The labrum is merely the anterior part of the upper wall of the head and, as in insects, is not an appendage. The mandibles, in the forms in which they are best developed, are fitted for biting, and consist of several parts (Fig. 19) ; but in some forms they are vestigial. The gnathochilarium (Fig. 20) is ccm-plicated in structure, the details of which vary greatly in different genera. ¥\g,. 19. — A mandi- ble of Jidi'.s; c, cardo; d,d,teeth\ m, muscle; ma, mala; p, pecti- nate plate; s, stipes (After Latzel) . Fig. 20. — The gnathochilarium. or second jaws of three diplopods; A, Spirostrep- ttis; B,Julus; C, Glomeris: r, cardo; A.hypostoma; /g, lingua; m, menttun* pm, promentum; st, stipes (After Silvestri). CHARACTERISTICS OF INSECTS AND THEIR RELATIVES 17 In one subdivision of the class Diplopoda, which is represented by the gentis Polyxemis and a few others, the mandibles are one- jointed; and be- «.*■/ tween the mandi- ^^■lo . blesandthe gnathochilarium there is a pair of one-jointed lobes, which have not been fovmd in other diplopods; these are the "max- illute" (Fig. 2i). The correspondence of the parts of the gnathochilarium of Polyxenus and its allies with the parts of the gnathocil- larium of other di- plopods has not been satisfactorily determined. Most of our more common millipedes possess stink-glands, which open by pores on a greater or less number of the body segments. These glands are the only means of defence possessed by millipedes, except the hard cuticula protecting the body. The millipedes as a rule are harmless, living in damp places and feeding on decaying vegetable matter; but there are a few species that occasionally feed upon growing plants. For a more detailed account of the Diplopoda see Pocock ('ii). Fig. 21. — The second pair of jaws, maxillulse, and the third pair of jaws, maxillae or gnathochilarium, of Polyxenus; the parts of the maxillae or gnathochila- rium are stippled and some are omitted on the right side of the figure: vib, basal membrane of the labium; la, "labium" of Carpenter, perhaps the mentum and promentum of the gnathochilarium; mx, basal seg- ment of the maxilla, perhaps the stipes of the gnathochilarium; wx. /o, lobe of the maxilla; mx.p, maxihary palpus; /z, tongue or hypopharynx; mxl, maxillula; fl. flagellate process (After Carpenter). 18 AN INTRODUCTION TO ENTOMOLOGY Class PAUROPODA The Panropods The members of this class are small arthropods in which the head is distinct, and the segments of the body form a single continuous region. Most of the body-segments bear each a single pair of legs. Although most of the terga of the body-segments are usually fused in couples, the legs are not grouped in double pairs as in the Diplopoda. The antennce. are branched. The reproductive organs open in the third segment back of the head. The Pauropoda or pauropods are minute creatures, the described species measuring only about one twenty-fifth inch in length, more or less. They resemble centipedes in the elongated form of the body and in the fact that the legs are not grouped in double pairs as in the Diplopoda, although the terga of the body-region are usually fused in couples. These characteris- tics are well-shown by the dorsal and ventral views of Pauropus (Fig. 22 and 23). Although the pauropods resemble the chilopods in the distribution of their legs, they differ widely in the position of the openings of the reproductive organs. These open in the third seg- ment back of the head; that of the female is single, those of the male are double. The head is distinct from the body-region. It bears one pair of antenna and two pairs of jaws; the eyes are absent but there is an eye- like spot on each side of the head (Fig. 24). The first pair of jaws are large, one- jointed mandibles; the second pair are short pear-shaped organs. Between these two pairs Fig. 22. — A pauropod, Pauropus huxleyi, dor- sal aspect (After Ken- yon). Pig. 23. — Pauropus huxleyi, ventral as- pect (After Lub- bock). CHARACTERISTICS OF INSECTS AND THEIR RELATIVES 19 Fig. 24 — Eurypatiropus spina- sus; face showing the base of the antennse, the mandibles, and the eye-like spots (After Kenyon). of jaws, there is a horny framework forming a kind of lower lip to the mouth (Fig. 25). The homologies of the mouth-parts with those of the alHed classes of arthropods have not been determined. The body-region consists of twelve segments. This is most clearly seen by an examination of the ventral aspect of the body. When the body is viewed from above the number of segments appears to be less, owing to the fact that the terga of the first ten segments are fused in couples. Nine of the body-segments bear well-developed legs. The appendages of the first segment are vestigial, and the last two segments bear no appendages. The most distinctive feature of mem- bers of this class is the form of the antennae, which differ from tliose of all other arthropods in structure. Each antenna (Fig. 26) consists of four short Dasal segments and a pair of one-jointed branches borne by the fourth segment. One of these branches bears a long, many- ringed filament with a rounded apical knob; and the other branch bears two such filaments with a globular or pear- shaped body between them. This is prob- ably an organ of special sense. The pauropods live under leaves and stones and in other damp situations. Representatives of two quite distinct families are found in this country and in various other parts of the world. In addition to these a third family, the BrachypauropodidcE, is found in Europe. In this family the pairs of terga consist each of two distinct plates. Our two „. ^ A ^ c v ^ J, ^- famiUes are the fol- rig. 26. — Antenna of Eurypatiropus sptnosus (A f ter Kenyon) . lowmg : Fig. 25. — Mouth-parts of Eury- pauropus ornatus; nid, man- dible; mx, second iaws; /, lower lip (After Latzel). 20 AN INTRODUCTION TO ENTOMOLOGY Family Pauropodidce. — In members of this family the head is not covered by the first tergal plate and the anal segment is not covered by the sixth tergal plate. The best known representatives of this family belong to the genus Pauropus (Fig. 22). This genus is widely distributed, represen- tatives having been found in Europe and in both- North and South America. They are active, measure about one twenty-fifth inch in length, and are white. %.r Family Eiirypauropida. — The members of this family are characterized by the wide form of the body, which bears some resemblance to ^ that of a sow-bug. The head is concealed by the first tergum of the body-region; and the anal -.^ segment, by the penultimate tergum. Our most I ^ ^ famihar representative is Eurypanropus spinosus T\g. 27.— Lnrypauro- rpia. 27). This, unlike Pauropus, is slow m its pus spinosus {Aitev Kenyon). movements. Class CHILOPODA The Centipedes or Chilopods The members of this class are air-breathing arthropods in which the head is distinct, and the remaining segments of the body form a continuous region. The numerous pairs of legs are not grouped in double pairs, as in the Diplopoda. The antennce are long and many-jointed. The appendages of the first body-segment are jaw-like and f miction as organs of offense, the poison-jaws. The opening of the reproductive organs is in the next to the last segment of the body. The animals constituting the class Chilopoda or chilopods are commonly known as centipedes. They vary to a considerable degree in the form of the body, but in all except perhaps the sub-class Notostigma the body-segments are distinct, not grouped in couples as in the diplopods (Fig. 28). They are sharply distinguished from the three preceding classes in the possession of poison-jaws and in having the opening of the reproductive organs at the caudal end of the body The antennae are large, flexible, and consist of fourteen or more segments. There are four pairs of jaws including the jaw-like CHARACTERISTICS OF INSECTS AND THEIR RELATIVES 21 appendages of the first body-segment. These are the mandibles (Fig. 29, A), which are stout and consist each of two segments; the maxillcB (Fig. 29, B, a), which are foHaceous, and usually regarded as biramous ; the second maxillcB or palpognaths, which are leg-like in form, consisting of five or six segments, and usually have the coxas united on the middle line of the body (Fig. 29, B, 6), and the poison- claws or toxicognaths, which are the appendages of the first body-segment (Fig. 29, C). The poison-claws consist each of six seg- ments, of which the basal one, or coxa is usually fused with its fellow, the two forming a large coxal plate, and the distal one is a strong pierc- ing fang in which there is the opening of the duct leading from a poison gland, which is in the appendage. The legs consist typically of six segments, of which the last, the tarsus, is armed with a single terminal claw. The last pair of legs are directed backwards, and are often greatly modified in form. The class Chilopoda includes two quite distinct groups of animals which are regarded by Pocock ('u) as sub-classes, the Pleuro- stigma and theNoto- stigma. The names A'^/M W^W \ ^ of the sub-classes refer to the position ^ a of the spiracles. Sub-Class PLEUROSTIGMA The typical Centipedes In the typical cen- tipedes, the sub-class Pleurostigma, the spiracles are paired and are situated in the sides of the segments that bear them. Each leg-bearing segment contains a distinct tergum and sternum, the number of sterna never exceeding that of the terga. The eyes Fig. 28. — A centipede Bothropolys miilti- dentatus. Fig. 29. — Mouth-parts of a centipede, Geophilus flavi- dus. A, right mandible, greatly enlarged. B, the two pairs of maxillae, less enlarged; a, the united coxae of the maxillae; b, the united coxae of the second maxillae or palpognaths. C, the poison claws or toxicognaths (After Latzel) 22 AN INTRODUCTION TO ENTOMOLOGY when present are simple ocelli; but there may be a group of ocelli on each side of the head. Figure 28 represents a typical centipede. Sub-Class NOTOSTIGMA. Sctitigera and its Allies In the genus Scutlgera and its allies, which constitute the sub-class Notostigma, there is a very distinctive type of respiratory organs. There is a single spiracle in each of the spiracle-bearing segments, which are seven in number. These spiracles open in the middle line of the back, each in the hind margin of one of the seven prominent terga of the body-region. Each spiracle leads into a short sac from which the tracheal tubes extend into the pericardial blood-sinus. There are fifteen leg-bearing segments in~ the body region; but the terga of these segments are reduced to seven by fusion and suppression. The eyes differ from those of all other members of the old group Myriapoda in being compound, the ommatidia resembling in structure the ommatidia of the compound eyes of insects. The following species is the most familiar representative of the Notostigma. The house centipede, Scuttgera forceps. — This centipede attracts attention on account of the great length of its appendages (Fig. 30), and the fact that it is often seen, in the regions where it is common, running on the walls of rooms in dwelling houses, where it hunts for flies and other insects. It prefers damp situations; in houses it is most frequently found in cellars, bathrooms, and closets. Sometimes it becomes very abundant in conservatories, living among the stored pots and about the heating pipes. It is much more common in the South than in the North. Fig- 30. — SaUigcra forceps. CHARACTERISTICS OF INSECTS AND THEIR RELATIVES 23 The body of the adult measures an inch or a Httle more in length. It is difficult to obtain perfect specimens, as they shed their legs when seized. Class SYMPHYLA The Symphylids The members of this class are small arthropods in which the head is distinct, and the segments of the body form a single con- tinuous region. Most of the body-segments bear a single pair of legs. The antenncB are very long and many-jointed. The head bears a Y-shaped epicranial suture, as in insects. The opening of the reproductive organs is in the third segment behind the head. The class Symphyla includes a small number of many-legged arthropods which exhibit striking affinities with insects, and especially with the Thysanura. The body is centipede-like in form (Fig 31). The head is distinct, and is not bent dow!? as it is in the diplopods and pauro- pods ; it is shaped as in Thysanura and bears a Y-shaped epicranial suture. The body-region bears fifteen terga, which are distinct, not grouped in couples as in the two preceding classes; and there are eleven or twelve pairs of legs. The antennae are long and vary greatly in the number of the segments. There are noeyes. The mandibles, the "maxillui^" (paragnatha). the maxillae, and the sec- ond maxillae or labium are present. Fig. 3 1 . — ScolopendreUa (After Latzel). ig. 32.— Mouth-parts of ScolopendreUa seen from below: wi, mandible; inx, maxillse; s, stipes; p, pal- pus; /, second maxillas or labium. The mandible on the right side of the figur '. is omitted (After Hansen). The mandibles (Fig. 32, md) are two- jointed; the maxillulcB (Fig. 33, m) are small, not segmented, and are attached to a median lobe o.' hypopharynx (Fig. 33, h); they are hidden when the mouth-part-,' are viewed from below as represented in Figure 32 ; the maxillcB (Fig, 24 AN INTRODUCTION TO ENTOMOLOGY 2,2, mx) resemble in a striking degree the maxillas of insects, consisting of a long stipes, (s), which bears a minute palpus, {p), and an outer and inner lobe; th.e second maxillcB or labium (Fig. 32,/) also resembles the corresponding part of the more generalized insects, being composed of a pair of united gnathites. The legs of the first pair are reduced in size and in the number of their segments. The other legs ^popharynx ^ (h) consist each of five segments; the last segment aridmaxillulae(m) bears a pair of claws. Excepting the first two ?After^ Hansen f pairs of legs, each leg bears on its proximal seg- ment a slender cylindrical process, the parapodium (Fig. 34, p). These parapodia appear to correspond with the styli of the Thysanura. At the caudal end of the body there is a pair of appendages, which are believed to be homologous with the cerci of insects (Fig. 35, c). A striking peculiarity of the symphylids is that Fig. 34-— A leg of i]yQy possess only a single pair of tracheal tubes, p, parapodium. which open by a pair 01 spiracles, situated m the head beneath the insertion of the antennse. The members of this class are of small size, the larger ones measuring about one-fourth inch in length. They live in earth under stones and decay- ing wood, and in other damp situations. Imma- ture individuals possess fewer body-segments and legs than do adults. Less than thirty species have been described; but doubtless many more remain to be discovered. The known species are classed in two genera: pig. 35.— The caudal Scolopendre'.la and Scutigerella. In the former the ^nd of the body of J J J ScolopendreUa; I, posterior angles 01 the terga are produced and leg; c, cercus (After angular; while in the latter they are rounded. Latzel). A monograph of the Symphyla has been published by Hansen ('03) . Class MYRIENTOMATA The Myrientoniatids The members of this class are small arthropods in which the body ia elongate, as in the Thysamira, fttsiform, pointed behind, and depressed; it may be greatly extended and retracted. The antennas and cerci are CHARACTERISTICS OF INSECTS AND THEIR RELATIVES 25 absent. The oral apparatus is suctoral, and consists of three pairs of gnathites. There are three pairs oj thoracic legs, and three pairs of vestigial abdominal legs. The abdomen is composed of eleven segments and a telson. The opening of the reproductive organs is unpaired, and near the hind end of the body. The head bears a pair of organs, termed pseudoculi, the nature of which has not been definitely determined. The known members of this class are very small arthropods, the body measuring from one- fiftieth to three-fiftieths of an inch in length. The form of the body is shown by Figure 36. These exceedingly interesting creatures are found in damp situations, as in the humus of gardens; as yet very little is known of their geographical dis- tribution, as almost all of the studies of them have been made by two Italian naturalists. The first discovered species was described in 1907 by Pro- fessor F. Silvestri of Portici, who regarded it as the type of a distinct order of insects, for which he propo ed the name Protura. Later Professor Antonio Berlese of Florence described several additional species, and published an extended monograph of the order (Berlese '09 b). Professor Berlese concluded that these arthropods are more closely allied to the "Myriapoda" and especially to the Pauropoda than they are to the insects, and changed the name of the order, in an arbitrary manner, to Myrientomata. It seems clear to me that in either case whether the order is classed among the insects or assigned to some other position it should be known by the name first given to it, that is, the Protura Fig. 36. — Acerentomon doderoi: A, dor- sal aspect; B, ventral aspect; 1,1,1, vestigial abdominal legs (After Berlese). 26 AN INTRODUCTION TO ENTOMOLOGY In the present state of our knowledge of the affinities of the classes of arthropods, it seems best to regard the Protura as representing a separate class, of rank equal to that of the Paiiropoda, Sjnnphyla, etc. ; and for this class I have adopted the name proposed for the group by Berlese, that is the Myrientomata. The class Myrientomata includes a single order. Order PROTURA As this is the only order of the class Myrientomata now known it must be distinguished by the characteristics of the class given above. Two families have been established : the Acerentomidas, charac- terized by the absence of spiracles and tracheae ; and the Eosentomidse the members of which possess two pairs of thoracic spiracles and simple trachea. That the Protura are widely distributed is evident from the fact that in addition to those found in Italy, representatives of the order have been found in peat in Hampshire, England, and others have been taken near New York City, and near Washington, D. C. Class HEXAPODA The Insects The members of this class are air-breathing arthropods, with distinct head, thorax, and abdomen. They have one pair oj antennce, three pairs of legs, and Msually one or two pairs of wings in the adult state. The opening of the reproductive organs is near the caudal end of the body. We have now reached in our hasty review of the classes of arthro- pods the class of animals to which this book is chiefly devoted, the Hexapoda,* or Insects, the study of which is termed entomology. Insects are essentia Ty terrestrial ; and in the struggle for existence they are the most successful of all terrestrial animals, outnumbering both in species and individuals all others together. On the land they abound under the greatest variety of conditions, special forms having been evolved fitted to live in each of the various situations where other animals and plants can live; but insects are not restricted to dry land, for many aquatic forms have been developed. The aquatic insects are almost entirely restricted to small bodies of fresh water, as streams and ponds, where, they exist in great num- bers. Larger bodies of fresh water and the seas are nearly destitute of them except at the shores. *Hexapoda: hex (^^), six; pons (iroiJs), afoot. and the destruction of many flowering ^ ^^^^^ .^ plants that depend upon insects for the m CHARACTERISTICS OF INSECTS AND THEIR RELATIVES 27 As might be inferred from a consideration of the immense number of insects, the part they play in the economy of nature is an exceed- ingly important one. Whether this part is to be considered a bene- ficial or an injurious one when judged from the human standpoint would be an exceedingly difficult question to determine. For if insects were to be removed from the earth the whole face of nature would be changed. While the removal of insects from the earth would eliminate many pests that prey on vegetation, would relieve many animals of annoying parasites, and would remove some of the most terrible diseases to which our race is subject, it would result in the destruction of many groups of animals that depend, either ,*:p=^^ ^ z-.^^^^"*^ directlv or indirectly, upon insects for food, Aa' // fertilization of their blossoms. Truly this ^^-'^ world would speedily become a very differ- ent one if insects were exterminated. It may seem idle to consider what would be the result of the total destruction of insects; but it is not wholly so. A care- ful study of this question will do much to open our eyes to an appreciation of the wonderful "web of life" of which we are a Fig- 37- — Wasp with head, part. thorax, and abdomen Most adult insects can be readily dis- tinguished from other arthropods by the form of the body, the segments being grouped into three distinct regions, head, thorax, and abdomen (Fig. 37), by the possession of only three pairs of legs, and in most cases by the presence of wings The head bears a single pair of antennae, the organs of sight, and the mouth-parts. To the thorax, are articulated the organs of locomotion, the legs and the wings when they are present. The abdomen is usually without organs of locomotion but ^. „ ,, , , , r XI 1 .1 ■, Fig. 38.— Nymph of the red- trequently bears other appendages at legged locust. the caudal end. These characteristics are also possessed by the immature forms of several of the orders of insects; although with these the wings are ^^^^ 28 AN INTRODUCTION TO ENTOMOLOGY rudimentary (Fig. 38). But in other orders of insects the immature forms have been greatly modified to adapt them to special modes of life, with the result that they depart widely from the insect type. For example, the lar\^se of bees, wasps, flies, ^nd many beetles are legless and more or less worm-like in form (Fig. 4) ; while the larv^se of butter- flies and moths possess abdominal as well as thoracic legs (Fig. 39). Fig. 39. — A larva of a handmaid moth, Datana. Although the presence of wings in the adult state is characteristic of most insects, there are two orders of insects, the Thysanura and the Collembola, in which wings are absent. These orders represent a branch of the insect series that separated from the main stem before the evolution of wings took place; their wing- less condition is, therefore, a primitive one. There are also certain other insects, as the lice and bird-lice, that are wingless. But it is ^. believed that these have descended from / winged insects, and have been degraded by their parasitic life ; in these cases the wingless condition is an acquired one. Beside these there are many species belonging to orders in w'hich most of the species are winged that have acquired a wingless condition in one or both sexes. Familiar examples of these are the females of the Coccidas (Fig. 40), and the females of the canker-worm moths. In fact, wingless forms occur m most of the orders of winged insects. As the structure and transformations of insects are described in detail in the following chapters, it is unnecessary to dwell farther on the characteristics of the Hexapoda in this place. Fig. 40. — A mealy-bug, Dactylopius. CHAPTER II. THE EXTERNAL ANATOMY OF INSECTS I. THE STRUCTURE OF THE BODY-WALL a. THE THREE LAYERS OF THE BODY-WALL Three, more or less distinct, layers can be recognized in the body- wall of an insect: first, the outer, protecting layer, the cuticula; second, an intermediate, cellular layer, the hypodermis; and third, an inner, delicate, membranous layer, the basement membrane. These layers can be distinguished only by a study of carefully prepared, microscopic sec- tions of the body-wall. Figure 41 represents the ap- pearance of such a section. As the outer and inner layers are derived from the hypo- derm s, this layer will be described first. The hypodermis. — The ac- tive living part of the body- wall consists of a layer of cells, which is termed the hypo- dennis (Fig. 4^, h). The hypodermis is a portion of one of the germ-layers, the ectoderm. In other words, that portion of the ectoderm which in the course of the development of the insect comes to form a part of the body- wall is termed the hypodermis; while to invaginated portions of the ectoderm other terms are applied, as the epithelial layer of the trachea?, the epithelial layer of the fore-intestine, and the epithelial layer of the hind-intestine. The cells of which the hypodermis is composed vary in shape; but they are usually columnar in form, constituting what is known to histologists as a columnar epitheliimi. Sometimes the cells are so flattened that they form a simple pavement epithelium. I know of no case in which the hypodermis consists of more than a single layer of cells; although in wing-buds and buds of other appendages, where the cells are fusiform, and are much crowded, it appears to be irregu- (29) Fig. 41. — A section of the body-wall of an insect: c, cuticula;^, hypodermis; bm, basement membrane; e, epidermis, d, dermis; tr, trichogen; s, seta. 30 AN INTRODUCTION TO ENTOMOLOGY larly stratified. This is due to the fact that the nuclei of different cells are in different levels. The trichogens. — Certain of the hypodermal cells become highly- specialized and produce hollow, hair-like organs, the setas, with which they remain connected through pores in the cuticula. Such a hair- forming cell is termed a Mchogen (Fig. 41, tr); and the pore in the cuticula is termed a tnchopore. The cuticula. — Outside of the hypodermis there is a firm layer, which protects the body and serves as a support for the internal organs; this is the cuticula (Fig. 41, c). The cuticula is produced by the hypodermis; the method of its production is discussed in a later chapter where the molting of insects is treated. The cuticula is not destroyed by caustic potash ; it is easy, therefore, to separate it from the tissues of the body by boihng or soaking it in an aqueous solution of this substance. Chitin. — The well-known firmness of the larger part of the cuticula of adult insects is due to the presence in it of a substance which is termed chitin. This substance bears some resemblance in its physical properties to horn ; but is very different from horn in chemical com- position. In thin sheets it is yellowish in color; thicker layers of it are black. It is stained yellow by picric acid and pink by safranin. Chitinized and non-chitinized cuticula. — When freshly formed, the cuticula is flexible and elastic, and certain portions of it, as at the nodes of the body and of the appendages, remain so. But the greater part of the cuticula, especially of adult insects, usually becomes firm and inelastic; this is probably due to a che mical change resulting in the production of chitin. What the natureof this change is or how it is produced is not yet known, but it is evident that a change occurs ; we may speak, therefore, of chitinized cuticula and non-chitinized cuticula. This difference is well-shown in sections of the cuticula stained by picro-carmine, which colors the chitinized portions yellow and the non-chitinized parts pink; it can be shown also by other double stains, as eosin-methylene-blue. Chitinized cuticula is inelastic, while non-chitinized cuticula is elastic. The elasticity of non-chitinized cuticula is well-shown by the stretching of the body-wa'l after a molt and before the hardening of the cuticula. It is also shown by the expanding of the abdomen of females to accommodate the growing eggs, the stretching of the body- wall taking place in the non-ch'.tinized portions between the segments. An extreme case of this is shown by the queens of Termites. THE EXTERNAL ANATOMY OF INSECTS 31 The formation of chitinisnot restricted to the hypodermis, but is a property of the invaginated portions of the ectoderm: the fore- intestine, the hind-intestine, and the tracheae are all lined with a cuticular layer, which is continuous with the cuticula of the body -wall and is chitinized. The most marked case of internal formation of chitin is the development of large and powerful teeth in the proven- triculus of many insects. The epidermis and the dermis. — Two quite distinct parts of the cuticula are recognized by recent writers; these are distinguished as the epidermis and the dermis respectively. The epidermis is the external portion ; in it are located all of the cuticular pigments; and from it are formed all scales, hairs, and other surface structures. It is designated by some writers as the primary aiticida, (Fig. 41, e). The dermis is situated beneath the epidermis. It is formed in layers, which give sections of the cuticula the well-known laminate appearance. It is sometimes termed the secondary cuticula (Fig. 41, d) The basement membrane. — The inner ends of the hy podermal cells are bounded by a more or less distinct membrane; this is termed the basement membrane (Fig. 41, bm). The basement membrane is most easily seen in those places where the inner ends of the hypodermal cells are much smaller than the outer ends; here it is a continuous sheet connecting the tips of the hypodermal cells. b. THE EXTERNAL APOPHYSES OF THE CUTICULA The outer surface of the cuticula bears a wonderful variety of pro- jections. These, however, can be grouped under two heads : first, those that form an integral part of the cuticula; and second, those that are connected with the cuticula by a joint. Those that form an integral part of the cuticula are termed apophyses; those that are con- nected by a joint are termed appendages of the cuticula. The cuticular nodules. — The most frequently occurring out- growths of the cuticula are small, more or less conical nodules. These vary greatly in size, form, and distribution over the surface of the body in diifersnt species cf insects, and are frequently of taxGv.omic value. The fixed hairs. — On the wings of some insects, as the Trichoptera and certain of the Lepidoptera, there are in addition to the more obvious setae and scales many very small, hair-like structures, which 32 AN INTRODUCTION TO ENTOMOLOGY differ from setae in being directly continuous with the cuticula, and not connected with it by a joint; these are termed the fixed hairs, or aculeae. The mode of origin and development of the fixed hairs has not been studied. The spines. — The term spine has been used loosely by writers on entomology. Frequently large setae are termed spines. In this work such setae are called spine-like setae; and the term spine is applied only to outgrowths of the cuticula that are not separated from it by a joint. Spines differ also from spine-like setae in being produced by undifferentiated hypodermal cells and are usually if not always of multicellular origin, while each seta is produced by a single trichogen cell. The accompanying diagram (Fig. 42) illustrates this difference. C. THE APPENDAGES OF THE CUTICULA Under this head are included those outgrowths of the cuticula that are connected with it by a joint. Of these there are two quite dis- tinct types represented by the spurs and the setae respectively. The spurs. — There exist upon the legs of many insects appendages which on account of their form and position have been termed spurs. Spurs resemble the true spines described above and differ from setae in being of multicellular origin; they differ from spines in being appendages, that is, in being connected with the body-wall by a joint. The setae. — The setas are what are commonly called the hairs of in- sects. Each seta (Fig. 42, 5) is an appendage of the body-wall, which arises from a cup-like cavity in the cuticula, the alveolus, situated at the outer end of a per- foration of the cuticula, the tnchopore; and each seta is united at its base with the wall of the trichopore by a ring of thin membrane, the articular membrane of the seta. The setffi are hollow; each is the product of a single hypodermal cell, a trichogen (Fig. 42), and is an extension of the epidermal layer of the cuticiila. Fig. 42. — Diagram illustrating the difference be- tween a spine (sp) and a seta (s). THE EXTERNAL ANATOMY OF INSECTS 33 In addition to the trichogen there may be a gland-cell Opening into the seta, thus forming a glandular hair, or a nerve may extend to the seta, forming a sense-hair; each of these types is discussed later. The most common type of seta is bristle-like in form; familiar examples of this type are the hairs of many larvae. But numerous modifications of this form exist. Frequently the setae are stout and firm, such are the spine-like setce; others are Jurnished with lateral prolongations, these are the plumose hairs; and still others are flat, wide, and comparatively short, examples of this form are the scales of the Lepidoptera and of many other insects. The taxonomic value of setcB. — In many cases the form of the setae and in others their "arrangement on the cuticula afford useful charac- teristics for the classification of insects. Thus the scale-like form of the setae on the wing-veins of mosquitoes serves to distinguish these insects from closely allied midges; and the clothing of scales is one of the most striking of the characteristics of the Lepidoptera. The arrangement of the setae upon the cuticula, in some cases at least, is a very definite one. Thus Dyar ('94) was able to work out a classification of lepidopterous larvae by a study of the setae v..ith which the body is clothed. A classification oj setce. — If only their function be considered the hairs or setae of insects can be grouped in the three following classes : (i) The clothing hairs. — Under this head are grouped those hairs and scales whose primary function appears to be merely the protection of the body or of its appendages. So far as is known, such hairs con- tain only a prolongation of the trichogen cell that produced them. It should be stated, however, that this group is merely a provisional one; for as yet comparatively little is known regarding the relation of these hairs to the activities of the insects possessing them. In some cases the clothing hairs have a secondary function. Thus the highly specialized overlapping scales of the wings of Lepidoptera, which are modified setae, may serve to strengthen the wings; and the markings of insects are due almost entirely to hairs and scales. The fringes on the wmgs of many insects doubtless aid in flight, and the fringes on the legs of certain aquatic insects also aid in locomotion. (2) The glandular hairs. — Under this head are grouped those hairs that serve as the outlets of gland cells. They are discussed in the next chapter, under the head of hypodermal glands. (3) The sense-hairs — In many case a seta, more or less modified in form, constitutes a part of a sense-organ, either of touch, taste, or smell ; examples of these are discussed in the next chapter. 34 AN INTRODUCTION TO ENTOMOLOGY d. THE SEGMENTATION OF THE BODY The cuticular layer of the body-wall, being more or less rigid, forms an external skeleton; but this skeleton is flexible along certain transverse lines, thus admitting of the movements of the body, and producing the jointed appearance characteristic of insects and of other arthropods. An examination of a longitudinal section of the body-wall shows that it is a continuous layer and that the apparent segmentation is due to infoldings of it (Fig. 43). The body-seg- ments, somites, or metameres.^ — Each section of the body .^. _. ^ . .^ j- 1 ^- t ^i. Fig. 43. — Diagram of a longitudinal section of the between two of the body- wall of an insect. infoldings described above is termed a body-segment, or somite, or metamere. The transverse conjunctivae. — The infolded portion of the body- wall connecting two segments is term^ed a conjunctiva. These con- junctivae may be distinguished from others described later as the transverse conjunctivce. The conjunctivee are less densely chitinized than the other portions of the cuticula; their flexibility is due to this fact, rather than to a comparative thinness as has been commonly described. e. THE SEGMENTATION OF THE APPENDAGES The segmentation of the legs and of certain other appendages is produced in the same way as that of the body. At each node of an appendage there is an infolded, flexible portion of the wall of the appendage, a conjunctiva, which renders possible the movements of the appendage. /. THE DIVISIONS OF A BODY-SEGMENT In many larvae, the cuticula of a large part of the body-wall is of the non-chitinized type ; in this case the wall of a segment may form a ring which is not divided into parts. But in most nymphs, naiads, and adult insects, there are several densely chitinized parts in the wall of each segment; this enables us to separate it into well-defined portions. The tergum, the pleura, and the sternum. — The larger divisions of a segment that are commonly recognized are a dorsal division, the THE EXTERNAL ANATOMY OF INSECTS 35 tergiim; two lateral divisions, one on each side of the body, the pleura; and a ventral division, the sternum. Each of these divisions may include several definite areas of chitinization. In this case the sclerites of the tergum are referred to collectively as the tergites, those of each pleurum, as the pleurites, and those constituting the sternum, as the siernites. The division of a segment into a tergum, two pleura, and a sternum are most easily seen in the wing-bearing segments, but it can be recognized also in the prothorax of certain generalized insects. This is especially the case in many Orthoptera, as cockroaches and walking- sticks, where the pleura of the prothorax are distinct from the tergum and the sternum. In the abdomen it is evident that correlated with the loss of the abdominal appendages a reduction of the pleura has taken place. The lateral conjunctivae. — On each side of each abdominal segment of adults the tergum and the sternum are united by a strip of non- chitinized cuticula; these are the lateral conjunctivas. Like the transverse conjunctivse, the lateral ones are more or less infolded. The sclerites. — Each definite area of chitinization of the cuticula is termed a sclerite. The sutures. — The lines of separation between the sclerites are termed sutures. Sutures vary greatly in form ; they may be infolded conjunctivae ; or they may be mere lines indicating the place of union between two sclerites. Frequently adjacent sclerites grow together so completely that there is no indication of the suture ; in such cases the suture is said to be obsolete. The median sutures. — On the middle line of the tergites and also of the sternites there frequently exist longitudinal sutures. These are termed the median sutures. They represent the lines of the closure of the embryo, and are not taken into account in determining the number of the sclerites. The dorsal median suture has been well-preserved in the head and thorax, as it is the chief line of rupture of the cuticula at the time of molting. The piliferous tubercles of larvae. — The setae of larvae are usually borne on slightly elevated annular sclerites ; these are termed pilif- erous tubercles. The homologizing of the sclerites. — ^While it is probable that the more important sclerites of the body in winged insects have been derived from a common winged ancestor and, therefore, can be homologized, many secondary sclerites occiu: which can not be thu«, homoiogized. 36 AN INTRODUCTION TO ENTOMOLOGY g. THE REGIONS OF THE BODY The segments of the body in an adult insect are grouped into three, more or less well-marked regions: the head, the thorax, and the abdomen. Each of these regions consists of several segments more or less closely united The head is the first of these regions; it bears the mouth-parts, the eyes, and the antennae. The thorax is the second region ; it bears the legs and the wings if they are present. The abdomen is the third region; it may bear appendages connected with the organs of repro- duction. II. THE HEAD The external skeleton of the head of an insect is composed of several sclerites more or less closely united, forming a capsule, which includes a portion of the viscera, and to which are articulated certain appendages. a. THE CORNEAS OF THE EYES The external layer of the organs of vision, the corneas of the eyes, is, in each case, a translucent portion of the cuticula. It is a portion of the skeleton of the head, which serves not merely for the admission of light but also to support the more delicate parts of the visual apparatus. The corneas of the compound eyes. — The compound eyes are the more commonly observ^ed eyes of insects. They are situated one on each side of the head, and are usually conspicuous. Sometimes, as in dragon-flies, they occupy the larger part of the surface of the head. The compound eyes are easily recognized as eyes; but when one of them is examined with a microscope it is found to present an appearance very different from that of the eyes of higher animals, its surface being divided into a large number of six-sided divisions (Fig. 44) ; hence the term compound eyes applied to them. A study of the internal structure of this organ has shown that each of these hexagonal divisions is the outer end of a distinct element of the eye. Each of these elements is termed an ommattdium. The number of ommatidia of which a compound p. ^ ^^ i-^f ®^'® ^^ composed varies greatly; there may be not cornea of a com- more than fifty, as in certain ants, or there may pound eye. j^g many thousand, as in a butterfly or a dragon-fly. As a rule, the immature stages of insects with a gradual metamor- phosis and also those of insects with an incomplete metamorphosis. THE EXTERNAL ANATOMY OF INSECTS 37 that is to say nymphs and naiads possess compound eyes. But the larvae of insects with a complete metamorphosis, do not possess well- developed compound eyes; although there are frequently a few sep- arate ommatidia on each side of the head. These are usually termed ocelli; but the ocelli of larva> should not be confused with the ocelli of nymphs, naiads, and adults. The corneas of the ocelli. — In addition to the compound eyes most nymphs, naiads, and adult insects possess other eyes, which are termed ocelli. The cornea of each ocellus is usually a more or less nearly circular, convex area, which is not divided into facets. The typical number of ocelli is four; but this number is rarely found. The usual number is three, a median ocellus, which has been derived from a pair of ocelli united, and a distinct pair of ocelli. Frequently the median ocellus is lacking, and less frequently, all of the ocelli have been lost. The position of the ocelli is discussed later. h. THE AREAS OF THE SURFACE OF THE HEAD In descriptions of insects it is frequently necessary to refer to the different regions of the surface of the head. Most of these regions were named by the early insect anatomists; and others have been described by more recent writers. This terminology is really of comparatively little morphological value; for in some cases a named area includes several sclerites, while in others only a portion of a sclerite is included. This is due to the fact that but few of the primitive sclerites of the head have remained distinct, and some of them greatly over- shadow others in their development. The terms used, however, are sufficiently accurate to meet the needs of describers of species, and will doubtless continue in use. It is necessary, therefore, that students of entomology become familiar with them. The best landmark from which to start in a study of the areas of the surface of the head is the epicranial suture, the inverted Y-shaped suture on the dorsal part of the head, in the more generalized insects (Fig. 45, e. su.). Behind the arms of this suture there is a series of paired sclerites, which meet on the dorsal wall of the head, the line of union being the stem of the Y, a median suture ; and between the arms of the Y and the mouth there are typically three single sclerites (Fig. 45, F, C, L). It is with these unpaired sclerites that we will begin our definitions of the areas of the head. Fig. 45 —Head of a The front. — The front is the unpaired sclerite between the arms of the epicranial suture (Fig. 45, F). 38 AN INI ROD UCT ION TO ENTOMOLOGY Fig 46. — Head of a cockroach; m, muscle impres- sions. In the more generalized insects at least, if not in all, the front bears the median ocellus ; and in the Plecoptera, the paired ocelli also. Frequently the suture between the front and the following sclerite, the clypeus, is obsolete; but as it ends on each side in the invagination which forms an anterior arm of the tentorium or endo-skeleton (Fig. 46, at), its former position can be inferred, at least in the more generalized insects, even when no other trace of it remains. In Figure 46 this is indicated by a dotted line. The clypeus. — The clypeus is the intermediate of the three unpaired sclerites between the epi- cranial suture and the mouth (fig. 46, c). To this part one condyle of the mandible articulates. Although the clypeus almost always appears to be a single sclerite, except when divided trans- versely as indicated below, it really consists of a transverse row of three sclerites, one on the median line, and one on each side articulating with the mandible. The median sclerite may be designated the clypeus proper, and each lateral sclerite, the ante- coxal piece of the mandible. Usually there are no indications of the sutures separating the clypeus proper from the antecoxal pieces; but in some insects they are distinct. In the larva of Corydalus, the ante- coxal pieces are not only distinct but are quite large (Fig. 47, ac, ac). In some insects the clypeus is completely or partly divided by a transverse suture into two parts (Fig. 45). These may be designated as the first clypeus and the second clypeus, respectively; the first clypeus being the part next the front (Fig. 45, Ci) and the second clypeus being that next the labrum (Fig. 45, C2). The suture between the clypeus and the epicranium is termed the clypeal suture. The labrum. — The labrum is the movable flap which constitutes the upper lip of the mouth (Fig. 45, L). The labrum is the last of the series of unpaired sclerites between the epicranial suture and the mouth. It has the appearance of an appendage but is really a portion of one of the head segments. The epicranium. — Under the term epi- cranium are included all of the paired sclerites of the skull, and some- times also the front. The paired sclerites constitute the sides of Fig;. 4Z ■ — Head of a larva of Corydahis, dorsal aspect THE EXTERNAL ANATOMY OF INSECTS 39 the head and that portion of the dorsal surface that is behind the arms of the epicranial suture. The sclerites constituting this region are so closely united that they were regarded as a single piece by Straus-Durckheim (1828), who also inc uded the front in this region, the epicranial suture being obsolete in the May beetle, which he used as a type. The vertex. — The dorsal portion of the epicraniiim; or, more specifically, that portion which is next the front and between the compound eyes is known as the mrtex (Fig. 45, V, V). In many insects the vertex bears the paired ocelli. It is not a definite sclerite; but the term vertex is a very useful one and will doubtless be retained. The occiput. — The hind part of the dorsal surface of the head is the occiput. When a distinct sclerite, it is formed from the tergal portion of the united postgenas described below (Fig. 47, 0, 0). The genae. — The gencB are the lateral portions of the epicranium. Each gena, in the sense in which the word was used by the older writers, includes a portion of several sclerites. Like vertex, however, the term is a useful one. The postgenae. — In many insects each gena is divided by a well-marked suture. This led the writer, in an earlier work ('95), to restrict the term gena to the part in front of the suture (Fig. 48, G), and to propose the term postgena for the part behind the suture (Fig. 48, Pg). The gula. — The gula is a sclerite forming the ventral wall of the hind part of the head in certain orders of insects, and bearing the labium or second maxillae (Fig. 49, Gu). In 'the more generalized orders, the sclerite corresponding to the gula does not form a part of the skull. The sutures forming the lateral boundaries of the gula are termed the gular sutures. The ocular sclerites. — In many insects each compound eye is situated in the axis of an annular sclerite; these sclerites bearing the compound eyes are the ocular sclerites (Fig. 50, os). The antennal sclerites. — In some insects there is at the base of each antenna an annular sclerite ; these are the antennal sclerites (Fig. 50, as). The antennal sclerites are most distinct in the Plecoptera. Fig. 48. — Hoad and neck of a cock- roach. -Head of Corydiilus, adult, ventral aspect. 40 AN INTRODUCTION TO ENTOMOLOGY The trochantin of the mandible. — In some insects, as Orthoptera there is a distinct sclerite between each mandible and the gena; this is the trochantin of the mandible (Fig. 45, ir). The maxillary pleurites. — ^In some of the more generalized insects, as certain cockroaches and crickets, it can be seen that each maxilla is articulated at the ventral end of a pair of sclerites, between which is the invagination that forms the posterior arm of the tentorium; these are the maxillary pleurites; the pos- terior member of this pair of sclerites can be seen in the lateral view of the head of a cockroach (Fig. 48, m. em). The cervical sclerites. — The cervical scler- ites are the small sclerites found in the neck of many insects. Of these there are dorsal, lateral, and ventral sclerites. The cervical sclerites v/ere so named by Huxley ('78); „. TT , f recently they have been termed the ^"«/er5^g- cricket, ental surface mental plates by Crampton ('17), who con- of the dorsal wall. g^^^^-g ^j^g^^ ^^ ^^ homologous with sclerites found in the intersegmental regions of the thorax of some generalized insects. The lateral cervical sclerites have long been known as the jugular sclerites {pieces jugulaires, Straus Durckheim, 1828). C. THE APPENDAGES OF THE HEAD Under this category' are classed a pair of jointed appendages termed the antenncE, and the organs known collectively as the mouth- parts. The antemiae. — The antennce are a pair of jointed appendages articulated with the head in front of the eyes or between them. The antennae vary greatly in form; in some insects they are thread-like, consisting of a series of similar segments; in others certain segments are greatly modified. The thread-like form is the more generalized. In descriptive works names have been given to particular parts of the antennae, as follows (Fig. 51): The Scape. — The first or proximal segment of an antenna is called the scape (a). The proximal end of this segment is often subglobose, appearing like a distinct segment; in such cases it is called the bulb (a'). THE EXTERNAL ANATOMY OF INSECTS 41 The Pedicel. — The pedicel is the second segment of an antenna {b). In some insects it differs greatly in form from the other segments. The Cldvola.— The term cla- vola is applied to that part of the antenna distad of the pedi- cel (c); in other words, to all of the antenna except the first and second segments. In some insects certaia parts of the cla- vola are specialized and have received particular names. These are the ring-joints, the funicle, and the club. The Ring-j oinis .~ln certain Fig. 51.— Antennaofachalcis-fly. -^g^^^g (^_g_^ Chalcidids) the proximal segment or segments of the clavola are much shorter than the suc- ceeding segments; in such cases they have received the name of ring-joints (c*). The Club. — In many insects the distal seg- ments of the antennae are more or less enlarged. In such cases they are termed the club (c^). The Fiinicle. — The funicle (c^) is that part of the clavola between the club and the ring- joints; or, when the latter are not specialized, between the club and the pedicel. The various forms of antennse are designated by special terms. The more common of these forms are represented in Fig. 52. They are as follows : 1. Setaceous or bristle-like, in which the segments are successively smaller and smaller, the whole organ tapering to a point. 2. Ftliform or thread-like, in which the segments are of nearly uniform thickness. 3. Momlijorm or necklace-form, in which the segments are more or less globose, suggesting a string of beads. 4. Serrate or saw-like, in which the segments are triangular and project like the teeth of a saw. 5. Pectinate or comb-like, in which the seg- ments have long processes on one side, like the teeth of a comb. 6. Cldvate or club-shaped, in which the segments become gradually broader, so that the whole organ assumes the form of a club. 7. Capitate or with a head, in which the terminal segment or segments form a large knob. 8. Lamellate in which the segments that compose the knob are extended on one side into broad plates. When an antenna is bent abruptly at an angle like a bent knee (Fig. 51) it is said to be geniculate. Fig. 52. — Various forms of antennas. 42 AN INTRODUCTION TO ENTOMOLOGY The mouth-parts. — The mouth-parts consist typically of an upper lip, labrum, an under lip, labium, and two pairs of jaws acting hori- zontally between them. The upper jaws are called the mandibles; the lower pair, the maxilke. The maxillae and labium are each furnished with a pair of feelers, called respectively the maxillary palpi, and the labial palpi. There may be also within the mouth one or two tongue- like organs, the epipharynx and the hypopharynx. The mouth-par s of a locust will serve as an example of the typ cal form of the mouth- parts (Fig. 53). The mouth-parts enumer- ated in the preceding paragraph are those commonly recognized in insects; but in certain insects there exist vestiges of a pair of lobes between the mandibles and the maxillsp, these are the parag- natha. No set of organs in the body of an insect vary in form to a greater degree than do the mouth-parts. Thus with some the mouth ''s formed for chewing, while with others it is formed for sucking. Among the chewing insects some are predaceous, and have jaws fitted for seizing and tearing their prey ; others feed upon vegetable matter, and have jaws for chewing this kind of food. Among the sucknig insects the butterfly merely sips the nectar from flowers, while the mosquito needs a powerful instrument for piercing its victim. In this chapter the typical form of the mouth-parts as illustrated by the biting insects is described. The various modifications of it presented by the sucking insects are described later, in the discussions of the characters of those insect.^. Fig- 53- — Mouth-parts of a locust: la, lab- rum ;m£?, mandible; mx, maxilla; h, hypo- pharynx; /, labium. THE EXTERNAL ANATOMY OF INSECTS 43 The lab rum. — The Idhnmi or upper lip (Fig. 53), is a more or less flap-like organ above the opening of the mouth. As it is often freely movable, it has the appearance of an appendage of the body; but it is not a true appendage, being a part of one of the body segments that enter into the composition of the head. The mandibles. — The mandibles are the upper pair of jaws (Fig. 53). They represent the appendages of one of the segments of the head. In most cases they are reduced to a single segment; but in some insects, as in certain beetles of the family Scarabasidae, each mandible consists of several more or less distinct sclerites. The paragnatha. — In some insects there is between the mandibles and the maxillae a pair of more or less appendage-like organs borne by the hypopharynx. These are the "paragloss^" of writers on the Thysanura and Collemh ola and the "superlinguae" of Fol- som ('00). They were termed the maxillulae, a diminutive of maxillae by Hansen ('93), who regards them as homologous with the first maxillae of the Crustacea. But it has been shown by Crampton ('21) that they are homologous with the paragnatha of Crustacea. In Figure 54, A. represents a ventral view of the hypopharynx, parag- natha, and mandibles of the crustacean Ligyda; and B. the same parts of a naiad of a May-fly, Heptagenia. Paragnatha have been found in the Thysanura, Dermoptera, Orthoptera, Carrodentia, the naiads of Ephemerida, and the larvae of Coleoptera. The Maxilla;. — The maxilla: are the second pair of jaws of insects. Like the mandibles they are the appendages of one of the segments of the head. The maxillag are much more complicated than the mandibles, each maxilla consisting, when all of the parts are present, of five primary parts and three appendages. The primary parts are the cardo or hinge, the stipes or foot.- stalk, the palpifer or palpus-bearer, the subgalea or helmet-bearer, and the lacinia or blade. The appendages are the maxillary palpus or feeler, the galea Fig. 54. — A. Posterior (ventral") view of mandibles and hypopharynx of the crustacean Ligyda ;^ h, hypopharynx; p, paragnatha; m, mandibles: B. .Same of a nymph of the Mayfly Heptagenia (From Crampton). 44 AN INTRODUCTION TO ENTOMOLOGY or superior lobe, and the digitus or finger. The maxilla may also bear claw-like or tooth-like projections, spines, bristles, and hairs. In the following description of the parts of the maxillae, only very general statements can be made. Not only is there an infinite variation in the form of these parts, but the same part may have a very different outline on the dorsal aspect of the maxilla from what it has on the ventral. Compare Fi;j.55 and Fig. 56, which represent the two aspects of the maxilla of Hydrophilus. Excepting Fig. 56, the figures of maxilla; represent the ventral aspect of this organ. The cardo or hinge (a) is the first or proximal part of the maxilla. It is usually more or less triangular in outline, and is the part upon which nearly all of the motions of this organ depend In many cases, however, it is not the only part directly joined to the body; for frequently muscles extend direct to the L:iibgalea, without passing through the cardo. The stipes or footstallc ih) is the part next in order proceeding distad. It is usually triangular, and articulates with the cardo by its base, with the palpifer by its lateral margin, and with the subgalea by its mesal side. In many insects the stipes is united with the subgalea, and the two form the larger portion of the body of the maxilla (Fig. 53). The stipes has no appendages; but the palipfer on the one ide, and the subgalea on the other, may become united to the stipes without anys trace of suture remaining, and their appendages will then appear to be borne by the stipes. Thus in Fig. 53 it appears to be the stipes that bears the galea, and that receives muscles from the body. The palpifer or palpus-bearer (c) is situated upon the lateral (outer) side of the stipes; it does not, however, extend to the base of this organ, and frequently projects distad beyond it. It is often much more developed on the dorsal side of the maxilla than on the ventral (Figs. 55 and 56). It can bereadily distinguished when it is distinct by the insertion upon it of the ap- pendage which gives to it its name. The maxillary palpus or feeler (d) is the most conspicuous of the appendages of the maxilla. It is an organ composed of from one to six freely movable segments, and is articulated to the palpifer on the latero-distal angle of the body of the maxilla. The subgalea or heknet-bearer (e) when developed as a distinct sclerite is most easily distinguished as the one that bears the galea. It bounds the stipes more or less completely on its mesal (inner) side, and is often directly connected with the body by muscles. In many Coleoptera it is closely united to the lacinia; this gives the lacinia the appearance of bearing the galea, and of being connected with the body (Fig. 56). In several orders the subgalea is united to the stipes; consequently in these orders the stipes appears to bear the galea, and to be joined directly to the body if any part besides the cardo is so connected. Fig. 55. — Ventral as- pect of a maxilla of Hydrophilus. Fig. 56. — Dorsal as- pect of a maxilla of Hydrophilus. THE EXTERNAL ANATOMY OF INSECTS 45 Fig' 57- — Maxilla of Cicindela. The galea or helmet (/) is the second in prominence of the appendages of the maxilla. It consists of one or two segments, and is joined to the maxilla mesad of the palpus. The galea varies greatly in form: it is often more or less flattened, with the distal segment concave, and overlapping the lacinia like a hood. It was this form that suggested the name galea or helmet. In other --^\\ 'HI A 1 r^ 'i^' ^ cases the galea resembles a palpus in form (Fig. Jx.^ X \\ V> \^I~^^ 5"^- "^^^^ galea is also known as the outer lohe, ^^ the upper lobe, or the superior lobe. The lacinia or blade (g) is borne on the mesal (inner) margin of the subgalea. It is the cutting or chewing part of the maxilla, and is often furnished with teeth and spines. The lacinia is also known as the inner lobe, or the inferior lobe. The digitus or finger Qi) is a small appendage sometimes borne by the lacinia at its distal end. In the Cicindelidse it is in the form of an articu- lated claw (Fig. 57); but in certain other beetles it is more obviously one of the segments of the maxilla (Figs. 55 and 56). The labium or second maxillcs. — The labium or under lip (Fig. 53), is attached to the cephalic border of the gula, and is the most ventral of the mouth-parts. It appears to be a single organ, although some- times cleft at its distal extremity; it is, however, composed of a pair of appendages grown together on the middle ine of the body. In the Crustacea the parts corresponding to the labiimi of insects consists of two distinct organs, resembling the maxillse; and in the embryos of insects the labium arises as \ \ \V'- "1 T » i-i/ d- a pair of append- ages. In naming the parts of the labium, entomo- logists have usually taken some form of it in which the two parts are completely grown together, that is, one which is not cleft on the middle line (Fig. 58). I will first describe such a labium, and later one in which the division into two parts is carried as far as we find it in insects. Fig. 58. — Labium of Harpalus. 46 AN INTRODUCTION TO ENTOMOLOGY The labium is usually described as consisting of three principal parts and a pair of appendages. The principal parts are the submentum, the mentum, and the ligula; the appendages are the labial palpi. The submentum. The basal part of the labium consists of two transverse sclerites; the proximal one, which is attached to the cephaUc border of the gula, is the submentum (a). This is often the most prominent part of the body of the labium. The mentum is the more distal of the two primary parts of the labium (b). It is articulated to the cephaHc border of the submentum, and is often so slightly developed that it is concealed by the submentum. The Itgula includes the remaining parts of the labium except the labial palpi. It is a compound organ; but in the higher insects the sutures between the different sclerites of which it is composed are usually obsolete. Three parts, however, are commonly distinguished (Fig. 58), a central part, often greatly prolonged, the glossa (c^) and two parts, usually small membranous projections, one on each side of the base of the glossa, the paraglosscB (c^) . Sometimes, how- ever, the paraglossas are large, exceeding the glossa in size. The labial palpi. From the base of the ligula arise a pair of appendages, the labial palpi. Each labial palpus consists of from one to four freely movable segments. In the forms of the labium just described, the correspondence of its parts tc the parts of the maxillae is not easily seen; but this is much more evident in the labium of some of the lower insects, as for example a cockroach (Fig. 59). Here the organ is very deeply cleft; only the submentum and mentum remain united on the median line; while the ligula consists of two distinct maxilla-like parts. It is easy in this case to trace the correspondence referred to above. Each lateral half of the submentum corresponds to the cardo of a maxilla; each half of the mentum, to the stipes; while the remaining parts of a maxilla are represented by each half of the ligula, as follows: near th- base of the ligula there is a part (c') which bears the labial palpus; this appears in the figure like a basal segment of the palpus; but in many insects it is easily seen that it is undoubtedly one of the primary parts of the organ; it has been named pig_ CQ_ Labium of a ^^^^ palpiger, and is the homologue of the palpifer of cockroach. a maxilla. The trunk of each half of the ligula is formed by a large sclerite (c*) ; this evidently corres- ponds to the subgalea. At the distal extremity of this subgalea of the labium there are two appendages. The lateral one of these (f^) is the paraglossa, and obviously corresponds to the galea. The mesal one (<,-) corresponds to the lacinia or inner lobe. This part is probably wanting in those insects in which the glossa consists of an undividei: part; and in this case the glossa probably represents the united and more or less elongated subgalese. The epipharynx. — In some insects there is borne on the ental stir- face of the labium, within the cavity of the mouth, an unpaired fold, which is membranous and more or less chitinized; this is the epi- ph&rynx. THE EXTERNAL ANATOMY OF INSECTS 47 The hypopharynx. — The hypophdrynx is usually a tongue-like organ borne on the floor of the mouth cavity. This more simple form of it is well-shown in the Orthoptera (Fig. 53). To the hypopharnyx are articulated the ])aragnatha when they are present. The hypo- pharynx is termed the lingua by some writers. d. THE SEGMENTS OF THE HEAD The determination of the number of segments in the head of an insect is a problem that has been much discussed since the early days of entomology. The first important step towards its solution was made by Savigny (1816), who sug- gested that the movable appendages of the head were homodyanmous with legs. This conclusion has been accepted by all; and as each segment in the body of an insect bears only a single pair of appendages, there are at least four segments in the head; i.e., the antennal, the mandibular, the maxillary, and the second maxillary or labial. In more recent times workers on the embryology of insects have demonstrated the presence of 'wo additional segments. First, there has been found in the embryos of many insects a pair of evanescent appendages situated between the antennae and the mandibles. These evidently correspond to the second antennae of Crustacea, and indicate the presence of a second antennal segment in the head of an insect. This conclusion is confirmed by a study of the development of the nervous system. And in the Thysanura and Collembola vestigs-s of the second antennas persist in the adults of certain members of these orders. Second, as the compound eyes are borne on movable stalks in certain Crusta- cea, it was held by Milne-Edwards that they represent another pair of appendages; but this view has not been generally accepted. It is not necessary, however, to discuss whether the eyes represent appendages or not; the existence of an ocjlar segment has been demonstrated by a study of the development of the nervous system. It has been shown that the brain of an insect is formed from three pairs of primary ganglia, which correspond to the three principal divisions of the brain, the protecerebrum, the deutocerehrum, and the triiocerebrum. And it has also been shown that the protocerebrum innervates the compound eyes and ocelli; the deutocerehrum, the antennae; and the tritocerebrum, the labrum. This demon- strates the existence of three premandibular segments: an ocular segment or protocerebral segment, without appendages, unless the compound eyes repre- sent them; an antennal or deutocerebral segment, bearing antennae; and a second antennal or tritocerebral segment, of which the labrum is a part, and to which the evanescent appendages between the antennae and the mandibles doubt- less belong. As Viallanes has shown that the tritocerebrum of Crustacea inner- vates the second antennae, we are warranted in considering the tritocerebral segment of insects to be the second antennal segment. l^olsom ('00) in his work on the development of the mouth-parts of Annrida described a pair of primary ganglia which he believed indicated the presence of a segment between the mandibular and maxillary segments. He named the ap- pendages of this segment the superlinguce; they are the paragnatha described above. The existence of the supposed ganglia indicating the presence of a super- lingual segment has not been confirmed by other investigators and is no longer maintained by Folsom. 48 AN INTRODUCTION TO ENTOMOLOGY The suboesophageal ganglion is formed by the union of three pairs of primitive ganglia, pertaining respectively to the mandibular, the maxillary, and the labial segments of the embryo. LIST OF THE SEGMENTS OF THE HEAD First, ocular, or protocerebral. Second, antennal, or deutocerebral. Third, second antennal, or tritocerebral. Fourth, mandibular. Fifth, maxillary. Sixth, labial, or second maxillary. III. THE THORAX a. THE SEGMENTS OF THE THORAX The prothorax, the meso'ihorax, and the metathorax. — The thorax is the second or intermediate region of the body; it is the region that in nymphs, naiads, and adults bears the organs of locomotion, the legs, and the wings when they are present. This region is composed of three of the body-segments more or less firmly joined together; the segments are most readily distinguished by the fact that each bears a pair of legs. In winged insects, the wings are borne by the second and third segments. The first segment of the thorax, the one next the head, is named the prothorax; the second thoracic segment is the mesothorax; and the third, the metathorax. The simplest form of the thorax in adult insects occurs in the Apterygota (the Thysanura and the Collembola) where although the seg- ments differ in size and proportions, they are distinct and quite similar (Fig. 60). In the Pterygota, or winged insects, the prothorax is either free or closely united to the mesothorax ; in many cases it is greatly reduced in size; it bears the first pair of legs. The meso- thorax and the metathorax are more or less closely united, forming a box, which bears the wings and the second and third pairs of legs. This union of these two segments is often so close that it is ver\^ difficult to distin- guish their limits. Sometimes the matter is farther complicated by a union with the thorax of a part or of the whole of the first Fig. 60. — Lepisma saccharina (After Lubbock) . THE EXTERNAL ANATOMY OF INSECTS 49 abdominal segment. In the Acridiid^, for example, the sternum of the first abdominal segment forms a part of the intermediate region of the body, and in the Hymenoptera the entire first abdominal segment pertains to this region. The alitrunk. — ^When, as in the Hymenoptera, the intermediate region of the body includes more than the three true thoracic seg- ments it is designated the alitrunk. The propodeum or the median segment. — ^When the alitrunk con- sists of four segments the abdominal segment that forms a part of it is termed the -propodeum or the median segment. In such cases the true second abdominal segment is termed the first. h. THE SCLERITES OF A THORACIC SEGMENT The parts of the thorax most generally recognized by entomologists were described nearly a century ago by Audouin (1824) ; some addi- tional parts not observed by Audouin have been described in recent times, by the writer ('02), Verhoeff ('03), Crampton ('09), and Snodgrass ('09, '10 a, and '10 6). The following account is based on all of these works. In designating the parts of the thorax the prefixes pro, meso, and meta are used for designating the three thoracic segments or corres- ponding parts of them; and the prefixes pre and post are used to designate parts of any one of the segments. Thus the scutum of ths prothorax is designated the proscutum; while the term prescutum is applied to the sclerite immediately in front of the scutum in each of the thoracic segments. This system leads to the use of a number of hybrid combinations of Latin and Greek terms, but it is so firmly established that it would not be wise to attempt to change it on this account. Reference has already been made to the division of a body-segment into a tergum, two pleura, and a sternum ; each of these divisions will be considered separately; and as the maximum number of parts are found in the wing-bearing segments, one of these will be taken as an illustration. The sclerites of a tergum. — In this discussion of the external ana- tomy of the thorax reference is made only to those parts that form the external covering of this region of the body. The infoldings of the body-wall that constitute the internal skeleton are discussed in the next chapter. The notum. — In nymphs and in the adults of certain generalized insects the tergum of each wing-bearing segment contains a single 50 AN INTRODUCTION TO ENTOMOLOGY chitinized plate; this sclerite is designated the notuni. The term notum is also applied to the tergal plate of the prothorax and to that of each abdominal segment. The three thoracic nota are designated as the pronotum, the mesonotum, and the metanotum respectively. The notum of a wing-bearing segment is the part that bears the wings of that segment, even when the tergum contains more than one sclerite. Each wing is attached to two processes of the notum, the anterior notal process (Fig. 61, a n p) and the posterior notal process (Fig. 61, p n p); and the posterior angles of the notum are produced into the axillary cords, which form the posterior margins of the basal membranes of the wings The postnotum or postscuteUum. — In the wing-bearing segments of most adult insects the tergum consists of two principal sclerites; the notum already described, and behind this a narrower, transverse sclerite which is commonly known as the postscuteUum, and to which Snodgrass has applied the term postnotum (Fig. 61, P N). The divisions of the notum. — In most specialized insects the notum of each wing-bearing segment is more or less distinctly divided by transverse lines or sutures into three parts; these are known as the prescUtum (Fig. 61, Psc), the scutum (Fig. 61, Set), and the scutellum (Fig. 61, Scl). It has been commonly held, since the days of Audouin, that the tergum of each thoracic segment is composed typically of four sclerites, the prescutum, scutum, scutellum, and postscuteUum. But the investigations of Snodgrass indicate that in its more genera- lized form the tergum contains a single y^j,.^ sclerite, the notum; that the postscuteUum Tg-- or postnotum is a secondary tergal chitini- ^^ zation in the dorsal membrane behind the notum, in more specialized insects; and that the separation of the notum into tliree parts, the prescutum, scutum, and scutellum, is a still later specialization that has arisen independently in diflerent orders, and does not indicate a division into homologous parts in all orders where it exists. The patagia. — In many of the more speciaHzed Lepidoptera the pronotum Fig.61.— Diagram of a generalized is produced on each side into a fiat thoracic segment (From Snod- lobe, which in some cases is even con- S^^^^'- stricted at the base so as to become a stalked plate, these lobes are the patagia. THE EXTERNAL ANATOMY OF INSECTS 51 The parapsides. — In some Hymenoptera the scutum of the meso- thorax is divided into two parts by the prescutum; these separated halves of the scutum are called the parapsides (see Fig. 1130A). The sclerites of the pleura. — ^In the accompanying figure (Fig. 61) the sclerites of the left pleurum of a wing-bearing segment are repre- sented diagrammatically; these sclerites are the following: The episternum. — Each pleurum is composed chiefly of two sclerites, which typically occupy a nearly vertical position, but usually are more or less oblique. In most insects the dorsal end of these sclerites extends farther forward than the ventral end, but in the Odonata the reverse may be true. The more anterior in position of these two sclerites is the episternum (Fig. 61, Eps). In several of the orders of insects one or more 01 the epistema are divided by a distinct suture into an upper and a lower part. These two parts have been designated by Crampton ('09) as the anepistSr- num and the katepisternum respectively (Fig. 62). The epimerum. — The epimerum is the more posterior of the two principal sclerites of a pleurum (Fig. 61). It is separated from the episternum by the pleural suture (Fig. 61 , PS) which extends from the pleural wing process above (Fig. 61, Wp) to the pleural coxal process below (Fig. 61, CxP). In some of the orders of insects one or more of the epimera are divided by a distinct suture into an upper and a lower part. These two parts have been desig- nated by Crampton ('og) as the anepimerum and the katepimerum respectively (Fig. 62). The preepisternum. — In some of the more generalized insects there is a sclerite situated in front of the episternum; this is the pre- episternum..' The paraptera. — i'n many insects there is on each side a small sclerite between the upper end of the episternum and the base of the wing ; these have long been known as the paraptera. ^^- ^^■—^^^^''^^^^^V^^^ Snodgrass (10 a) has shown that there are in of the meso- and meta- ..... thorax of Maniispa some msects two sclerites in this region, which , rugicolHs; i i anepis- ^g designates the episternal paraptera or ternum; 2,2,katcpister- '^ -^ r r num; j, ?, anepimer- preparaptera (Fig. 61, iP and 2P); and that um; <^, 4, katepimerum; ^^^ ^j. occasionally two are similarly situated between the epimerun and the base of the wing, the epimeral paraptera or postparaptera (Fig. 61, 3F). 52 AN INTRODUCTION TO ENTOMOLOGY The spiracles. — The external openings of the respiratory system are termed spiracles. Of these there are two pairs in the thorax. The first pair of thoracic spiracles open, typically, one on each side in the transverse conjunctiva between the prothorax and the meso- thorax ; the second pair open in similar positions between the meso- thorax and the me athorax. In some cases the spiracles have migrated either forward or backward upon the adjacent segment. For a discussion of the number and distribution of the spiracles, see the next chapter. The periiremes. — In many cases a spiracle is surrounded by a cir- cular sclerite; such a sclerite is termed a peritreme. The acetabula or coxal cavities. — In some of the more specialized insects, as many beetles for example, the basal segment of the legs is inserted in a distinct cavity ; such a cavity is termed an acetabulum or coxal caz'ity. When the epimera of the prothorax extend behind the coxse and reach the prostemum, the coxal cavities are said to be closed (Fig. 63) ; when the epimera do not extend behind the coxa; to the prosterum, the coxal cavities are described as open (Fig. 64) . The sclerites of a sternum. — In the more generalized insects the sterniim of a wing-bearing segment may consist of three or four sclerites. These have been designated, beginning with the anterior one, the presternum (Fig. , ^v the sternellum (Fig. 61, ^^^c\ Sl),a.ndt\-\epoststernellum >^ /-\ ^\\ (Fig. 61, Psl). / /V ^ '^^^^J^^^^^^^ In the more special- / / \ ' ^ ^ 'Xl^ / ized insects only one of / / \^^^] \/~yv^ / ^y\ these, the sternum, re- / I ^^K| ^ \C X—-^^^! \ mains distinctly visible. \ ^^^m-- A '^/ ^^ / ' It is an inteTes!:ing fact I \v.//'""'^l-J_J^^^^^\ y^ I that while in the speciali- \ | \ '^ I zation of the tergum | y v. j there is an increase in ^-^^ 63.-Prothorax of Harpalus, ventral aspect; the ntimber of the scleri- c, coxa; em, epimerum; es, episternum; /, tes in this division of a ^^"^^= "' P^o^o^um; ., ., ., prostemum. segment, in the specialization of the sternum there is a reduction. It is a somewhat unfortunate fact that the term sterntmi has been used in two senses : first, it is applied to the entire ventral division of a segment ; and second, it is applied to one of the sclerites entering THE EXTERNAL ANATOMY OF INSECTS 53 Fig. 64. — ^Prothorax of Penlhe; c, coxa; cc, coxal cavity ;/, femur ; 5, prosternum; ir, trochanter. into the composition of this division when it consists of more than a single sclerite. To meet this difhctilty Snodgrass has proposed that the term eusternum be apphed to the sclerite that has been known as the sternum; and that the word sternum be used only to designate the entire ventral divi- sion of a segment. C. THE ARTICULAR SCLERITES OF THE APPENDAGES At the base of each leg and of each wing there are typically several sclerites between the appendage proper and the sclerites of the trunk of the segment ; these sclerites, which occupy an intermediate position between the body and its appendage, are termed the articular sclerites. Frequently one or more of the articular sclerites become consoli- dated wdth sclerites of the trunk so as to appear to form a part of its wall; this is especially true of those at the base of the legs. The articularscleritesof thelegs. — ^The proximal segment of the leg, the coxa, articulates with the body by means of two distinct articula- tions, which may be termed the pleural articulation of the coxa and the ventral articulation of ike coxa respectively. The pleural articulation is with the ventral end of the foot of the lateral apodeme of the seg- ment, i. e. with the pleural coxal process, which is at the ventral end of the suture between the epistemum and the epimerun (Fig. 61, CxP). The ventral arti- culation is with a sclerite situated between the coxa and the epistemum; this sclerite and others asso- ciated with it may be termed the articular sclerites of the legs. The articular sclerites of the legs to which distinctive names have been applied are the following : The irochantin. — The maximtmi number of articular sclerites of the legs are found in the more generalized insects; in the more specialized insects the number is reduced by a consolidation of some of them with Fig. 65.— The base of a leg of a cock- roach. 54 , AN INTRODUCTION TO ENTOMOLOGY adjacent parts. The condition found in a cockroach may be taken as typical. In this insect the trcchantin (Fig. 65, t) is a triangular sclerite, the apex of which points towards the middle line of the body, and is near the ventral articulation of the coxa (Fig. 65,3/). In most specialized insects the trochantin is consolidated with the antecoxal piece, and the combined sclerites, which appear as one, are termed the trochantin. The antecoxal piece. — Between the trochantin and the epistemum there are, in the cockroach studied, two sclerites; the one next the trochantin is the antecoxal -piece. This is the articular sclerite that articulates directly with the coxa (Fig. 65, ac). As stated above, the antecoxal piece is usually consolidated with the trochantin, and the term trochantin is applied to the combined sclerites. Using the term trochantin in this sense, the statement commonly made that the ventral articulation of the coxa is with the trochantin is true. The second antecoxal piece. — The sclerite situated between the antecoxal piece and the episternum is the second antecoxal piece (Fig. 65, n^ac). This is quite distinct in certain generalized insects; but it is usually lacking as a distinct sclerite. The articular sclerites of the wings.- — In the Ephemerida and Odo- nata the chitinous wing-base is directly continuous with the walls of the thorax. In all other orders there are at the base of each wing several sclerites which enter into the composition of the joint by which the wing is articulated to the thorax ; these may be termed collectively the articular sclerites of the wings. Beginning with the front edge of this joint and passing backward these sclerites are as follows: The tegula. — In several orders of insects there is at the base of the costal vein a small, hairy, sHghtly chitinized pad; this is the tegula (Fig. 66, Tg) . In the more highly specialized orders, the Lepidoptera, the Hymenoptera, and the Diptera, the tegula is largely developed so as to form a scale-like plate overlapping the base of the wing. The tegulas of the front wings of Lepidoptera are specially large and are carried by special tegular plates of the notum. These, in turn, are supported by special internal tegular arms from the bases of the pleural wing-processes (Snodgrass, '09) The axillaries. — Excepting the tegula, which is at the front edg3 of the wing-joint, the articular sclerites of the wings have been termed collectively the axillaries. Much has been written about these sclerites, and many names have been applied to them. The simplest terminology is that of Snodgrass ('09 and '10 a) which I here adopt. THE EXTERNAL ANATOMY OF INSECTS 55 The first axillary. — This sclerite (Fig. 66, i Ax) articulates with the anterior notal wing -process and is specially connected with the base of the subcostal vein of the wing. In rare cases it is divided into two. The second axillary. — The second axillary (Fig. 66, 2 Ax) articulates with the first axillary proximally and usually with the base of the radius distally ; it also articulates below with the wing-process of the pleurum, constituting thus a sort of pivotal element. The third axillary. — The third axillary (Fig. 66, 3 Ax) is interposed between the bases of the anal veins and the fourth axillary when this sclerite is present. When the fourth axillary is absent, as it is in Fig. 66. — Diagram of a generalized wing and its articular sclerites (From Snodgrass) . nearly all insects except Orthoptera and Hymenoptera, the third axillary articulates directly with the posterior notal wing-process. The fourth axillary. — When this sclerite is present it articulates with the posterior notal wing-process proximally and with the third axillary distally (Fig. 66, 4 Ax). Usually this sclerite is absent; it occurs principally in Orthoptera and Hymenoptera. The median plates. — The median plates of the wing-joint are not of constant shape and occurrence; when present, these plates are associated with the bases of the media, the cubitus, and the first anal vein when the latter is separated from the other anals. Often one of them is fused with the third axillary and sometimes none of them are present. d. THE APPENDAGES OF THE THORAX The appendages of the thorax are the organs of locomotion. They consist of the legs and the vcings. Of the former there are three 56 AN INTRODUCTION TO ENTOMOLOGY pairs, a pair borne by each of the three thoracic segments; of the latter there are never more than two pairs, a pair borne by the meso- thorax and a pair borne by the metathorax. One or both pairs of wings may be wanting. The legs. — Each leg consists of the following named parts and their appendages: coxa, trochanter, femur, tibia, and tarsus. The coxa. — The coxa is the proximal segment of the leg ; it is the one by which the leg is articulated to the body (Fig. 67). The coxa varies much in form, but it is usually a truncated cone or nearly globular. In some insects the coxse of the third pair of legs are more or less flattened and immovably attached to the metastemtmi; this is the case in beetles of the family Carabidae for example. In such cases the coxae really form a part of the body-wall, and are liable to be mistaken for primary parts of the metathorax instead of the proximal segments of appendages. In several of the orders of injects the coxa is apparently composed of two, more or less dis- tinct, parallel parts; this is the case, for example, in in- sects of the trichopterous genus Neuro- ma (Fig. 68, Cx and epm). But it has been shown by Snodgrass ('09) that the posterior part of the sup- posed double coxa, the "rreron" (Fig. 68, epm) is a detached por- tion of the epimej-um. The siyli — In certain generalised insects, as Machilis of the order B C !Fig. 67. — Legs of insects: A, wasp; B, ichneumon-fiy; C, bee; c, coxa; tr, trochanter; /, femur; //, tibia; k,. tarsus; m, metatarsus. THE EXTERNAL ANATOMY OF INSECTS 57 Thysanura, the coxa of each middle and hind leg bears a small appendage, the stylus (Fig. 69). The styli are of great interest as they are believed to correspond to one of the two branches of the legs of Crustacea; thus indicating that insects have descended from forms in which the legs were biramous. In several genera of the Thysanura one or more of the abdominal segments bear each a pair of styli ; in Machilis they are found on the second to the ninth abdominal segments. These styli are regarded as vestiges of abdominal legs. The trochanter. — The trochanter is the second part of the leg. It consists usually of a very short, triangular or quadrangular segment, between the coxa and the femur. Sometimes the femur appears to articulate directly with the coxa ; and the trochanter to be merely an appendage of the prox'mal end of the femur {e. g. Carabidae) . But the fact is that in these insects, although the femur may touch the coxa, it does not articulate with it; and the organs that pass from the cavity of the coxa to that of the femur must pass through the ' trochanter. In some Hymenoptera the tro- chanter consists of two segments (67, B). The femur. — The femur is the third part of the leg; and is usually the largest part. It consists of a single segment. The tibia. — The tibia is the fourth part of the leg. It consists of a single segment; and Fig. 68.— Lateral aspect ^^ usually a little more slender than the femur, of the mesothorax of although it often equals or exceeds it in length. In such species as burrow in the ground, the distal extremity is greatly broadened and shaped more or less like a hand. Near the distal end of the tibia there are in most insects one or more spurs, which are much larger than the hairs and spines which arm the leg; these are called the tibial spurs, and are much used in classification. The tarsus. — The tarsus is the fifth and most distal part of the leg, that which is popularly called the foot. It consists of a series of segments, varying in number from one to six. The most common ntmi- ber of segments in the tarsus is five. In many insects, the first segment of the tarsus is much longer, Neuronia (From Snod- grass). Fig. 69.— A s, stylus. of Machilis; 58 AN INTRODUCTION TO ENTOMOLOGY and sometimes much broader, than the other segments. In such cases this segment is frequently designated as the metatarsus (Fig. 67, C, m). In some insects the claws borne by the distal end of the tarsus are outgrowths of a small terminal portion of the leg, the sixth segment of the tarsus of some authors. This terminal part with its appendages has received the name pr(starsus (De Meijere '01). As a rule the prajtarsus is withdrawn into the fifth segment of the tarsus or is not present as a distinct segment. On the ventral surface of the segments of the tarsus in many insects are cushion-like structures; these are called puMlU. The cuticula of the pulvilli is traversed by ntimerous pores which open either at the surface of the cuticula or through hollow hairs, the tenent-hairs, and from which exudes an adhesive fluid that enables the insect to walk on the lower surface of objects. With many insects (e. g. most Diptera) the distal segment of the tarsus bears a pair of pulvilli, one beneath each claw. In such cases there is frequently between these pulvilli a third single appendage of similar structure ; this is called the empodium; writers on the Orthop- tera commonly called the appendage between the claws the arolium. In other insects the empodium is bristle-like or altogether wanting. In many insects the pul villus of the distal segment of the tarsus is a circular pad projecting between the tarsal claws. In many descriptive works this is referred to as the pulvillus , even though the other pulvilli are well-developed. The pulvilH are called the onychii by some writers. The claws borne at the tip of the tarsus are termed the tarsal claws or ungues; they vary much in form; they are usually two in number, but sometimes there is only one on each tarsus. The wings. — The wings of insects are typically two pairs of mem- branous appendages, one pair borne by the mesothorax and one pair by the metathorax; pro thoracic wings are unknown in living insects but they existed in certain paleozoic forms. Excepting in the subclass Apterygota which includes the orders Thysanura and CoUembola, wings are usually present in adult insects. Their absence in the Apterygota is due to the fact that they have not been evolved in this division of the class Hexapoda; but when they are absent in adult members of the subclass Pterygo- ta, which includes the other orders of insects, their absence is due to a degradation, which has resulted in their loss. THE EXTERNAL ANATOMY OF INSECTS 59 The loss of wings is often confined to one sex of a species; thus with the canker-worm moths, for example, the females are wingless, while the males have well-developed wings; on the other hand, with the fig-insects, Blastophaga, the female is winged and the male wingless. Studies of the development of wings have shown that each wing is a Saclike fold of the body-wall; but in the fully developed wing, its saclike nature is not obvious; the upper and lower walls become closely applied throughout the greater part of their extent ; and since they become very thin, they present the appearance of a single delicate membrane. Along certain lines, however, the walls remain separate, and are thickened, forming the firmer framework of the wing. These thickened and hollow lines are termed the veins of the wing; and their arrangement is described as the venation of the wing. The thin spaces of the wings which are bounded by veins are called cells. When a cell is completely surrounded by veins it is said to be closed; and when it extends to the margin of the wing it is said to be open. The (liferent types of insect wings. — What may be regarded as the typical form of insect wing is a nearly flat, dehcate, membranous appendage of the body, which is stiffened by the so-called wing- veins ; but striking modifications of this form exist; and to certain of them distinctive names have been applied, as follows : In the Coleoptera and in the Dermaptera, the front wings are thickened and serve chiefly to protect the dorsal wall of the body and the membranous hind wings, which are folded beneath them when not in use. Front wings of this type are termed wing-covers or elytra. The front wings of the Heteroptera, which are thickened at the base like elytra, are often desig- nated the hemelytra. The thickened fore wings of Orthoptera are termed iegmina by many writers. The hind wings of Diptera, which are knobbed, thread-like organs, are termed halteres. The hind wings of the males of the family Coccid^ are also thread- Fig. 70.— Diagram of a wing showing ijj^g margins and angles. _ I he reduced front wmgs of the Strepsiptera are known as the pseudo-halteres. 60 AN INTRODUCTION TO ENTOMOLOGY The margins of wings. — Most insect wings are more or less triangular in outline; they, therefore, present three margins: the costal margin or costa (Fig. 70, a-b); the outer margin (Fig. 70, b-c); and the inner margin (Fig. 70, c-d). The angles of wings. — The angle at the base of the costal margin of a wing is the humeral angle (Fig. 70, a); that between the costal margin and the outer margin is the apex of the wing (Fig. 70. 6); Fig. 71. — Wing of Conops; ae, a ciliary excision; /, posterior lobe. and that between the outer margin and the inner margin is the anal angle (Fig. 70, c). The axillary cord. — The posterior margin of the membrane at the base of the wing is usually thickened and corrugated; this cord-like structure is termed the axillary cord. The axillary cord normally arises, on each side, from the posterior lateral angle of the notum, and thus serves as a mark for determining the posterior limits of the notum. The axillary membrane. — The membrane of the wing base is termed the axillary membrane; it extends from the tegula at the base of the costal margin to the axillary cord ; in it are found the axillary sclerites. The alula.— In certain families of the Diptera and of the Coleop- tera the axillary membrane is expanded so as to form a lobe or lobes which fold beneath the base of the wing when the wings are closed; this part of the wing is the alula or alulet. The aivlse are termed the squamce by some writers, and the calypteres by others. Fie 72. — ^Wings of the honeybee; hamuli. THE EXTERNAL ANATOMY OF INSECTS 61 The axillary excision. — In the wings of most Diptera and in the wings of many other insects there is a notch in the inner margin of the wing near its base (Fig. 71, ae), this is the axillary excision. The posterior lobe of the wing. — That part of the wing lying between the axillary excision when it exists, and the axillary membrane is the posterior lobe of the wing. The posterior lobe of the wing and an alula are easily differentiated as the alula is margined by the axillary cord. The methods of uniting the two wings of each side. — It is obvious that a provision for ensuring the synchronous action of the fore and hind wings adds to their efficiency; it is as important that the two pairs of wings should act as a unit as it is that the members of a boat's crew should pull together. In many insects the synchronous action of the wings is ensured by the fore wing overlapping the hind wing. But in other insects special structures have been developed which fasten together the two wings of each side. The different types of these structures have received special names as follows: The hamuli. — With certain insects the costal margin of the hind wings bears a row of hooks, which fasten into a fold on the inner margin of the fore wings (Fig. 7 2) ; these hooks are named the hdmtdi. The frenulum and the frenulum hook. — In most moths there is a strong spine-like organ or a bunch of bristles borne by the hind wing at the htuneral angle (Fig. 73,/); this is the frenulum or little bridle. As a rule the frenulum of the female consists of several bristles ; that of the male, of a single, strong, spine-like organ. In the males of certain moths, where the frenulum is highly developed, there is a membranous fold on the fore wing for receiving the end of the frenulum, this is the frenulum hook (Fig. 7s,fh). The jugum. — In one family of moths, the HepiaHdae, the posterior lobe of the fore wing is a slender, finger-like organ which is stiffened by a branch of the third anal vein, and which projects beneath the costal margin of the hind wing. As the greater part of the inner margin of the fore Fig- 73. — Wings of Thyridopteryx ephemerce- formds; f, frenulum; fh, frenulum hook. 62 AN INTRODUCTION TO ENTOMOLOGY wing overlaps the hind wing, the hind wing is held between the two (Fig. 74). This type of the posterior lobe of the fore wing is termed the jugum or yoke. The structure of the jugum is shown in Figure 75. The fibula. — In several groups of insects an organ has been developed that serves to unite the fore and hind wings, but which functions in a way quite different from that of the jugum. Like the jugum it is found at the base of the fore wing ; but unlike the jugum it extends back above the base of the hind wing and is clasped over an elevated part of the hind wing; this organ is the fibula or clasp. In some insects, as in the Trichoptera, the fibula consists only of a specialized posterior lobe of the fore wing; in others, as in the genus Corydalus of the order Neuroptera, the proximal part of the fibula is margined by the axillary cord, showing that the axillary membrane enters into the composition of this organ (Fig. 76). The hypothetical type of the primitive wing-venation. — A careful study of the wings of many insects has shown that the fundamental type of venation is the same in all of the orders of winged insects. But this fact is evident only when the more primitive or generalized members of different orders are compared with each other. In most of the orders of insects the greater nrmiber of species have become so modified or specialized as regards the structure of their wings that it is diffi- cult at first to trace out the primitive type. This agreement in the important features of the venation of the wings of the generalized members of the different orders of insects is still more evident when the wings of nymphs, naiads, and pupae are studied. It has been demonstrated that in the development of wings of generalized insects the longitudinal wing-veins are formed about preexisting trachese. In the develop- ment of the wing, these tracheae grow out into the wing-bud, and later the wing-veins are formed about them. Fig. 74.- below; -Wings of a hepialid, seen from c, accessory vein. THE EXTERNAL ANATOMY OF INSECTS 6;: The wings of nymphs, naiads, and pupag are broad at the base, and consequently the tracheae that precede the wing-veins are not crowded together as are the wing-veins at the base of the wings of Fig. 75. — Jugum of a hepialid. Fig. 76. — Fibula of Corydalus. adults. For this reason the identity of the wing-veins can be deter- mined more surely in the wings of immature insects than they can be in the wings of adults. This is especially true where two or more veins coalesce in the adult wing while the tracheae that precede these veins are distinctly separate in the immature wing. A study was made of the tracheation of the wings of immature insects of representatives of most of the orders of insects, and, assum- ing that those features that are possessed by all of them must have been inherited from a common ancestor, a diagram was made repre- senting the hypothetical tracheation of a nymph of the primitive winged insect (Fig. 77). In this diagram the trachese are lettered Fig- 77- — Hypothetical tracheation of a wing of the primitive nymph. with the abbreviations used in designating the veins that are formed about them in the course of the development of the wing. The dia- gram will serve, therefore, to indicate the typical venation of an insect 64 AN INTRODUCTION TO ENTOMOLOGY wing, except that the tracheae are not crowded together at the base of the wing as are the veins in the wings of adults.* Longitudinal veins and cross-veins. — The veins of the wing can be grouped under two heads: first, longitudinal veins, those that normally extend lengthwise the wing; and second, cross-veins, those that normally extend in a transverse direction. The insertion of the word normally in the above definitions is important; for it is only in comparatively generalized wings that the direction of a vein can be depended upon for determining to which of these two classes it belongs. The principal wing-veins. — The longitudinalwing- veins constitute the principal framework of the wings. In the diagram representing the typical venation of an insect wing (Fig. 77), only longitudinal veins are indicated ; this is due to the fact that the diagram was based on a study of the tracheation of wings, and in the more generalized wings the cross-veins are not preceded by tracheae; moreover in the wings of more generalized paleozoic insects there were no definite cross-veins, but merely an irregular network of thickened lines between the longitudinal veins. There are eight principal veins; and of these the second, third, fourth, and fifth are branched. The names of these veins and the abbreviations by which they are known are as follows, beginning with the on3 nsarest the costal margin of the wing: Nam3s of vsins Ahhrcjiitions Costa C Subcosta Sc Radius R Media M Cubitus Cu First Anal ist A Second Anal 2dA ThirdAnal 3dA The chief branches of the wing-veins. — The chief branches of the principal veins are numbered, beginning with the branch nearest to the costal margin of the wing. The term used to designate a branch of a vein is formed by compounding the name of the vein with a *For many details regarding the development of the wings of insects, their structure, and the terminology of the wing-veins, that can not be included in this work, see a volume by the writer entitled The Wings of Insects. This is published by The Comstock Publishing Company, Ithaca, N. Y. THE EXTERNAL ANATOMY OF INSECTS 65 numeral indicating the number of the branch ; thus, for example, the first branch of the radius is radius-one or vein Ri. In the case of radius and media, each of which has more than two branches, each division of the vein that bears two or more branches has received a special name. Thus after the separation of radius-one from the main stem of radius there remains a division which is typi- cally four-branched; this division is termed the radial sector, or vein Rsi the first division of the radial sector, which later separates into radius-two and radius-three, is designated as radius-two-plus- three or vein R2+3; and the second division is termed radius-four- plus-five or vein R4+5. Media is typically separated into two divi- sions, each of which is two-branched ; the first division is media-one- pl'us two or vein Mi +2, the second is media-three-plus-four or vein M3+4. The veins of the anal area. — -The three anal veins exhibit a wide range of variation both as to their persistence and to their form when ^/?..» Sc _ /?, /?.., ^ '^ f^r ^^-w /?5 iJ.A Fig. 78. — A wing of Rhyphus. present. In those cases where the anal veins are branched there is no indication that the branching has been derived from a uniform primitive type of branching. For this reason in describing a branched anal vein merely the number of branches is indicated. In some cases, as in the Odonata, there is a single anal vein the identity of which can not be determined. In such cases this vein is designated merely as the anal vein or vein A, and its branches as Ai, Ai, Az, etc. The reduction of the number of wing-veins. — In many wings the number of the veins is less than it is in the hypothetical type. In some cases this is due to the fact that one or more veins have faded out in the course of the evolution of the insects showing this deficiency; frequently in such wings vestiges of the lacking veins remain, either as faint lines in the positions formerly occupied by the veins or as 66 AN INTRODUCTION TO ENTOMOLOGY short fragments of the veins. A much more common way in which the niimber of veins has been reduced is by the coalescence of adja- cent veins. In many wings the basal parts of two or more principal veins are united so as to appear as a single vein ; and the number of the branches of a vein has been reduced in very many cases by two or more branches becoming united throughout their entire length. When a vein consists of two or more of the primitive veins united, the name applied to the compound vein should indicate this fact. In the wing of Rhyphus (Fig. 78), for example, radius is only three- branched; but it would be misleading to designate these branches as Ri, R2, and R3, for this would indicate that veins R4 and R5 are lacking. The first branch is evidently Ri ; the second branch is composed of the Fig. 79. — A wing of Tabanus. coalesced R2 and R3, it is, therefore, designated as R2+3; and the third branch, which consists of the coalesced R4 and R5, is designated as R4+5. A second method of coalescence of veins is illustrated by a wing of Tabanus (Fig. 79). In this wing the tips of cubitus-two and the second anal vein are united ; here the coalescence began at the margin of the wing and is progressing towards the base. The united portions of the two veins are designated as 2d A+Cu2. When it is desired to indicate the composition of a compound vein it can be readily done by combining the terms indicating its elements. But in descriptions of hymenopterous wings where a compound vein may be formed by the coalescence of several veins the logical carrying out of this plan would result in a very cumbersome terminology, one that it is impracticable to use in ordinary descrip- tions. In such cases the compound vein is designated by the term indicating its most obvious element. Thus, for example, in the fore THE EXTERNAL ANATOMY OF INSECTS 67 wing of Pampkilius, where veins M4, Cui, and Cu2 coalesce with the first anal vein, the united tips of these veins is designated as vein ist A, the first anal vein being its most obvious element (Fig. 80), although it is really vein M4+Cui+Cu2 + ist A. Serial veins. — In the wings of some insects, where the wing-vena tion has been greatly modified, as in certain Hymenoptera, there exist what appears to be simple veins that in reality are compound veins composed of sections of two or more veins joined end to end with no indication of the point of union. Compound veins formed in this Fig. 80. — Wings of Pampkilius. manner are termed serial veins. Examples of wings in which there ar e serial veins are figured in the chapter treating of the Hymenoptera. In designating serial veins either the sign & or a dash is used between the terms indicating the elements of the vein, instead of the sign + as the latter is used in designating compound veins formed by the coalescence of veins side by side. If the serial vein consists of only two elements the sign & is used; thus the serial vein in the wings of braconids, which consists of the medial cross-vein and vein M2, is designated as w & M2. In those cases where sections of several veins enter into the com- position of a serial vein, the serial vein is designated by the abbrevia- tion of the name of the basal element connected by a dash with the AN INTRODUCTION TO ENTOMOLOGY abbreviation of the name of the terminal element. Thus a serial vein, the basal element of which is the cubitus and the terminal ele- ment vein Ml, is designated as vein Cu — Mi. A serial vein thus formed exists in the hind wings of certain ichneumon flies. The increase of the number of wing-veins. In the wings of many- insects the number of veins is greater than it is in the hypothetical type. This multiplication of veins is due either to an in^reisi in the Fig. 8i. — Wings of Osmylns hyalinatus. number of the branches of the principal veins by the addition of secondary branches, termed accessory veins, or to the development of secondary longitudinal veins between these branches, termed inter- calary veins. In no case is there an increase in the number of principal veins. The accessory veins. — The wings of Osmylus (Fig. 8i) are an exam- ple of wings in which accessory veins have been developed ; here the radial sector bears many more branches than the typical niimber; those branches that are regarded as the primitive branches are lettered Ri, Ro, R3, R4, and R5 respectively (Fig. 82); the other THE EXTERNAL ANATOMY OF INSECTS 6y branches are the secondarily developed accessory veins. Two types of accessory veins are recognized the marginal accessory veins and the definitive accessory veins. The marginal accessory veins are twig-like branches that are the result of bifurcations of veins that have not extended far back from the margin of the wing; many such short branches of veins exist in the vvings of Osmylus (Fig. 8i). The number and position of the marginal accessory veins are not constant, differing in the wings of the two sides of the same individual. The definitive accessory veins differ from the marginal accessory Fig. 82. — Base of fore wing shown in Figure 81. veins in having attained a position that is comparable in stability to that of the primitive branches of the principal veins. In those cases where the accessory veins are believed to have been developed in regular order they are designated by the addition of a letter to the abbreviation of the name of the vein that bears them; thus if vein R2 bears three accessory veins they are designated as veins R2a, R2b, and R2C, respectively. The intercalary veins. — The intercalary veins are secondarily developed longitudinal veins that did not arise as branches of the primitive veins, but were developed in each case as a thickened fold in a corrugated wing, more or less nearly midway between two pre- existing veins, with which primarily it was connected only by cross- veins. Excellent examples of unmodified intercalary veins are com- '0 ^.V INTRODUCTION TO ENTOMOLOGY Fig. 83. — Wing of a May-fly (After Morgan). mon in the Ephemerida, where most of the intercalary veins remain distinct from the veins between which they were developed, being connected with them only by cross-veins, the proximal end of the intercalary vein being free (Fig. 83). When it is desirable to re- fer to a parti- cular interca- lary vein it can be done by combining the initial /, indicating intercalary, with the designation of the area of the wing in which the intercalary vein occurs. For example, in the wings of most May-flies there is an intercalary vein between veins Cui and Cu2, i e. in the area Cui ; this intercalary vein is desig- nated as ICui. The adven- titious veins. — In certain in- sects there are secon dary veins that are neither acces- sory veins nor intercalary veins as de- fined above; these are termed adven- titious veins. Examples of these are the supplements of the wings of Fig. 84.- -Wings of Prionoxystus. certain Odonata and the spurious vein of the Syrphids. The anastomosis of veins. — The typical arrangement of wing-veins is often modified by an anastomosis of adjacent veins; that is, two THE EXTERNAL ANATOMY OF INSECTS 71 veins will come together at some point more or less remote from their extremities and merge into one for a greater or less distance, while their extremities remain separate. In the fore wing of Prionoxystus (Fig. 84), for example, there is an anastomosis of veins R3 and R4+5. The named cross-veins. — In the wings of certain insects, as the dragon-fiies, May-flies, and others, there are many cross-veins; it is impracticable in cases of this kind to name them. But in several of the orders of insects there are only a few cross-veins, and these have been named. Figure 85 represents the hypothetical primitive type 3dA 2d A Fig. 85.— The hypothetical primitive type of wing-venation with the named cross-veins added. of wing-venation with the named cross-veins added in the positions in which they normally occur ; these are the following : The humeral cross-vein (h) extends from the subcosta to costa near the humeral angle of the wing. The radial cross-vein (r) extends between the two principal divi- sions of radius, i. e. from vein Ri to vein Rg. The sectorial cross-vein {s) extends between the principal divisions of the radial sector — i. e., from vein R2+3 to vein R4+5 or from vein R3 to vein R4. The radio-medial cross-vein (r—m) extends from radius to media, usually near the center of the wing. When in its typical position this cross- vein extends from vein R4-1.5 to vein Mi +2. The medial cross-vein (m) extends from vein M2 to vein M3. This cross-vein divides cell M2 into cells, ist Mo and 2d M2; see Figure 87 where the cells are lettered. The medio-cubital cross-vein {m — cu) extends from media to cubitus. 72 AN INTRODUCTION TO ENTOMOLOGY R^AU Cu ^/.+.+ The arculus. — In many insects there is what appears to be a cross- vein extending from the radius to the cubitus near the base of the wing; this is the arculus. The arculus is designated in figures of wings by the abbreviation ar. Usually when the arculus is present the media appears to arise from it; the fact is, the arculus is com- pound, being composed of a section of media and a cross-vein. Figure 86 is a dia- gram representing the typical struc- ture of the arculus. That part of the arculus which is a section of media is designated as the anterior arculus (aa) and that part formed by a cross-vein, the posterior arculus (pa) . The terminology of the cells of the wing. — Each cell of the wing is designated by the name of the vein that normally forms its front margin when the wings are spread. See Figure 87 where both the veins and the cells of the wing are lettered. The cells of the wing fall naturally into two groups: first, those on the basal part of the wing; and second, those nearer the distal end of the wing. The former are bounded by the stems of the principal veins, the latter, by the branches of these veins; a corresponding distinction is made in designating the cells. Thus a cell lying behind the main stem of radius and in the basal part of the wing is designated as cell R; while a cell lying behind radius-one is designated as cell Ri. Fig. 86. — Diagram of an arculus of a dragon-fly. /?, /?. + 3 Fig, 87. — A wing of Rhyphus. It should be remembered that the coalescence of two veins results in the obliteration of the cell that was between them. Thus when THE EXTERNAL ANATOMY OF INSECTS 73 veins R2 and Rz coalesce, as in the wings of Rhyphus (Fig. 87), the cell lying behind vein i?2+3 is cell Rz, and not cell R^+z, cell R2 having been obliterated. When one of the principal cells is divided into two or more parts by one or more cross- veins, the parts may be numbered, beginning v\'-ith the proximal one. Thus in Rhyphus (Fig. 87), cell M2 is divided by the medial cross-vein into cell istMi and cell 2dMi. When two or more cells are united by the atrophy of the vein or veins separating them, the compound cell thus formed is designated by a combination of the terms applied to the elements of the com- pound cell. When, for example, the stem of media is atrophied, the cell resulting from the combination of cells R and M is designated as cell R+M. The application of this system of naming the cells of the wing is an easy matter in those orders where there are but few cross-veins ; but in those orders where there are many cross-veins it is not practicable to apply it. In the latter case we have to do with areas of the wing rather than with separate cells. These areas are designated as are the cells of the few- veined wings with which they correspond; thus the area immediately behind vein R2 is area R2. The corrugations of the wings. — The wings of comparatively few insects present a flat surface ; in most cases the membrane is thrown into a series of folds or corrugations. This corrugating of the wing in some cases adds greatly to its strength, as in the wings of dragon-flies; in other cases the corrugations are the result of a folding of the wing when not in use, as in the anal area when this part is broadly ex- panded. It rarely happens that there is occasion to refer to individual members of either of these classes of folds, except perhaps the one between the costa and the radius, which is the subcostal fold and that which is normally between the cubitus and the first anal vein, the cubito-a lal fold. Convex a)id concave veins. — When the wings are corrugated, the wing-veins that follow the crests of ridges are termed convex veins; and those that follow the furrows, concave veins. The furrows of the wing. — There are found in the wings of many insects one or more suture-like grooves in the membrane of the wing; these are termed the furrows of the wing. The more important of these furrows are the four following: The anal furrow when present is usually developed in the cubito anal fold; but in the Heteroptera it is found in front of the cubitus. 74 AN INTRODUCTION TO ENTOMOLOGY The median furrow is usually between radius and media. The nodal furrow is a transverse suture beginning at a point in the costal margin of the wing corresponding to the nodus of the Odonata and extending towards the inner margin of the wing across a varying ntunber of veins in the different orders of insects. The axillary furrow is a line that serves as a hinge which faciHtates the folding of the posterior lobe of the wing of many insects under that ^^ part of the wing w^^^^^^^^^^^^^T'^^Ciilr^ ^-llr^ — '"^'^ ^^ veins of the \ \ ^ — ~— I^r~~~~~"^ wing where they \J \.___ ><^ ^^s/**'^'^-^,.^^ ^^~-~-- y are crossed by ^^""'■~~~~~-----_l____^i^--"^'^ furrows. The ^. „„ _. , ,, bullae are usually Fig. 88. — Wmgs of Myrmecia; b, b, b, bullae. , . , paler m color than the other portions of the wing ; they are common in the wings of the Hymenoptera (Fig. 88), and of some other insects. The ambient vein. — Sometimes the entire margin of the wing is stiffened by a vein-like structure; this is known as the ambient vein. The humeral veins. — In certain Lepidoptera and especially in the Lasiocampidas, the hiimeral area of the hind wings is greatly expanded and in many cases is strengthened by the development of secondary veins. These are termed the humeral veins. The pterostigma or stigma. — A thickened, opaque spot which exists near the costal margin of the outer part of the wing in many insects is known as the pterostigma or stigma. The epipleurcB. — A part of the outer margin of the elytra of beetles when turned down on the side of the thorax is termed the epipleura. The discal cell and the discal vein. — The term discal cell is applied to a large cell which is situated near the center of the wing; and the term discal vein, to the vein or series of veins that limits the outer end of the discal cell. These terms are not a part of the uniform terminol- ogy used in this book, and can not be made so, being applied to different parts of the wing by writers on different orders of insects. They are included here as they are frequently used, as a matter of convenience, by those who have adopted the uniform terminology. The discal cell of the Lepidoptera is cell R+M + lstM2; that of the Dipcera is cell ist M2; and that of the Trichoptera is cell R2+3. THE EXTERNAL ANATOMY OF INSECTS 75 The anal area and the preanal area of the wing. — In descriptions of wings it is frequently necessary to refer to that part of the wing supported by the anal veins ; this is designated as the anal area of the wing; and that part lying in front of the anal area, including all of the wing except the anal area, is termed the preanal area. IV. THE ABDOMEN a. THE SEGMENTS OF THE ABDOMEN The third and terminal region of the body, the abdomen, consists of a series of approximately similar segments, which as a rule are without appendages excepting certain segments near the caudal end of the body. The body-wall of an abdominal segment is usually comparatively simple, consisting in adults of a tergum and a sternum, united by lateral conjunctivce. Sometimes there are one or two small sclerites on each lateral aspect of a segment; these are probably reduced pleura. The number of segments of which the abdomen appears to be composed varies greatly in different insects. In the cuckoo-flies (Chrysididae) there are usually only three or four visible; while in many insects ten or eleven can be distinguished. All intergrades between these extremes occur. The apparent variation in the number of abdominal segments is due to two causes: in some cases, some of the segments are tele- scoped ; and in others, adjacent segments coalesce, so that two or more segments appear as one. A study of embryos of insects has shown that the abdomen con- sists typically of eleven segments; although this number may be reduced during the development of the insect by the coalescence of adjacent segments. In some insects there is what appears to be a segment caudad of the eleventh segment; this is termed the telson. The telson differs from the segments preceding it in that it never bears appendages. Special terms have been applied, especially by writers on the Coleoptera, to the caudal segments of the abdomen. Thus the terminal segment of a beetle's abdomen when exposed beyond the elytra is termed the pygldmm; the tergite cephalad of the pygidium, especially in beetles with short elytra, the propygtdium; and the last abdominal stemite, the hypopygium. The term hypopygium is also applied to the genitalia of male Diptera by writers on that order of insects. 76 AN INTRODUCTION TO ENTOMOLOGY b. THE APPENDAGES OF THE ABDOMEN In the early embryonic stages of insects, each segment of the abdomen, except the telson, bears a pair of appendages (Fig. 89) . This indicates that the primitive ancestor of insects possessed many legs, like a centipede. But the appendages of the first seven abdominal segments are usually lost during embryonic life, these segments being without appen- dages in postembryonic stages, except in certain Thysanura and CoUembola, and in some larvse. Reference is made here merely to the primary appendages of the segments, those that are homodyna- mous with the thoracic legs; secondarily developed appendages, as for example, the tracheal gills, are present in the immature instars of many insects. The styli or vestigial legs of certain Thysanura. — In certain Thysanura the coxa of each middle and hind thoracic leg bears a small appendage, the stylus (Fig. 90) ; and on from one to nine abdominal segments there is a pair of similar styli. These abdominal styli are believed to be homodynamous with those of the thoracic legs, and must, therefore, be regarded as vestiges of abdominal legs. The collophore of the Collembola. — Although in the postembryonic stages of Collembola the collophore is an unpaired organ on the middle line of the ventral aspect of the first abdominal segment, the fact that it arises in the embryo as a pair of appendages comparable in position to the thoracic legs, has led to the belief that it represents the legs of this segment. The structure of the collophore is described more fully later in the chapter treating of the Collembola. The spring of the CoUembola. — The spring of the Collembola, like the collophore, is believed to represent a pair of primary append- ages. This organ is discussed in the chapter treating of the Col- lembola. The genitalia. — ^In most insects there are more or less prominent appendages connected with the reproductive organs. These append- ages constitute in males the genital daspers and in females the ovi- positor; to them have been applied the general term genitalia, they are also known as the gonapophyses. The genitaha, when all are developed consist of three pairs of appendages. Writers vary greatly in their views regarding the seg- Fig. Sg.-Em- bryo of 7^3'- drop kilns showing ab- dominal ap- pendages. THE EXTERNAL ANATOMY OF INSECTS 77 ments of the abdomen to which these appendages belong. One cause of difference is that some writers regard the last segment of the abdo- men as the tenth abdominal segment while others believe it to be the eleventh, which is the view adopted in this work, this segment bears the cerci when they are present. The three pairs of appendages that constitute the genitalia are borne by the eighth and ninth segments, two pairs being borne by the ninth segment. The outer pair of the ninth segment constitute the sheath of the ovipositor. See ac- count of the genitalia of the Orthoptera in Chapter eight. The genitalia of many in- sects have been carefully fig- ured and described and special terms have been applied to each of the parts. But as most of these descriptions have been based upon studies of repre- sentatives of a single order of insects or even of some smaller group, there is a great lack of uniformity in the terms applied to homologous parts in the different orders of in- sects; such of these tenns as are commonly used are defined later in the characterizations of the several orders of insects. The cerci. — In many insects there is a pair of caudal appendages which are known as the cerci; these are the appendages of the eleventh abdominal segment, the last segment of the body except in the few cases where a telson is present. The cerci vary greatly in form; in some insects, as in most Thy- sanura, in the Plecoptera, and in the Ephermerida, they are long and Fig. 90. — Ventral aspect of MachiHs; c, cer- cus; Z/>, labial palpus; mf, median caudal filament; mp, maxillary palpus; o, oviposi- tor; s, s, styli. That part of the figure representing the abdomen is after Ou de- mans. 78 AN INTRODUCTION TO ENTOMOLOGY many jointed; while in others they are short and not segmented. The function of the cerci is different in different insects ; they are \ believed to be tactile in some, olfactory in others, / and in some males they aid in holding the female / during copulation. The median caudal filament. — ^In many of the Ephemerida and in some of the Thysanura, the last abdominal segment bears a long, median filament, which resembles the many-jointed cerci of these insects (Fig. 91); this filament is believed to be a prolongation of the tergum of this segment and not a true appendage like the cerci. The prolegs of larvae. — The question whether the prolegs of larv^as represent true appendages or are merely hypodermal outgrowths has been much dis- cussed. Several embryologists have shown that in embryos of Lepidoptera and of saw-flies limb-rudi- ^nia^sacchanna. ments appear on all or most of the abdominal seg- ments; and that they very soon disappear on those segments which in the larva have no legs while on other segments they are transferred into functional prolegs. If this view is estab- lished we must regard such prolegs as representing primitive abdo- minal appendages, that is as true abdominal legs. V. THE MUSIC AND THE MUSICAL ORGANS OF INSECTS Much has been written about music ; but the greater part of this literature refers to music made by man for human ears. Man, how- ever, is only one of many musical animals; and, although he excels all others in musical accompHshments, a study of what is done by our hiunbler relatives is not without interest. The songs of birds command the attention of all observers. But there is a great orchestra which is performing constantly through the warmer portions of the year, which is almost unnoticed by man. Occasionally there is a performer that cannot be ignored, as:— "The shy Cicada, whose noon- voice rings So piercing shrill that it almost stings The sense of hearing." (Elizabeth Akers.) But the great majority fiddle or drum away unnoticed by human ears. THE EXTERNAL ANATOMY OF INSECTS 79 Musical sounds are produced by many different insects, and in various ways. These sounds are commonly referred to as the songs of insects; but properly speaking few if any insects sing; for, with some possible exceptions, the note of an insect is always at one pitch, lacking musical modulations like those of the songs of man and of birds. The sound produced by an insect may be a prolonged note, or it may consist of a series of short notes of varying length, with intervals of rest of varying lengths. These variations with differences in pitch give the wide range of insect calls that exists. In some cicadas where the chambers containing the musical organs are covered by opercula, the insect can give its call a rhythmic increase and decrease of loudness, by opening and closing these chambers. As most insect calls are strident, organs specialized for the pro- duction of these calls are commonly known as stridulating organs. But many sounds of insects are produced without the aid of organs specialized for the production of sound. The various ways in which insects produce sounds can be grouped under the following heads : First. — By striking blows with some part of the body upon sur- rounding objects. Second. — By rapid movements of the wings. In this way is produced what may be termed the music of flight. Third. — By rasping one hard part of the body upon another. Under this head fall the greater number of stridulating organs. Fourth. — By the rapid vibration of a membrane moved by a muscle attached to it. This is the type found in the cicadas. Fifth. — By the vibration of membranes set in motion by th':j rush of air through spiracles. The reality of this method has been ques- tioned. Sixth. — By rapid changes of the outline of the thorax due to the action of the wing muscles. a. SOUNDS PRODUCED BY STRIKING OBJECTS OUTSIDE THE BODY Although the sounds produced by insects by striking blows with some part of the body upon surrounding objects are not rapid enough to give a musical note, they are referred to here for the sake of completeness. The most familiar sounds of this kind are those produced by the insects known as the death-watch. These are small beetles of the family Ptinidse, and especially those of the genus Anohium. These are wood-boring insects, frequently found in the woodwork of old 80 AN INTRODUCTION TO ENTOMOLOGY houses and in furniture, where they make a ticking sound by striking their heads against the walls of their burrows. The sound consists of several, sharp, distinct ticks, followed by an interval of silence, and is believed to be a sexual call. The name death-watch was applied to these insects by supersti- tious people who believed that it presaged the death of some person in the house where it is heard. This belief probably arose from the fact that the sound is most likely to be heard in the quiet of the night, and would consequently be observed by watchers by sick-beds. The name death-watch has also been applied to some species of the Psocidas, Clothtlla pulsatoria and Atropos divinatoria, which have been believed to make a ticking sound. This, however, is doubted by some writers, who urge that it is difficult to believe that such minute and soft insects can produce sounds audible to himian ears. The death-watches produce their sounds individually; but an interesting example of an insect chorus is cited by Sharp ('99, p. 156), who, quoting a Mr. Peal, states that an ant, presumably an Assamese species, "makes a concerted noise loud enough to be heard by a human being at twenty or thirty feet distance, the sound being produced by each ant scraping the horny apex of the abdomen three times in rapid succession on the dry, crisp leaves of which the nest is usually com- posed." h. THE MUSIC OF FLIGHT The most obvious method by which insects produce sounds is by beating the air with their wings during flight. It can be readily seen that if the wing-strokes are sufficiently rapid and are uniform, they will produce, like the flapping reeds of a mouth organ, a musical note. When, however, we take into account the fact that to produce the lowest note regularly employed in music, the C of the lowest octave, requires 32 vibrations a second, i. e., nearly 2,000 vibrations per minute, it will seem marvellous that muscular action can be rapid enough to produce musical notes. Nevertheless, it is a fact that many insects sing in this way ; and too their notes are not confined to the lower octaves. For example, the common house fly hums F of the middle octave, to produce which, it must vibrate its wings 345 times per second or 20,700 times per minute. As a rule, the note produced by the wings is constant in each species of insect. Still with insects, as with us, the physical condition of the singer has its influence. The vigorous honey-bee makes the A of 435 vibrations, while the tired one hums on the E of 326 vibrations. THE EXTERNAL ANATOMY OF INSECTS 81 While it is only necessary to determine the note produced by vibrating wings to ascertain the rate of vibration, a graphical demon- stration of the rate is more convincing. Such a demonstration has been made by Marey ('69) who fixed a fly so that the tip of the wing just touched the smoked surface of a revolving cylinder, and thus obtained a wavy line, showing that there were actually 320 strokes in a second. This agrees almost exactly with the nimiber inferred from the note prodviced. The music of flight may be, in many cases, a mere accidental result of the rapid movement, and in no sense the object of that movement, like the hum of a trolley car ; but there are cases where the song seems to be the object of the movement. The honeybee produces different sounds, which can be understood by man, and probably by bees, as indicating different conditions. The contented hum of the worker collecting nectar may be a song, like the well-known song of a hen wandering about on a pleasant day, or may be an accidental sound. But the honeybee produces other sounds that communicate ideas. The swarming sound, the hum of the queenless colony, and the note of anger of a belligerent bee can be easily distinguished by the experi- enced beekeeper, and doubtless also by the bee colony. It seems probable, therefore, that in each of these cases the rate of vibration of the wings is adjusted so as to produce a desired note. This is also probably true of the song of the female mosquito, which is pitched so as to set the antennal hairs of the male in vibration. While the music of flight is a common phenomenon, many insects have a silent flight on account of the slowness of the wing-movement. C. STRIDULATING ORGANS OF THE RASPING TYPE The greater number of the insect sounds that attract our attention are produced by the friction of hard parts of the cuticula by which a vibrating surface is set in motion. In some cases, as in many of the Orthoptera, the vibrating surface is apart of the wings that is special- ized for this purpose; but in other cases, a specialized vibrating sur- face has not been obser\^ed. Stridulating organs of the rasping type are possessed by represen- tatives of several of the orders of insects ; but they are. most common in the order Orthoptera, and especially in the families Acridiidse, Locustidas, and Gryllidae, where the males of very many species possess them. Very few other Orthoptera stridulate; and with few exceptions it is only the males that sing. 82 AN INTRODUCTION TO ENTOMOLOGY In each of these families the vibrating element of the stridulating organ is a portion of one or of both of the fore wings ; but this is set in motion in several different ways. In some exotic Acridiid^ abdominal stridulating organs exist. The stridulating organs of the Locustidae. — With many species of the Locustidae we find the males furnished with stridulating organs ; but these are comparatively simple, and are used only in the day time. Two methods of stridulation are used by members of this family. The simpler of these two methods is employed by several common species belonging to the (Edipodinas; one of which is the Carolina locust, Dissosteira Carolina, whose crackling flight is a common feature of country roadsides. These locusts, as they fly, rub the upper sur- face of the costal margin of the hind wings upon the lower surface of the thickened veins of the fore wings, and thus produce a loud but not musical sound. The second method of stridulation practiced by locusts consists in rubbing the inner surface of the hind femora, upon each of which there is a series of bead-like prominences (Fig. 92), against the outer surface of the fore wings With these insects, there is a thickening of the radius in the basal third of each fore wing, and a widening of the two areas between this vein and the costal margin of the wing, which serves as a sounding board (Fig. 93). The two wings and femora constitute a pair of vioHn-like organs; the thickened radius in each case cor- responding to the strings; the membrane of the wing, to the body of the instrument ; and the file of the femur, to the bow. These two organs are used simultaneously. When about to stridulate, the insect B— Fig. 92. — A, hind femora of Slenobolhrus; B, file greatly enlarged. Fig- 93- — Fore wing of a male of Stenobothrus. C, costa. R, radius; Sc, subcosta; THE EXTERNAL ANATOMY OF INSECTS 83 B i^^^.'fi^ places itself in a nearly horizontal position, and raising both hind legs at once rasps the femora against the outer surface of the wings. The most common representatives of insects that stridulate in this way belong to the genus Steno- bothrns. The stridulating organs of the Gryllidae and the Tettigoniidae. — The stridulating organs of the Gryl-lid^ and the Tettigoniidae are of the same type, and are the most highly specialized found in the Orthoptera. They consist of modified portions of the fore wings ; both the vibrating and the rasp- ing elements of the organs pertaining to the wings. It is by rubbing the two fore wings together that sound is produced. In what is probably the more generalized con- dition of the organs, as seen in Gryllus, each fore wing bears a rasping organ, the file (Fig. 94, /) a hardened area, the scraper (Fig. 94, s), , against which the file of the other wing acts, and •I I; t; Eli If If 11 ) vibrating areas, the tympana (Fig. 94, t, t). As the file of either wing can be used to set the tympana of the wings in vibration, we may say Fig- 94- — Fore wing of that Gryllus is ambidextrous. Grvllus; A, as seen from above, that When the cricket wishes to make his call, he part of the wing elevates his fore wings so that they make an angle which IS bent down . , . „ ^ . , V, , . , on the side of the of about forty-five degrees with the body; then abdomen is not holding them in such a position that the scraper shown; 5, scraper;^, ^ , _, f^ , , , , .'.tympana. B,base of one rests on the file of the other, he moves the of wing seen from ^i^gs back and forth laterally, so that the file and below; s, scraper; ° , , rr^i • , f, file. C, file great- scraper rasp upon each other. This throws the ly enlarged. wings into vibration and produces the call. It is easy to observe the chirping of crickets. If one will move slowly towards a cricket that is making his call, and stop when the cricket stops chirping until he gains confidence and begins again, one can get sufficiently near to see the operation clearly. This can be done either in the day time or at night with the aid of a light. The songs of the different genera of crickets can be easily dis- tinguished, and that of each species, with more care. Writers on the Orthoptera have carefully described the songs of our more common crickets, andespeciallythoseof the tree crickets. The rate of chirping 84 ^iV INTRODUCTION TO ENTOMOLOGY is often influenced by temperature, being slower in cool nights than in warm ones; and becoming slower towards morning if the tem- perature falls. In certain genera of crickets as Nemohius and CEcanthus, while each fore wing is furnished with a file and tympana, the scraper of the right wing is poorly formed and evidently not functional. As these insects use only the file of the right wing to set the tympana of the wings in vibration, they may be said to be right-handed. Fig- 95- — Wings of a female nymph of CEcanthus ("From Comstock and Needham). In the Locustidag a similar modification of the function of the stridulating organs has taken place. In all of our common represen- tatives of the family, at least, only one of the files is used. But in these cases it is the file of the left wing that is functional ; we may say, therefore, that so far as observed the Locustidae are left-handed. Different genera exhibit great differences as to the extent of the reduc- tion of the unused parts of the stridulating organs. The file is present in both wings of all of the forms that I have studied ; but the imused file is sometimes in a vestigial condition. The scraper is less persistent, being frequently entirely lacking in one of the wings. In some cases, the tympana of one wing have been lost; but in others the tympana of both wings are well preserved, although only one file THE EXTERNAL ANATOMY OF INSECTS 85 is used. In these cases it is probable that the tympana of both wings are set in vibration by the action of the single functional file. The determination of the homologies of the parts of the wing that enter into the composition of the stridulating organs was accomplished by a study of the tracheation of the wings of n3nnphs (Comstock and Needham, 'qS-'qq). The results obtained by a study of the wings of CEcauthus will serve as an illustration. Figure 95 represents the wings of a female n}Tnph of this genus, with the tracheae lettered. The only parts to which we need to give attention in this discussion are the cubital and anal areas of the fore wing; for it is this part of the wing that is modified in the male to form the musical organ. Both branches of cubitus are present, and Cui bears three accessory branches. The three anal tracheae are present and are quite simple. Fig. 96. — Fore wine Needham). of a male nymph of CEranthus (From Comstock and The homologies of the trachea of the fore wing of a male nymph, Figure 96, were easily determined by a comparison with the tracheae of the female. The most striking difference between the two sexes is a great expanding of the area between the two branches of cubitus in the male, brought about by the bending back of the basal part of Cuo. The next step in this study was to compare the wing of an adult male. Figure 97, with that of the nymph of the same sex; and the solution of the problem was soon reached. It can be easily seen that the file is on that part of Cu2 that is bent back toward the inner mar- gin of the wing (Fig. 97, /); the tympana are formed between the branches of cubitus (Fig. 97, /, t); and the scraper is formed at the outer end of the anal area (Fig. 97,5). AN INTRODUCTION TO ENTOMOLOGY A similar study was made of the wings of Conocephalus. as an example of the Tettigoniidae, Figure 98 represents the wings of a male nymph; and Figure 99 the fore wing of an adult. The most striking feature, and one character- istic of the family, is that the musical organ occupies an area near the base of the wing which Fig- 97- — Fors v/ing of an adult male of (Ecanlhus; f, vein jg gj^a.11 com- bearing the file; 5, scraper; /,/, tympana. , . , pared with the area occupied by the musical organs of the Gryllidae. But here, as in the Gryllidee, the file is borne by the basal part of Cu2, the Fig. 98. — Wings of a male nymph of Conocephalus, (From Comstock and Needham). tympana are formed between the br-anches of cubitus, and the scraper is formed at the outer end of the anal area. THE EXTERNAL ANATOMY OF INSECTS 87 Rasping organs of other than orthopterous insects. — Rasping organs are found in many other than orthopterous insects and vary M Fig. 99. — Right fore wing of an adult male of Conocephalus, seen from below; /, file; s, scraper. greatly in foiTn and in their location on the body. Lack of space for- bids any attempt to enumerate these variations here ; but examples of various types of stridulating organs will be described in later chapters when treating of the insects that possess them. As in the Orthoptera, they consist of a rasp and a scraper. The rasp is a file-like area of the surface of a segment of the body or of an appendage; and the scraper is a hard ridge or point so situated that it can be drawn across the rasp by movements of the body or of an append- age. In some cases the ap- paratus con- sists of two rasps so situ- ated that they can be rubbed together. With many beetles one of Fig. 100. — Stridulating organ of an ant, Myrmica rubra (From Sharp after Janet) ; J, scraper; f,'file. the two parts of the stridulating organ is situated upon the elytra ; and it is quite probable that in these cases the elytra acts as vibrating surfaces, as do the wings of locusts and crickets. But in many cases as where a part of a leg is rubbed against a portion of a thoracic segment, there appears to be no vibrating surface unless it is the wall of the body or of the appendage that acts as a sounding board. In the stridulating organ of Myrmica rubra, var. IcBvinodis, figured by Janet (Fig. 100), the scraper is the posterior border of one abdominal segment, and the file is situated on the dorsum of the following segment. It is quite conceivable that in this case S8 AN INTRODUCTION TO ENTOMOLOGY the dorsal wall of the segment bearing the file is made to vibrate by the successive impacts of the scraper upon the ridges of the file. In fact this seems to me more probable than that the sound produced is merely that of the scraper striking against the successive ridges of the file. There is at least one recorded case where the body wall is specialized to act as a sounding board. According to Sharp ('95, p. 200), in the males of the Pneumorides, a tribe of South African Acridiidse, where the phonetic organ is situated on the abdomen, this part is inflated and tense, no doubt with the result of increasing the volume and quality of the sound. Ordinarily the stridulating organs of insects are fitted to produce notes of a single degree of pitch; but Gahan ('00) figures those of some beetles that are evidently fitted to produce sounds of more than one degree of pitch ; the file of Hispopria foveicollis, consists of three parts, one very finely striated, followed by one in which the striae are much coarser, and this in turn followed by one in which the striation is intermediate in character between the other two. While the stridulating organs of the Orthoptera are possessed almost exclusively by the males, in the Coleoptera, very many species of which stridulate, the phonetic organs are very commonly possessed by both sexes, and serve as a mutual call. In one genus of beetles, Phoftapate, stridulating organs have been found only in the females (Gahan, '00). It seems evident that in the great majority of cases the sounds produced by insects are sexual calls; but this is not always so. It was pointed out long ago by Charles Darwin that "beetles stridulate under various emotions, in the same manner as birds use their voices for many purposes besides singing to their mates. The great Chiasog- nathus stridulates in anger or defiance ; many species do the same from distress or fear, if held so that they cannot escape; by striking the hollow stems of trees in the Canary Islands, Messrs. Wollaston and Crotch were able to discover the presence of beetles belonging to the genus Acalles by their stridulation. Lastly the male Ateuchus stridulates to encourage the female in her work and from distress when she is removed" {The Descent of Man). The most remarkable case where stridulating organs have been developed for other than sexual pusposes is that of the larvae of certain Lucanidas and Scarabaeidae described by Schiodte ('74)- In these larvae there is a file on the coxa of each middle leg, and the hind legs are shortened and modified so as to act as scrapers. The most highly THE EXTERNAL ANATOMY OF INSECTS 89 specialized example of this type of stridulatinj^ organ is possessed by the larvce of Passalus, in which the legs of the third pair are so much shortened that the larv£e appear to have only four legs ; each hind leg is a paw-like structure fitted for rasping the file (Fig. loi). These insects are social, a pair of beetles and their progeny living to- gether in decaying wood. The adults prepare food for the larvce; and the col- ony is able to keep together by stridu- latory signals. a. THE MUSICAL ORGANS OF A CICADA With the cica- das there exists a type of stridulating organ peculiar to them, and one that is the most complicated organ of sound found in the animal kingdom. Yet, while the cicadas are the most noisy of the insect world, the results obtained by their com- plicated musical apparatus are not comparable with those pro- duced by the comparatively simple vocal organs of birds and of man. It is said that in some species of Cicada both sexes stridulate ; but as a rule the females are mute, possessing only vestiges of the musical apparatus. The structure of the stridulating organs varies somewhat in details in different species of Cicada; but those of Cicada plebeia, which were described and figured by Carlet ('77), may be taken as an example of the more perfect form. In the male of this species there is a pair of large plates, on the ventral side of the body, that extend back Fig. 1 01. — Stridulating organ of a larva of Passalus; a, b, portions of the metathorax; c, coxa of the second leg; d, file; e, basal part of femur of middle leg; /, hairs with chitinous process at base of each; g, the diminutive third leg modified for scratching the file (From Sharp). 90 AN INTRODUCTION TO ENTOMOLOGY Fig. I02. — The musical apparatus of a cicada; fm, folded membrane; /, base of leg; Ic, lateral cavity; m, mirror; o, operculum, that of the opposite side removed; 5/>, spiracle; /, timbal; ir, ventral cavity (After Car let). from the hind border of the thorax and overlap the basal part of the abdomen; these are the opercula (Fig. 102, 0). The opercula are expansions of the ster- nellimi of the meta- ^ r^^ thorax, and each serves as a lid covering a pair of cavities, con- taining the external parts of the musical apparatus ot one side of the body. The two cavities covered by a single operculum may be de- signated as the ventral cavity (Fig. 102, v. c.) and the lateral cavity (Fig. 102, 1. c.) respec- tively. Each cavity is formed by an infolding of the body- wall. In the walls of these cavities are three membranous areas; these are known as the timbal, the folded membrane, and the mirror. The timbal is in the lateral cavity on the lateral wall of the parti- tion separating the two cavities (Fig. 102, t); the other two mem- branes are in the ventral cavity. The folded membrane is in the anterior wall of the ventral cavity (Fig. 10 2, /. m.); and the mirror is in the posterior wall of the same cavity (Fig. 102, m). Within the body, there is in the region of the musical apparatus a large thoraco- abdomnal air chamber, which co,mmunicates with the exterior througih a pair of spiracles (Fig. 102 sp); and a large muscle, which extends from the furca of the second abdominal segment to the inner face of the timbal. By the contraction of this muscle the timbal is pulled towards the center of the body; and when the muscle is relaxed, the elasticity of the chitinous ring supporting the timbal causes it to regain its form er position. By a very rapid repetition of these movements of the timbal the sound is produced. It is probable that the vibrations of the timbal are transmitted to the folded membrane and to the mirror by the air contained in the large air chamber mentioned above; as the strings of a piano are made to vibrate by the notes of a near-by violin. The sound, how- ever, is produced primarily by the timbal, the destruction of which THE EXTERNAL ANATOMY OF INSECTS 91 renders the insect a mute; while the destruction of the other mem- branes, the timbal remaining intact, simply reduces the sound. The chief function of the opercula is doubtless the protecting of the deHcate parts of the musical organ; but as they can be lifted slightly and as the abdomen can be moved away from them to some extent, the chambers containing the vibrating parts of the organ can be opened and closed, thus giving a rhythmic increase and decrease of the loudness of the call. e. THE SPIRACULAR MUSICAL ORGANS There has been much discussion of the question whether insects, and especially Diptera and Hymenoptera, possess a sound -producing organ connected with the spiracles or not. Landois ('67) believed that he found such an organ and figures and describes it in several insects. It varies greatly in form in different insects. In the Diptera it consists of a series of leaf-like folds of the intima of the trachea; these are held against each other by a special humming ring, which lies close under the opening of the spiracle; and is found within t^^'o or all four of the thoracic spiracles. These membranous folds of the intima are set in vibration by the rush of air through the spiracles. In the May-beetle, according to Landois, a buzzing organ is foimd near each of the fourteen abdominal spiracles. It is a tongue-like fold projecting into the lumen of the trachea under the base of the closing apparatus. On its upper surface it is marked with very fine arched furrows. He concludes that this tongue is put in vibration by the breathing of the insect, and hence the buzzing of the flying beetle. If insects produce sounds in the way described by Landois. they have a voice quite analogous to our own. But the validity of the conclusions of Landois has been seriously questioned; the subject, therefore, demands further investigation. See also Duncan ('24). /. THE ACUTE BUZZING OF FLIES AND BEES Many observers have found that when the wings of a fly or of a bee are removed or held so that they can not vibrate the insect can still produce a sound. The sound produced under these circumstances is higher, usually an octave higher, than that produced by the wings. It is evident, therefore, that these insects can produce sounds in two ways; and an extended search has been made for the organ or organj producing the higher note. 92 AN INTRODUCTION TO ENTOMOLOGY Landois believed that the spiracular organs referred to above were the source of ttie acute sound. But more recently Perez ('78) and Bellesme ('78) have shown that when the spiracles are closed artifi- cially the insect can still produce the high tone. Perez attributes the sound to the vibrations of the stumps of the wings against the solid parts which surround them or of the sclerites of the base of the wing against each other. But Bellesme maintains that the sound is pro- duced by changes in the form of the thorax due to the action of the wing-muscles.* When the wing-muscles are at rest the section of this region, according to this writer, represent an elhpse elongated ver- tically; the contraction of the muscles transforms it to an elHpse elongated laterally; the thorax, therefore, constitutes a vibrating body which moves the air like a tine of a tuning fork. Bellesme states that by fastening a style to the dorsal wall of the thorax he obtained a record of the rate of its vibrations, the num.ber of which corresponded exactly to that required to produce the acute sound which the ear perceives. The fact that the note produced when the wings are rem.oved is higher than that produced by the wings is supposed by Bellesme to be due to the absence of the resistance of air against the wings, which admits of the maximum rate of contraction of the wing-muscles. g. MUSICAL NOTATION OF THE SONGS OF INSECTS Mr. S. H. Scudder ('93) devised a musical notation by which the songs of stridulating insects can be recorded. As the notes are always at one pitch the staff in this notation consists of a single horizontal line, the pitch being indicated by a separate statement. Each bar represents a second of time, and is occupied by the equivalent of a semibreve ; consequently a quarter note 1 , or a quarter rest 1, repre- sents a quarter of a second ; a sixteenth note t, or a sixteenth rest ~1 a sixteenth of a second and so on. For convenience's sake he intro- duced a new form of rest, shown in the second example given below, which indicates silence through the remainder of a measure; this differs from the whole rest commonly employed in musical notation by being cut oft" obliquely at one end. *This view was maintained by Siebold at a much earlier date in his Anatomy of the Invertebrates. THE EXTERNAL ANATOMY OF INSECTS 93 The following examples taken from his paper on "The Songs of our Grasshoppers and Crickets" will serve to illustrate this method of notation. The chirp of Gryllotalpa horealis (Fig. 103) "is a guttural sort of sound, like grii or greeu, repeated in a trill indefinitely, but seldom grii gru gru gru grfl grfl g^a grn grii ^gra^ Fig. 103. — The chirp of Gryllotalpa borealis (From Scudder). for more than two or three minutes, and often for less time. It is pitched at two octaves above middle C." XT! xr! xr!. ct! xt! Fig. 104. — The chirp of the katydid (From Scudder). The note of the true katydid, Cyrtophyllus concavus, (Fig. 104) "which sounds like xr, has a shocking lack of melody; the poets who have sung its praises must have heard it at a distance that lends enchantment." "They ordinarily call 'Katy' or say 'She did' rather than 'Katy did' ; that is they rasp their fore wings twice more fre- quently than thrice." Mr. Scudder in his account of this song fails to indicate its pitch. h. INSECT CHORUSES Most insect singers are soloists, singing without reference to other singers or in rivalry with them. But there are a few species the members of which sing in unison with others of their kind that are near them. The most familiar sound of autimin evenings in rural places in this country is a chorus of the snowy tree cricket, CEcanthus niveus. Very many individuals of this species, in fact all that are chirping in any locality, chirp in unison. Early in the evening, when the chirping first begins, there may be a lack of unanimity in keeping time; but this lasts only for a short period, soon all chirp in unison, and the monotonous beat of their call is kept up uninterrupted throughout the night. Individual singers will stop to rest, but when they start again they keep time with those that have continued the chorus. Other instances of insect choruses have been recorded. Sharp ('99, 156) quotes accounts of two produced by ants; one of these is given on an earlier page (p. 80). CHAPTER HI THE INTERNAL ANATOMY OF INSECTS Before making a more detailed study of the internal anatomy of insects, it is well to take a glance at the relative positions of the differ- ent systems of organs within the body of insects and other arthropods. One of the most striking features in the structure of these animals is that the body-wall serves as a skeleton, being hard, and giving sup- port to the other organs of the body. This skeleton may be repre- sented, therefore, as a hollow cylinder. We have now to consider the arrangement and the general form of the organs contained in this cylinder. The accompanying diagram (Fig. 105), which represents a vertical, longitudinal section of the body, will enable the student to gain an Fig. 105. — Diagram showing the relations of the internal organs; a , alimentary c anal ; A, heart; ot, muscle; w, nervous system; r, reproductive organs. idea of the relative positions of some of the more important organs. The parts shown in the diagram are as follows: The body-wall, or skeleton; this is made up of a series of overlapping segments; that part of it between the segments is not hardened with chitine, thus remaining flexible and allowing for the movements of the body. Just within the body-wall, and attached to it, are represented a few of the muscles {m) ; it will be seen that these muscles are so arranged that the contraction of those on the lower side of the body would bend it down, while the contraction of those on the opposite side would act in the opposite direction, other muscles not shown in the figure provide for movements in other directions. The alimentary canal (a) occupies the centre of the body, and extends from one end to the other. The heart (/i) is a tube open at both ends, and lying between the alimentary canal and the muscles of the back. The central part of the nervous system {n) is a series of small masses of nervous matter connected by (94) THE INTERNAL ANATOMY OF INSECTS 95 two longitudinal cords: one of these masses, the brain, lies in the head above the alimentary canal ; the others are situated, one in each segment, between the alimentary canal and the layer of muscles of the ventral side of the body; the two cords connecting these masses, or ganglia, pass one on each side of the oesophagus to the brain. The reproductive organs (r) lie in the cavity of the abdomen and open near the caudal end of the body. The respiratory organs are omitted from this diagram for the sake of simplicity. We will now pass to a more detailed study of the different systems of organs. I. THE HYPODERMAL* STRUCTURES The active living part of the body-wall is the hypodermis, already described in the discussion of the external anatomy of insects. In addition to the external skeleton, there are derived from the hypo- dermis an internal skeleton and several types of glands. a, THE INTERNAL SKELETON Although the skeleton of an insect is chiefly an external one, there are prolongations of it extending into the body-cavity. These inwardly directed processes, which serve for the attachment of muscles and for the support of other viscera are termed collectively the internal skeleton or endo-skeleton. The internal skeleton is much more highly developed in adult insects than it is in the immature instars. Sources of the internal skeleton. — The parts of the internal skele- ton are formed in two ways : first by the chitinization of tendons of muscles; and second, by invaginations of the body-wall. Chitinized tendons. — Chitinized tendons of the muscles that move the mouth-parts, of muscles that move the legs, and of other muscles are of frequent occurrence. As these chitinized tendons help support the internal organs they are considered as a part of the internal skeleton. Invaginations of the body-wall or apodemes. — The second and more important source of the parts of the internal skeleton consists of invaginations of the body- wall. Such an invagination is termed an dpodeme. The more important apodemes, if not all, arise as invagina- tions of the body-wall between sclerites or at the edge of a sclerite on the margin of a body-segment; although by the fusion of sclerites about an apodeme, it may appear to arise from the disc of a sclerite. 96 AN INTRODUCTION TO ENTOMOLOGY Frequently, in the more generalized insects, the mouth of an apodeme remains open in the adult insects. In Figure io6 are represented two apodemes that exist in the thorax of a locust, Melanophis. Each of these {ap and ap) is an invagination of the body- wall, between the epistemum and the epimeron of a segment, immediately above the base of a leg. These are known as the lateral apodemes of the thorax and serve as points of attachment of muscles. rrvi 1 r J i Fig. io6. — Ental su-face of The number of apodemes may be very \^^ pkurites of the meso- and metathorax of Melano- plus, showing the lateral apodemes, ap, ap. large, and it varies greatly in different insects. Among the more important apo- demes are the following: — The tentorium. — The chief part of the internal skeleton of the head is termed the tentorium. This was studied by Comstock and Kochi ('02). We found that in the generalized insects studied by us it is composed of two or three pairs of apodemes that, extend- ing far into the head, meet and coalesce. The three pairs of apodemes that may enter into the formation of the tentorium were termed the anterior, the posterior, and the dorsal arms of the tentorium, respectively. The coalesced and more or less expanded tips of these apodemes constitute the body of the tentorium. From the body of the tentoritim there extend a variable number of processes or chitinized tendons. The posterior arms of the tentorium.— The posterior arms of the tentorium (Fig. 107, 109, no, pt) are the lateral apodemes of the Fig. 107. — Tentorium of a cockroach, dor- sal aspect. Fig. 108.— Part of the tentorium of a cric- ket, ventral aspect. maxillary segment. In many Orthoptera the open mouth of the apodeme can be seen on the lateral aspect of the head, just above the THE INTERNAL ANATOMY OF INSECTS 97 articulation of the maxilla (Fig. 48). In the Acridiidae (Fig. 109) these apodemes bear a striking resemblance to the lateral apodemes of the thorax (Fig. 106), except that the ventral process of the maxil- lary apodeme is much more prominent, and the two frorri the opposite sides of the head meet and coalesce, thus forming the caudal part of the body of the tentorium. The anterior arms of the tentorium. — Each anterior arm of the tentorium (Fig. 107, 108, no, at) is an invagination of the body-wall which opens on the margin of the antecoxal piece of the mandible when it is distinct ; if this part is not distinct the apodeme opens between the clypeus and the front Fie.io9.-Headof (Fig- 46, a/). Melano plus, can- The dorsal arms of the tentorium. — Each dorsal a aspec . ^^,^ ^^ ^-^^ tentorium arises from the side of the body of the tentorium between the anterior and posterior arms and extends either to the front or to the margin of the antennal sclerite (Fig. 107, 108, no, dt). The frontal plate of the tentorium. — In the cockroaches the anterior arms of the tentoriimi meet and fuse, forming a broad plate situated between the crura cerebri and the mouth ; this plate was termed by us the frontal plate of the tentorium (Fig. 107, fp). On each side, an extension of this plate connects it with the body of the tentoriiun; these enclose a circular opening through which pass the crura cerebri. Other cervical apodemes and some chitinized tendons are described in the paper cited above. The endothorax. — The internal skeleton of the thorax is commonly termed the endothorax; under this head are not included the internal processes of the appendages. The endothorax is composed of invaginations of each of the sections of a thoracic ring. Those por- torium of Mela- tions that are derived from tergites are termed aspect'. Thedistal phragmas; those derived from the pleurites, lateral end of the dorsal apodemes; and those, from the sternites, furcce. ^^"^^ The phragmas. — A phragma is a transverse partition extending entad from the front or the hind margin of a tergite; three of them are commonly recognized; these were designated by Kirby and Spence (1826) the prophragma, the mesophragma, and the nieta- phragma; but, as they do not arise one from each segment of the 98 AN INTRODUCTION TO ENTOMOLOGY ' thorax, and arise differently in different insects, these terms are mis- leading. No phragma is borne by the prothorax; the mesothorax may bear two and the metathorax one, or the mesothorax one and the metathorax two. A more definite terminology is that used by Snod- grass ('09) by which the anterior phragma of any segment is termed the prephragma of that segment, and the posterior phragma of any segment is termed the postphragma of that segment. The lateral apodemes. — Each lat- eral apodeme is an invagination of the body-wall between the epister- num and the epimeron. The lateral apodemes are referred to above (Fig. 106). ThefurccB. — Each furca is an invagination of the body-wall arising between the sternum and the sternellum (Fig. in); when the sternel- lum is obsolete, as it is in most insects, the furca arises at the caudal margin of the segment (Fig. 112). Fig. Ill . — Ventral aspect of the metathorax of Stenopelmatus. The position of the furca within the body is represented by a dotted line. b. THE HYPODERMAL GLANDS A gland is an organ that possesses the function of either trans- forming nutritive substances, which it derives from the blood, into some useful substance, as mucus, wax, or venom, or of assimilating and removing from the body waste material. The different glands vary greatly in structure; many are unicellular, the gland consisting of a single cell, which differs from the other cells of the epithe- litmi of which it is a part in being larger and in possessing the secreting and ex- creting functions; others are multicel- lular, consisting of more than one cell. Fig. 112.— Ventralaspectof the usually of many cells. In these cases 'Si^^IsTL'^^^l^oat the glandular area usually becomes furcae within the body are invaginated, and provided with an indicated by dotted lines. efferent duct ; and often the invagination is much branched. The glands found in the body of an insect can be grouped under three heads; the hypodermal glands, the glands of the alimentary THE INTERNAL ANATOMY OF INSECTS 99 canal, and the glands of the reproductive organs. In this place reference is made only to the hypodermal glands, those developed from the hypodermis. The Molting-fluid glands. — Under this head are classed those unicellular, hypo- dermal glands that secrete a fluid that facilitates the process of molting, as des- cribed in the next chapter (Fig. 113). While molting-fluid glands are very numerous and conspicuous in certain insects, those living freely exposed where there exists the greatest liability to rapid desiccation, Tower ('06) states that he has never found these glands in larvae Fig. 1 13. — Molting-fluid glands of the last larval instar of Leptinotarsa decimlineata, just epidermis; Id, larval dermis; mf, molting fluid; pe, forming pupal epidermis; h, hypoder- mis; g, molting fluid, gland (After Tower). before pupation; le, larval that live in burrows, or in the soil, or in cells; in these cases the molting fluid is apparently secreted by the entire hypo- dermal layer. Glands connected with setae. — There are in insects several kinds of glands in which the outlet of the gland is through the Itimen of a seta. The function of the excretions of these glands is various as indicated below. There are also differences in the manner of issuance of the excre- tion from the seta. In some cases, as in the tenent hairs on the feet of certain insects, the excretion can be seen to issue through a pore at the tip of the seta. In some kinds of venomous setae the tip of the seta breaks off in the wound made by it and thus sets free the venom. But in most cases the manner of issuance has not been deter- mined, although it is commonly believed to be by means of a minute pore or pores in the seta, the thickness of the wall of the seta making it improbable that the excretion passes from the seta by osmosis. The structure of a glandular seta is illustrated by Figure 114; the essential difference between such a seta and an ordinary one, that is a Fig. 1 14. — Glandular s ;ta; j, seta; c, cuticula; h, hypodermis; bm, basement membrane; tr, tricho- gen; g, gland (After Holmgren). 100 AN INTRODUCTION TO ENTOMOLOGY clothing hair, is that there is connected with it, in addition to the trichogen cell which produced it, the gland cell which opens through it. In most of the published figures of glandular set® there is no indi- cation that these organs are supplied with nerves ; but in some cases a nerve extending to the gland cell is clearly shown. This condition may be found to be general when more extended investigations of glandular cells have been made. The best known kinds of glandular set£e are the following : Venomous setcE and spines. — These are best known in larvas of Lepidoptera, several common species of which possess stinging hairs; among these are Lagoa crtspata, Sihine stimulea, Automeris io, and the brown-tail moth, Euproctis chrysorrhcsa. Androconia. — The term androconia* is applied to some peculiarly modified scales on the wings of certain male butterflies. These are the outlets of glands, which secrete a fluid with an agreeable odor; the supposed function of which is to attract the opposite sex, like the beautiful plumage and songs of male birds. The androconia differ marvelously from ordinary scales in the variety of their forms (Fig. 115). They usually occur in patches on the upper sur- face of the fore wings; and are usually concealed by other scales; but they are scattered in some butterflies. The most familiar examples of grouped androconia are those that occur in the discal stigma of the hair-streaks, in the brand of certain skippers and in the costal fold of others, and in the scent-pouch of the male of the monarch butterfly The specific scent-glands of females. — The well-known fact that if an unfertilized female moth be confined in a cage or otherwise in the open many males of the Fig. 115.— Androconia from the same Species as the female will be attracted wmgs of male butterflies (After . . ., , . Kellogg). to it, and sometmies evidently from a great distance, leads to the conclusion that there must emanate from the female a specific odor. The special glands producing this odor have not been recognized. Tenent hairs. — In many insects the pulvilli or the empodia are clothed with numerous hairs that are the outlets of glands which "Androconia: andro- {a.vfjp^avbpbs),rr.a\e\ conia {kovIo) , 6\\si. THE INTERNAL ANATOMY OF INSECTS 101 secrete an adhesive fluid; this enables the insect to walk on the lower surface of objects (Fig. ii6). Fig. Ii6. — A, terminal part of a tenent hair from Eiipokis, showing canal in the hair and opening near the tip; B, cross-section through a tarsal segment of Telephorus; c, cuticula; g, gland of tenent hair; h, h, tactile hairs; hy, hypo- dermis; n, nerve; s, sense-cell of tactile hair; t, t, tenent hairs (After Dewitz). The osmeteria. — In many insects there are hypodermal glands that o^en into sac-like invaginations of the body-wall which can be evaginated when the insect wishes to make use of the secretion pro- duced by these glands ; svLch an organ i^ termed an osmeterium. The invagination of the osmeteriimi admits of an accumulation of the products of the gland within the cavity of the sac thus formed; when the osmeteriunj is evaginated the secretion becomes exposed to the air, being then on, the outside of the osmeterium, and rapid diffusion, of the secretion results. The most familiar examples of osmeteria are those of the larvee of the swallow-tailed butterflies, which are forked, and are thrust out from the upper part of the prothorax when the caterpillar is disturbed, and which diffuse a dis- agreeable odor (Fig. 117). They are ob- viously organs of defense. Osmeteria are present in the larvae of certain blue butterflies, Lycasnidae. These are in the seventh and eighth abdominal segments, and secrete a honey-dew, which attracts ants that attend and probably protect the larvse. The osmeteria of many other caterpillars have been described. Fig. 117 — Larva of Papilio thoas; 0, osmeterium expanded. 102 AN INTRODUCTION TO ENTOMOLOGY Fig. 1 1 8. — Wax-plates of the honej-bee (After Cheshire). Glands opening on the surface of the body. — There are several kinds of hypodermal glands, differing widely in function, that open on the surface of the body; among the best known of these are the following: Wax-glands. — The worker honeybee has four pairs of wax-glands; these are situated on the ventral wall of the second, third, fourth, and fifth abdominal segments, and on that part of the segment which is overlapped by the preceding segment; each gland is simply a disc- like area of the hypodermis (Fig. 1 1 8). The cuticle covering each gland is smooth and delicate, and is known as a wax plate. The wax exudes through these plates and accumu- lates, forming little scales, which are used in making the honey- comb. Wax -glands exist in many of the Homoptera. In some of these the unicellular wax- glands are distributed nearly all o\'er the body; and the product of these glands forms, in some, a po.wdery covering; in others, a clothing of threads; and in still others a series of plates (Fig. 119). Certain coccids excrete wax in con- siderable quantities. China wax, which was formerly an article of commerce, is the excretion of a coccid known as Pe-la (Ericerus Pe-la). Froth-glands of spittle-insects. — In the spittle-insects (Cercopidse) there are large hypodermal glands in the pleural regions of the seventh and eighth abdominal segments, which open through numerous minute pores in the cuticula. These glands secrete a muci- laginous substance, which is mixed with a fluid excreted from the anus, and thus fits it for the retention of bubbles of air included in it by means of abdominal appendages (Guilbeau '08). Stink-glands. — Glands that secrete a liquid having a fetid odor and that are doubtless defensive exist in many insects. In the stink-bugs Fig. 119. — Orthesia, greatly en- larged. THE INTERNAL ANATOMY OF INSECTS 103 (Pentatomidas) the fluid is excreted through two openings, one on each side of the lower side of the body near the middle coxae; in the bed- bug {Cimex) , the stink-glands open in the dorsal wall of the first three abdominal segments ; in Dytiscus, the glands open on the prothorax; and in certain Coleoptera they open near the caudal end of the body. These are merely a few examples of the many glands of this type that are known. The cephalic silk-glands. — In the Lepidoptera, Trichoptera, and Hymenoptera, there is a pair of glands that secrete silk, and which open through the lower lip. These glands are designated as the cephalic silk-glands to distinguish them from the silk-glands of certain Neuroptera and Coleoptera in which the sillc is produced by modified Malpighian vessels and is spun from the anus. The cephalic silk-glands are elongate and coiled; they often extend nearly the whole length of the body ; the two ducts unite and the single terminal duct opens through the low^er lip, and is not connected with the mouth cavity. These glands are a pair of salivary glands which have been transformed into silk organs. According to Carriere Fig. 1 20. — ^The salivary glands of the honeybee (After Cheshire). Fig. 121. — The man- dibular gland of a honeybee. and Burger ('97), who studied their development in the embryo of a bee, they are developed from the rudiments of the spiracles of the first thoracic segment. In the later development they move 104 AN INTRODUCTION TO ENTOMOLOGY cephalad and the paired openings become a single one. This is the reason that in the adult there are no spiracles in the prothorax. The Salivary glands. — The term salivary glands is a general one, applied to various glands opening in the vicinity of the mouth. The number of these varies greatly in different insects; the maximum number is found in the Hymenoptera. In the adult worker honey- bee, for example, there are four pairs of glands opening into the mouth; three of these are represented in Figure 120 and the fourth in Figure 121. These are designated as the supracerebral glands (Fig. 120, i), the postcersbral glands (Fig. 120. 2), the thoracic glands (Fig. 120, j), and the mandibulary glands (Fig. 121), respectively. II. THE MUSCLES There exist in insects a wonderfully large number of muscles ; some of these move the segments of the body, others move the appen- dages of the body, and still others are found in the viscera. Those of the viscera are described later in the accounts of the organs in which they occur. The muscles that move the segments of the body form several layers just within the body-wall, to which they are attached. The inner layer of these is well shown in Figure 122, which is a copy of one of the plates in the great work by Lyonet (1762) on the anatomy of a caterpillar, Cossus Ugniperda. The two figures on this plate represent two larvae which have been split open lengthwise, one on the middle line of the back (Fig. 5), and one on the middle line of the ventral surface (Fig. 4) ; in each case the alimentary canal has been removed, so that only those organs that are attached quite closely to the body-wall are left. The bands of parallel fibers are the muscles that move the segments. It should be borne in mind, however, that only a single layer of muscles is represented in these figures, the layer that would be seen if a caterpillar were opened in the way indicated. When these muscles are cut away many other muscles are found extending obliquely in various directions between these muscles and the body-wall. In the head and thorax of adult insects the arrangement of the muscles is even more complicated ; for here the muscles that move the appendages add to the complexity of the muscular system. As a rule, the muscles of insects are composed of many distinct fibers, which are not enclosed in tendinous sheaths as with Verte- THE INTERNAL ANATOMY OF INSECTS 105 Fig. 122. — Internal anatomy of a caterpillar, Cossus ligniperda; i, principal longitudinal trachse; 2, central nervous system; j, aorta; 4, longitudinal dorsal muscles; 5, longtiudinal ventral muscles; 6, wings of the heart ;_ 7, tracheal trunks arising near the spiracles; 8, reproductive organs; 9, vertical muscles; 10, last abdominal ganglion (From Lyonet). 106 AN INTRODUCTION TO ENTOMOLOGY brates. But the muscles that move the appendages of the body- are furnished with a tendon at the end farthest from the body (Fig. 123). The muscles of in- sects appear very differ- ently from those of Ver- tebrates. In insects, the Fig. 123.— A leg of a May-beetle (After Straus- muscles are either color- Durckheim). , , less and transparent, or yellowish white; and they are soft, almost of a gelatinous consistency; notwithstanding this they are very efficient. The fibers of insect muscles are usually, if not always, of the striated type. Much has been written regarding the muscular power of insects, which has been supposed to be extraordinarily great; the power of leaping possessed by many and the great loads, compared to the weight of the body of the insect, that insects have drawn when harnessed to them by experimenters, have been cited as illustrating this. But it has been pointed out that these conclusions are not warranted; that the comparative contractile force of muscles of the same kind depends on the ntmiber and thickness of the fibers, that is, on the comparative areas of the cross-sections of the muscles com- pared ; that this sectional area increases as the square of any linear dimension, while the weight of similar bodies increases as the cube of any linear dimension; and consequently, that the muscles of the legs of an insect one fourth inch long and supporting a load 399 times its own weight, would be subjected to the same stress, per square inch of cross-section, as they would be in an insect 100 inches long of precisely similar shape, that carried only its own weight. We thus see that it is the small size of insects rather than an unusual strength of their muscles, that makes possible the apparently marvelous exhibitions of muscular power. Detailed accounts of the arrangement of the muscles in particular insects have been published by various writers; among the more important of these monographs are the following: Lyonet (1762), on the larva of a cossid moth; Straus-Diu-ckheim (1828), on a May- beetle; Newport (1839), on the larva of a Sphinx moth; Lubbock (1858), on the larva Fygcsra bucephala; Berlese ('09a), on several insects; and Forbes ('14) on caterpillars. THE INTERNAL ANATOMY OF INSECTS 107 III. THE ALIMENTARY CANAL AND ITS APPENDAGES a. THE MORE GENERAL FEATURES The alimentary canal is a tube extending from one end of the body to the other. In some larvae, its length is about the same as that of the body; in this case it extends in a nearly straight line, occupying u^ Fig. 124." — Internal anatomy of a cockroach, Periplaneta orientalis; a, antennas: bi, 62, 63, first, second, and third legs; c, cerci : d, ventricular ganglion: e, salivary duct; /, salivary bladder, g, gizzard or proventriculus; h, hepatic coeca; i, mid-intestme; j, Malpighian vessels; k, small mtestine; /, large intestine: m, rectum; n, first abdominal ganglion; o, ovary; p, sebaceous glands (From Rolleston). 108 AN INTRODUCTION TO ENTOMOLOGY the longitudinal axis of the body, as is represented in the diagram given above (Fig. 105). In most insects, however, it is longer than the body, and is consequently more or less convoluted (Fig. 124); great variations exist in the length of the alimentary canal as com- pared to the length of the body; it is longer in herbivorous insects than it is in those that are carnivorous. The principal divisions. — Three chief divisions of the alimentary canal are recognized; these are termed the fore-intestme, the mid- intestine, and the hind-intestine, respectively. In the embryological development of the alimentary canal, the fore-intestine and the hind- intestine each arises as an invagination of the ectoderm, the germ layer from which the hypodermis of the body-wall is derived (p. 29). The invagination at the anterior end of the body, which develops into the fore-intestine, is termed the stomodceum; that at the posterior end, which develops into the hind-intestine, the proctodcBum. Between these two deep invaginations of the outer germ layer of the embryo, the stomodasum and the proctodaeum, and ultimately connecting them, there is developed an entodermal tube, the mesenteron, which becomes the mid-intestine. These embryological facts are briefly stated here merely to elucidate two important features of the alimentary canal: first, the fore-intestine and the hind-intestine are invaginations of the body wall and consequently resemble it in structure, the chitinous lining of these two parts of the alimentary canal is directly continuous with the cuticula of the body wall, and the epithelium of these two parts and the hypodermis are also directly continuous; and second, the striking differences, pointed out later, in the structure of the mid- intestine from that of the fore- and hind-intestines are not surprising when the differences in origin are considered. Imperforate intestines in the larvae of certain insects. — In the larvae of certain insects the Itrmen of the alimentary canal is not a continuous passage; in these larvas, while food passes freely from the fore- intestine to the mid-intestine, there is no passage of the waste from the mid-intestine to the hind-intestine ; there being a constr iction at the point where the mid-intestine and hind-intestine join, which closes the passage during a part or the whole of the larval life. This condition has been observed in the following families: — (a) Hymenoptera. — Proctotrypidas (in the first larval instar), Ichneumonids, Formicidae, Vespidse, and Apidae. (6) Diptera. — Hippoboscidae. THE INTERNAL ANATOMY OF INSECTS 109 (c) Neiiroptera. — Myrmeleonidce, Osmylidas, Sisyridae, and Chrysopidas. In these families the lan^se spin silk from the anus. (d) Coleoptera. — In the Campodeiform larvse of Stylopidse and Meloidae. b. THE FORE-INTESTINE The layers of the fore-intestine. — The following layers have been recognized in the fore-intestine : The intima. — This is a chitinous layer which lines the cavity of the fore-intestine; it is directly continuous with the cuticula of the body- wall; and is molted with the cuticula when this is molted. The epithelium. — This is a cell layer which is continuous with the hypodermis; it is sometimes quite delicate so that it is difficult to demonstrate it. The basement membrane. — Like the hypodermis the epithelium is bounded on one side by a chitinous layer and on the other by a base- ment membrane. The longitudinal muscles. — Next to the basement membrane there is a layer of longitudinal muscles. The circular muscles. — Out- side of the longitudinal muscles there is a layer of circular muscles. The peritoneal membrane. — Surrounding the alimentary canal there is a coat of con- nective tissue, which is termed the peritoneal membrane. This is one of a few places in which connective tissue, so abundant in Vertebrates, is found in in- sects. The regions of the fore- intestine. — Several distinct reg- ions of the fore-intestine are recognized; but the extent of these regions differ greatly in different insects. The pharynx. — The pharynx is not a well-defined region of the intestine ; the term pharynx is commonly applied to a region between the mouth and the oesophagus; in mandibulate insects the pharynx Fig. 125. — Longitudinal section through the head of Anosa plexippus, showing the interior of the left half; mx, left maxilla, the canal of which leads into the pharynx; ph, pharynx; 0, oesophagus; m, ni, muscles of the pharynx; sd, salivary duct (After Burges). no AN INTRODUCTION TO ENTOMOLOGY is not distinct from the mouth-cavity; but in sucking insects the pharynx is a highly specialized organ, being greatly enlarged, muscu- lar, and attached to the wall of the head by muscles. It is the pump- ing organ by which the liquid food is drawn into the alimentary canal. The pharnyx of the milkweed butterfly (Fig. 125) is a good example of this type of pharynx. The oesophagus. — The oeso- phagus is a simple tube which traverses the caudal part of the head and the cephalic part of the thorax. There are variations in the application of the term oesophagus depending on the presence or absence of a crop and of a proventriculus, which are modified portions of the oesophagus; when either or both of these are present, the term oesophagus is commonly restricted to the unmodified part of the fore-intestine. The crop. — In many insects a portion of the oesophagus is dilated and serves as a reservoir of food ; this expanded part, when present, is termed the crop. In the cock- roach (Fig. 124) it is very large, comprising the greater part of the fore-intestine ; in the ground-beetle Carahus (Fig. 126, c), it is much more restricted; this is the case also in the honeybee, where it is a nearly spherical sac in which the nectar is stored as it is col- lected from flowers and carried to the hive. In some insects the crop is a lateral dilatation of the oesophagus, and in some of these it is stalked. The proventriculus. — In certain stances, the terminal portion of Fig. 126. — Alimentary canal of Carabus auratus; h, head; or,, oesophagus; c, crop; pv, proventriculus; mi, mid- intestine covered with villiform gastric coeca; mv, Malpighian vessels; hi, part of hind-intestine; r, rectum; ag, anal glands ; mr, muscular reservoir (After Dufour). insects that feed on hard sub- the fore-intestine, that part im- THE INTERNAL ANATOMY OF INSECTS 111 Fig. 127.— Cross-section of the proventriculus of a larva of Corydahis. mediately in front of the mid-intestine or ventriculus, is a highly speciahzed organ in which the food is prepared for entrance into the more delicate ventriculus; such an organ is teiTned the proveninculus (Fig. 126, pv). The characteristic features of a proventriculus are a remarkable development of the chitinous intima into folds and teeth and a great in- crease in the size of the muscles of this region. The details of the structure of this organ vary greatly in different insects; a cross-section of the proven- triculus of the larva of Corydalus (Fig. 127) will serve to illustrate its form. In the proventriculus, the food is both masticated and more thoroughly mixed with the digestive fluids. The cesophageal valve. — When the fore-intestine projects into the mid- intestine, as shown in Figure 128, the folded end of the fore-intestine is termed the cesophageal valve. C. THE MID-INTESTINE The mid-intestine is the inter- mediate of the three principal divisions of the alimentary canal, which are distinguished by differ- ences in their embr>'ological origins, as stated above. The mid-intestine is termed by different writers the niesenteron, the stcnnack, the chylific ventricle, the chylestomach, and the ventnciilns. The layers of the mid-intestine.— The structure of the mid-intestine differs markedly from that of the fore-intestine. In the mid-intestine there is no chitinous intima, and the relative positions of the circular and longitudinal muscles are reversed. Fig. 128. — The oesophageal valve of a larva of Simidium; F, fore-intestine: M, mid-intestine; u, point of union of fore-intestine and mid-intestine; />, peritoneal membrane; i, intima of fore-intestine; e, epithe- lium of fore-intestine ; pt, peritrophic membrane; m, muscleb 112 AN INTRODUCTION TO ENTOMOLOGY The sequence of the different layers is as follows : a lining epithelium, which is supported by a basement membrane, a layer of circular muscles, a layer of longitudinal muscles, and a peritoneal membrane. The epithelium. — The epitheliiim of the mid-intestine is very con- spicuous, being composed of large cells, which secrete a digestive fluid. These cells break when they discharge their secretion and are replaced by new cells, which are developed in centers termed nidi (Fig. 129, m). The extent of the digestive epithelium is increased in many insects by the development of pouch-like diverticula of the mid-intestine, these are the gastric cceca (Fig. 124, h). These differ greatly in num- ber in different insects and are wanting in some. In some predaceous beetles they are villiform and very numerous (Fig. 126, mi). The peritrophic membrane. — In many insects there is a membranous tube which is form- ed at or near the point of union of the fore-intestine and the mid- intestine and which incloses the food so that it does not come in contact with the delicate epithe- liimi of the mid-intestine; this is known as the peritrophic mem- brane (Fig. 128, pt). As a rule this membrane is found in insects that eat solid food and is lacking in those that eat liquid food. It is obvious that the digestive fluid and the products of digestion pass through this membrane. It is continuously formed at its point of origin and passes from the body inclosing the excrement. d. THE HIND-INTESTINE The layers of the hind-intes- tine.— The layers of the hind-in- testine are the same as those of the fore-intestine described above, except that a greater or less number of circular muscles exist between the basement membrane of the epithelial layer and the layer of longitudinal muscles. The Fig. 129. — Resting epithelium of mid- intestine of a dragon-fly naiad; b, bases of large cells filled with digestive fluid; cm, space filled by circular mus- cles; /m, longitudinal muscles; «, nidus in which new cells are developing (From Needham). THE INTERNAL ANATOMY OF INSECTS 113 sequence of the layers of the hind-intestine is, therefore, as follows: the intinia, the epithelium, the basement membrane, the ental circular muscles, the longitudinal muscles, the ectal circular muscles, and the peritoneal membrane. The regions of the hind-intestine. — Three distinct regions are commonly recognized in the hind-intestine, these are the small intestine (Fig. 124, k), the large intestine (Fig. 124, /), and the rectum (Fig. 124, m). The Malpighian vessels. — There open into the beginning of the hind-intestine two or more simple or branched tubes (Fig. 124, ;), these are the Malpighian vessels. The nimiber of these vessels varies in different insects but is very constant within groups; there are either two, four, or six of them; but, as a result of branching, there may appear to be one hundred or more. The function of the Mal- pighian vessels has been much discussed ; it was formerly believed to be hepatic, but now it is known that normally it is urinary. The Malpighian vessels as silk-glands. — There are ceriain larvse that in making their cocoons spin the silk used from the anus. These larvce are chiefly found among those in which the passage from the mid-intestine to the hind-intestine is closed. The silk spun from the anus is secreted by the Malpighian vessels. Among the larvse in which the Malpighian vessels are known to secrete silk are those of the Myrmeleonidse, Osmylus (Hagen 1852), Sisyra (Anthony '02), Lebia scapularis (Silvestri '05), and the Coccidag (Berlese '96). Berlese states that the Malpighian vessels secrete the woof of the scale of the Coccidae. The caecum. — In some insects there is a pouch-like diverticulum of the rectum, this is the ccecum. The anus. — The posterior opening of the alimentary canal, the anus, is situated at the caudal end of the abdomen. IV. THE RESPIRATORY SYSTEM Insects breathe by means of a sj^stem of air-tubes, which ramify in all parts of the body and its appendages ; these air-tubes are of two kinds, which are termed trachece and tracheoles, respectively. In adult insxts and in most nymphs and larvae, the air is received through openings in the sides of the segments of the body, which are known as spiracles or stigmata. Many insects that live in water are furnished with special devices for obtaining air from above the water; but with naiads and a few 114 AN INTRODUCTION TO ENTOMOLOGY aquatic larvae the spiracles are closed; in these insects the air is purified by means of gill-like organs, termed tracheal gills. A few insects have blood-gills. Two types of respiratory systems, therefore, can be recognized: first, the open type, in which the air is received through spiracles; and second, the closed type, in which the spiracles are not functional. a. THE OPEN OR HOLOPNEUSTIC TYPE OR RESPIRATORY ORGANS That form of respiratory organs in which the trachese communicate freely with the air outside the body through open spiracles is termed the open or holopneustic type.* As the open type of respiratory organs is the most common one, those features that are common to both types will be discussed under this head as well as those that are peculiar to this type. Under the head of closed respiratory organs will be discussed only those features distinctly characteristic of that type. I. The Spiracles The position of the spiracles. — The spiracles are situated one on each side of the segments that bear them or are situated on the lateral aspects of the body in the transverse conjunctivse. The question of the position of the spiracles has not been thor- oughly investigated; but I believe that normally the tracheae, of Fig. 130. — Lateral view of a silk worm thowing the spiracles (After Verson) which the spiracles are the mouths, are invaginations of the transverse conjunctivas between segments. From this normal position a spiracle may migrate either forward or backward upon an adjacent segment (Fig. 130). The number of spiracles. — The normal number of spiracles is ten pairs; when in their normal position, there is a pair in front of the *H61opneustic : holo (5Xoj), whole; pneiima {nveufia), breath. THE INTERNAL ANATOMY OF INSECTS 115 second and third thoracic segments and the first to the eighth abdom- inal segments, respectively. There are none in the corresponding position in front of the first thoracic segment. See account of cephalic silk-glands p. 103. The two pairs of thoracic spiracles are commonly distinguished as the mesothoracic and the metathoracic spiracles ; that is each pair of spiracles is attributed to the segment in front of which it is normally situated. Following this terminology there are no prothoracic spiracles ; although sometimes the first pair of spiracles is situated in the hind margin of the prothorax, having migrated forward from its normal position. It would be better to designate the thoracic spiracles as the first and second pairs of thoracic spiracles, respec- tively; in this way the same term would be applied to a pair of spiracles w^hatever its position. There are many references in entomological works to "prothoracic spiracles," but these refer to the pair of spiracles that are more commonly designated the mesothoracic spiracles. In many cases the abdominal spiracles have migrated back upon the segment in front of which they are normally situated, being fre- quently situated upon the middle of the segment. The statements made above refer to the normal number and dis- tribution of spiracles ; but a very wide range of variations from this type exists. Perhaps the most abnormal condition is that found in the genus Smynthnrus of the Collembola, where there is a single pair of spiracles which is borne by the neck. In the Poduridae, also of the Collembola, the respiratory system has been lost, there being neither tracheae nor spiracles. Terms indicating the distribution of the spiracles. — The following terms are used for indicating the distribution of the spiracles; they have been used most frequently in descriptions of larvag of Diptera. These terms were formed by combining with pneiistic (from pneo, to breathe) the following prefixes: peri-, around, about; pro-, before; meta- after; and amphi, both. Peripneustic. — Having spiracles in a row on each side of the body, the normal t>^e. Propneustic. — With only the first pair of spiracles. Metapneustic. — With only the last pair of spiracles. Amphipneustic. — With a pair of spiracles at each end of the body. 116 AN INTRODUCTION TO ENTOMOLOGY Fig. 131. — Spiracles; a, of the larva of Corydalus; b, of the ]ar\^a of Droso- phila amoena. The structure of spiracles. — In their simplest form the spiracles or stigmata are small round or oval openings in the body-wall. In many cases they are provided with hairs to exclude dust ; in some, as in the larv^a of Corydalus, each spiracle is furnished with a lid (Fig. 131, a); in fact, very many forms of spiracles exist. Usually each spir- acle opens by a single apertiu-e; but in some larvae and pupas of Diptera they have several openings (Fig. 131, b). The closing apparatus of the tracheae. — Within the body, a short distance back of the spiracle, there is an apparatus consisting of several chitinous parts, surrounding the trachea, and moved by a muscle, by which the trachea can be closed by compression (Fig. 132). This is the closing apparatus of the trachea. The closing of this appara- tus and the contraction of the body by the respiratory muscles is sup- posed to force the air into thetracheoles, which are the essential res- piratory or- gans. Fig. 11,2. — Diagrams representing the closing apparatus of the tracheae; a, b,c, chitinous parts of the apparatus; m, muscle; A, apparatus open; B, apparatus closed; C, spiracle and trunk of trachea showing the position of the apparatus. (From Judeich and Nitsche). 2. THE TRACHEA Each spiracle is the opening of an air-tube or trachea. The main tracheal trunk which arises from the spiracle soon divides into several branches, these in turn divide, and by repeated divisions an immense number of branches are formed. Every part of the body is supplied with tracheae. In a few insects the group of tracheas arising from a spiracle is not connected with the groups arising from other spiracles; this is the case in Machilis (Fig. 133). In most insects, however, each group of trachccB is connected with the corresponding groups in adiacent seg- THE INTERNAL ANATOMY OF INSECTS 117 ments by one or more longitudinal tracheae, and is also connected The tracheae of Machilis (From Oudemans). with the group on the opposite side of the same segment by one or more transverse tracheas (Fig. 134). The structure of the tracheae.— The fact that in their embryological development the tracheee arise as invaginations of the body- wall, makes it easy to understand the structure of the trachcce. The three layers of the body-wall are directly continuous with corresponding layers in the wall of a trachea (Fig. 135). These layers of -a trachea are designated as the intima, the epithe- Ihmi, and the basement membrane. The mtinia is the chitinous inner layer of the trachea. It is directly continuous with the cuticula of the body- wall, and like the cuticula is molted at each ecdysis. A peculiar feature of the intima of tracheas is the fact that it is furnished with thickenings which extend spirally. These give the Fig. 134. — Larva of tracheas their charac- Fig. 135. Cantharis vesicnloria, ^^^■^^^:^^ transversely and ^ the body- wall ; c, cuti- showmg the distnbu- . ^ cula; h, hypodermis; bm, tion of tracheae (From striated appearance, basement membrane; sp, Henneguy after jf ^ • ^^ ^f ^^^ ^f spiral thickening of the ih- Beauregard). ^ tima, the tasnidium. the larger tracheas be pulled apart the intima will tear between the folds of the spiral thickening, and the latter will uncoil from within the trachea like a Section of a trachea 118 AN INTRODUCTION TO ENTOMOLOGY thread (Fig. 135). The spiral thickening of the intima of a trachea is termed the tcemdiunt. In some insects there are several parallel tcenidia; so that when an attempt is made to uncoil the thread a ribbon-like band is produced, composed of several parallel threads. This condition exists in the larger tracheae of the larva Corydalus. The epithelium of the trachea is a cellular layer, which is directly continuous with the hypodermis of the body -wall. The basement membrane is a delicate layer, which supports the epithelium, as the basement membrane of the body-wall supports the hypodermis. 3. The Tracheoles The tracheoles are minute tubes that are connected with the tips of tracheae or arise from their sides, but which differ from tracheae in their appearance, structure, and mode of origin ; they ai'e not small tracheae, but structures that differ both histologically and in their origin from tracheae. The tracheoles are exceedingly slender, measuring less than one micron in diameter; ordinarily they do not taper as do tracheae; they contain no tasnidia; and they rarely branch, but often anasto- mose which gives them a branched appearance (Fig. 136, t and 138 B, t). Each tracheole is of unicellular origin, and is, at first, intracellular in position, being developed coiled within a single cell of the epithelium of a trachea. In this stage of its development it has no connection with the lumen of the trachea in the wall of which it is developing, being separated from it by the intima of the trachea. A subsequent molting of the intima of the trachea opens a connection between the lumen of the tracheole and the trachea. At the same time or a little later the tracheole breaks forth from its mother cell, uncoils, and extends far beyond the cell in which it was developed. The tracheoles are probably the essential organs of respiration, the tracheae acting merely as conduits of air to the tracheoles. 4. The Air-Sacs In many winged insects there are expansions of the tracheee, which are termed air-sacs. These vary greatly in nimiber and size. In the honeybee there are two large air-sacs which occupy a consider- able part of the abdominal cavity; while in a May-beetle there are hundreds of small air-sacs. The air-sacs differ from trachea in lacking tasnidia. THE INTERNAL ANATOMY OF INSECTS 119 As the air-sacs lessen the specific gravity of the insect they proba- bly aid in flight ; as fiUing the lungs with air makes it easier for a man to float in water; in each case there is a greater volimie for the same weight. 5. Modifications of the open type of respiratory organs in aquatic insects There are many insects in which the spiracles are open that live in water; these insects breathe air obtained from above the surface of the water. Some of these insects breathe at the surface of the water, Fig. 136.- -Part of a tracheal gill of the larva of Corydalus; T, trachea; t, tracheoles. as the larvce and pupse of mosquitoes, the larvas of Eristalis, and the Nepidas; others get a supply of air and carry it about with them beneath the surface of the water, as the Dytiscidse, the Notonectidae and the Corisidas. The methods of respiration of these and of other aquatic insects with open spiracles are described in the accounts of these insects given later. h. THE CLOSED OR APNEUSTIC TYPE OF RESPIRATORY ORGANS That type of respiratory organs in which the spiracles do not function is termed the closed or apneustic* type; it exists in naiads and in a few aquatic larv^ae. 7. The Tracheal Gills In the immature insects mentioned above, the air in the body is purified by means of organs known as tracheal gills. Fig- 137- — Part of a tuft of tracheal gills of a larva of Corydalus. *Apneustic: apneiistos {drrvevaTos), without breath. 120 AN INTRODUCTION TO ENTOMOLOGY These are hair-like or more or less plate-like expansions of the body- wall, abundantly supplied with trachece and tracheoles. Figures 136 and 137 represents a part of a tuft of hair-like tracheal gills of a lar\'a of Corydalus and figiu-e 13 S a plate-like tracheal gill of a naiad of a damsel -fly. In these tracheal gills the tracheoles are separated from the air in the water only by the delicate wall of the tracheal gill which admits of the transfer of gases between the air in the tracheoles and the air in the ■^^iater. Tracheal gills are usually borne by the abdomen, sometimes by the thorax, and in case of one genus of stone-flies by the head . They pertain almost exclusively to the immature stages of insects ; but stone- flies of the genus Pteronarcys retain them throughout their existence. In the naiads of the Odonata the rectum is supplied with many tracheae and functions as a tracheal gill. Fig. 138. — Tracheal gill of a damsel- fly: A, entire gill showing the tracheae; B, part of gill more magnified showing. both tracheae (T) and tracheoles (t). 2. Respiration of Parasites It is believed that internal parasitic larvae derive their air from air that is contained in the blood of their hosts, and that this is done by osmosis through the cuticula of the larva, the skin of the larva being furnished with a network of fine tracheae (Seurat '99). 3. The blood-gills Certain aquatic lar\^ae possess thin transparent extensions of the body wall, which are filled with blood, and ser\^e as respiratory organs. These are termed blood-gills. Blood-gills have been observed in comparatively few insects; among them are certain trichopterous larv^ae; the larva of an exotic beetle, Pelobitis; and a few aquatic dipterous larvae, Chironontus and Simulium. It is probable that the ventral sacs of the Thysanura, described in the account of that order, are also blood-gills. THE INTERNAL ANATOMY OF INSECTS 121 V. THE CIRCULATORY SYSTEM The general features of the circulatory system. — In insects the cir- culatory system is not a closed one, the blood flowing in vessels during only a part of its course. The greater part of the circulation of this fluid takes place in the cavities of the body and of its appendages, where it fills the space not occupied by the internal organs. Almost the only blood-vessel that exists in insects lies just beneath the body-wall, above the alimentary canal (Fig. 105, h). It extends from near the caudal end of the abdomen through the thorax into the head. That part of it that lies in the abdomen is the heart; the more slender portion, which traverses the thorax and extends into the head is the aorta. On each side of the heart, there is a series of triangular muscles extending from the heart 1) l^H ^° ^^^® lateral wall of the body. These con- stitute the dorsal diaphragm or the wings of the heart. They are discussed later under the head: Suspensoria of the Viscera. .^^J^ The heart. — The heart is a tube, which is usually closed at its posterior end; at its anterior end it is continuous with the aorta. The heart is divided by constrictions into chambers which are separated by valves (Fig. 139). The munber of these chambers varies greatly in different insects; in some, as in Phasma and in the larva of Corethra, there is only one, in others, as in the cockroach, there are as many as thirteen, but usually there are not more than eight. The blood is admitted to the heart through slit-like openings, the ostia of the heart; usually there is a pair of ostia in the lateral walls of each chamber. Each ostium is furnished with a valve which closes it when the chamber contracts. The wall of the heart is composed of two dis- tinct layers: aninner muscular layer; and an outer, connective tissue or peritoneal layer. The muscular layer consists chiefly of annular but longitudinal fibers have also been observed. Fig. 139. — Heart of a May -beetle; a, lateral aspect of the aorta; b, interior of the heart showing valves; c, ventral aspect of the heart and wing-mus- cles, the muscles are represented as cut away from the caudal part of the heart; d, dorsal aspect of the heart (After Straus-Durck- heim). muscles ; 122 AN INTRODUCTION TO ENTOMOLOGY The ptilsations of the heart.— When a heart consists of several chambers, they contract one after another, the wave of contraction passing from the caudal end of the heart forwards. As the valves between the chambers permit the blood to move forward but not in the opposite direction, the successive contraction of the chambers causes the blood received through the ostia to flow toward the head, into the aorta. The aorta. — The cephalic prolongation of the heart, the aorta- (Fig. 139, a), is a simple tube, which extends through the thorax into the head, where it opens in the vicinity of the brain. In some cases, at least, there are valves in the aorta. The circulation of the blood. — The circulation of the blood can be observ^ed in certain transparent insects, as in young naiads, in larvae of Trichoptera, and in insects that have just molted. The blood flows from the open, cephalic end of the aorta and passes in quite definite streams to the various parts of the body-cavity and into the cavities of the appendages. These streams, like the ocean currents, have no walls but flow in the spaces between the internal organs. After bathing these organs, the blood returns to the sides of the heart, which it enters through the ostia. Accessory circulatory organs. — Accessory pulsating circulatory organs have been described in several insects. These are sac-like structures which contract independently of the contractions of the heart. They have been found in the head in several Orthoptera ; in the legs of Hemiptera, and in the caudal filaments of Ephemerida. VI. THE BLOOD The blood of insects is a fluid, which fills the perivisceral cavity, bathing all of the internal organs of the body, and flowing out into the cavities of the appendages of the body. In only a comparatively small portion of its cotirse, is the blood enclosed in definite blood- vessels; these, the heart and the aorta are described above. The blood consists of two elements, a fluid plasma and cells similar to the white corpuscles of the blood of vertebrates, the leucocytes. The blood of insects differs greatly in appearance from the blood of vertebrates, on account of the absence of red blood-corpuscles. In most insects the blood is colorless ; but in many species it has a yellow- ish, greenish, or reddish color. In the latter case, however, the color is not due to corpuscles of the type which gives the characteristic color to the blood of vertebrates. THE INTERNAL ANATOMY OF INSECTS 123 The leucocytes are nucleated, colorless, amoeboid cells similar to the white corpuscles of vertebrates, in appearance and function ; they take up and destroy foreign bodies and feed upon disintegrating tissue. It is believed that the products of digestion of disintegrating tissue by the leucocytes pass into the blood and serve to nourish new tissue. The blood receives the products of digestion of food, which pass in a liquid form, by osmosis, through the walls of the alimentary canal. On the other hand it gives up to the tissues which it bathes the materials needed for their growth. In insects oxygen is supplied to the tissues and gaseous wastes are removed chiefly by the respiratory system and not by means of the blood as in vertebrates. VII. THE ADIPOSE TISSUE On opening the body of an insect, especially of a larva, one of the most conspicuous things to be seen is fatty tissue, in large masses. These often completely surround the alimentary canal, and are held in place by nimierous branches of the tracheae with which they are supplied. Other and smaller masses of this tissue adhere to the inner surface of the abdominal wall, in the vicinity of the nervous system, and at the sides of the body. In adult insects it usually exists in much less quantity than in larvse. The chief function of the adipose tissue is the storage of nutriment ; but it is believed that it also has a urinary function, as concretions of uric acid accumulate in it during the life of the insect. VIII. THE NERVOUS SYSTEM a. THE CENTRAL NERVOUS SYSTEM The more obvious parts of the central nervous system are the following: a ganglion in the head above the oesophagus, the brain; a ganglion in the head below the oesophagus, the suhoesophageal ganglion; a series of ganglia, lying on the floor of the body cavity in the thorax and in the abdomen, the thoracic and the abdominal ganglia; two longitudinal cords, the connectives, uniting all of these ganglia in a series ; and many nerves radiating from the ganglia to the various parts of the body. The connectives between the brain and the suhoesophageal ganglion pass one on each side of the oesophagus ; these are termed the crura cerebri, or the legs of the brain ; in the remainder of their course, the two connectives are quite closely parallel (Fig. 124). 124 AN INTRODUCTION TO ENTOMOLOGY The series of ganglia is really a double one, there being typicall}^ a pair of ganglia in each segment of the body ; but each pair of ganglia are more or less closely united on the middle line of the body, and often appear to be a single ganglion. In some cases the ganglia of adjacent segments coalesce, thus reducing the number of distinct gangha in the series. It has been demonstrated that the brain is composed of the coalesced ganglia of three of the head segments, and the suboesophageal ganglion of the coalesced ganglia of the remaining four segments. Fig. 140.— Successive stages in the coalescence of thoracic and of abdominal ganglia m Diptera; A, Chironomus; B, Empis; C, Tabanus; D Sar- cophaga (From Henneguy after Brandt). The three parts of the brain, each of which is composed of the pair of ganglia of a head segment, are designated as the protocerebrum, the deutocerebrum, and the tritocerebrum, respectively. The protocere- brum innervates the compound eyes; the deutocerebrum, the antennas; and the tritocerebrum, the labrum. The suboesophageal ganglion is composed of four pairs of primar}^ ganglia; these are the ganglia of the segments of which the mandibles, the maxillulae, the maxillas, and the labium, respectivelv, are the appendages. The three pairs of thoracic ganglia often coalesce so as to form a smgle ganglionic mass; and usually in adult insects the number of abdommal ganglia is reduced in a similar way. THE INTERNAL ANATOMY OF INSECTS 125 Successive stages in the coalescence of the thoracic and abdominal ganglia can be seen by a study of the nervous system of the larva, pupa, and adult of the same species, a distinct cephalization of the central nervous system taking place during the development of the insect. Varying degrees of coalescence of the thoracic and of the abdominal ganglia can be seen by a comparative study of the nervous systems of different adult insects (Fig. 140). The transverse band of fibers that unite the two members of a pair of ganglia is termed a commissure. In addition to the commissures that pass directly from one member of a pair of ganglia to the other, there is in the head a com- missure that encircles the oesophagus in its passage from one side of the brain to the other, this is the sub- osophageal commissure (Fig. 141). The nerves that extend Fig. 141.— Lateral view of the cesophagus of a r ^u centra] chain of caterpillar, showing the subcesophageal com- ^^om me central cnam ot missure; b, brain; oe, oesophagus; sc, sub- ganglia to the different oesophageal commissure; .g.suboesophageal ^^ f ^^ ^ . ^ ganglion; ^g, paired ganglion (After Lienard). -^ j j-/c^ o of the central nervous sys- tem ; the core of each nerv^e fiber being merely a process of a ganglionic cell, however long it ^^ may be. „,, .^ ^P ^' V r a^ b. THE CESOPHAGEAL SYMPATHETIC NER- VOUS SYSTEM In addition to the central nervous sys- tem as defined above there are three other nervous complexes which are commonly described as separate systems although they are connected to the central nervous system by nerves. These are the oeso- phageal sympathetic Fig. 142. — Lateral view of the nerves of the head in the lar\'a of Corydalus; a, antennal nerve; ao, aorta; ar paired nerves connecting the frontal ganglion with the brain; &, brain; c/, clypeo-labral nerve; cow, connective; cr, cnira cerebri; /g, "frontal ganglion; /h , frontal nerve ; i, unpaired nerve connecting the frontal ganglion with . the brain; /, labial nerve; Ig, the paired ganglia; md, mandibular nerve; m, p, q, s, u, z, nerves of the oesopha- geal sympathetic system; mx, maxillary nerve; o, optic nerves; oes, oesophagus; ph, pharynx; pii, pharyngeal nerve; r, recurrent nerve; sc, subcesophageal commis- sure; sg, subcesophageal ganglion; st, stomagastric nerve; v, ventricular ganglion (From Hammar). nervous system, the ventral sympathetic nervous 126 AN INTRODUCTION TO ENTOMOLOGY system, and the peripheral sensory nerv^ous system. The first of these is connected with the brain; the other two, with the thoracic and abdominal ganglia of the central nerv^ous system. The oesophageal sympathetic ner\'ous system is intimately associated with the oesophagus and, as just stated, is connected with the brain. It is described by different writers under various names; among these are visceral, vagus, and stomato gastric. It consists of two, more or less distinct, divisions, an unpaired median division and a paired lateral division. The unpaired division of the oesophageal s\Tnpathetic nervous system is composed of the following parts, which are represented in Figures 141, 142, 143, and 144: the frontal ganglion (Jg), this is a minute gang- lion situated abov^e the oesophagus a short distance in front of the brain; the unpaired nerve connecting the frontal ganglion with the brain (i), this is a small nerve extending from the brain to the frontal gangHon; the paired nerves connecting the frontal ganglion with the brain (ar), these are arching nerv^es, one on each side, extending from the upper ends of the crura cerebri to the frontal ganglion; the frontal nerve (fn), this nerve arises from the anterior bor- der of the frontal ganglion and extends cephalad into the clypeus, where it bifur- cates; the pharyngeal nerves (pn), these extend, one on each side, from the frontal ganglion to the the recurrent nerve (r), this is a single the caudal border of the frontal Fig. 143. — Dorsal view of the nerves of the head in the larv'a of Corydalus; e, ocelU; mnd. mandible; other lettering as in Figvu-e 142 (From Hammar). lower portions of the pharynx median nerve, which arises from ganglion, and extends back, passing under the brain and between the THE INTERNAL ANATOMY OF INSECTS 127 aorta and the oesophagus, to terminate in the ventricular ganghon; the ventricular ganglion (v), this is a minute ganghon on the middle line, a short distance caudal of the brain, and between the aorta and the oesophagus; and the stomogastric nerves (st), these are two nerves which extend back from the caudal border of the ventricular ganglion, they are parallel for a short distance, then they separate and pass, one on each side, to the sides of the alimentary canal which they follow to the pro ventri cuius. The paired division of the oesophageal sympathetic nervous system varies greatly in form in different insects. In the larv^a of Corydalus, there is a single pair of ganglia (Fig. 142 and 143, Ig), one on each side of the oesophagus; each of these ganglia is connected with the brain b}^ two nerves {m and u) but they are not connected with each other nor with the unpaired division of this system. In a cockroach (Fig. 144), there are two pairs of ganglia (ag and pg); the two ganglia of each side are connected with each '\ other and with the recurrent nerve of the unpaired division. As yet comparatively little is known regarding the function of the oesophageal sympathetic nervous sys- tem of insects ; nerves extending from it have been traced to the clypeus, the muscles of the pharynx, the oeso- phagus, the mid-intestine, the sahvary glands, the aorta, and the heart. Its function is probably analogous to that of the sympathetic nervous sys- tem of Vertebrates. --sn Fig. 144. — The a-sophageal sympa- thetic nervous system of Peri- planeta orientalis; the outlines of the brain {h) and the roots of the antennal nerve which cover a por- tion of the sympathetic nervous system are given in dotted lines; ag, anterior ganglion; pg, posterior ganglion; /g, frontal ganglion; sn, nerves of the salivary glands; r, recurrent nerve (After Hofer). THE VENTRAL SYMPATHETIC NERV- OUS SYSTEM The ventral sympathetic nervous system consists of a series of more or less similar elements, each connected with a ganglion of the ventral chain of the central nervous system. Typi- cally there is an element of this system arising in each thoracic and 128 AN INTRODUCTION TO ENTOMOLOGY abdominal ganglion; and each element consists of a median nerve extending from the ganglion of its origin caudad between the two connectives, a pair of lateral branches of this median nerve, and one or more ganglionic enlargements of each lateral branch. Frequently the median ner\^e extends to the ganghon of the following segment. A simple form of this system exists in the larva ol Cossus ligniperda (Fig. 122); and a more compli- cated one, in Locusta viridissima (Fig. 145). From each lateral branch of the median nerve a slender twig extends to the closing apparatus of the tracheae. d. THE PERIPHER.\L SENSORY NERVOUS SYSTEM Immediately beneath the hypodermal layer of the body- wall, there are many bipolar and multipolar nerve-cells whose prolongations form a network of ner\^es; these constitute the peripheral sensory y.ervous system or the subhypodermal nerve plexus. The fine nerves of this system are branches of larger nerves which arise in the central nervous sys- tem; and the terminal prolongations of the bipolar nerve-cells innervate the sense-hairs of the body-wall. Figure 146 represents a surface view of a small part of the peripheral sensory nervous system of the silkworm, Bmnbyx mcri, as figured by Hilton ('02); the bases of several sense hairs are also shown. The tern; gs gang- details of this figure are as follows: h, h, h, the bases lion of the svm- r , . 1 • , pathetic system o* sense-hairs; s, s, s, bipolar nerve cells; m, m, m, (From Berlese). multipolar cells; n, n, n, nerves. All of these struct- ures are united, forming a network. Of especial interest is the fact that the terminal prolongation of each bipolar nerve-cell enters the cavity of a sense-hair and that the other pro- longation is a branch of a larger nerv-e which comes from the central nerv^ous system. The peripheral sensory nervous system is so delicate that it can not be seen except when it is stained by some dye that differentiates nervous matter from other tissues. For this purpose the intra vitam methylen blue method of staining is commonly used. Fig. 145. — Part of the ventral chain of gangha of Lo- custa viridissima and of the ven- tral sympathetic nervous sys- tem; g, ganglion of the central nervous system ; M, nerve; c, con- nective; m, me- dian nerve of the sympathetic sys- THE INTERNAL ANATOMY OF INSECTS 129 IX. GENERALIZATIONS REGARDING THE SENSE- ORGANS OF INSECTS The sense-organs of insects present a great variety of forms, some of which are still incompletely understood, in spite of the fact that they have been investigated by many careful observers. In the limited space that can be devoted to these organs here only the more general features of them can be described and some of the disputed questions regarding them briefly indicated. A classification of the sense-organs. — The different kinds of sense- organs are distinguished by the nature of the stimulus that acts on [46. — Surface view of subhypodermal nerves and nerve-cells from the silkworm (From Hilton) each. This stimulus may be either a mechanical stimulus, a chemical one, or light. The organs of touch and of hearing respond to mechani- cal stimuli; the former, to simple contact with other objects; the latter, to vibratory motion caused by waves of sound. The organs of taste and of smell are influenced only by soluble substances and it seems probable that chemical changes are set up in the sense-cells by these substances ; hence these organs are commonly referred to as the chemical sense-organs ; no criterion has been discovered by which the organs of taste and of smell in insects can be distinguished. The organs of sight are acted upon by light ; it is possible that the action of light in this case is a chemical one, as it is on a photographic plate, 130 AN INTRODUCTION TO ENTOMOLOGY but the eyes have not been classed among the chemical sense-organs. For these reasons the following groups of sense-organs are recognized: The mechanical sense-organs. — -The organs of touch and of hearing. The chemical sense-organs. — The organs of taste and of smell. The organs of sight. — The compound eyes and the ocelH. The cuticular part of the sense-organs. — In most if not all of the sense-organs of insects there exists one or more parts that are of cuti- cular formation. The cuticular parts of the organs of sight and of hearing are described later, in the accounts of these organs; in this place, a few of the modifications of the cuticula found in other sense- organs are described. Each of the cuticular formations described here is found either within or at the outer end of a pore in the cuticula ; as some of these formations are obviously setae and others are regarded as modified setag, this pore is usually termed the trichopore; it has also been termed the neuropore, as it is penetrated by a nerve-ending. As the cuticular part of this group of sense-organs, those other than the organs of hearing and of sight, is regarded as a seta, more or less modified, these organs are often referred to as the setiferous sense-organs; they are termed the Hautsinnesorgane by German writers. Special terms have been applied to the different types of setiferous sense-organs, based on the form of the cuticular part of each; but these types cannot be sharply differentiated as intergrades exist between them. In Figure 147 are represented the cuticular parts of several of these different types; these are designated as follows: The thick-walled sense-hair, sensillum trichodeum. — In this type the cuticular part is a seta, the base of which is in an alveolus at the end of a trichopore and is connected with the wall of the trichopore by a thin articular mem- brane (Fig. 147, a.) Fig- 147-^Various forms of the cuticular portion of the setiferous sense-organs. The lettering is explained in the text. THE INTERNAL ANATOMY OF INSECTS 131 If the sense-hair is short and stout, it is termed by some writers a sense-bristle, sensillum chceticum; but there is Httle use for this dis- tinction. In the thick-walled sense-hairs, the wall of the seta is fitted to receive only mechanical stimuli, being relatively thick, and as these organs lack the characteristic features of the organs of hearing, they are believed to be organs of touch. The sense-cones. — The sense-cones vary greatly in form and in their relation to the cuticula of the body-wall; their distinctive feature is that they are thin-walled. For this reason, they are believed to be chemical sense-organs, the thinness of the wall of the cone permitting osmosis to take place through it. In the sense-cones, too, there is no joint at the base, as in the sense-hairs, the articular membrane being of the same thickness as the wall of the cone ; there is, therefore, no provision for movement in response to mechanical stimuli. In one type of sense-cone, the sensillum hasiconicuni, the base of the cone is at the surface of the body -wall (Fig. 147, 6). In another type, sensillum caloconicum, the cone is in a pit in the cuticula of the body- wall (Fig. 147, c). Two forms of this type are represented in the figure; in one, the sense-cone is conical; in the other, it is fungi- form. Intergrades between the basiconicum and the cceloconicum types exist (Fig. 147, d). The flask-like sense-organ, sensillum ampullaceuni. — This is a modification of the sense-cone type, the characteristic feature of which is that the cone is at the bottom of an invagination of the articu- lar membrane; in some cases the invagination is very deep so that the cone is far within the body- wall (Fig. 147, ^) ; intergrades between this foi-m and the more common sensillum cceloconicum exist (Fig. 147, /)• The pore-plate, sensillum placodeum. — In this type the cuticular part of the organ is a plate closing the opening of the trichopore ; in some cases, this plate is of considerable thickness with a thin articular membrane (Fig. 147, g); in others it is thin throughout (Fig. 147, h). The olfactory pores. — This type of sense-organ is described later. X. THE ORGANS OF TOUCH The organs of touch are the simplest of the organs of special sense of insects. They are widely distributed over the surface of the body and of its appendages. Each consists of a seta, with all the character- istics of setse already described, a trichogen cell, which excreted the 132 AN INTRODUCTION TO ENTOMOLOGY seta, and a bipolar nen^e-cell. These organs are of the type known as sensillum trichodeum referred to in the preceding section of this chapter. According to the observ-ations of Hilton ('02) the terminal pro- longation of the ner\'e-cell enters the hair and ends on one side of it at some distance from its base (Fig. 148). The proximal part of this nen-e-cell is connected with the peripheral sensory ner\^ous system, as already described (page 128). The presence of this nerv-ous connection is believed to distinguish tactile hairs from those termed clothing hairs, and from the scales that are modified setas. If this distinction is a good one, it is quite probable that many hairs and scales that are now regarded as merely clothing will be found to be sense-organs, when studied by improved histological methods. In fact Guenther ('01) and others have shown that some of the scales on the wings of Lepidoptera, especially those on the veins of the wings, are supplied with nerves ; but the function of these scales is unknown. Hilton states that he "fotmd no evidence to indicate nerves ending in gland cells or trichogen cells by such branches as have been described and figured by Blanc ('90), but in every case the very fine nerve termination could be traced up past the hypodermal cell layer with no branches." Many figures of unbranched nerve fibers ending in sense-hairs are also given by O. vom Rath ('96). A very different form of nerve-endings in sense-hairs is given by Berlese ('09, a). This author represents the nerve extending to a sense-hair as dividing into many bipolar ner\-e-endings. XI. THE ORGANS OF TASTE AND OF SMELL {The chemical sense-organs) It is necessary to discuss together the organs of taste and of smell, as no morphological distinction between them has been discovered. If a chemical sense-organ is so located that it comes in contact with the food of the insect, it is commonly regarded as an organ of taste, if not so situated, it is thought to be an organ of smell. In the present state of our knowledge, this is the only distinction that can be made between these two kinds of organs. Many experiments have been made to determine the function of the various chemical sense-organs but the results are, as yet, far from conclusive. The problem is made difficult by the fact that these THE INTERNAL ANATOMY OF INSECTS 133 organs are widely distributed over the body and its appendages, and in some parts, as on the antennae of many insects, several different types of sense-organs are closely associated. Those organs that are characterized by the presence of a thin- walled sense-cone (Fig. 147, h-j) or by a pore-plate (Fig. 147, g, h) are believed to be chemical sense-organs. It is maintained by Berlese ('09, a) that an essential feature of these chemical sense-organs is the presence of a gland -cell, the excretion ofwhich, passing through the thin wall of the cuticular part, keeps the outer surface of this part, the sense-cone or pore-plate, moist and thus fitted for the reception of chemical stimuli. According to this view a chemical sense-organ consists of a cuticular part, a trichogen cell or cells which produced Fig. 148. — Sections through the body-wall and sense -hairs of the silk- worm; c, cuticula; h, hair; hy, hypodermis; n, nerve; s, bipolar nerve-cell (From Hilton). The line at the right of the figure indi- cates one tenth millimeter. this part, a gland-cell which excretes a fluid which keeps the part moist, and a nerve-ending. It is interesting to note that tactile hairs may be regarded as specialized clothing hairs, specialized by the addition of a nervous connection, and that sense-cones and pore-plates may be regarded as specialized glandular hairs with a nervous connection; in the latter case, the specialization involves a thinning of the wall of the hair so as to permit of osmosis through it. In the different accounts of chemical sense-organs there are marked differences as regards the form of the nerve-endings. In many of the descriptions and figures of these organs the nerve-ending is represented as extending unbranched to the chitinous part of the organ, resembling in this respect those represented in Figure 148. In other accounts the gland-cell is surrounded by an involucre of nerve -cells (Fig. 149). 134 AN INTRODUCTION TO ENTOMOLOGY In the t3-pes of chemical sense-organs action of the chemical stimuli is supposed to ■^'jM Fig. 149. — Section of the external layers of the wall of an antenna of Acrida turrita; Ct, cuticula; Ip, hypo- dermis; A^, nerve; iVi", involucre of nerve-cells sur- rounding the glandular part of a sense-organ; Sbc, sensillumbasiconicum; 5ff , sensillum coc-loconicum. Three sense-organs are figured; a surface view of the first is represented, the other two are shown in section. (From Berlese). described above the be dependent upon os- mosis through a deli- cate cuticular mem- brane. It should be noted, however, that several writers have de- scribed sense-cones in which there is a pore; but the accuracy of these observations is doubted by other writers. A very different type of sense-organs which has been termed olfactory pores is de- scribed in the conclud- ing section of this Chapter. XII. THE ORGANS OF SIGHT a. THE GENERAL FEATURES The two types of eyes of insects. — It is shown in the preceding chapter that insects possess two types of eyes, the ocelli or simple eyes and the compound or facetted eyes. Typically both types of eyes are present in the same insect, but either may be wanting. Thus many adult insects lack ocelli, while the larvffi of insects with a complete metamorphosis lack compound eyes. When all are present there are two compound eyes and, typically, two pairs of ocelli ; but almost invariably the members of one pair of ocelli are united and form a single median ocellus. The median ocel- lus is wanting in many insects that possess the other two ocelli. The distinction between ocelli and compound eyes. — The most obvious distinction between ocelli and compound eyes is the fact that in an ocellus there is a single cornea while in a compound eye there are many. Other features of compound eyes have been regarded as dis- tinctively characteristic of them; but in the case of each of these features it is found that they exist in some ocelli. THE INTERNAL ANATOMY OF INSECTS 135 Each ommatidivim of a compound eye has been considered as a separate eye because its nerve-endings constituting the retinula are isolated from the retinulae of other ommatidia by surrounding acces- sory pigment cells; but a similar isolation of retinulas exist in some ocelli. It has also been held that in compound eyes there is a layer of cells between the corneal hypodermis and the retina, the crystalline-cone- cells, which is absent in ocelli ; but in the ocelli of adult Ephemerida there is a layer of cells between the lens and the retina, which, at least, is in a position analogous to that of the crystalline-cone-cells; the two may have had a different origin, but regarding this, we have, as yet, no conclusive data. The absence of compound eyes in most of the Apterygota. — Typically insects possess both ocelli and compound eyes ; when either kind of eyes is wanting it is evidently due to a loss of these organs and not to a generalized condition. Although compound eyes are almost universally absent in the Apterygota in the few cases where they are present in this group they are of a highly developed type and not rudimentary; the compound eyes of Machilis, for example, are a^ perfect as those of winged insects. The absence of compound eyes in larvae. — The absence of com- pound eyes in larvse is evidently a secondary adaptation to their particular mode of life, like the internal development of wings in the same forms. In the case of the compound eyes of larvae, the develop- ment of the organs is retarded, taking place in the pupal stage instead of in an embryonic stage, as is the case m ith nymphs and naiads. While the development of the compound eyes as a whole is retarded in larvae, a few ommatidia may be developed and function as ocelli during larval life. b. THE OCELLI There are two classes of ocelli found in insects : first, the ocelli of adult insects and of nymphs and naiads, which may be termed the primary ocelli; and second, the ocelli of most larvae possessing ocelli, which may be termed adaptive ocelli. The primary ocelli. — The ocelli of adult insects and of nymphs and naiads having been orig'nally developed as ocelli are termed the primary ocelli. Of these there are typically two pairs; but usually when they are present there are only three of them, and in many cases only a single pair. 136 AN INTRODUCTION TO ENTOMOLOGY When there are three ocelh, the double nature of the median ocel- lus is shown by the fact that the root of the ner\-e is double, while that of each of the other two is single. In certain generalized insects, as some Plecoptera, (Fig. 150) all of the ocelli are situated in the front; but in most insects, the paired ocelli have either migrated into the suture between the front and the vertex (Fig. 151), or have proceeded farther and are situated in the vertex. The structure of primary ocelli is described later. The adaptive ocelli. — Some larva?, as those of the Tenthredinida?, possess a single pair of ocelli, which in their position and in their structure agree with the ocelli of the adult insects ; these are doubtless primary ocelli. But most larvas have lost the primary ocelli; and if they possess ocelli the position of them and their structure differ greatly from the positions and structure of primary ocelli. Except in the few cases where primary ocelli have been retained by larv^as, the ocelli of larvas are situated in a position corresponding to the position of the compound eyes of the adult (Fig. 152); and there are frequently several of these ocelli on each side of the head. This has led to the belief that they represent a few degenerate ommatidia, which have been retained by the lan^a, while the development of the greater niimber of ommatidia has been retarded. For this reason they are termed adaptive ocelli. The number of adaptive ocelli varies greatly, and sometimes is not con- stant in a species; thus in the larva of Corydalus, there may be either six or seven ocelli on each side of the head. There are also great variations in the struct- ure of adaptive ocelli. These variations pro- bably represent different degrees of degeneration or of retardation of development. The extreme of simplicity is found in certain dipterous larvas ; according to Hesse (01) an ocellus of Cerato- pogon consists of only two sense-cells. As examples of com- plicated adaptive ocelli, those of lepidopterous larvas can be cited. Fig. 150. — Head of a naiad of Pteronacys; dt, spots in the cuti- cula beneath which the dorsal arms of the tentorium are at- tached; the three ocelli are on the front (F), between these two spots. Fig. 151. — Head of a cricket. THE INTERNAL ANATOMY OF INSECTS 137 Fig. 152. — Head of a larva of Corydalus, dorsal aspect. The ocellus cf Gastropacha mbi, which is described and figured by Pankrath ('90), resembles in structure, to a remarkable degree, an ommatidium, and the same is true of the ocellus of the larva of Arctia caja figured by Hesse ('01). The structure of a visual cell. — The dis- tinctively characteristic feature of eyes is the presence of what is termed visual cells. In insects, and in other arthropods, a visual cell is a nerve-end-cell, which contains a nucleus and a greater or less amount of pigment, and bears a characteristic border, termed the rhabdomere; this is so called because it forms a part of a rhab- dom. The visual cells are grouped in such a way that the rhabdomeres of two or mere of them are united to form what is known as a rhabdcm or optic rod. A group of two visual cells with therhabdom formed by their united rhabdomeres is shown in Figure 153, A and B. The form of the rhabdomere varies greatly in the visual cells of different insect eyes; and the number of rhab- domeres that enter into the composi- tion of a rhabdom also varies. Figure 153, C represents in a dia- grammatic manner the structure of rhabdomere a s described by Hesse (' o i ) . The rhabdomere (r) consists of many minute rodlets each with a minute knob at its base and connected with a nerve fibril. The structure of a primary ocellus. — The primary ocelli vary greatly in the details of the form of their parts, but the essential features of their structure are accompanying diagram (Fig. 154). In some ocelli, as for example the lateral ocelli of scorpions, the visual cells are interpolated among ordinary hypodermal cells, Fig- 153- — Two visual cells from an ocellus of a pupa of Apis mellifica. A, longitudinal sec- tion ; B, transverse section; n, n, nerves; nu, nucleus; r, rhabdom; p, pigment (After Redikorzew), C, diagram il- lustrating the structure of a rhabdomere; r, rhabdomere; c, cell-body (From Berlese after Hesse). illustrated by the 138 AN INTRODUCTION TO ENTOMOLOGY Fig. 154. — A diagram illustrating the structure of a primary ocellus; c, cornea; c. hy, corneal hypodermis; ret, retina; n, ocellar nerve; p, accessory pigment cell; r, rhabdom. the two kinds fonning a single layer of cells beneath the cornea; but in the ocelli of insects, the sense-cells form a distinct layer beneath the hypo- dermal cells. In this type of ocellus the fol- lowing parts can be dis- tinguished : The cornea . — T h e cornea (Fig. 154, c) is a transparent portion of the cuticula of the body- wall ; this may be lenti- cular in form or not. The corneal hypoder- mis.— The hypodermis of the body-wall is con- tinued beneath the cornea (Fig. 154, c. hy.); this part of the hypo- dermis is termed by many writers the vitreous layer of the ocellus; but the term corneal hypodermis, being a self- explanatory term, is preferable. Other terms have been applied to it, as the lentigen layer and the corneagen, both referring to the fact that this part of the hypodermis produces the cornea. The retina. — Beneath the corneal hypodermis is a second cellular layer, which is termed the retina, being composed chiefly or entirely of visual cells (Fig. 154, ret). The visual cells of the retina are grouped, as described above (Fig. i53)> so that the rhabdomeres of several of them, two, three or four, unite to form a rhabdom; such a group of retinal cells is termed a retinula. The visual cells are nerve-end-cells, each constituting the termina- tion of a fiber of the ocellar nerve, and are thus connected with the central nervous system. Accessory pigment cells. — In some ocelli there are densely pig- mented cells between the retinulas, which serve to isolate them in a similar way to that in which the retinula of an ommatidium of a com- pound eye is isolated (Fig. 154, p). Even in cases where accessory pigment cells are wanting a degree of isolation of the rhabdoms of the retinulas of an ocellus is secured by pigment within the visual cells (Fig. 153. P)- THE INTERNAL ANATOMY OF INSECTS 139 Ocelli of Ephemerida.— It has been found that the ocelli of certain adult Ephemerida differ remarkably from the more common type of ocelli described above. These peculiar ocelli have been described and figured by Hesse (oi) and Seiler (05). In them the cuticula over the ocellus, the cornea, is arched but not thickened and the corneal hypo- dermis is a thin layer of cells immediately beneath it. Under the hypodermis there is a lens-shaped mass of large polygonal cells ; and between this lens and the retina there is a layer of closely crowded columnar cells. The development of these ocelli has not been studied; hence the origin of the lens-shaped mass of cells and of the layer of cells between it and the retina is not known. C. THE COMPOUND EYES A compound eye consists of many quite distinct elements, the ommatidia, each represented externally by one of the many facets of which the cuticular layer of the eye is composed. As the ommatidia of a given eye are similar, a description of the stn.icture of one will serve to illustrate the structure of the eye as a whole. The structure of an ommatidium. — The compound eyes of different insects vary in the details of their structure; but these variations are merely modi- fications of a common plan ; this plan is well -illustrated by the compound eyes of Machilis, the structure of which was worked out by Seaton ('03). Figure 155 represents a longitudinal section and a series of transverse sections of an ommatidium in an eye of this insect, which consists of the following parts. The cornea. — The cornea is a hexa- gonal portion of the cuticular layer of the eye and is biconvex in form (Fig. 155, c). The corneal hypodermis. — Beneath each facet of the cuticular layer of the eye are two hypodermal cells Fig- 155- — -An ommatidium of Machilis. The lettering is ex- plained in the text. 140 AN INTRODUCTION TO ENTOMOLOGY which constitute the corneal hypodermis of the ommatidium. These cells are quite distinct in Machilis and their nuclei are prominent (Fig. 155, hy); but in many insects they are greatly reduced, and consequently are not represented in many of the published figures of compound eyes. The crystalline-cone-celis . — Next to the corneal hypodermis there are four cells, which in one t3rpe of compound eyes, the eucone eyes, form a body known as the crystalline -cone, for this reason these cells are termed the crystalline-cone-cells (Fig. 155, cc). Two of these cells are represented in the figure of a longitudinal section and all four, in that of a transverse section. In each cell there is a prominent nucleus at its distal end. The iris -pigment-cells. — Surrounding the crystalline-cone-cells and the corneal hypodermis, there is a curtain of densely pigmented cells, which serves to exclude from the cone light entering other ommatidia ; for this reason these cells are termed the iris -pigment (Fig. 155, i). They are also known as the distal retinula cells; but as they are not a part of the retina this term is misleading. There are six iris -pigment -cells surrounding each crystalline -cone; but as each of these cells forms a part of the iris of three adjacent ommatidia, there are only twice as many of these cells as there are ommatidia. This is indicated in the diagram of a transverse section (Fig. 155, i)- The retinula. — At the base of each ommatidium, there is a group of visual cells forming a retinula (Fig. 1 55, r) ; of these there are seven in Machilis; but they vary in number in the eyes of different insects. The visual cells are so grouped that their united rhabdomeres form a rhabdom, which extends along the longitudinal axis of the ommati- dium (Fig. 155, rA). The distal end of the rhabdom abuts against the proximal end of the crystalHne-cone ; and the nerve-fibers of which the visual cells are the endings pass through the basement membrane (Fig. 155, b) to the optic nerve. The visual cells are pigmented and thus aid in the isolation of the ommatidium. The accessory pigment -cells. — In addition to the two kinds of pig- ment-cells described above there is a variable ntmiber of accessory pigment -cells (Fig. 155, ap), which lie outside of and overlap them. From the above it will be seen that each ommatidium of a eucone eye is composed of five kinds of cells, three of which, the corneal hypo- dermis, the crystalHne-cone-cells, and the retinular cells produce solid structures; and three of them are pigmented. THE INTERNAL ANATOMY OF INSECTS 141 Three types of compound eyes are recognized: first, the eucone eyes, in these each ommatidium contains a true crystalHne-cone, as described above, and the nuclei of the cone-cells are in front of the cone; second, the pseudocone eyes, in these the four cone -cells are filled with a transparent fluid medium, and the nuclei of these cells are behind the refracting body; and third, the acone eyes, in which although the four cone -cells are present they do not form a cone, either solid or liquid. d. THE PHYSIOLOGY OF COMPOUND EYES The compound eyes of insects and of Crustacea are the most com- plicated organs of vision known to us. It is not strange therefore, that the manner in which they function has been the subject of much dis- cussion. It is now, however, comparatively well-understood; although much remains to be determined. In studying the physiology of compound eyes, three sets of struc- tures, found in each ommatidium, are to be considered: first, the dioptric apparatus, consisting of the cornea and the crystalline -cone; second, the percipient portion, the retinula, and especially the rhab- dom; and third, the envelope of pigment, which is found in three sets of cells, the iris pigment-cells, the retinular cells, and the accessory or secondary pigment -cells. The dioptrics of compound eyes is an exceedingly complicated subject ; a discussion of it would require too much space to be intro- duced here. It has been quite fully treated by Exner ('91). to whose work those especially interested in this subject are referred. The im-portant point for our present discussion is that by means of the cornea and the crystalline-cone, light entering the cornea from within the limits of a certain angle passes through the cornea and the crystal- line-cone to the rhabdom, which is formed of the combined rhab- domeres of the nerve-end-cells, constituting the retinula, the precipient portion of the ommatidium. The theory of mosaic vision.-^The first two questions suggested by a study of physiology of compound eyes have reference to the nature of the vision of such an eye. What kind of an image is thrown upon the retinula of each ommatidium? And how are these images com- bined to form the image perceived by the insect? Does an insect with a thousand ommatidia perceive a thousand images of the object viewed or only one? The theory of mosaic vision gives the answers to these questions. This theory was proposed by J. Miiller in 1826; and the most recent 142 AN INTRODUCTION TO ENTOMOLOGY investigations confirm it. The essential features of it are the follow- ing: only the rays of light that pass through the cornea and the crystalline -cones reach the precipient portion of the eye, the others fall on the pigment of the eye and are absorbed by it ; in each ommatidium the cornea transmits to the crystalline -cone light from a very limited field of vision, and when this light reaches the apex of the crystaUine- cone it forms a point of light, not an image; hence the image formed upon the combined retinulae is a mosaic of points of light, which com- bined make a single image, and this image is an erect one. Figure 156 will serve to illustrate the mosaic theory of vision. In this figure are represented the corneas (c), the crystalline -cones (cc), and the rhabdoms (r.) of several adja- cent ommatidia. It can be seen, from this diagram, that each rhabdom receives a point of light which comes from a limited portion of the object viewed (O) ; and that the image (I) received by the percipient portion of the eye is a single erect image, formed by points of light, each of which corresponds in density and color to the corresponding part of the object viewed. The distinctness of vision of a com- pound eye depends in part upon the niun- ber and size of the ommatidia. It can be Fig. 156.— Diagram iUustrat- readily seen that the image formed by mg the tneory of mosaic a j vision. many small ommatidia will represent the details of the object better than one formed by a smaller niunber of larger ommatidia ; the smaller the portion of the object viewed by each ommatidium the mere detailed "will be the image. The distinctness of the vision of a compound eye depends also on the degree of isolation of the light received by each ommatidium, which is determined by the amount and distribution of the pigment. Two types of compound eyes, differing in the degree of isolation of the light received by each ommatidium, are recognized; to one type has been applied the term day-eyes, and to the other, night-eyes. Day-eyes. — The type of eyes known as day-eyes are so-called because they are fitted for use in the day-time, when there is an abundance of light. In these eyes the envelope of pigment sur- rounding the transparent parts of each ommatidiiim is so complete that only the light that has traversed the cornea and crystalline -cone THE INTERNAL ANATOMY OF INSECTS 143 of that ommatidium reaches its rhabdom. The image foiTQed in such an eye is termed by Exner an apposed image; because it is formed by apposed points of light, falHng side by side and not overlapping. Such an image is a distinct one. Night-eyes. — In the night-eyes the envelope of pigment surround- ing the transparent parts of each ommatidium is incomplete ; so that rays of light entering several adjacent corneas can reach the same retinula. In such an eye there will be an overlapping of the points of light; the image thus formed is termed by Exner a superimposed image. It is obvious that such an image is not as distinct as an ap- posed image. It is also obvious that a limited amount of light will produce a greater impression in this type of eye than in one where a considerable part of the light is absorbed by pigment. Night-eyes are fitted to perceive objects and the movement of objects in a dim light, but only the more general features of the object can be perceived by them. Eyes with double function. — It is a remarkable fact that with many insects and Crustacea the compound eyes function in a bright light as day-eyes and in a dim light as night- eyes. This is brought about by movements in the pigment. If an insect having eyes of this' kind be kept in a light place for a time and then killed while still in the hght, its eyes will be found to be day-eyes, that is eyes fitted to form apposed images. But if another insect of the same species be kept in a dark place for a time and then killed while still in the dark, its eyes will be found to be night-eyes, that is eyes fitted to form superimposed images. Figure 157 represents two preparations showing the structure of the compound eyes -of a diving-beetle, studied by Exner. In one (Fig. 157, ^), each rhabdom. is surrounded by an envelope of pigment, so that it can receiv eonly :57.— Ommatidia ^^^ ^^^^^ passing through the crystalline-cone of from eyes of Colym- the ommatidiimi of which this rhabdom is a part. coStiont fif n^g'lft! This is the condition found in the individual eye condition (From killed in the light, and illustrates well the struct- ■'^^'^^'"^- ure of a day-eye. In the other preparation (Fig. 157,5), which is from an individual killed in the dark, it can be seen that the pigment has moved up between the crystalline -cones so that 144 AN INTRODUCTION TO ENTOMOLOGY the light passing from the tip of a cone may reach several rhabdoms, making the eye a night-eye. These changes in the position of the pigment are probably due to amoeboid movements of the cells. Divided Eyes. — In many insects each compound eye is divided into two parts; one of which is a day-eye, and the other a night-eye. The two parts of such an eye can be readily distinguished by a differ- ence in the size of the facets; the portion of the eye that functions as a day-eye being composed of much smaller facets than that which functions as a night-eye. A study of the internal structure of a divided eye shows that the distribution of the pigment in the part composed of smaller facets is that characteristic of day-eyes ; while the part of the eye composed of larger facets is fitted to produce a superimposed image, which is the distinctive characteristic of night-eyes. Great differences exist in the extent to which the two parts of a divided eye are separated. In many dragon-flies the facets of a part of each compound eye are small, while those of the remainder of the eye are much larger ; but the two fields are not sharply separated. In some Blepharocera the two fields are separated by a narrow band in which there are no facets, and the difference in the size of the facets of the two areas is very marked. The extreme condition is reached in certain May-flies, where the two parts of the eye are so widely separa- ted that the insect appears to have ' two pairs of compound eyes (Fig i s 8) . The tapetum. — In the eyes of many animals there is a structure that reflects back the light that has entered the eye, causing the well- known shining of the eyes in the dark. This is often observed in the Fig. 158.— Front of head of Cloeon, g gg ^f ^^^g ^^^ -j^ ^^^ ^ gg ^f j^oths showing divided eves; a, night-eye; ; ,. , &, day eye; c, ocellus (From Sharp), that are attracted to our light at night. The part of the eye that causes this reflection is termed a tapetum. The supposed function of a tapetimi is to increase the effect of a faint light, the light being caused to pass through the retina a second time, when it is reflected from the tapetum. The structure of the tapetum varies greatly in different animals; in the cat and other carnivores it is a thick layer of wavy fibrous tissue; in spiders it consists of a layer of cells behind the retina containing THE INTERNAL ANATOMY OF INSECTS 145 small crystals that reflect the light ; and in insects it is a mass of fine tracheae surrounding the retinula of each ommatidium. XIII. THE ORGANS OF HEARING Fig. 159. — Side view of a locust with the wings removed; t, tympanum. a. THE GENERAL FEATURES The fact that in many insects there are highly specialized organs for the production of sounds indicates that insects possess also organs of hearing; but in only a few cases are these organs of such form that they have been gen- erally recognized as ears. The tympana. — In most of the jimiping Orthoptera there are thinned portions of the cuticula, which are of a structure fitted to be put in vibration by waves of sound. For this reason these have been commonly regarded as organs of hearing, and have been termed tympana. In the Acridiidse, there is a tympantim on each side of the first abdominal segment (Fig. 159); and in the Locustidas and in the Gryllidas, there is a pair of tympana near the proximal end of each tibia of the first pair of legs (Fig. 160). The chordotonal organs. — An ear to be effective must consist of something more than a membrane that will be put in vibration by means of sound; the vibrations of such a tympanum must be trans- ferred in some way to a nerv- vous structure that will be influenced by them if the sound is to be perceived. Such structures, closely associated with the tympana of Orthoptera, were discovered more than a half century ago by Von Siebold (1844) and have been studied since by many investigators. The morphological unit of these essential auditory Fig. 160. — Fore leg of a katydid; t, tympa- 146 AN INTRODUCTION TO ENTOMOLOGY Fig. i6i. — Diagrammatic representation of the auditory organs of a locustid (After Graber) . structures of insects is a more or less peg-like rod contained in a tubular nerve-ending (Fig. i6i, A and B); this nerve-ending may or may not be associated with a specialized tympaninn. To all sense-organs char- acterized by the presence of these auditory pegs, Graber ('82) applied the term chordotonal organs or fiddle-string-like organs. The scolopale and the scolopophore. — The peg-like rod characteris- tic of a chor- dotonal organ of an insect was named by Graber the scolopale; and to the tubular nerve-ending containing the scolopale, he applied the term scolopophore. The integumental and the subintegumental scolopo- phores. — With respect to their position there are two types of scolopophores ; in one, the nerve-ending is attached to the body-wall (Fig. 161, A); in the other, it ends free in the body-cavity (Fig. 161, B). These two types are designated respectively as integumental scolo- pophores and subintegumental scolopophores. The structure of a scolopophore. — In a scolopophore there can be distinguished an outer sheath (Fig. 161, I), which appears to be continuous either with the basement membrane of the hypodermis or with that of the epithelium of a trachea, and within this sheath the complicated nerve-ending; this nerve-ending is repre- sented diagrammatically in Figure 161 from Graber and in detail in Figure 162 from Hess ('17). In Figure 162 the following parts are represented: a bipolar sense-cell {sc) with its nucleus (sen) ; the proximal pole of this sense -cell is connected with the central nerv- ous system by a nerve; and its distal pole is connected with the scolopale (5) by an axis -fiber (a/) ; surrounding the distal prolongation of the sense -cell and the scolopale there is an enveloping or accessory cell (ec), in which there is a prominent nucleus {ecn) ; distad of the enveloping cell is \..aj ^ Fig. 162.— A scol op o- phore of the i n t e g u - mental type (From Hess). THE INTERNAL ANATOMY OF INSECTS 14/ the cap-cell {cc), in which there is a nucleus {ccn); extending from the end -knob {ek) of the scolopale and surrounded by the cap -cell there is an attachment fiber or terminal ligament {tl), by which the scolopophore is attached to the body-wall, the scolopophore repre- sented being of the integumental type; at the base of the scolopale and partly surrounding it, there is a vacuole (v). The structure of a scolopale. — The scolopalse or auditory pegs are exceedingly minute and are quite uniform in size, regardless of the size of the insect in which they are ; but they vary in form in different insects. They are hollow (Fig. 162,5); but the wall of the scolopale is almost always thickened at its distal end, this forming an end-knob (Fig. 162, e^). They are traversed by the axis -fiber of the sense-cell. The vacuole at the base of the scolopale connects with the lumen of the scolopale; this vacuole is filled with watery fluid. In Figure 163 is shown a part of the scolopo- phore represented in Figure 162, more enlarged (A), and three cross-sections (B, C, D) of the scolopale. The wall of the scolopale is composed at either end of seven ribs (r), each of which is divided in the central portion, making fourteen ribs in this part. The entire scolopale, except possibly the terminal ligament, is bathed in the watery liquid, and is free to vibrate (Hess '17). It should be remembered that the' scolopalae of different insects vary greatly in form; the one is merely given as an example of one type. The simpler forms of chordotonal organs. — In the simplest form of a chordotonal organ there is a single scolopophore; usually, how- ever, there are two or more closely parallel scolopophores. In figure 164, which represents a chordotonal organ found in the next to the last segment of the body of a larva of Chironomus, these two types are represented, one part of the organ being composed of a single scolopo- phore, the other of several. The chordotonal ligament. — In Figure 164 the nerve connecting the chordotonal organ with the central nervous system is represented at n; and at li is shown a structure not yet mentioned, the chordo- tonal ligament, which is found in many chordotonal organs. Figure 165 is a diagrammatic representation of the relations of the chordo- tonal organs of a larva of Chironomus to the central nervous system Fig. 163.— Part of the scolopophore shown in Figure 162 more Hesir^^"^ (^^°"^ figured here 148 AN INTRODUCTION TO ENTOMOLOGY and to the body-wall. Here each chordotonal organ is approxi- mately T-shaped; the proximal nerve forming the body of theT; the scolopophore, one arm; and the chor- dotonal ligament, the other arm. It will be observed that in this type of chordotonal organ the scolopophore and the ligament form a fiddle- string -like structure between two points in the wall of a single segment. It is believed that in cases of this kind the integu- Fig. 165.— Diagram , , , representing the mentactsasatympa- chordotonal organs Fig. i64.-Chordotonal organ num or sounding of a larva of CW of a larva of ChironoLs board. T'T" ^ (From Graber). , '^^'^''• O. THE CHORDOTONAL ORGANS OF LARV.E Chordotonal organs have been observed in so many larvae that we may infer that they are commonly present in larvce. These organs are very simple compared with those of certain adult insects, described later. Those figured in the preceding paragraphs will serv^e to illustrate the typical form of larval chordotonal organs. Even in the more complicated ones, there are comparatively few scolopophores ; and, as a rule, they are not connected with specialized t^nnpana, but extend between distant parts of the body- wall, which probably acts as a sound- ing board. In certain larvse, however, the scolopophores are attached to specialized areas of the body-wall. Hess ('17) has shown that the pleural discs of cerambycid larvas, which are situated one on each side of several of the abdominal segments, serve as points of attachment of scolopophores. C. THE CHORDOTONAL ORGANS OF THF LOCUSTID^ In the Locustidae there are highly specialized ears situated one on each side of the first abdominal segment. The external vibrating THE INTERNAL ANATOMY OF INSECTS 149 Fig. 1 66. — Side view of a locust with the wings removed; /, tympanum. part of these organs, the tympanum, is conspicuous, being a thinned portion of the body-wall (Fig. i66). Closely applied to the inner surface of each tympanum (Fig. 167, T), there is a ganglion known as Muller's organ {go), first described by Muller (1826). This ganglion contains many ganglion- cells and scolopalae and is the termination of a nerve extending from the central nervous system, the auditory nerve {n). Figure 168 represents a section of Muller's organ, showing the ganglion -cells and scolopalse. Intimately associated with the Muller's organ are two horny processes (Fig. 167, o and ti) and a pear-shaped vesicle (Fig. 167, bi); and near the margin of the tympantmi, there is a spiracle (Fig. 167, st), which admits air to a space inside of the tympa- num, the tympanal air-chamber. As the nerve-end- ings in Muller's organ are attached to the t}Tnpanum, it is a chordotonal organ of the integumental type; it is attached to a vibratile mem- brane, between two air spaces. d. THE CHORDOTO- NAL ORGANS OF THE TETTIGONIID^ AND OF THE GRYLLID^ In the long-horned grasshoppers and in the crickets, there is a pai r of tympana near the proximal end of the tibia of each fore leg. In Fig. 167 — Ear of a locust, Caloptenus ifa/icus,seeniTom inner side; T, tympanum; TR, its border; o,ii, two horn-like processes; 5x, pear-shaped vesicle; w, audi- tory nerve; ga, terminal ganglion or Muller's organ; 5<, spiracle; M, tensor muscle of the tympanum (From Packard after Graber). 150 AN INTRODUCTION TO ENTOMOLOGY many genera, these t>Tnpana are exposed and easily obser\^ed (Fig. 169) ; but in some genera each is covered by a fold of the body-wall and is consequently within a cavity, which communicates with the out- side air by an elongated opening (Fig. 170, a and b). Within the legs bearing these tympana, there are complicated chordotonal organs. Very de- tailed accounts of these organs have been published by Graber ('76), Adelung ('92) and Schwabe (06); in this place, for lack of fpace, only their more general features can be described. Figure 171 represents a longi- tudinal section of that part of a fore tibia of Decticus verrucivorus in which the chordotonal organs are situated, and Figure 172 represents a cross-section of the same tibia, passing through the tympana and scolo- -(-i^g air-chambers formed by the folds of the body- wall. In the fol- lowing account the references, in most cases, are to both of these figures. g- Fig 168. — Section of MuUer's organ; ganglion -cells; h, nerve; s, palae (After Graber). Fore leg of a katydid; i, tympa- a Fig. 1 70. — Tibia of a locustid with covered tympana; a, front view; 6, side view; o, opening (After Schwabe). The trachea of the leg.— The trachea of the leg figured in part here is remarkable for its great size and for its division into two branches, THE INTERNAL ANATOAIY OF INSECTS 151 the front trachea (Ti) and the hind trachea (Te) ; these two branches reunite a short distance beyond the end of the chordotonal organs. It is an interesting fact that these large tracheas of the legs containing the chor- dotonal organs open through a pair of supernumery spir- acles, differing in this respect from the tra- chea of the other legs. The spaces of the leg. — By reference to Figure 172, it will be seen that the two branches of the leg trachea occupy the middle space of the leg between the two tympana (Tie and j'iy Tii) and separate an outerspace, theupper one in the figure, from an inner space. The outer space (E) con- tains a chordotonal organ, of which the scolopale is repre- sented at S ; and the inner space contains small trachese (t) , muscles (m) , the tibial nerve (Ntb), and a tendon (Tn). The interstices of the outer and inner spaces are filled with blood. In the outer space some leucocytes and fat-cells (Gr) are represented. The supra-tympanal or subgenual organ. — In the outer space of the tibia, a short distance above the t>'mpana, there is a ganglion (Fig. Fig. 171. — Longitudinal section of a fore tibia of Decticus verrucivorus (From Berlese after Schwabe). 152 ^iV INTRODUCTION TO ENTOMOLOGY 171, Os) composed of nerve-endings, which are scolopophores of the integumental type. Two nerves extend to this gangHon, one frcm each side of the leg, and each divides into many scolopophores. The attachment fibers of the scolopophores converge and are attached to the wall of the leg. Two terms have been applied to this organ, both indicat- ing its position in the leg; one refers to the fact that it is above the tympana, the other, that it is below the knee. The intermediate or- gan.— Immediatelv below Fig. 172. —Transverse section of the fore tibia of fUp oimrp tvtnnflnal nro-nn Decticus verrucivorus (From Berlese after tfie SUpra-tympanai organ, Schwabe). In comparing this figure with the and betw^een it and the preceding, note that in that one the external parts are at the left, in this one, at the right. organ described in the next paragraph, is a ganglion composed of scolopophores of the subintegtmiental type; this is termed the intermediate organ (Fig. 171, Oi). Siebold's organ or the crista acustica. — On the outer face of the front branch of the large trachea of the leg there is a third chordo- tonal organ, the Siebold's organ or the crista acusttca. A surface view of the organ is given in Figure 171 and a cross-section is represented in Figure 172. It consists of a series of scolopophores of the subintegu- mental type, which diminish in length toward the distal end of the organ (Fig. 171). The relation of Siebold's organ to the trachea is shown in Figure 172. It forms a ridge or crest on the trachea, shown in setion at cr in Figure 172 ; this suggested the name crista acustica, usedcby some writers. e. THE Johnston's organ There has been found in the pedicel of the antenna of many insects, representing several of the orders, an organ of hearing, which is known as the Johnston's organ, having been pointed out by Christopher Johnston (1855). This organ varies somewhat in form in different THE INTERNAL ANATOMY OF INSECTS 153 insects and in the two sexes of the same species ; but that of a male mosquito will serv^e as an example illustrating its essential features. The following account is based on an in- vestigation by Professor Ch. M. Child ('94). In an an- tenna of a mos- quito (Fig. 173) the scape or first segment, which contains the muscles of the antenna, is much smaller than the pedicel or second seg- ment, and is usually over- looked, being concealed b y the large, glob- ular pedicel; the clavola con- sists of thirteen slender seg- ments. Excepting one or two terminal segments, each segment of the clavola bears a whorl of long, slender sets; these are more prominent in the male than in the female. Figure 174 represents a longitudinal section of the base of an antenna; in this the following parts are shown: S, scape; P, pedicel, C, base of the first segment of the clavola; cp, conjunctival plate connecting the pedicel with the first segment of the clavola; pr, chitinous processes of the conjunctival plate; m, muscles of the antenna; N, principal antennal nerve; n, nerve of the clavola; immediately within the wall of the segments there is a thin layer of hypodermis; the lumen of the pedicel is largely occupied by a ganglion composed of scolopophores, the attachment fibers of which are attached to the chitinous proce-^ses of the conjunctival plate. Fig. 173. — Antennae of mosquitoes, Culex; female; 5, scape; p, pedicel. 154 AN INTRODUCTION TO ENTOMOLOGY As to the action of the auditory apparatus as a whole, it was shown experimentally by Mayer ('74) that the different whorls of setae borne by the segments of the clavola, and which gradually decrease in length on successive segments, are caused to vibrate by different notes; and it is believed that the vibrations of the setae are transferred to the conjunctival plate by the clavola, and thence to the nerve-end- ^^ ings. It was formerly believed that the great specialization of the Johnston's or- gan in male mosqui- toes enabled the males to hear the songs of the females and thus more readily to find their mates. But it has been found that in some species, at least, of mosquitoes and of midges in which the males have this organ highly specialized the females seek the m^ales. This has led some writers to doubt that the Johnston's organ is auditory in function. But the fact remains that its distinctive feature is the presence of scolopalcC, which is the dis' tinctive characteristic of the auditory organs of other insects. Fig. 174. — Longitudinal section of the base of an anten- na of a male mosquito, Corethra culiciformis (After Child). XIV. SENSE-ORGANS OF UNKNOWN FUNCTIONS In addition to the sense-organs discussed in the foregoing account there have been described several types of supposed sense-organs which are as yet very imperfectly understood. Among these there is one that merits a brief discussion here on account of the frequent references to it in entomological literature. Many different names have been apphed to the organs of this type; of these that of sense- domes is as appropriate as any, unless the conclusions of Mclndoo, referred to below, are confim:ed^ in which case his term olfactory pores will be more descriptive. THE INTERNAL ANATOMY OF INSECTS 155 Fig. a b 175. — Sense-domes (From Berlese). The sense-domes are found in various situations, but they occur chiefly on the bases of the wings and on the legs. Each sense-dome consists of a thin, hemispherical or more nearly spherical membrane, which either projects from the outer end of a pore in the cuticula (Fig. 175, a) or is more or less deeply enclosed in such a pore (Fig. 175, 6); intergrades between the two types represented in the accom- panying figures occur. When a sense-dome is viewed in section a nerve- ending is seen to be connected with the dome-shaped or bell- like membrane. A striking feature of these organs is the absence of any gland -cells connected with them, such as are found in the chemical sense-organs described on an earlier page. In one very important respect there is a marked difference in the accounts of these organs that have been published. The organs were first discovered long ago by Hicks ('57); but they have been more carefully studied in recent years by several writers, who have been able to make use of a greatly improved histological technic; among these writers are Berlese ('09 a), Vogel ('n), Hochreuter (12'), Lehr ('14), and Mclndoo ('14). All of the writers mentioned above except the last named maintain that the sense-cell ends in a structure, in the middle of the sense-dome, which differs in appearance from both the membrane of the sense- dome and the body of the sense-cell. This structure varies in form in different sense- domes; in some it is cylindrical, and is consequently described as a peg; in others, it is greatly flattened so that it is semilunar in form when seen in section. In Figure 175, ^, which represents a section made transversely to the long axis of this part it appears peglike ; but in Figure 175,0, which represents a longitudinal view of it, it is semilunar in form. According to Mclndoo (Fig. 176) no structure of this kind is Fig. 176 — Olfactory pore of Mclndoo (From Mclndoo) 156 AN INTRODUCTION TO ENTOMOLOGY present, but the sense- fiber of the sense-cell pierces the bottom of the cone and enters the roimd, oblong, or slitlike pore-aperture. "It is thus seen that the cytoplasm in the peripheral end of the sense- fiber comes in direct contact with the air containing odorous par- ticles and that odors do not have to pass through a hard membrane in order to stimulate the sense-cell as is claimed for the antenna! organs". XV. THE REPRODUCTIVE ORGANS a. THE GENERAL FEATURES In insects the sexes are distinct. Formerly Termitoxema, a genus of wingless, very aberrant Diptera, the members of which live in nests of Termites, was believed to be hermaphroditic, but this is now doubted. individuals in which one side has the external characters of the male and the other those of the female are not rare ; such an individual is termed a gynandromorph; in some gynandromorphs, both testes and ovaries are present but in no case are both functional ; these there- fore are not true hermaphrodites. In females the essential reproductive organs consist of a pair of ovaries, the organs in which the ova or eggs are developed, and a tube leading from each ovary to an external opening, the oviduct. In the male, the essential reproductive organs are a pair of testes, in which the spermatozoa are developed and a tube leading from each testis to an external opening, the vas deferens. In addition to these essential organs, there are in most insects accessory organs, these consist of glands and of reservoirs for the reproductive elements. The form of the essential reproductive organs and the number and form of the accessory organs vary greatly in different insects. It is impossible to indicate the extent of these variations in the limited space that can be devoted to this subject in this work. Instead of attempting this it seems more profitable to indicate by diagrams, one for each sex, the relations of the accessory organs that may exist to the essential organs. In adult insects the external opening of the reproductive organs is on the ventral side of the abdomien near the caudal end of the body. The position of the opening appears to differ in different insects and in some cases in the two sexes of the same species. The lack of uni- formity in the published accounts bearing on this point is partly due to differences in numbering the abdominal segments; some authors describing the last segment of the abdomen as the tenth while others THE INTERNAL ANATOMY OF INSECTS 157 believe it to be the eleventh; embryological evidence supports the latter view. In most insects there is a single external opening of the reproduc- tive organs ; but in the Ephemerida and in a few other insects the two efferent ducts open separately. Secondary sexual characters. — In addition to differences in the essential reproductive organs and in the genital appendages of the two sexes, many insects exhibit what are termed secondary sexual characters. Among the more striking of these are differences in size, coloring, and in the form of certain organs. Female insects are usually larger than the males of the same species; this is due to the fact that the females carry the eggs ; but in those cases where the males fight for their mates, as stag-beetles, the males are the larger. Strik- ing differences in the color- I ing of the two sexes are A common, especially in the / \ Lepidoptera. In many y(m ^ insects the antennse of the /^^^ i^^ male are more highly ^^^■in ll'l^^ specialized than those of 0'm$%, Im^^^ the female; and this is M^Vi^'\tm m^wy'^Wk ^^^^ ^^^° °^ ^^^ ^^^^ °^ P/'/ffllv'^t'l ItllHt'fPl^ certain insects. These are IHIiiflHW li/i(nnl^ merely a few of the many UH.\\E^^ ^IImM known secondary sexual ^^^Mw i.¥ characters found in insects. V^^ ^^ • # dc b. THE REPRODUCTIVE ^••■■% \\: 1^ ^ Fig. 178 — ^SX// /"^^^ ORGANS OF THE Repro- ^f /^ M FEMALE ductive ft I ff^iijM^ organs of • - - - -I ^0iJ^=^ '^^^ general features of Japyx, --. I f^--X3) /p. the ovary.— In the more ^f?*^^^ fp\ fi' I — CZL • (After H v^; v;>'-S5ac=;^ usual form of the ovaries Grassi). IeJ ^^ of insects, each ovary is Fig. 177.— Diagram of thereproduc- a compact, more or less spindle- tive organs of a female insect; o, . , . , j j. . ovary; orf, oviduct; c, egg-calyx; v, shaped body composed of many paral- vagina; 5,spermatheca; 6c, bursa lei ovarian tubes (Fig. 177, o) , which copulatrix; sg, spermathecal . , rr *. -i. u gland; eg, colleterial glands. open mto a common efferent tube, the oviduct. In Campodea, however, there is a single ovarian tube; and in certain other Thysanura the ovarian tubes have a metameric arrangement (Fig. 178). The nimi- 158 AN INTRODUCTION TO ENTOMOLOGY ber of ovarian tubes differs greatly in different insects; in many Lepidoptera there are only four in each ovary; in the honeybee, about 150; and in some Termites, 3000 or more. The wall of an ovarian tube..— The ovarian tubes are lined with an epithelial layer, which is supported by a basement membrane; out- side of this there is a peritoneal envelope, composed of connective tis- sue; and sometimes there are muscles in the peritoneal envelope. The zones of an ovarian tube. — Three different sections or zones are recognized in an ovarian tube; first, the terminal filament, which is the slender portion which is farthest from the oviduct (Fig. 179, t); second, the germarium, this is a comparatively^ short chamber, between the other two zones (Fig. 179, g); and third, the vitellarium, which constitutes the greater portion of the ovarian tube. The contents of an ovarian tube. — In the germarium are found the primordial germ-cells from which the eggs are devel- oped; and in the vitellarium are found the developing eggs. In addition to the cells that develop into eggs there are found, in the ovarian tubes of m.any insects, cells whose function is to furnish nutriment to the developing eggs; these are termed nurse-cells. Depending upon the presence cr ab- sence of nurse-cells and on. the location of the nurse-cells when present, three types of ovarian tubes are recognized: first, those without distinct nurse-cells (Fig. 179, A) ; second, those in which the eggs and masses of nurse-cells alternate in the ovarian tube (Fig. 179, B); and third, those in which the nurse-cells are restricted to the germarium (Fig. 179, C), which thus becomes a nutri- tive chamber. In the latter type the developing eggs are each con- nected by a thread with the nutritive chamber. The egg-follicles. — The epitheliimi lining of the ovarian tube becomes invaginated between the eggs in such a way that each egg is Fig. 179. — Three types of ovarian tubes; e, e, e, eggs; n, n, n, nurse-cells (After Berlese). THE INTERNAL ANATOMY OF INSECTS 159 enclosed in an epithelial sac or egg-follicle, which passes down the tube with the egg (Fig. 179). There is thus a tendency to strip the tube of its epithelium, but a new one is constantly formed. The functions of the follicular epithelium. — It is believed that in some cases, and especially where the nurse-cells are wanting, the follicular epitheliiun serves a nutritive function. Bat the most obvious function of this epithelium is the formation of the chorion or egg-shell, which is secreted on its inner surface. The pit-like mark- ings so common on the shells of insect eggs indicate the outlines of the cells of the follicular epithelium. The ligament of the ovary. — In many insects, the terminal fila- ments of the several ovarian tubes of an ovary unite and form a slender cord, the ligament of the ovary, which is attached to the dorsal diaphragm ; but in other insects this ligament is wanting, the terminal filaments ending free in the body cavity. The oviduct. — The common outlet of the ovarian tubes is the ovi- duct (Fig. 177, od). In most insects the oviducts of the two ovaries unite and join a common outlet, the vagina; but in the Ephemerida and in some Dermaptera each oviduct has a separate opening. The egg-calyx. — In some insects each oviduct is enlarged so as to form a pouch for storing the eggs, these pouches are termed the egg- calyces (Fig. 1 7 7 , c) . The vagina. — The tube into which the oviducts open is the vagina (Fig. 177, v). The vagina differs in structure from the oviducts, due to the fact that it is an invagination of the body-wall, and, like other invaginations of the body-wall, is lined with a cuticular layer. The spermatheca — The spermatheca is a sac for the storage of the seminal fluid (Fig. 177,5). As the pairing of the sexes takes place only once in most insects and as the egg-laying period may extend over a long time, it is essential that provision be made for the fertilization of the eggs developed after the union of the sexes. The eggs become frll- grown and each is provided with a shell before leaving the ovarian tubis. At the time an egg is laid a spermatozoan may pass from the spermatheca, where thousands of them are stored, into the egg through an opening in the shell, the mncropyle, which is described in the next chapter (Fig. 184 and 185). In some social insects, eggs that are developed years after the pairing took place are fertilized by spermatozoa that have been stored in the spermatheca. The bursa copulatrix. — In many insects there is a pouch for the reception of the seminal fluid before it passes to the spermatheca. 160 AN INTRODUCTION TO ENTOMOLOGY This pouch is known as the bursa copulatrix or copulatory pouch. In some insects this pouch is a diverticulum of the vagina (Fig. 177, he); in others it has a distinct external opening, there being two external openings of the reproductive organs, the opening of the vagina and the opening of the bursa copulatrix. When the bursa copulatrix has a distinct external opening there may or may not be a passage from it to the vagina. In at least some Orthoptera {Melanoplus) there is no connection between the two; when the eggs are laid they are pushed past the opening of the bursa copulatrix where they are fertilized. In the Lepidoptera (Fig. 180), there is a passage from the bursa copulatrix to the vagina. In this case the seminal fluid is I'eceived by the bursa copulatrix at the time of pairing, later it passes to the spermatheca, and from here it passes to the vagina. A bursa copulatrix is said to Fig. 180. — Reproductive organs of the female of the milkweed butterfly; o, anus; b, opening of the bursa copula- trix; ov, ovarian tubes; /, terminal filaments of the ovary; v, opening of the vagina (After Burgess). be wanting in Hymenoptera, Diptera, Heteroptera and Homoptera except the Cicadas. The coUeterial glands. — There are one or two pairs of glands that open into the vagina near its outlet (Fig. 177, eg) ; to these has been applied the general term coUeterial glands. Their function differs in different insects ; in some insects they secrete a cement for gluing the eggs together, in others they produce a capsule or other covering which protects the eggs. The spermathecal gland. — In many insects there is a gland that opens either into the spermatheca or near the opening of the sperma- theca, this is the spermathecal gland (Fig. 177, sg). C. THE REPRODUCTIVE ORGANS OF THE MALE The reproductive organs of the male are quite similar in their more general features to those of the female ; but there are striking differ- ences in details of form. The general features of the testes. — As the reproductive elements developed in the testes, the spermatazoa, always remain small, the testes of a male are usually much smaller than the ovaries of the female of the same species. THE INTERNAL ANATOMY OF INSECTS 161 In the more common form, each testis is a compact body (Fig. i8i, /) composed of a variable number of tubes corresponding with the ovarian tubes, these are commonly called the testicular follicles; but it would have been better to have termed them the testicular tubes, reserving the term follicle for their divisions. The testicular follicles vary in number, form, and in their arrangement. In many insects as the Neuroptera, the Hemiptera, the Diptera, and in Campodea and Japyx, each testis is composed of a single follicle. In some beetles, Carabidae and Elateridse, the follicle is long and rolled into a ball. In some Thy- sanura the testicular follicles have a metameric arrangement. In some Coleoptera, each testis is separated into several masses, each having its own outlet leading to the vas deferens; while in some other insects the two testes approach each other during the pupal stage and constitute in the adult a single mass. The structure of a testicular follicle.— Like the ovarian tubes, the testicular follicles are lined with an epithelial layer, which is sup- ported by a basement membrane, outside of which there is a peritoneal envelope composed And in these follicles a series of zones are distinguished in which the genital cells are found in different stages of development, corresponding to the successive generations of these cells. In addition to the terminal filament four zones are recog- nized as follows: The germarium. — This includes the primordial germ-cells and the spermatogonia. The zone of growth. — Here are produced the spermatocytes of the first order and the spermatocytes of the second order. The zone of division and reduction. — In this zone are produced the Spermatids or immature spermatozoa. The zone of transformation. — Here the spermatids become sper- matozoa. A discussion of the details of the development of the successive generations of the genital cells of the male, or spermatogenesis, does not fall within the scope of this volimie. Fig. i8i. — Diagram of the reproductive or- gans of a male insect ; the right testis is shown in section; ag, acces- sory glands; ed, eja- culatory duct ; sv, semi- nal vesicles; /, testes; vd, vasa deferentia. of connective tissue. 162 AN INTRODUCTION TO ENTOMOLOGY The spermatophores. — In some insects the spermatozoa become enveloped in a sac in which they are transferred to the female; this sac is the spermatophore. Spermatophores have been observed in Gryllidas, Locustidae, and certain Lepidoptera. Other structures. — A ligament of the testis, corresponding to the ligament of the ovary, is often present ; the common outlet of the testi- cular follicles, corresponding to the oviduct is termed the vas deferens (Fig. 181, vd); an enlarged portion of the vas deferens serving as a reservoir for the products of the testis is known as a seminal vesicle (Fig. 181, sv); the invaginated portion of the body-wall, correspond- ing with the vagina of the female, is the ejaculatory duct (Fig. 181, ed); accessory glands, corresponding to the colleterial glands of the female, are present (Fig. 181, ag); the function of these glands has not been determined, they may secrete the fluid part of the semen, and they probably secrete the spermatophore when one is formed; tJw penis, this is merely the chitinized terminal portion of the ejaculatory duct, which can be evaginated with a part of the invaginated portion of the body-wall. It is furnished with powerful muscles for its protrusion and retraction. XVI. THE SUSPENSORIA OF THE VISCERA The organs discussed here do not constitute a well-defined system, but are isolated structures connected with different viscera. As in most cases they appear to serve a suspensory function, they are grouped together provisionally as the sus- pensoria of the viscera. The dorsal diaphragm. — This is a mem- branous structure which extends across the abdominal cavity immediately below the „. „ ^. , heart, to which it is attached along its median Fig. 182.— Diagram show- o^u w 1 • c ^u- a- u mg the relation of the hne. The lateral margms of this diaphragm dorsal diaphragm and are attached to the sides of the body by a the ventral diaphragm . . ^ . , , . . ■ ■, . to other viscera; a, senes of triangular prolongations, which have ahmentary canal; d, been commonly known as the wings of the dorsal diaphragm; h, , ._. x ^, •, 1 i- , • heart; n, ventral nerv- heart [Fig. 1^9, c). The dorsal diaphragm IS dS J^^*^"^' ^' ^^"^^^^ composed largely of very delicate muscles. Its relation to the heart is illustrated by the accompanying diagram (Fig. 182, d). There are differences of opinion as to the function of the dorsal diaphragm. An important function is probably to protect the heart THE INTERNAL ANATOMY OF INSECTS 163 from the peristaltic movements of the aHmentary canal. It also supports the heart; and it may play a part in its expansion. The dorsal diaphragm is also known as the pericardial diaphragm. The ventral diaphragm. — The ventral diaphragm is a very delicate membrane which extends across the abdominal cavity immediately above the ganglia of the central nervous system. It is quite similar in form to the dorsal diaphragm; it is attached along each side of the body, just lateral of the great ventral muscles, by a series of pro- longations resembling in form the wings of the heart. The position of the ventral diaphragm is illustrated in Figure 182, y. This diaphragm has been described as a ventral heart; but I believe that its function is to protect the abdominal gangHa of the central nervous system from the peristaltic movements of the alimen- tary canal. The thread-like suspensoria of the viscera. — Under this head may be classed the ligament of the ovary and the ligament of the testis, already described. In addition to these, there is, in some insects at least, a thread-like ligament that is attached to the intestine. XVII. SUPPLEMENTARY DEFINITIONS There are found in the bodies of insects certain organs not referred to in the foregoing general account of the internal anatomy of insects. These organs, though doubtless very important to the insects in which they occur, are not likely to be studied in an elementary course in entomology and, therefore, a detailed account of them may well be omitted from an introductory text-book. This is especially true as our knowledge of the structure and functions of these organs is so incomplete that an adequate discussion of the conflicting views now held would require more space than can be devoted to it here. The organs in question are the following: The oenocytes. — The term cenocytes is applied to certain very large cells, that are fotmd in clusters, often metamerically arranged, and connected with the tracheae and the fat body of insects. The name was suggested by the Hght yellow color which often characterizes these cells, the color of certain wines ; but the name is not a good one, as oenocytes vary greatly in color. Several otlier names have been applied to them but they are generally known by the name used here. Two types of oenocytes are recognized: first, the larval oenocytes; and second, the imaginal oenocytes. 164 AN INTRODUCTION TO ENTOMOLOGY The larv'al oenocytes are believed by Verson and Bisson ('91) to be ductless glands which take up, elaborate, and return to the blood definite substances, which may then be taken up by other cells of the body. Other views are held by other writers, but the view given above seems, as this time to be the one best supported by the evidence at hand. As to the function of the imaginal oenocytes, there are some obser- vations that seem to show that they are excretory organs without ducts, cells that serve as storehouses for excretory products, becoming more filled with these products with the advancing age of the insect. The pericardial cells. — The term pericardial cells is applied to a distinct type of cells that are found on either side of the heart in the pericardial sinus or crowded between the fibers of the pericardial diaphragm. These cells can be rendered very conspicuous by injecting ammonia carmine into the living insect some time before killing and dissecting it; by this method the pericardial cells are stained deeply while the other cells of the body remain uncolored. It is believed that the pericardial cells absorb albimiinoids origina- ting from the food and transform them into assimilable substances. The phagocytic organs.— The term phagocyte is commonly applied to any leucocyte or white blood corpuscle that shows special activity in ingesting and digesting waste and harmful materials, as disinte- grating tissue, bacteria, etc. The action of ' phagocytes is termed phagocytosis; an excellent example of phagocytosis is the part played by the leucocytes in the breaking down and rebuilding of tissues in the course of the metamorphosis of insects; this is discussed in the next chapter. Phagocytosis may take place in any part of the body bathed by the blood and thus reached by leucocj^tes. In addition to this widely distributed phagocytosis, it is believed that in certain insects there are localized masses of cells which perform a similar function; these masses of cells are known as the phagocytic organs. Phagocytic organs have been found in many Orthoptera and in earwigs; they are situated in the pericardial region; and can be made conspicuous by injecting a mixture of ammonia carmine and India ink into the body cavity ; by this method the pericardial cells are stained red and the phagocytic organs black. The light-organs. — The presence of organs for producing light is widely distributed among living forms both animal and vegetable. THE INTERNAL ANATOMY OF INSECTS 165 The most commonly observed examples of light-producing insects are certain members of the Lampyridae, the fireflies and the glow-worms, and a member of the Elateridce, the "cucujo" of the tropics. With these insects the production of light is a normal function of highly specialized organs, the light-organs. Examples of insects in which the production of light is occasionally observed are larvse of mosquitoes, and certain lepidopterous larvs;. In these cases the production of light is abnormal, being due either to the presence in the body of light -producing bacteria or to the ingestion of luminescent food. The position of the specialized light-organs of insects varies greatly; in the fireflies, they are situated on the ventral side of the abdomen; in the glow-worms, along the sides of the abdomen; and in the cucujo, the principal organs are in a pair of tubercles on the dorsal side of the prothorax and in a patch in the ventral region of the metathorax. The structure of the light-organs of insects varies in different insects, as is shown by the investigations of several authors. A good example of highly specialized light-organs are those of Photinus marginellus, one of our common fireflies. An excellent account of these is that of Miss Townsend ('04), to which the reader is referred. A detailed accotmt of the origin ana development of the light-organs of Phoiurus pennsylvanica is given by Hess ('22). CHAPTER IV. THE METAMORPHOSIS OF INSECTS Many insects in the course of their Hves undergo remarkable changes in form ; a butterfly was once a caterpillar, a bee lived first the life of a clumsy footless grub, and flies, which are so graceful and active, are developed from maggots. In the following chapters considerable attention is given to descriptions of the changes through which various insects pass; the object of this chapter is merely to discuss the more general features of the metamorphosis of insects, and to define the terms commonly used in descriptions of insect transformations. I. THE EXTERNAL CHARACTERISTICS OF THE META- MORPHOSIS OF INSECTS The more obvious characteristics of the metamorphosis of insects are those changes in the external form of the body that occur during postembrv^onic development. In some cases there appears to be but little in common between the successive forms presented by the same insect, as the caterpillar, chrysalis, and adult stages of a butterfly. On the other hand, in certain insects, the change in the form of the body during the postembryonic life is comparatively little. Based on these differences, several distinct types of metamorphosis have been recognized; and in those cases where the insect in its successive stages assumes different forms, distinctive terms are applied to the different stages. a. THE EGG Strictly speaking, all insects are developed from eggs, which are formed from the primordial germ-cells in the ovary of the female. As a rule, each egg is surrounded by a shell, formed by the follicular epithelium of the ovarian tube in which the egg is de\-eloped; and this egg, enclosed in its shell, is deposited by the female insect, usually on or near the food upon which the young insect is to feed. In some cases, however, the egg is retained by the female until it is hatched; thus flesh-flies frequently deposit active larvae upon meat, especially when they have had difficulty in finding it ; and t'. ere are other vivi- parous insects, which are discussed later. In tlr'.s place is discussed (166) THE METAMORPHOSIS OF INSECTS 167 i the more common type of insect eggs, those that are laid while still enclosed in their shell. The shape of the egg. — The terms ovoid and ovate have a definite meaning which has been derived from the shape of the eggs of birds ; but while many eggs of insects are ovate in form, many others are not. The more common form of insect eggs is an elongate oval, some- what curved; this type is illustrated by the eggs of crickets (Fig. 183, i); many eggs; are approx- imately spherical, as those of some butterflies (Fig. 183, 2) ; while some are of remarkable shape, two of these are represented in Figure 183,3, 4. The sculpture of the shell. — Almost always the external surface of the shell of an insect egg is marked with small, hexagonal areas; these are the imprints of the cells of the follicular epi- thelium, which formed the shell. In many cases the ornamentation of the shell is very conspicuous, consisting of prominent ridges or series of tubercles ; this is well -shown in the eggs of many Lepidoptera (Fig. 184). The micropyle. — It has been shown, in the course of the discussion of the reproductive organs of the female, that the egg becomes full-grown, and the protecting chorion or egg-shell is formed about it before it is fertilized. This renders necessary some provision for the entrance of the male germ -cell into the egg; this provision consists of one or more openings in the shell through which a spermatozoan may enter This opening or group of openings is termed the micropyle. Fig. 183. — Eggs of insects; i, CEcanthus nigri- cornis; 2, CEnis semidea; 3, Piezosterum stibiilatum; 4, Hydrometra ntarlini. Fig. 184.— Egg of the cotton- worm moth; the micropyle is shown in the center of the lower figure. 168 AN INTRODUCTION TO ENTOMOLOGY The number and position of the micropylar openings varies greatly in the eggs of different insects. Frequently they present an elaborate pattern at one pole of the egg (Fig. 184); and sometimes they open through more or less elongated papillse (Fig. 185). While in most cases it is necessary that an egg be fertilized in order that development may continue; there are many instances of par- thenogenesis among insects. The number of eggs produced by insects. — A very wide variation exists in the niimber of eggs produced by insects. In the sheep-tick, for example, a single large egg is produced at a time, and but few are produced during the life of the insect; on the other hand, in social insects, as ants, bees, and termites, a single queen may produce hundreds of thousands of eggs during her lifetime. These, however, are extreme examples; the Fig. 185.— Egg at peculiar mode of development of the larva of the Drosophilamelan- gheep-tick within the body of the female makes ogaster; m, micro- '^ ■' pyle. possible the production of but few eggs; while the division of labor in the colonies of social insects, by which the func- tion of the queen is merely the production of eggs, makes it possible for her to produce an immense number; this is especially trae where the egg-laying period of the queen extends over several years. The following may be taken as less extreme examples. In the solitary nest-building insects, as the fossores, the soHtary wasps, and the solitary bees, the great labor involved in making and provisioning the nest results in the reduction of the number of eggs produced to a comparatively small nimiber ; while many insects that make no pro- vision for their young, as moths, for example, may lay several hundred eggs. With certain chalcis-flies the mmiber of young produced is not dependent upon the number of eggs laid; for with these insects many embryos are developed from a single egg. This type of development is termed polyembryony. Modes of laying eggs. — Perhaps in no respect are the wonderful instincts of insects exhibited in a more remarkable way than in the manner of lajdng their eggs. If insects were reasoning beings, and if each female knew the needs of her young to be, she could not more accurately make provision for them than is now done by the great majority of insects. THE METAMORPHOSIS OF INSECTS 169 This is especially striking where the life of the young is entirely different from that of the adult. The butterfly or moth may sip nectar from any flower; but when the female lays her eggs, she selects with unerring accuracy the particular kind of plant upon which her larvae feed. The dragonfly which hunts its prey over the field, returns to water and lays her eggs in such a position that the young when it leaves the egg is either in or can readily find the element in which alone it is fitted to live. The ichneumon-flies frequent flowers; but when the time comes for a female to lay her eggs, she seeks the particular kind of larva upon which the species is parasitic, and will lay her eggs in no other. It is a remarkable fact that no larva leads so secluded a life that it cannot be found by its parasites. Thus the larvae of Tremex Columba bore in soHd wood, where they are out of sight and protected by a layer of wood and the bark of the tree in which they are boring; nevertheless the ichneumon-fly Thalessa lunator, which is para- sitic upon it, places her eggs in the burrows of the Tremex by means of her long drill-like ovipositor (Fig. i86). In contrast with the exam- ples just cited, some insects exhibit no remarkable instinct in their egg-laying. Our com- mon northern walking-stick, Diapheromera, drops its eggs-on the ground under the shrubs and trees upon which it feeds. This, however, is sufficient pro- vision, for the eggs are protected throughout the winter by the fallen leaves, and the young when hatched, readily find their food. Many species, the young of which feed upon foliage lay their eggs singly upon leaves; but many others, and this is especially true of those, the young of which are gregarious, lay their eggs in clusters. In some cases, as in the squash bug, the mass of eggs is not protected (Fig. 187) ; in others, where the duration of the egg-state is long, the eggs are protected by some covering. The females of our tent- caterpillars cover their eggs with a water-proof coating; and the tussock moths of the genus H enter ocampa cover their egg-clusters with a frothy mass. Fig. 186. — Thalessa lunator. 170 AN INTRODUCTION TO ENTOMOLOGY The laying of eggs in compact masses, however, is not correlated, in most cases, with gregarious habits of the larvae. The water- scavenger beetles, Hydrophilids, make egg-sacks out of a hardened silk-like secretion (Fig. i88) ; the locusts, Acridiidas, lay their eggs in oval masses and cover them with a .. ^, ,^ tough substance; the scale-insects of the genus Pulvinaria excrete a large cottony egg-sac (Fig. 189); ^O Fig. 187— Egi squash-bug. -mass of the Fig. 188. — Egg-sacoiHydrophiliis (After Miall). the eggs of the praying mantis are laid in masses and overlaid with a hard covering of silk (Fig. 190); and cockroaches produce pod-like egg-cases, termed ootheca, each containing many eggs (Fig. 191). Among the more remarkable of the methods of caring for eggs is that of the lace-winged flies, Chrysopa. These insects place each of their eggs on the simimit of a stitf stalk of hard silk (Fig. 192). Duration of the egg-state. — In the life-cycle of most insect s, a few days, and only a few, intervene between the laying of an egg and the emergence of the nymph, naiad, or loxxa. from " it. In some the duration of the egg-state is even shorter, the ' hatching of the egg taking place very soon after it is laid, or as sometimes in flesh-flies, before it is laid. On the Fig. 189. — Pulvinaria inniunerabilis, females on grape with egg sacs Fig. 190. -Egg- mass of a pray- even 1 m a n- tis. ^ other hand, in certain species, the greater part of the life of an individual is passed within the egg-shell. The common apple-tree tent-caterpillars, Clisiocampa aniericana, lays its eggs in early summer; but these eggs do not hatch till the fol- lowing spring; while the remainder of the life-cycle occupies only a THE METAMORPHOSIS OF INSECTS 171 few weeks. The eggs of Bittacus axe said to remain unhatched for two years; and a similar statement is made regarding the eggs of our common walking-stick. I'CS*^ b. THE HATCHING OF YOUNG INSECTS Only a few accounts have been published regarding the manner in which a young insect frees itself from the embryonic envelopes. In ^'^cockr7a?h ^^'"''^ °^ ^ some cases it is evident that the larva cuts its way out from the egg-shell by means of its mandibles ; but in others, a specialized organ has been developed for this purpose. The hatching spines. — An organ for rupturing the embryonic envelopes is probably commonly pre- sent. It has been des- cribed under several names. It was termed an egg-burster by Hagen, the ruptor ovi by C. V. Riley an egg-tooth by Heymons, and the hatching spines by Wheeler. C. THE MOLTING OF INSECTS Fig. 192.— Eggs, larva, cocoon, and adult of 'phe voung of insects Chrysopa. / ° cast periodically the outer parts of the cuticula; this process is termed molting or ecdysis. General features of the molting of insects. — The chitinization of the epidermis or primary cuticula adds to its efficiency as an armor, but it prevents the expansion of the body-wall rendered necessary by the growth of the insect; consequently as the body grows, its cuticula becomes too small for it. When this occurs a second epidermis is formed by the hypodermis; after which the old epidermis splits open, usually along the back of the head and thorax, and the insect works itself out from it. The new epidermis being elastic, accommodates itself to the increased size of the body ; but in a short time it becomes chitinized; and as the insect grows it in turn is cast off. The cast skin of an insect is termed the exuvice, the plural noun being used as in English is the word clothes. 172 AN INTRODUCTION TO ENTOMOLOGY Coincident with the formation of the new epidermis, new setas are formed beneath the old epidermis; these He closely a ppressed to the ou;:er surface of the new epidermis until released by the molting of the old epidermis. In the above account only the more gsneral features of the process of molting are indicated, the details, according to the observations of Tower ('06) are as follows. (See Figure 113, p. 99). In ths formation of the new epidermis it appsars as a thin, delicate lamella, spread evenly over the entire outer surface of the hypodermis; it grows rapidly in thickness until finally, just before ecdysis takes place, it reaches its final thickness. After ecdysis the epidermis hardens rapidly and its coloration is developed. As soon as ecdysis is over the deposition of the dermis or secondary cuticula begins. This layer is a carbohydrate related to cellulose, and is deposited in layers of alternating composition, through the period of reconstruction and growth, during which it reaches its maximum thick- ness. Preliminary to ecdysis a thin layer of molting fluid is formed, and through its action the old dermis is corroded and often almost entirely destroyed, thus facilitating ecdysis. This dissolving of the dermis, is, according to Tower, a most constant phenomenon in ecydsis" and has been found in all insects examined by him in varying degrees. It is said that the CcUembola molt after reacamg sexual maturity, in this respect agreeing with the Crustacea and the "Myriapoda," and differing from the Arachnida and from all other insects (Brindley '98). The molting fluid. — As indicated above, the process of molting is facilitated by the excretion of a fluid known as the molting fluid. This is produced by unicellular glands (Fig. 113, p. 99) which are modified hypodermal cells. These glands are found all through the life of the insect and upon all parts of the body; but are most abundant upon the pronotum, and are more abundant at pupation than at any other period. The number of postembryonic molts. — A very wide range of vari- ation exists as to number of molts undergone by insects after they leave the egg-shell. According to Grassi ('98, p. 292), there is only a single partial molt with Campodea and Japyx, while the May-fly Chloeon molts twenty times. Between these extremes every condition exists . Probably the majority of insects molt from four to six times; but there are many records of insects that molt many more times than this. Stadia. — The intervals between the ecdyses are called stadia. In numbering the stadia, the first stadium is the period between hatching and the first postembryonic ecdysis. Instars. — The term instar is appHed to the form of an insect during a stadium; in numbering the instars, the form assumed by the insect between hatching and the first postembryonic molt is termed the first instar. THE METAMORPHOSIS OF INSECTS 173 Head measurements of larvse.^ — It was demonstrated by Dyar ('90) that the widths of the head of a larva in its successive instars follow a regular geometric progression in their increase. The head was selected as a part not subject to growth during a stadium; and the width as the most convenient measurement to take. By means of this criterion, it is possible to determine, when studying the transfor- mations of an insect, whether an ecdysis has been overlooked or not. Experience has shown that slight variations between the computed and the actual widths may occur; but these differences are so slight that the overlooking of an ecdysis can be readily discovered. The following example will serve to illustrate the method employed. A larva of Papilio thoas was reared from the egg; and the widths of the head in the successive instars was found to be, expressed in millimeters, as follov\^s: .6; i.i; 1.6; 2.2; 3.4. By dividing 2.2. by 3.4 (two successive members of this series), the ratio of increase was found to be .676+ ; the number, .68 was taken, therefore, as sufficiently near the ratio for practical purposes. By using this ratio as a factor the following results were obtained : Width found in fifth instar = 3.4 Calculated width in fourth instar (3.4 X .68) = 2.312 " "third " (2.312 X .68) =.. .. 1.57 " " " second " (1.57 X .68) = 1.067 " " first (1.067 X .68) = 72s By comparing the two series, as is done below, so close a correspond- ence is found that it is evident that no ecdysis was overlooked. Widths found: — .6; i.i; 1.6; 2.2; 3.4 " calculated: — .7; 1.1-; 1.6-; 2.3. I The reproduction of lost limbs. — The repro- ^ duction of lost limbs has been observed in many insects ; but such reproduction occurs here much less frequently than in the other classes of the Arthropoda. The reproduction takes place dur- ing the period of ecdysis, the reproduced part becoming larger and larger with each molt; hence with insects, and with Arachnida as well, the power of reproducing lost limbs ceases with the attainment of sexual maturity; but not so with the Crustacea and the "Myriapoda" which molt after becoming sexually mature. In none Fig- 93-— A spider in of the observed examples of the reproduction which lost legs weie ^ ^ . ,. , , 11 being reproduced. of appendages has an entire leg been reproduced. 174 AN INTRODUCTION TO ENTOMOLOGY It appears to be necessary that the original coxa be not removed in order that the reproduction may take place. Figure 193 represents a spider in our collection in which two legs, the left fore leg and the right hind leg, were being reproduced when the specimen was captured. d. DEVELOPMENT WITHOUT METAMORPHOSIS {Ametabolous* Development) While most insects undergo remarkable changes in form during their postembryonic development, there are some in which this is not the case. In these the young insect just hatched from the egg is of practically the same form as the adult insect. These insects grow larger and may undergo slight changes in form of the body and its appendages ; but these changes are not sufficiently marked to merit being termed a metamorphosis. This type of development is known technically as ametabolous development. Development without metamorphosis is characteristic of the two orders Thysanura and CoUembola, which in other respects, also, are the most generalized of insects. The natiire of the changes in form undergone by an insect with an ametabolous development is illustrated by the development of Machilis alternata, one of the Thysanura. The first instar of this insect, according to Heymons ('07), lacks the clothing of scales, the styli on the thoracic legs, and the lateral rows of eversi- ble sacs on the abdominal segments; and the antennae and cerci are relatively shorter and consist of a much smaller number of segments than those of the adult. These changes, however, are comparable with those undergone by many animals in the course of their development that are not regarded as having a metamorpho- sis. In common usage in works on Entomology the term metamorphosis is used to indicate those marked changes that take place in the appearance of an insect tha t are correlated with the development of wings. In addition to the Thysanura and the CoUembola there are certain insects that develop without metmorphosis, as the Mallophaga and thePediculidae. But their ametabolous condition is believed to be an acquired one. In other words, it is beheved that the bird-lice and the true lice are descendants of winged insects whose form of body and mode of development have been modified as a result of parasitic life. The Ametabola. — Those insects that develop without meta- morphosis are sometimes referred to as the Ametabola. This term was first proposed by Leach (18 15), who included under it the Hce as well as the Thysanura and CoUembola. But with our present knowledge, if it is used it should be restricted to the Thysanura and CoUembola those insects in which a development without metamorphosis is a primitive not an acquired condition. *Ametabolous: Greek a, without; metabole (/xerapoXT^), change. IHE METAMORPHOSIS OF INSECTS 175 e. GRADUAL METAMORPHOSIS (Paurometabolous* Development) In several orders of insects there exists a type of development that is characterized by the fact that the young resemble the adult in the general form of the body and in manner of life. There is a gradual growth of the body and of the wing rudiments and genital appendages. Fig. 194. — Nymph of Mela- noplus, first instar (After Emerton). Fig. 195. — Nymph of Mela- noplus, second instar (After Emerton). Fig. 196. — Nymph of Melano- plus, third instar (After Emer- ton) Fig. 198. — Nymph of Melano- plus, fifth instar (After Emer- ton). jj^^ Fig. i97.^Nymph of Melano- plii%, fourth instar (After Emerton). Fig. iqg. — Melanoplus, adult. But the changes in form take place gradually and are not very great between any two successive instars except that at the last ecdysis there takes place a greater change, especially in the wings, than at any of the preceding ecdyses. This type of metamorphosis is desig- nated as gradual metamorphosis or paurometabolous development. The characteristic features ol paurometabolous development are correlated with the fact that the mode of life of the young and of the *Paurometabolous: pauros (iraCpos), little; metabole (Me^a^oXi}), change. 176 AN INTRODUCTION TO ENTOMOLOGY adult are essentially the same; the two living in the same situation, and feeding on the same food. The adult has increased power of loco- motion, due to the completion of the development of the wings; this enables it to more readily perform the functions of the adult, the spread of the species, and the making of provision for its continuance; but otherwise the life of the adult is very similar to that of the young. The development of a locust or short-horned grasshopper will serve as an example of gradual metamorphosis. Each of the instars of our common red-legged locust, Melanoplus femur-rubrum, is repre- sented in the accompanying series of figures. The adult (Fig. 199) is represented natural size; each of the other instars, somewhat enlarged; the hair line above the figure in each case indicates the length of the insect. The young locust just out from the egg-shell can be easily recog- nized as a locust (Fig. 194). It is of course much smaller than the adult; the proportion of the different regions of the body are some- what different ; and it is not furnished with wings ; still the form of the body is essentially the same as that of the adult. In the second and third instars (Fig. 195 and 196) there are slight indications of the development of wing-rudiments; and these rudimentary wings are quite conspicuous in the fourth and fifth instars (Fig. 197 and 198). The change at the last ecdysis, that from the fifth instar to the adult, is more striking than that at any preceding ecdysis; this is due to the complete expansion of the wings, which takes place at this time. The Paurometabola. — Those orders of insects that are characterized by a gradual metamorphosis are grouped together as the Paurometa- bola. This is not a natural division of the class Hexapoda but mer'^l\- indicates a similarity in the nature of the metamorphosis in the orders included. This group includes the Isoptera, Dermaptera, Orthop- tera, Corrodentia, Thysanoptera, Homoptera, and Hemiptera. The term nymph. — An immature instar of an insect that undergoes a gradual metamorphosis is termed a nymph. In old entomological works, and especially in those written in the early part of the last century, the term nymph was used as a synonym of pupa ; but in more recent works it is applied to the immature instar of insects that undergo either a gradual or incomplete metamorphosis. In this book I restrict the use of this term to designate an immature instar of an insect that undergoes a gradual metamorphosis. Deviation from the usual type. — It is to be expected that within so large a group of organisms as the Paurometabola there should have THE METAMORPHOSIS OF INSECTS 177 been evolved forms that exhibit deviations from the usual type of development. The more familiar examples of these are the following: The Saltatorial Orthoptera. — In the crickets, locusts, and long- homed grasshoppers, the wings of the nymphs are developed in an inverted position ; that surface of the wing which is on the outside in the adult is next to the body in the nymphal instars; and the rudi- mentary hind wings are outside of the fore wings, instead of beneath them, as in the adult. At the last ecdysis the wings assume the normal position. The Cicadas. — In the Cicadas there exists a greater difference between the nymphal instars and the adult than is usual with insects in which the metamorphosis is gradual. The nymphs live below the surface of the ground, feeding upon the roots of plants; the adults live in the open air, chiefly among the branches of trees. The forelegs of the nymphs are fossorial (Fig. 200); this is an adaptation for subterranean life, which is not needed and not possessed by the adults. And it is said that the last nymphal instar is quiescent for a period. The Coccidce. — In the Coccidas the mode of develop- ment of the two sexes differ greatly. The female never acquires wings, and in so far as external form is concerned the adult is degenerate. The male, on the other hand, exhibits a striking approach to com- plete metamorphosis, the last nymphal instar being enclosed in a cocoon, and the legs of the adult are not those of the nymph, being developed from imaginal Pig. 200.— disks. But the wings are developed externally. ^IJ^da (After ^^'^ Aleyrodidce.— In this family the type of meta- Riley ) . morphosis corresponds quite closely with that described later as complete metamorphosis; consequently the term larva is applied to the immature instars except the last, which is designated the pupa. The wings arise as histoblasts in the late embryo, and the growth of the wing-buds diu-ing the larval stadia takes place inside the body- wall. The change to the pupal instar, in which the wing-buds are external, takes place beneath the last larval skin, which is known as the pupa case or puparium. The adult emerges through a T-shaped opening on the dorsum of the puparium. Both sexes are winged. The AphididcB. — In the Aphididas there exists a remarkable type of development known as heterogamy or cyclic reproduction. This is characterized by an alternation of several parthenogenetic generations 178 ^.V INTRODUCTION TO ENTOMOLOGY with a sexual generation. And within the series of parthenogenetic forms there may be an alternation of winged and wingless forms. In some cases the reproductive cycle is an exceedingly complicated one ; and different parts of it occur on different food plants. The Thysanoptera. — In the Thysanoptera, as in most other insects with a gradual metamorphosis, the nymphs resemble the adults in the form of the body, and the wings are developed externally; but the last nymphal instar is quiescent or nearly so and takes no noiuishment. This instar is commonly described as the pupa. /. INCOMPLETE METAMORPHOSIS (Hemtmetabolous* Development) In three of the orders of insects, the Plecoptera, Ephemerida, and Odonata, there exists a t>^e of metamorphosis in which the changer Fig. 20I. — Transformation of a May-fly, Ephemera varia; A, adult; B, naiad (After Needham). that take place in the form of the body are greater than in gradual metamorphosis but much less marked than in complete metamorpho- sis. For this reason the terms incomplete metamorphosis and hemi- metabolous development have been applied to it. Both incomplete metamorphosis and complete metamorphosis are characterized by the fact that the immature instars exhibit adaptive modifications of form and structure, fitting them for a very different mode of life than that followed by the adult. This is often expressed by the statement that the imjnature instars are "sidewise developed" ; for it is believed that in these cases the development of the individual does not repeat the history of the race to which the individual belongs. *Hernimetabolous: lierni ("^A"'). lialf; metabole (/xerajSoX??'), change. THE METAMORPHOSIS OF INSECTS 179 This mode of development is termed cenogenesis* It contrasts strongly with gradual metamorphosis, where there is a direct develop- ment from the egg to the adult. In each of the orders that are characterized by an incomplete metamorphosis, the adaptive characteristics of the young insects fit them for aquatic life ; while the adults lead an aerial existence. The transformations of a May-fly (Fig. 201) will serve to illustrate this type of metamorphosis. The primitive insects were doubtless terrestrial ; this is shown by the nature of the respiratory system, which is aerial in all insects. In the course of the evolution of the different orders of insects, the immature forms of some of them invaded the water in search of food. This resulted in a sidewise development of these immature forms to better fit them to live in this medium ; while the adult continued their development in, what may be termed by contrast, a direct line. In some of the Plecoptera, as Capnia and others, the results of the ceno- genetic development are not marked except that the immature forms are aquatic. In the three orders in which the metamorphosis is incomplete, the cenogenetic development of the immature instars involved neither a change in the manner of development of the wings nor a retarding of the development of the compound eyes ; consequently these immature forms, although sidewise developed, constitute a class quite distinct from lar^^8e. The Hemimetabola. — The three orders in which the development is a hemimetabolous one are grouped together as the Hemimetabola; these are the Plecoptera, Ephemerida, and Odonata. This grouping together of these three orders is merely for convenience in discussions of types of metamorphosis and does not indicate a natural division of the class Hexapoda. The radical differences in the three types of aquatic respiratory organs characteristic of the three orders indicate that they were evolved independently. The term naiad. — The immature instars of insects with an incom- plete m.etamorphosis have been termed nymphs; but as a result of their sidewise development they do not properly belong in the same class as the immature instars of insects with a gradual metamorphosis. I, therefore, proposed to designate them as naiads (Comstock '18, h). The adoption of the term naiad in this sense affords a distinctive term for each of the three classes of immature insects corresponding to the three types of metamorphosis, i. e., nymphs, naiads, and larv^ae. *Ceao2:enesis: kainos {Kalvos), new; genesis. 180 AN INTRODUCTION TO ENTOMOLOGY Deviation from the usual type of incomplete metamorphosis. — The more striking deviations from the usual type of hemimetabolous devel- opment are the following: The Odonata. — In theOdonata the wings of the naiads are inverted; these insects resembling in this respect the Saltitorial Orthoptera. What is the upper surface of the wings with naiads becomes the lower surface in the adults, the change taking place at the last ecdysis. The Ephemerida. — In the Ephemerida, there exists the remarkable phenomenon of an ecdysis taking place after the insect has left the water and acquired functional wings. The winged instar that is interpolated between the last aquatic one and the adult is termed the sub-imago. g. COMPLETE METAMORPHOSIS (Holometabolus* Development) The representatives of several orders of insects leave the egg-shell in an entirely different form from that they assume when they reach maturity; familiar examples of these are caterpillars which develop into butterflies, maggots which develop into flies, and grubs which develop into beetles. These insects and others that when they emerge from the egg-shell bear almost no resemblance in form to the adult are said to undergo a complete metamorphosis or a holometabolous development. The Holometabola. — Those orders that are characterized by a holometabolous development are grouped together as the Holometab- ola. This group includes the Neuroptera, Mecoptera, Trichoptera, Lepidoptera, Diptera, Siphonaptera, Coleoptera, and Hymenoptera. This grouping together of these orders, while convenient for dis- cussions of metamorphosis, is doubtless artificial. It is not at all probable that the Holometabola is a monophylitic group. In other words complete metamorphosis doubtless arose several times inde- pendently in the evolution of insects. The term larva. — The form in which a holometabolous insect leaves the egg is called larva. The term was suggested by a belief of the ancients that the form of the perfect insect was masked, the Latin word larva meaning a mask. Formerly the term larva was applied to the immatiire stages of all insects; but more recent writers restrict its use to the immature in- *Holometabolous : holos (^Xos), complete; metahole {ixer a^o\-n) ^ change. THE METAMORPHOSIS OF INSECTS 181 stars of insects with a complete metamorphosis; and in this sense only is it used in this book. The adaptive characteristics of larvae. — The larvse of insects with complete metamorphosis, like the naiads of those with incomplete metamorphosis, exhibit an acquired form of body adapting them to special modes of life; and in this case the cenogenetic or "sidewise development" is much more marked than it is in insects with an incomplete metamorphosis. Here the form of the body bears but little relation to the form to be assumed by the adult, the nature of the larval life being the controlling factor. The differences in form between larvse and adults are augmented by the fact that not only have larvag been modified for special modes of life, but in most cases the adults have been highly specialized for a different mode of life; and so great are these differences that a quiescent pupa stage, during which certain parts of the body can be made over, is necessary. Here, as in the case of insects with an incomplete metamorphosis, we have an illustration of the fact that natural selection can act on any stage in the develop- ment of animal to better adapt that particular stage to the conditions under which it exists. Darwin pointed out in his "Origin of Species" that at whatever age a variation first appears in- the parent it tends to reappear at a corresponding age in the oflfspring. This tendency is termed homochronous heredity*. It is obvious that the greater the adaptive characteristics of the immature forms, the less does the ontogeny of a species represent the phylogeny of the race to which it belongs. This fact led Fritz Muller, in his "Facts for Darwin", to make the aphorism "There were perfect insects before larvae and pupae." The overlooking of this principle frequently results in the drawing of unwarranted con- clusions, by those writers on insects who cite adaptive larval characteristics as being more generalized than the corresponding features of the adult. The more obvious of the adaptive characteristics of larvag are the following : The form of the body. — As indicated above the form of the body of a larva bears but little relation to the form to be assumed by the adult, the nature of the larval life being the controlling factor in determining the form of the body. As different larvee live under widely differing situations, various types of larvse have been developed; the more important of these types are described later. The greater or less reduction of the thoracic legs. — In the evolution of most larvae there has taken place a greater or less reduction of the thoracic legs; but the extent of this reduction varies greatly. The larvae of certain Neuroptera, as Corydalus for example, have as perfect *Hom6chronous : homos {ofio's), one and the same; chronos (xP<^«'<'0. time. 182 AN INTRODUCTION TO ENTOMOLOGY legs as do naiads of insects with an incomplete m etamorphosis. The larvag of Lepidoptera have short legs which correspond to only a part of the legs of the adult. While the lar\'as of Diptera have no external indications of legs. Tke development of prolegs in some larvce. — A striking feature of many larvee is the presence of abdominal organs of locomotion ; these have been termed prolegs; the prolegs of caterpillars are the most familiar examples of these organs. The prolegs were so named because they were beheved to be merely adaptive cuticular formations and not true legs ; this belief arose from the fact that they are shed with the last larval skin. Some recent writers, however, regard the prolegs as true legs. It is now known that abdominal appendages are common in the embryos of insects; and these writers believe that the prolegs are developed from these embryonic appendages, and that, therefore, they must be regarded as true legs. If this is true, there has taken place a remarkable reversal in the course of development. The abdominal legs, except those that were modified into append- ages of the reproductive organs, the gonapophyses, were lost early in the phylogeny of the Hexapoda. The origin of complete metamorphosis must have taken place at a much later period; when, according to this belief, the abdominal appendages, which had been latent for a long time, W'ere redeveloped into functional organs. The development of tracheal gills. — A strilcing feature of many larvse is the possession of tracheal gills. This is obviously an adaptive characteristic the development of which was correlated with the assumption of aquatic life by forms that were primarily aerial; and it is also obvious that the development of tracheal gills has arisen indepandently many times; for they exist in widely separated families belonging to different orders of insects that are chiefly aerial. They are possesssd by a few lepidopterous larv^as, and by the representatives of several families of Neuroptera, Coleoptera and Diptera. On the other hand, in the Trichoptera the possession of tracheal gills by the larvce is characteristic of nearly all members of the order. The internal development of wings. — This is perhaps the most re- markable of the sidewise developments of larvae. Although larvae exhibit no external indications of wings, it has been found that the rudiments of these organs arise at as early a period in insects with a complete metamorphosis as they do in those with an incomplete metamorphosis ; and that during larval life the wing rudiments attain an advanced stage in their development. But as these rudiments are invaginated there are no external indications of their presence during larval hfe. The details of the internal development of wings are dis- cussed later. THE METAMORPHOSIS OF INSECTS 183 Occasionally atavistic individual larvae are found which have external wing-buds. As to the causes that brought about the internal development of wings we can only make conjectures. It has occurred to the writer that this type of wing- development may have arisen as a result of boring habits, or habits of an analogous nature, of the stem forms from which the orders of the Holometabola sprang. Projecting wing -buds would interfere with the progress of a boring insect; and, therefore, an embedding of them in the body, thus leaving a smooth contour, would be advantageous. In support of this theory attention may be called to the fact that the larvae of the most generalized Lepidoptera, the Hepialida;, are borers; the larvaj of the Siricidaj, which are among the more generalized of the Hymenoptera are borers; so too are many Coleoptera ; most lai-vjE of Diptera are burrowers ; and the larvag of Trichoptera live in cases. The retarding of the development of the compound eyes. — One of the most distinctively characteristic features of larvae is the absence of compound eyes. The life of most larvae is such that only limited vision is necessary for them ; and correlated with this fact is a retard- ing of th.e development of the greater portion of the compound eyes ; only a few separate ommatidia being functional during larval life. In striking contrast with this condition are the well-developed eyes of nymphs and naiads. The larvae of Corethra and Panorpa are the only lorva? known to me that possess compound eyes. The invaginated conditions of the head in the larvce of the more specialized Diptera. — The extreme of sidewise development is exhibited by the larvas of the more specialized Diptera. Here not only are the legs and wings developed internally but also the head. This phe- nomenon is discussed later. The different types of larvaB. — As a rule, the larvae of the insects of any order resemble each other in their more general characteristics, although they bear but little resemblance to the adult forms. Thus the grubs of Coleoptera, the caterpillars of Lepidoptera, or the mag- gots of Diptera, in most cases, can be recognized as such. Still in each of these orders there are larvae that bear almost no resemblance to the usual type. As examples of these may be cited the water- pennies (Parnidae, Coleoptera), the slug-caterpillars (Cochlidiids, Lepidoptera), and the larvae of Microdon (Diptera). To understand the variations in form of larvs it should be borne in mind that the form of the body in all larvae is the result of secondary adaptations to peculiar modes of life; and that this modification of form has proceeded in different directions and in varying degrees in different insects. 184 AN INTRODUCTION TO ENTOMOLOGY Among the many types of larvae, there are a few that are of such common occurrence as to merit distinctive names; the more im- portant of these are the following: Campodeiform. — In many paurometabolous insects and in some holometabolous ones, the early instars resemble Campodea more or less in the form of the body (Fig. 202); such naiads and larvae are described as campodeiform. In this type, the body is long, more or less flattened, and with or without caudal setae ; the mandibles are well developed; and the legs are not greatly reduced. Among the examples of this type are the larvae of most Neuroptera, and the active larvas of many Coleoptera (Cara- bidas, Dysticidce, and the first instar of Me- loidffi). Eruciform. — The eruciform type of larvas is well-illustrated by most larvae of Lepidoptera and of Mecoptera; it is the caterpillar form (Fig. 203). In this type the body is cyHndrical ; the thoracic legs are short, having only the terminal portions of them developed; and the abdomen is furnished with prolegs or with proleg-like cuticular folds. Although these larvas move freely, their powers of locomo- tion are much less than in the campodeiform type. Scarabeiform. — The common white grub, the larva of the May- beetle (Fig. 204) is the most famiHar example of a scarabeiform larva. Fig. 202. — Campodea staphylinus (After Lubbock). ^"^ Fig. 203. — The silk- worm, an eruciform larva (After Verson). In this type the body is nearly cylindrical, but usually, especially when at rest, its longitudinal axis is curved; the legs are short; and THE METAMORPHOSIS OF INSECTS 185 prolegs are wanting. This type is quite characteristic of the larv^ of the Scarabaeidas, hence the name ; but it occurs in other groups of insects. The movements of these larv« are slow; most of them Hve in the ground, or in wood, or in decaying animal or vegetable matter. Fig. 204. — Larva of Melolontha vulgaris (After Schiodte). Vermiform. — Those larvas that are more or less worm-like in form are termed vermiform. The most striking features of this type are the elongated form of the body and an absence of locomotive appendages (Fig. 205). Naupliiform. — The term naupliiform is applied to the first instar of the larv^a of Platygaster (Fig. 206), on account of its resemblance to the nauplius of certain Crustacea. The prepupa. — Usually the existence of an instar between the last larval one and the pupal instar is not recognized. But such a form exists; and the recogni- tion of it becomes important when a careful study is made of the development of holometabolous insects. As is shown later, during larval life the develop- ment of the wings is going on within the body. As the larva approaches maturity, the wings reach an advanced stage of development within sac-like invagi- nations of the body-wall. Near the close of the last larval stadium the insect makes preparation for the change to the pupa state. Some form a cell within which the pupa state is passed, the larvee of butter- flies suspend themselves, and most larvee of moths spin a cocoon. Then follows a period of apparent rest before the last larval skm is shed and the pupal state assumed. But this period is far from being a quiet one; within the apparently motionless body important changes p^ take place. The most easily observed of these changes is a change in the position of the wings. Kach of these passes out through the mouth of the sac in which it has been developed, and lies outside of the newly developed pupal cuti- cula, but beneath the last larval cuticula. Then follows a period of variable duration in different insects, in which the wings are really 205.— Larva of a crane-fly. ^.V INTRODUCTION TO ENTOMOLOGY Fig. 206. — Lar\'a of Platygaster (After Ganin.) outside of the body although still covered by the last larval cuticula; this period is the prepupal stadium. The prepupal instar differs markedly from both the last larval one and from the pupa ; for after the shedding of the last lar\^al cuticula important changes in the form of the body take place before the pupal instar is assiimed. The pupa. — The most obvious characteristics of the pupa state are, except in a few cases, inactivity and help- lessness. The organs of locomotion are functionless, and may even be soldered to the body throughout their entire length, as is usual with the pupcC of Lepidoptera (Fig. 207). In other cases, as in the Coleoptera (Fig. 208) and in the Hymenoptera, the wings and legs are free, but enclosed in more or less sac-like cuticular sheaths, which put them in the condition of the pro- verbial cat in gloves. More than this, in most cases, the legs of the adult are not fully formed till near the end of the pupal stadiimi. The term pupa, meaning girl, was applied to this instar by Linuceus on account of its resemblance to a baby that has been swathed or bound up, as is the custom with many peoples. Although the insect during the pupal stadium is apparently at rest, this, from a physiological point of view, is the most active period of its postembryonic exist- ence; for wonderful changes in the struc- p-g_ 207.— Pupa of a moth, cure of the body take plaoe at tliis time. In the development of a larva the primitive form of the body has been greatly modified to adapt it to its peculiar mode of life; this sidewise development results in the production of a type of body that is not at all fitted for the duties of adult life. In the case of an insect with incomplete meta- morphosis, the full grown naiad needs to be modified comparatively little to fit it for adult life; but the change from a maggot to a fly, or from a caterpiller to a butterfly, involves not merely a change in external form but a greater or less remodeling of its entire structiu-e. These changes take place during the period of apparent rest, the prepupal and pupal stadia. The chrymlis.— The term chrysalis is often applied to the pupae of butterflies. It was suggested by the golden spots with which the pups of certain butterflies are ornamented. Two forms of this word are in use: first, chrysaHs, the plural of which is chrysalides; and second, chrysahd, the plural of which is THE METAMORPHOSIS OF INSECTS 187 chrysalids. The singular of the first form and the plural of the second are those most often used. Active pupa. — The pupas of mosquitoes and of certain midges are remarkable for being active. Although the wings and legs are func- tionless, as with other pupae, these creatures are able to swim by means of movements of the caudal end of the body. In several genera of the Neuroptera {Chrysopa, Hemerobius, and Raphidia) the pupa becomes active and crawls about just before transforming to the adult state. Movements of a less striking character are made by many pupse, which work their way out of the ground, or from burrows in wood, before transforming. In some cases, as in the pupas of the carpenter- moths (Cossidas) the pupa is armed with rows of backward projecting teeth on the abdominal segments, which facilitate the movements within the burrow. '^he cremaster. — Many pupje, and especially those of most Lepidop- tera, are provided with a variously shaped process of the posterior end of the body, to which the term cremaster is applied. This process is cften provided with hooks which serve to suspend the pupa, as in butterflies, or to hold it in place, after it has partly emerged from the cocoon, and while the adult is emerging from the pupal skin, as in cocoon-making moths. In its more simple form, where hooks are lacking, it aids the pupa in working its way out of the earth , or from other closed situations. The msthod of fixing the cremaster in the disk of silk from which the pupa of a butterfly is suspended was well-illustrated by C. V. Riley ('79). The full grown larva spins this disk and hangs from it during the prepupal stadium by means of its anal prolegs (Fig. 209, a). When the last larval skin is shed, it is worked back to the caudal end of the body (Fig. 209, b); and is then grasped between two of the abdominal segments (Fig. 209, c,) while the caudal end of the body is removed from it; and thus the cremaster is freed, and is in a position from which it can be inserted in the disk of silk. Fig. 209. — Transformations of the milkweed butter- fly (From Riley). 188 AN INTRODUCTION TO ENTOMOLOGY The cocoon. — The pupal instar is an especially vulnerable one. During the pupal life the insect has no means of offence, and having exceedingly limited powers of motion, it has almost no means of defense unless an armor has been provided. Many larvae merely retreat to some secluded place in which the pupal stadium is passed ; others bury themselves in the ground ; and still others make provision for this helpless period by spinning a silken armor about their bodies. Such an armor is termed a cocoon. The cocoon is made by the full-grown larva; and this usually takes place only a short time before the beginning of the pupal stadium. But in some cases several months, elapse between the spinning of the cocoon and the change to pupa, the cocoon being made in the autumn and the change to pupa taking place in the spring. Of course a greater or less portion of this period is occupied by the prepupal stadium. Cocoons are usually made of silk, which is spun from glands already described. In some cases, as in the cocoons of Bombyx, the silk can be unwound and utilized by man. While silk is the chief material used in the making of cocoons, it is by no means the only material. Many wood-boring larvas make cocoons largely of chips. Many insects that undergo their transformation in the ground incorporate earth in the walls of their cocoons. And hairy cater- pillars use silk merely as a warp to hold together a woof of hair, the hairs of the larva being the most con- spicuous element in the cocoon. In those cases in which silk alone is used there is a great variation in the nature of the silk, and in the den- sity of the cocoon. The well-known cocoons of the satumiids illustrate one extreme in density, the cocoons of certain Hymenoptera, the other. The fiberous nature of the cocoon is usually obvious; but the cocoons of saw-flies appear parchment-like, and Fig. 2IO.— the cocoons of the sphecids appear like a delicate foil. cocoon^ of While in the more common type of cocoons the Trichosfibas wall is a closely woven sheet, there are cocoons that from which ^^^ lace-like in texture (Fig. 210). theadulthas Modes of escape from the cocoon. — The insect, having emerge . walled itself in with a firm layer of silk, is forced to meet the problem of a means of escape from this inclostire; a problem which is solved in greatly varied ways. THE METAMORPHOSIS OF INSECTS 189 ^iK=- In many insects in which the adult has biting mouth parts, the adult merely gnaws its way out by means of its mandibles In some cases, as the Cynipidee, it is said that this is the only use made of its mandibles by the adult. In some cases the mandibles with which the cocoon is pierced per- tain to the pupal instar, this is true of Chrysopa and Hemerobius; and the Trichoptera break out from their cases, by means of their mandibles, while yet in the pupal state. For those insects in which the adult has sucking mouth parts, the problem is even more difficult. Here it has been met in several quite distinct ways. The pupae of many Lepidop- tera possess a specialized organ for breaking through the cocoon; in some the anterior end of the pupa is furnished with a toothed crest {Lithocolletes hamadryella) ; in certain satur- niids there is a pair of large, stout, black spines, one on each side of the thorax, at the base of the fore wings with which the f dult fW^-^MW cuts a slit in the Fig. 212. — Cocoon oi Megalopvge oper- W 111 cocoon through '''^'''''^ /iK^ ^fs which the moth emerges, this was observed by Packard in Tropcsa luna; but as these spines are present in other saturniids, where the cocoon is too dense to be cut by them, and where an opening is made in some other way, it is probable that, as a rule, their function is loco- motive, aiding the.moth to work its way out from the cocoon, by a wriggling motion. One of the ways in which saturniids pierce their cocoons is that practiced by Bombyx and Telea. These insects soften one end of the cocoon by a liquid, which issues from the mouth; and then, by forcing the threads apart or by breaking them, make an opening. Fig. 211. — Longi- tudinal section of a cocoon of Callosamia pro- methea;v,valve- like arrange- ment for the escape of the adult. Fig. 213. — Old cocoon of Megalopyge opercularis. 190 AN INTRODUCTION TO ENTOMOLOGY Far more wonderful than any of the methods of emergence from the cocoon described above are those in which the larva makes pro- vision for the escape of the adult. The most familiar of these is that practiced by the larv^ of Samia cecropia and Callosamia promethea. These larvsd when they spin their cocoons construct at one end a coni- cal valve-like arrangement, which allows the adult to emerge without the necessity of making a hole through the cocoon (Fig. 2x1, ?;). A less familiar example, but one that is fully as wonderful, is that of a Megalopyge. The larva of this species makes a cocoon of the form shown in Figure 212. After an outer layer of the cocoon has been made, the larva constructs, near one end of it, a hinged partition ; this serves as a trap door, through which the moth emerges. That part of the cocoon that is outside of the partition is quite delicate and is easily destroyed. Hence most specimens of the cocoons in col- lections present the appearance represented in Figure 213. The puparium. — The pupal stadiimi of most Diptera is passed within the last larval skin, which is not broken till the adult fly is ready to emerge. In this case the larv^al skin, which becomes hard and brown, and which serves as a cocoon, is termed a puparium. In some families the puparium retains the form of the Xoxysl; in others the body of the lar\^a shortens, assuming a more or less barrel-shaped form, before the change to a pupa takes place (Fig. 214), Modes of escape from the puparium. — The pupae of the more generalized Diptera escape from the pupa- rium through a T-shaped opening, which is formed by a lengthwise split on the back near the head end and a crosswise spHt at the front end of this (Fig. 215), or rarely, through a cross-wise split between the seventh Fig. 214.— Pupa- and eighth abdominal segments. In the more special- num of Try- -^g^j Diptera there is developed a large bladder-like organ, which is pushed out from the front of the head, through what is known as the frontal suture, and by which the head end of the puparium is forced off. This organ is known as the ptilinum. After the adult escapes, the ptiliniim is withdrawn into the head. The Different types of pupae . — Three types -^ of pupae are commonly recognized; these are the following : Fig. 215.— Puparium of a Exarate pupcB.—Vup^ which, like those stratiomyud. of the Coleoptera and Hymenoptera, have the legs and wings free, are termed exarate pup«. THE METAMORPHOSIS OF INSECTS 191 Obtected pupcz. — Pupse which Hke the pupae of Lepidoptera, have the Hmbs glued to the surface of the body, are termed obtected pups. Coarctate Pupcs. — Pupag that are enclosed within the hardened larval skin, as is the case with the pupae of most of the Diptera, are termed coarctate pupae. The imago — The fully developed or adult insect is termed the imago. The life of the imago is devoted to making provision for the perpetuation of the species. It is during the imaginal stadium that the sexes pair, and the females lay their eggs. With many species this is done very soon after the last ecdysis ; but with others the egg- laying is continued over a long period; this is especially true with females of the social Hymenoptera. h. HYPERMETAMORPHOSIS There are certain insects, representatives of several different orders that exhibit the remarkable peculiarity in their development that the successive larval instars represent different types of larvse. Such insects are said to undergo a hypermetamorphosis. The transformations of several of these insects will be described later in the accounts of the families to which they belong; and for this reason, in order to avoid repetition, are not discussed here. The more striking examples are Mantispa, Meloe, Stylops, and Platy- gaster. i. VIVIPAROUS INSECTS There are many insects that produce either nymphs or larvee instead of laying eggs. Such insects are termed viviparous. This term is opposed to oviparous, which is applied to those insects that lay eggs that hatch after exclusion from the body. It has been pointed out in the discussion of the reproductive organs that, from the primordial germ -cells, there are developed in one sex spermatoza and in the other eggs; and it should be borne in mind that the germ-cells produced in the ovary of a female from the primordial germ-cells are eggs. These eggs grow and mature; in some cases they become covered with a shell, in others they are not so covered ; in some cases they are fertilized by the union of a spermatozoan with them, and in others they are never fertilized; but in all these cases they are eggs. We may say, therefore, that all insects are developed from eggs. A failure to recognize this fact has introduced confusion into entomological literature. Some writers have termed the germ-cells produced by agamic aphids pseudova or false eggs. But these germ-cells are as truly eggs as are those from which the males of the honeybee develop; they are merely unfertilized eggs. The term pseudovum conveys a false impression; while the phrase, an unfer- tilized egg, clearly states a fact. 192 AN INTRODUCTION TO ENTOMOLOGY Some writers make use of the term ovoviviparous indicating the production of eggs that have a well -developed shell or covering, but which hatch within the body of the parent; but the distinction is not fundamental, since viviparous ani- mals also produce eggs as indicated above. Among viviparous insects there are found every gradation from those in which the larvae are bom when very young to those in which the entire larval life is passed within the body of the parent. There also exist examples of viviparous larvae, viviparous pupae, and vivi- parous adults. And still another distinction can be made; in some viviparous insects the reproduction is parthenogenetic ; in others it is sexual. Viviparity with parthenogenetic reproduction. — In certain vivipar- ous insects the reproduction is parthenogenetic ; that is, the young are produced from eggs that are not fertilized. This type of reproduction occurs in larvae, pupae, and apparently in adults. Pcedogenetic Larvcs. — In 1862 Nicholas Wagner made the remark- able discovery that certain larvae belonging to the Cecidomyiidae give birth to living young. This discovery has been confirmed by other observers, and for this type of reproduction the term pcsdogenesis, proposed by Von Baer, has come into general use. This term is also spelled pedogenesis; the word is from pcedo or pedo, a child, and genesis. The phenomenon of paedogenesis is discussed later in the accounts of the Cecidomyiidse and of the Micromalthidag. Pcedogenetic pupce. — The most frequently observed examples of paedogenetic reproduction are by larvae; but that pupae also are some- times capable of reproduction is shown by the fact that Grimm ('70) found that eggs laid by a pupa of Chironomus grimmii, and of course not fertilized, hatched. Anton Schneider ('85) found that the adults of this same species of Chironomus reproduced parthenogenetically . This species, therefore , exhibits a transition frpm paedogenesis to normal parthenogenesis. Viviparous adult agamic females . — There may be classed under this class provisionally, the agamic females of the Aphididae ; as these are commonly regarded as adults. It has been suggested, however, that the agamic reproduction of the Aphids may be a kind of paedogenesis ; the agamic females being looked upon as nymphs. This however, is not so evident in the case of the winged agamic generation. On the other hand, the reproductive organs of the agamic aphids are incom- pletely developed, as compared with those of the sexual forms, lacking a spermatheca and colleterial glands. THE METAMORPHOSIS OF INSECTS 193 This discussion illustrates the difficulty of attempting to make sharp distinc- tions, whereas in nature all gradations exist between different types of structure and of development. Thus Leydig ('67) found a certain aphid to be both ovipar- ous and viviparous; the eggs and the individuals horn as nymphs being pro :luced from neighboring tubes of the same ovary. Viviparity with sexual reproduction. — Although most insects that reproduce sexually are oviparous, there are a considerable number in which sexual reproduction is associated with viviparity. Among these sexual viviparous insects there exist great differences in method of reproduction ; with some the young are bom in a very immature stage of development, a stage corresponding to that in which the young of oviparous insects emerge from the egg ; while with others the young attain an advanced stage of development within the body of the mother. Sexual viviparous insects giving birth to nymphs or larvce. — That type of viviparity in which sexual females give birth to very immature nymphs or larvae exists in more or less isolated members of widely separated groups of insects. As the assumption of this type of repro- duction involves no change in the structure of the parent, but merely a precocious hatching of the egg, it is not strange that it has arisen sporadically and many times. In some cases, however, the change is not so slight as the foregoing statement would imply ; as, for example, in the case of the viviparous cockroach, which does not secrete ootheccfi as do other cockroaches. Among the recorded examples of this type of viviparity are repre- sentatives of the Ephemerida, Orthoptera, Hemiptera, Lepidoptera, Coleoptera, Strepsiptera, and Diptera. Sexual viviparous insects giving birth to old larvcu.- — The mode of reproduction exhibited by these insects is doubtless the most excep- tional that occurs in the Hexapoda, involving, as it does, very import- ant changes in the structure of the reproductive organs of the females. With these insects the larv^ae reach maturity within the body of the parent, undergoing what is analogous to an intra-uterine development, and are bom as full-grown larvae. This involves the secretion of a "milk" for the nourishment of the young. This mode of reproduction is characteristic of a group of flies, including several famihes, and known as the Pupipara. This name was suggested for this group by the old belief that the young are born as pupae; but it has been found that the change to pupa does not take place till after the birth of the larva. 194 AN INTRODUCTION TO ENTOMOLOGY The reproduction of the sheep-tick, Melophagus ovinus, may be taken as an illustration of this type of development; this is described in the discussion of the Hippoboscidse, the family to which this insect belong:s. The giving birth to old larvae is not restricted to the Pupipara. Surgeon Bruce (quoted by Sharp. '99) has shown that the Tsetse fly, Giossina morsitans, reproduces in this way, the young changmg to pups immediately after birth. An intermediate type of development is illustrated by Hylemyia strigosa, a dung -frequenting fly belonging to the Anthomyiidag. This insect, according to Sharp ('99), produces living larvae, one at a time. "These larvae are so large that it would be supposed they are full-grown, but this is not the case, they are really only in the first stage, an unusual amount of growth being accompHshed in this stadium." j. NEOTEINIA The persistence with adult animals of larval characteristics has been termed neoteinia* or neotenia. When this term first came into use it was applied to certain amphibians, as the axolotle, which retains its gills after becoming sexually mature; but it is now used also in entomology. The most familiar examples of neoteinic insects are the glow- worms, which are the adult females of certain beetles, the complemen- tal females of Termites, and the females of the Strepsiptera. II. THE DEVELOPMENT OF APPENDAGES In the preceding pages the more obvious of the changes in the external form of the body during the metamorphosis of insects and some deviations from the more common types of development have been discussed. The changes in the form of the trunk that have been described are those that can be seen without dissection; but it is impracticable to limit a discussion of the development of the appen- dages of the body in. this way, for in the more specialized types of metamorphosis a considerable part of the development of the appen- dages takes place within the body-wall. "Neoteinia: neos {v4o%), youthful; teinein {reiveiv), to stretch. THE METAMORPHOSIS OF INSECTS 195 a. THE DEVELOPMENT OF WINGS Two quite distinct methods of development of wings exist in insects; by one method, the wings are developed as outward project- ing appendages of the body; by the other, they reach an advanced stage of development within the body. The former method of development takes place with nymphs and naiads, the latter with larv^ae.* I. The Development of the Wings of Nymphs and Naiads In insects with a gradual or with an incomplete metamorphosis the development of the appendages proceeds in a direct manner. The wings of nymphs and naiads are sac-like outgrowths of the body-wall, which appear comparatively early in life and become larger and larger with successive molts, the expanding of the wing-buds taking place immediately after the molt ; an illustration of this has been given in the discussion of gradual metamorphosis, page 175. 2. Development of the Wings in Insects with a Complete Metamorphosis Although there are differences in details in the development of the wings in the different insects undergoing a complete metamorphosis, the essential features are the same in all. The most striking feature is that the rudiments of the wings, the wing-buds, arise within the body and become exposed for the first time when the last lar\^al skin is shed. The development of the wings of the cabbage butterfly {Pontia rapce) will serve as an example of this type of development of wings. The tracing of that part of this development which takes place during the larval life can be observed by making sections of the body-wall of the wing-bearing segments of the successive instars of this insect. The first indication of a wing-bud is a thickening of the hypo- dermis; this thickening, known as a histoblast or an imaginal disc, has been observed in the embryos of certain insects, in the first larval instar of the cabbage butterfly it is quite prominent (Fig. 216, a). During the second stadium, it becomes more prominent and is invaginated, forming a pocket-like structure (Fig. 216, b). During the third stadium a part of this invagination becomes thickened and evaginated into the pocket formed by the thinner *Only the more general features of the development of wings are discussed here. For a fuller account see "The Wings of Insects" (Comstock 'i 8, a). 196 AN INTRODUCTION TO ENTOMOLOGY portions of tne invagination (Fig. 216, c). During the fourth stadium, the evaginated part of the histoblast becomes greatly extended (Fig. 216, d). It is this evaginated portion of the histo- blast that later be- comes the wing. Dur- ing the fifth stadium the wing-bud attains the form shown in Figure 216, e, which represents it dissected out of the wing-pocket At the close of the last larA^^l stadium, the fifth, the wing is pushed out from the wing-poc- ket, and lies under the old larval cuticula dur- ing the prepupal sta- dium. It is then of the form shown in Figure 216, /. The molt that marks the beginning of the pupal stadium, exposes the wing-buds, which in I the Lepidoptera be- y come closely soldered / to the sides and breast of the pupa. Imme- diately after the last molt when the adult emerges, the wings Fig. 216.— Several stages in the development of the expand greatly and wings of a cabbage butterfly (After Mercer). assume their definitive form. While this increase in size and changes in form of the developing wing are taking place, there occur other remarkable developments in its structure. A connection is made with a large trachea near which the histoblast is developed, shown in cross-section in the first four THE METAMORPHOSIS OF INSECTS 197 parts (a, b, c, and d) of Figure 216; temporary respiratory organs, consisting of bundles of tracheoles, are developed (e and/) ; and later, near the close of the larval period, the tracheas of the wing are devel- oped, and the bundles of tracheoles disappear. During the later stages in the development of the wing the basement membranes of the hypodermis of the upper and lower sides of the wing come together, except along the lines where the veins are to be developed later, and become united. In this way the wing is transformed from a bag-like organ to a sheet-like one. The lines along which the two sides of the wing remain separate are the vein cavities ; in these the trunks of the wing-trachea extend. During the final stages of the development of the wing, the walls of the vein-cavities are thickened, thus the wing- veins are formed ; and the spaces between the wing-vf ins become thin. By reference to Figure 216, c and d, it will be seen that the histo- blast consists of two quite distinct parts, a greatly thickened portion which is the wing-bud and a thinner portion which connects ths wing- bud with the hypodermis of the body-wall, and which constitutes the neck of the sac-like histoblast, this is termed the peripodal membrane, a term suggested by the similar part of the histoblast of a leg ; and the enclosed cavity is known as the peripodal cavity. In the more specialized Diptera, the peripodal membranes are very long and both the wing-buds and the leg-buds are far removed from the body-wall. A condition intermediate between that which exists in the Lepidoptera, as shown in Figure 216, and that of the more specialized Diptera was found by Kellogg (07) in the larva of Holorusia rubiginosa, one of the crane-flies (Fig. 217). h. THE DEVELOPMENT OF LEGS The development of the legs pi oceeds in widely different ways in different insects. In the ^. „,. ,,.,,, c .u Fig. 217. — Wing- bud in the larva of the more generalized forms, the giant crane-flv, Holorusia rubiginosa; legs of the embryo reach an J>'' hypodermis; pm peripodal mem- ^ . V, , brane; t, trachea; wb, wing-bud (After advanced stage of development Kellogg). before the nymph or naiad leaves the egg-shell, and are functional when the insect is born; on the other hand, in those specialized insects that have vermiform larvs, the development of the legs is retarded, and these organs do not become functional until the adult stage is reached. Almost every conceivable intergrade between these two extremes exist. 198 AN INTRODUCTION TO ENTOMOLOGY I. The Development of the Legs of Nymphs and of Naiads In insects with a gradual metamorphosis and also in those with an incomplete metamorphosis the nymph or naiad when it emerges from the eggshell has well-developed legs, which resemble quite closely those of the adult. The changes that take place in the form of the legs during the postembyronic development are comparatively slight ; there may be changes in the relative sizes of the different parts ; and in some cases there is an increase in the number of the segments of the tarsus; but the changes are not sufficiently great to require a descrip- tion of them here. 2. The Development of the Legs -in Insects with a Complete Metamor- phosis It is a characteristic of most larvae that the development of their legs is retarded to a greater or less extent. This retardation is least in campodeiform larv^^ more marked in cruciform larv^se, and reaches its extreme in vermiform larvae. The development of the legs of insects with campodeiform larvae. — Among the larvae classed as campodeiform the legs are more or less like those of the adults of the same species ; there may be differences in the proportions of the different segments of the leg, in the number of the tarsal segments, and in the number and form of the tarsal claws; but these differences are not of a nature to warrant a discussion of them here. These larvae lead an active life, like that of nymphs, and consequently the form of legs has not been greatly modified from the paurometabolous type. The development of the legs of insects with erucif orm larvae. — In caterpillars and other cruciform larvae the thoracic legs are short and fitted for creeping ; this mode of locomotion being best suited to their mode of life, either in burrows or clinging to foliage. This form of leg is evidently an acquired one being, like the internal development of wings, the result of those adaptive changes that fit these lan^ae to lead a very different life from that of the adults. In the case of caterpillars the thoracic legs are short, they taper greatly, and each consists of only three segments. It has been com- monly believed and often stated that the three segments of the larval leg correspond to the terminal portion of the adult leg; but studies of the development of the legs of adults have shown that the divisions of the lar\^al leg have no relation to the five divisions of the adult leg. THB METAMORPHOSIS OF INSECTS 199 It has been shown by Gonin ('92), Kellogg ('01 and '04), and Verson ('04) that histoblasts which are the rudiments of the legs of the adult exist within the body-wall of the caterpillar at the base of the larval legs. Late in the larval life the extremity of the legs of the adult are contained in the legs of the caterpillar. It has been shown that the cutting off of a leg of a caterpillar at this time results in a mutilation of the terminal part of the leg of the adult. The development of the legs of the adult within the body of cater- pillars has not been studied as thoroughly as has been the develop- ment of the wings ; but enough is known to show that in some respects the two are quite similar; this is especially true of the development of the tracheoles and of the tracheae. The development of the legs in insects with vermiform larvae. — In vermiform larv-ee the development of the entire leg is retarded. The leg arises as a histoblast, which is within the body and bears, in its more general features, a resemblance to the wing-buds of the same insect. The development of the legs of vermiform larvae has been studied most carefully in the larvae of Diptera. During the larval life the leg becomes quite fully developed within the peripodal cavity ; in Corethra, they are spirally coiled; in Miisca, the different segments telescope into each other. At the close of the larv^al period, the evagination of the legs takes place. C. THE DEVELOPMENT OF ANTENNAE /. The Transformation of the Antennae of Nymphs and of Naiads In the case of nymphs and of naiads the insect when it emerges from the eggshell has well-developed antennae. The changes that take place during the postembryonic development are, as a rule, com- paratively slight; in most insects, an increase in the number of the segments of the antennae takes place ; but in the Ephemerida, a reduc- tion in number of the antennal segments occurs. 2. The Development of the Antenna in Insects with a Complete Metamorphosis One of the marked characteristics of larvae is the reduced condition of the antennae; even in the campodeiform larvae of the Neuroptera, where the legs are comparatively well-developed, the antennae are greatly reduced. In cruciform larvae the development of the antennae follows a course quite similar to that of the legs. The larval antennae are small: 200 ^A^ INTRODUCTION TO ENTOMOLOGY the antennas of the adult are developed from histoblasts within the head and during the latter part of the larval life are folded like the bellows of a closed accor- dian; at the close of this period they become eva- ginated, but the definitive form is not assumed until the emergence of the adult. A similar course of devel- opment of the antennae takes place in vermiform larv£e (Fig. 218). d. THE DEVELOPMENT OF Fig. 218. — Sagittal section through headof old THE MOUTH-PARTS lar\^a of 5/mi order trichoptera. — The Caddice-flies. p. 555. ' order lepidotera.— The Moths, the Skippers, and the Butterflies, p, 571. order diptera. — The Flies, p. 773. V order siphonaptera. — The Fleas, p. 877. order hymenoptera. — The Bees, Wasps, Ants, and others, p. 884. HEX A POD A 215 TABLE FOR DETERMINING THE ORDERS OF THE HEX A POD A This table is merely intended to aid the students in determining to which of the orders a specimen that he is examining belongs. No effort has been made to indicate in the table the relation of the orders to one another. A. Winged. (The wing-covers, Elytra, of beetles and of earwigs are wings.) B. With two wings. C. Wings horny, leathery, or parchment-like. D. Mouth-parts formed for sucking. Wings leathery, shortened, or membranous at the tip. p. 350 Hemiptera. DD. Mouth-parts formed for biting. Jaws distinct. E. Wings horny, without veins. Hind legs not fitted for jumping. P- 464 COLEOPTERA EE. Wings parchment-like with a network of veins. Hind legs fitted for jumping, p. 230 Orthoptera CC. Wings membranous. D. Abdomen with caudal filaments. Mouth-parts vestigial. E. Halteres wanting, p. 308 Ephemerida EE. Halteres present (males of Coccidae). p. 394 Homoptera DD. Abdomen without caudal filaments. Halteres in place of second wings. Mouth-parts formed for sucking, p. 773 Diptera BB. With four wings. C. The two pairs of wings unlike in structure. D. Fore wings reduced to slender club-shaped appendages; hind wings fan-shaped with radiating veins. Minute insects, p. 546. .Strepsiptera DD. Front wings leathery at base, and membranous at tip, often over- lapping. Mouth-parts formed for sucking, p. 350. .. Hemiptera DDD. Front wings of same texture throughout. E. Front wings horny or leathery, being veinless wing-covers. {Ely- tra). F. Abdomen with caudal appendages in form of movable forceps. p. 460 Dermaptera FF. Abdomen without forceps-Hke appendages, p. 464. Coleoptera EE. Front wings leathery or parchment-like with a network of veins. F. Under wings not folded; mouth-parts formed for sucking. G. Beak arising from the front part of the head. p. 350. Hemiptera GG. Beak arising from the hind part of the lower side of the head. p. 394 Homoptera FF. Under wings folded lengthwise. Mouth-parts formed for chewing, p. 230. •■■••• Orthoptera CC. The two pairs of wings similar, membranous. D. Last joint of tarsi bladder-like or hoof -like in form and without claws, p. 341 Thysanoptera DD. Last joint of tarsi not bladder-like. E. Wings entirely or for the greater part clothed with scales. Mouth- parts formed for sucking, p. 571 Lepidoptera EE. Wings naked, transparent, or thinly clothed with hairs. F. Mouth-parts arising from the hinder part of the lower surface of the head, and consisting of bristle-like organs inclosed in a jointed sheath, p. 394 Homoptera FF. Mouth-parts in normal position. Mandibles not bristle-like. G. Wings net-veined, with many veins and cross-veins. H. Tarsi consisting of less than five segments. L Antennae inconspicuous, awl-shaped, short and slender. J . First and second pairs of wings of nearly the same length ; tarsi three-jointed, p. 314 Odonata JJ. Second pair of wings either small or wanting; tarsi four jointed, p. 308 Ephemerida II. Antennae usually conspicuous, setiform, filiform clavate, capitate, or pectinate. J. Tarsi two- or three-jointed. K. Second pair of wings the smaller, p. 33 1 . Corrodentia 21G AN INTRODUCTION TO ENTOMOLOGY KK. Second pair of wings broader, or at least the same size as the first pair. p. 325. . . . Plecoptera JJ. Tarsi four-jointed; wings equal, p. 273. .Isoptera HH. Tarsi consisting of five segments. I. Abdomen with setiform, many-jointed anal filaments. (Certain Way-flies), p. 308 ." Ephemerida II. Abdomen without many-jointed anal filaments. J. Head prolonged into a trunk-like beak. p. 550.MECOPTERA JJ. Head not prolonged into a beak. p. 281.. .Neuroptera GG. Wings with branching veins and comparatively few cross- veins, or veinless. H. Each of the veins of the wing extending along the middle of a brown line. p. 338 Embiidina HH. Wings not marked with brown lines. I. Tarsi two-or three-jointed. J. Hind wings smaller than the fore wings. K. Cerci present; body less than three millimeters in length, p. 270 Zoraptera KK. Cerci absent; larger insects, p. 331. .Corrodentia JJ. Posterior wings as large as or larger than the anterior ones. (Certain Stone-flies), p. 325 Plecoptera II. Tarsi four- or five-jointed. J. Abdomen with setiform, many-jointed anal filaments. (Certain May-flies), p. 308 Ephemerida J J. Abdomen without many- jointed anal filaments. K. Prothorax horn}-. First wings larger than the second, naked or imperceptibly haiTy. Second wings without, or with few, unusually simple, veins. Jaws (mandibles) well developed. Palpi small, p. 884. . . . Hymenoptera KK. Prothorax membranous or, at the most, parchment - like. Second wings as large as or larger than the first, folded lengthwise, with many branching veins. First wings naked or thinly clothed with hair. Jaws (mandibles) inconspicuous. Palpi long. Moth-like insects, p. 555 Trichoptera AA. Wingless or with vestigial or rudimentary wings. B. Insects with a distinct head and jointed legs, and capable of locomotion. C. Aquatic insects. D. Mouth-parts fitted for piercing and sucking. E. Free-swimming nymphs, p. 350 Hemiptera EE. Larvae parasitic in sponges (Sisyridse). p. 281 Neuroptera DD. Mouth-parts fitted for chewing. E. Either somewhat caterpillar-like larvae that live in portable cases or campodeiform larvae that spin nets for catching their food. (Caddice- worms). p. 555 Trichoptera EE. Neither case-bearing nor net-spinning larvae. F. Naiads, that is, immature insects that resemble adults in having the thorax sharply differentiated from the abdomen, and, except in very 3^oung individuals, with rudimentary wings. G. Lower lip greatly elongated, jointed, capable of being thrust for- ward, and armed at its extremity with sharp hooks, p. 314.ODONATA GG. Lower lip not capable of being thrust forward. H. Usually with filamentous tracheal gills on the ventral side of the thorax, p. 325 Plecoptera HH. Tracheal gills borne by the first seven abdominal seg- ments, p. 308 Ephemerida FF. Larvae, that is, immature forms that do not resemble adults in the form of the body, and in_ which the developing wings are not visible externally. G. Several segments of the abdomen furnished with prolegs. p. 571 Lepidoptera GG. With only anal prolegs or with none. HEX A POD A 217 H. With paired lateral filaments on most or on all of the ab- dominal segments. (Sialidas). p. 281 Neuroptkra See also HalipHdas and Gyrinidae. p. 464 Coleoptera HH. Without paired lateral filaments on the abdomen, p. 464. Coleoptera CC. Terrestrial insects. D. External parasites. E. Infesting the honey-bee. {Braula). p. 773 Diptera EE. Infesting birds or mammals. F. Body strongly compressed. (Fleas), p. 877 Siphonaptera FF. Body not strongly compressed. G. Mouth-parts formed for chewing. (Bird-lice), p. 335. Mallophaga GG. Mouth-parts formed for piercing and sucking. H. Antenn.-E inserted in pits, not visible from above. (Pupi- para). p. 773 Diptera HH. Antennae exserted, visible from above. G. Tarsi with a single claw which is oppo.sed by a toothed pro- jection of the tibia. (Lice), p. 347 Anoplura GG. Tarsi two-clawed, p. 350 Hemiptera DD. Terrestrial insects not parasites. E. Mouth-parts apparently retracted within the cavity of the head so that only their apices are visible, being overgrown by folds of the genae. F. Abdomen consisting of ten or eleven segments. (Campodeidag and Japygidae). p. 220 Thysanura FF. Abdomen consisting of not more than six segments, p. 225. Collembola EE. Mouth-parts mandibulate, either fitted for chewing or with sickle-shaped mandibles formed for seizing prey. (See also EEE.) F. Larvae with abdominal prolegs. G. Prolegs armed at the extremity with numerous minute hooks. (Caterpillars), p. 571 Lepidoptera GG. Prolegs not armed with minute hooks. H. With a pair of ocelli, one on each side. (Larvae of saw-flies). p. 884 Hymenoptera HH. With many oceUi on each side of the head. p. 550 " Mecoptera FF. Without abdominal prolegs. G. Body clothed with scales. (Machilidae and Lepismatidas). p. 220 Thysanura GG. Body not clothed with scales. H. Antennae long and distinct. I. Abdomen terminated by strong movable forceps, p. 460. Dermaptera II. Abdomen not terminated by forceps. J. Abdomen strongly constricted at base. (Ants. etc.). p. 884 Hymenoptera JJ. Abdomen not strongly constricted at base. K. Head with a long trunk-like beak. {Boreus). p. 550. Mecoptera KK. Head not prolonged into a trunk. L. Insects of small size, more or less louse-like in form, with a very small prothorax, and without cerci. (Book-lice and Psocids). p. 331 Corrodentia LL. Insects of various forms, but not louse-like, prothorax not extremely small; cerci present. M. Hind legs fitted for jumping, hind femora en- larged. (Wingless locusts, grasshoppers, and crickets), p. 230 Orthoptera MM. Hind femora not greatly enlarged, not fitted for jumping. 218 AN INTRODUCTION TO ENTOMOLOGY N. Prothorax much longer than the mesothorax; front legs fitted for grasping prey. (Mantidas). p. 230 Orthoptera NN. Prothorax not greatly lengthened. O. Cerci present ; antennae usually with more than fifteen joints, often many-jointed. P. Cerci with more than three joints. Q. Body flattened and oval. (Blattidas). p. 230 Orthoptera QQ. Body elongate. R. Head very large. (Termopsis) . p. 273. ISOPTERA RR. Head of moderate size. p. 268. Grylloblattid^ PP. Cerci short, with one to three joints. Q. Body linear with very long linear legs. (Walking-sticks), p. 230 ... Orthoptera QQ. Body elongate or not, if elongate the legs are not linear. R. Body elongate; front tarsi with first joint swollen, p. 338. . .Embiidina RR. Front tarsi not enlarged. S. Minute insects, less than 3 mm. in length; antennae nine- jointed. p. 270 Zoraptera SS. Larger insects; antennae usually more than nine-jointed. (White-ants) . p. 273 Isoptera 00. Cerci absent; antennae usually with eleven joints, p. 464 Coleoptera HH. Antennae short, not pronounced; larval forms. I. Body cylindrical, caterpillar-like. p. 550.MECOPTERA n. Body not caterpillar-like. J. Mandibles sickle-shaped; each mandible with a furrow over which the maxilla of that side fits, the two forming an organ for piercing and sucking. (Ant-lions, aphis- lions, hemerobiids). p. 281 Neuroptera J J. Mouth-parts not of the ant-lion type. K. Larva of Raphidia. p. 281 Neuroptera KK. Larvae of beetles, p. 464 Coleoptera EEE. Mouth-parts haustellate, fitted for sucking; mandibles not sickle-shaped. F. Body covered with a waxy powder or with tufts or plates of wax. (Mealy-bugs, Orthezia). p. 350 Hemiptera FF. Body more or less covered with minute scales, or with thick long hairs ; proboscis if present coiled beneath the head. (Moths) . p. 57 1 Lepidoptera FFF. Body naked, or with isolated or bristle-like hairs. G. Prothorax not well developed, inconspicuous or invisible from above, p. 773 Diptera GG. Prothorax well developed. H. Last joint of tarsi bladder-like or hoof -like in form and usually without claws; mouth-parts forming a triangular unjointed beak. p. 550 Thysanoptera HH. Last joint of tarsi not bladder-like, and furnished with one or two claws; mouth-parts forming a slender; usually jointed beak. I. Beak arising from the front part of the head. p. 350. Hemiptera n.Beak arising from the back part of the head. p. 394. . . Homoptera HEX A POD A 219 BB. Either without a distinct head, or without jointed legs, or incapable of locomotion. C. Forms that are legless but capable of locomotion; in some the head is distinct, in others not. Here belong many larvee representing several of the orders, and the active pup£e of mosquitoes and certain midges. It is impracticable to separate them in this key. CC. Sedentary forms, incapable of locomotion. D. Small abnormal insects in which the body is either scale-like or gall- like in form, or grub-like clothed with wax. The waxy covering may be in the form of powder, or large tufts or plates, or a continuous layer, or of a thin scale, beneath which the insect lives. (Coccidas). p. 350.HEMIPTERA DD. Pupae, the inactive stage of insects with a complete metamor- phosis; capable only of a wriggling motion, and incapable of feeding. E. Obtected pupae, pupae in which the legs and wings are glued to the surface of the body; either in a cocoon or naked, p. 571 . Lepidoptera EE. Coarctate pupae, pupag enclosed in the hardened larval skin. p. 773 DiPTERA EEE. Exarate pups, pupas that have the legs and wings free; either in a cocoon or naked. This type of pupa is characteristic of all of the orders in which the metamorphosis is complete except the Lepidop- tera and Diptera. CHAPTER VI ORDER THYSANURA^ The Bristle-Tails The members of this order are wingless insects in which the wingless condition is believed to be a primitive one, there being no indication that they have descended from winged ancestors; the mouth-parts are formed for chewing; and the adult insects resemble the young in form. In these three respects, these insects resemble the next order, the Collembola; but they differ from the Collembola in that the abdominal segments are not redticed in number and the cerci are usually filiform and many-jointed; some members of the order have also a caudal fila- ment. The members of this order are known as bristle-tails, a name suggested by the pres- ence, in most of them, of either two or three many-jointed filiform appendages at the cau- dal end of the body (Fig. 221, c, and mf) . The paired caudal appendages are the cerci; the median one, when three are present, is the median caudal filament, a prolongation of the eleventh abdominal segment. In fdpyx (Fig. 222), the cerci are not jointed but are strong, curved appendages, resembling the forceps of earwigs. The bristle-tails are most often found under stones and other objects lying on the ground; but some species live in houses. While most species prefer cool situations, there is one, the fire-brat, that fre- quents warm ones, about fire- places and in bakehouses. The antennae are long and many- jointed. In the MachiHdas Fig. 221. — Machilis, ventral aspect: c, cer- cus; Ip, labial palpus; mf, median caudal filament: tnp, maxillary palpus; 0, ovi- positor; s, s, styli. "Thysanura: thysanos (dvpavos), a tassel; oura {oipd), the tail. (220) THYSANURA 221 -Japyx sol- (After Lub- (Machilis), the eyes are very perfect; for this reason, they are used in Chapter III to illustrate the structure of the compound eyes of insects. In all other Apterygota they are more or less degenerate or are lost entirely. In the Lepismatidae (Lepisma), the degeneration of the eyes has progressed far, they being reduced to a group of a dozen ommatidia, on each side of the head. In the Campodeida? and the Japygida?, the eyes have disappeared. The mouth-parts are formed for chewing ; those of Machilis will serve to illustrate their form. The mandibles are elongate with a toothed apex and a sub-apical projection teimi- nated by a grinding surface (Fig. 223, A); the paragnatha are comparatively well developed (Fig. 224); on the outer edge of each there is a small lobe, which Carpenter ('03), who regarded the organs as true appendages, believed to be a vestigial palpus, and at the tip there are two dis- tinct lobes, which this author homologized with the galea and the lacinia of a typical maxilla ; the maxillce (Fig. 223, B) bear prominent palpi. In the Campodeidas and the Japygidse, the jaws are apparently sunk in the head. This con- dition is due to their being overgrown by folds of the genas. In the Machilidas and the Lepismatida3 the jaws are not overgrown; these two families are known, on this account, as the Ectotrophi or Ectotro- phous Thysanura; while the Campodeidffi and the Japygidae are grouped together as the Ento- trophi or Entotrophous Thysanura. The over- growing of the mouth- parts by folds of the genae is characteristic of the Collembola also and is discussed more fully in the next chapter. The three thoracic segments are distinctly separate. There is noth- ing in the structure of the thorax to indicate that these insects have descended from winged ancestors. The three pairs of legs are well developed. In the genus Machilis the coxae of the second and third pairs of legs each bears a stylus (Fig. 221, s). Fig. 223. — A, mandibles of Machilis; B, maxilla of Machilis. (After Oudemans.) 222 AN INTRODUCTION TO ENTOMOLOGY The abdomen consists of eleven segments. The eleventh segment bears the cerci, which are filiform and many-jointed except in the Japygidae, where they are forceps-like. In the Machilida^ and the Lepismatidas the eleventh abdominal segment bears a long, many-jointed median caudal filament; styli and eversible ventral sacs are also usually present ; these vary in ninnber in different genera. The styli are slender appendages (Fig. 221, s). Each stylus consists of two segments, a very short basal one and a much longer termi- nal one. The maximum number of styli is found in Machilis (Fig. 221), where they are borne by the second and third thoracic legs and the second to the ninth abdominal seg- ments. In Lepisnia there are only three pairs; these are borne by the seventh, eighth, and ninth abdominal segments. The abdominal styli are borne by large plates, one on each side of the ventral aspect of each abdominal segment. These plates are termed coxites, as they are believed to be flat- tened coxae of abdominal legs which have otherwise disappeared. A result of the large size and position of the coxites is a reduction in the size of the sternum in the abdominal segments. This is well shown in Machilis (Fig. 221); in the first seven abdominal segments, there is in each a median triangular sclerite ; this is the sternum ; in the eighth and ninth segments no sternum is visible. Fig. 224. — One of the paragnatha of Ma- chilis. (After Car- penter.) Fig. 225.- — Cross-section of an abdominal segment of Machilis showing the styli and the ventral sacs. The ventral sacs of the left side are retracted ; those of the right side, expanded. (After Oudemans.) In the families MachilidcC and Lepismatidas the females have an ovipositor, which consists of two pairs of filiform gonapophyses aris- ing from between the coxites of the eighth and ninth abdominal segments respectively. THYSANURA 223 Fig. 226.— Ovary of Ja- pyx. (After Grassi.) The ventral sacs are sac-like expansions of the wall of the coxites which can be everted, probably by blood -pressure, and are withdrawn into the cavity of the coxite by muscles (Fig. 225). In Figure 221, the openings into the retracted ventral sacs are represented ; there is one pair in the first abdominal seg- ment; two pairs in each of the four following segments; and a single pair each in the seventh and eighth ab- dominal segments. In Lepisma the ventral sacs are wanting. The func- tion of the ventral sacs has not been definitely determined; but it seems probable that they are blood-gills. The presence in the Thysanura of styli and of ventral sacs, which are evidently homologous with those of the Symphyla, is an indication of the primitive condition of these insects. The generalized form of the reproductive organs of the Thy- sanura is another indication of this. In Japyx the ovarian tubes have a metameric arrangement (Fig. 226); and in Machilis (Fig. 227) we find an intermediate form between a metameric arrange- ment of the ovarian tubes and a compact ovary. These facts, and especially the presence of styli and ventral sacs, are opposed to the view held by some writers that the Thysanura are degenerate instead of primitive insects. It is true that degenerate fea- tures are present in the order, as the loss of eyes in Japyx and Campodea; but this loss is correlated with the life of these insects in dark places, like the loss of eyes in certain cave-beetles, and is not important in the determination of the zoological position of the order. The young of the Thysanura resemble the adults in form, there being no marked metamorphosis. In Campodea and Japyx the molt is partial (Grassi '89). This is a small order; less than twenty American species have been described; these represent four families. The distinguishing characteristics of the families are given in the following table. A Body clothed with scales. With three filiform caudal appendages, a pair of cerci and a median caudal filament. Compound eyes present. Jaws not over- grown by folds of the genae. (The Ectotrophi). B. The abdominal tergites reflexed to the under surface so as to form an imbrication covering the sides of the coxites (Fig. 221). Compound eyes large and contiguous. Prothorax smaller than the mesothorax. Middle and hind legs with styli. Saltatorial insects Machilid^ BB. Abdominal tergites not covering the sides of the coxites. Eyes small and distant. Prothorax as large as or larger than the mesothorax. Middle and hind legs without styli. Not saltatorial insects Lepismatid^ Fig.227. — Ovary of Machilis: c, coxite of the eighth abdomi- nal segment; s, stylus ; 0, ovi- positor. (After Oudemans.) 224 ^l.V INTRODUCTION TO ENTOMOLOGY AA. Body not clothed with scales. Median caudal filament wanting. Eyes wanting. Jaws overgrown by folds of the genae. (The Entotrophi). B. Cerci many-jointed and filiform Campodeid^ BB. Cerci forceps-like Japygid^ Family Machilid^.. — This family is represented by the genus Mdchilis, of which several species occur in North America. These insects are found in heaps of stones and in other concealed places; they are very active and leap with agility when disturbed. They are about 12 mm. in length. Family Lepismatid^-. — The best-known repre- sentative of this family is the silverfish or fish-moth, Leptsma saccharina (Fig. 228). It is silvery white with a yellowish tinge about the antennae and legs and measures about 8 mm. in length. It is often a troublesome pest in laundries, libraries, and mu- setims, as it injures starched clothes, the bindings of books, labels, and other things on which paste or glue is used. The popular names were suggested by the clothing of scales with which the body is covered. This pest can be destroyed by the use of pyrethnim or by a poisoned bait, consist- ing of a thin boiled starch paste to which has been add- ed from three to five per cent white arsenic; the paste is spread on bits of cardboard, which are put in the places frequented by the pest. Another common representative of this fam- ily is the Hre-hrsit, Thermobiadomestica. This species resembles the fish-moth in general ap- pearance except that it has dusky markings on its upper surface. It is remarkable for frequenting warm and even hot places about ovens, ranges, and fireplaces. It can be destroyed in the same manner as the preceding species. Family Campodeid^-. — The best-known member of this family is Campodea staphyllnus (Fig. 229). It lives in damp places under stones, fallen trees, or in rotten wood and leaves. It is a very delicate, small, white insect, about 6 mm. in length. It has on the first abdominal seg- ment a pair of appendages which occupy a position corresponding to that of the thoracic Fig. 22g.~Campodea legs and each consists of two or three segments. ffphyl^nus. (After Family Japygid^..— This familv is repre- Lubbock.) ,11,1 T- r 1 ■ 1 1 ■ sented by the genus Japyx, of which two species have been found in this country. These insects can be recognized by the forceps-like form of the cerci (Fig. 222). They are small, deli- cate, uncommon insects, found under stones. Fig. 228. — Lepisma saccharina. (After Lubbock.) CHAPTER Vir ORDER COLLEMBOLA* The Spring-Tails The members of this order resemble the Thysanura in being wingless insects in which the wingless condition is believed to be a primitive one, there being no indication that they have descended from winged ancestors, and in that the adult insects resemble the young in form. They differ Fig. 230. — Side view of Tomocerus plumbens: (After Willem.) CO, collophore; c, catch; 5 spring. from the Thysanura as follows: the abdominal segments are reduced in number, there being only six of them; the first abdominal segment bears a ventral tube, the collophore, furnished with a pair of eversible sacs which assist the insects in walking on smooth surfaces; the fourth abdominal segment usually bears a pair of appendages, which constitute a spring- ing organ; and the third abdominal segment Mstially bears a short pair of appendages, the catch, which hold the spring when it is folded under the abdomen. The common name spring-tails has been appHed to these insects on account of the caudal springing organ that is possessed by most members of the order. The spring- tails are minute insects, often of microscopic size and rarely as large as 5 mm. in length. Most of the species live on decaying matter. These insects are common under stones and decayed leaves and wood, in the chinks and crevices of bark, among moss, and on herbage in damp places. Sometimes they occur abundantly in winter on the surface *Collembola: colla (K6XXa), glue; embolon {efj.^o\ov), a bolt, bar; — from their collophores. (225) Fig. 231 -An ommatid- ium of Podura aquat- ic a. (After Willem.) 226 AN INTRODUCTION TO ENTOMOLOGY of snow, where they appear as minute black specks, which spring away on either side from our feet as we walk; and some species collect in great numbers on the surface of standing water. Sev- eral species are known to be photogenic. The body consists of the head, three thoracic segments, and six abdominal segments (Fig. 230). The prothorax is usually small and in several genera is overlapped by the tergumof themesothorax; in the Sminthuridas the body-segments are more or less fused together. The structure of the abdomen is remarkable, as it consists of only six segments; there is no indication of the manner in which the reduc- tion of the number of segments has taken place. The anus is at the caudal end of the body; the genital opening is on a small papilla on the fifth abdominal segment. The antenuce consist of from four to six segments, usually of four. They vary greatly in their comparative length; in some genera the last segment or the last two segments are divided into many rings or subsegments(Fig.23o) . The eyes of the Col- lembola are commonly described as a group of eight, or fewer, distinct simple eyes on each side of the head. But these so-called simple eyes are not ocelli ; they are more or less degenerate omma- tidia, each group being the vestige of a com- pound eye. In Podura aquatica, these eyes, as figured by Willem ('00), Fig. 232.-^4, longitudinal section of an ommatid- are clearly ommatidia of ium and of the postantennal organ oi Anurida the eucone type (Fig. maritima; B, a surface view of the postantennal ) j^^ gome Other Col- organ. (After Willem.) C),ommatidium; Pa, post- 1 u 1 -a -j antennal organ; hy, hypodermal cells; N, optic lembola, as m Anunda nerve; n, branch of the optic nerve; /, /, tuber- maritima (Fig. 232, 0), cles surrounding the postantennal organ; g, the reduction of the om- wmem')'^"''''""^^^''^^'^''"^^""''^^''^^''" '^^^^''^ matidia has progressed ' ^"^ so far that they present the appearance of ocelli ; and in still others the eyes are lost entire- ly. Primary ocelli have not been found in the Collembola. The mouth-parts are typically mandibulate; the jaws consisting of a pair each of mandibles, paragnatha, and maxillae. The parag- natha of Orchesella cincta were described by Folsom ('99) ; and those of Anurida maritima by the same writer ('00). These organs were termed the superlingucB by Folsom. One of the most striking characteristics of the Collembola is that the jaws are apparently retracted into the cavity of the head so that only their tips are visible. But it has been show:n by Folsom ('00), COLLEMBOLA 227 Fig. 233. — Hind foot of Ach- orutes maturiis. (After Fol- som.) who studied the development of the mouth-parts of Anurida maritima, that, strictly speaking, the jaws are not "retracted," as is usually stated, but are overgrown by the genae. In an early embryonic stage, a downward projection of the gena ap- pears on each side of the head, and these "mouth-folds" become larger and larger in successive stages until the condition seen in the fully developed insect is reached. The development of mouth-folds is not restricted to the Collembola, but occurs also in the Entotrophous Thysan- ura, and to a less marked extent in many of the Pterygota, especially in some Orthoptera, where the gena of each side is prolonged into a small, but distinct, fiat fold over the base of the mandible. In some of the Poduridae the mouth- parts are fitted for piercing and sucking, the mandibles and maxillcC being stylif orm and projecting in a conspicuous cone. In some of the Collembola there is a sense organ situated between the base of the antenna and the ocular field ; this is known as the postantennal organ; its presence or absence and its form when present afford characters used in the description of these insects. In its simplest form it is a claviform hyaline tubercle (Sminthurus) . A more complicated type is that of Anurida maritima, which has been figured by Willem ('00). In Figure 232, Pa repre- sents a longitudinal section of this organ. It is a nerve-end-cell, branching from the optic nerve and extending to the surface of the body, where it is covered by a very thin cuticular layer. It is pro- tected by a ring of tubercles {t, t), two of which are shown in the sectional view (A) and eight in the surface view (B). The function of this organ has not been determined; it has been suggested that it is an organ of smell. The legs of the Collembola consist each of five segments, which correspond to the five principal divisions of the legs of the higher insects. Willem ('00) considers the two antecoxal pieces as segments of the legs and- consequently states that the legs are composed of seven segments. The tarsi in most genera bear two claws, an outer, larger one, the unguis, and an inner, smaller one, the unguiculus ; these claws are apposable (Fig. 233) ; in some genera the inner claw is wanting. One of the most characteristic features of the Collembola is the collophore, or ventral tube, which is situated on the ventral aspect of the first abdominal segment (Fig. 230, co). This organ varies greatly in form in the different genera; in some it is a simple tubercle, di- vided into two halves by a central slit; in others it is enlarged and becomes a jointed tube divided at its free end into two lobes. The 228 AN INTRODUCTION TO ENTOMOLOGY collophore bears at its extremity a pair of eversible sacs through the walls of which exude a viscid fluid. By means of this organ these insects are enabled to cling to the lower surface of smooth objects. The collophore is developed from a pair of appendages, which in the course of their development become fused together at their base. The third abdominal segment usually bears a pair of short append- ages, whose basal segments are fused; this is the tenaculum, or catch (Fig . 2 3 o , c) , which holds th e spring when it is folded under the abdomen . The spring or fur ada (Fig. 230, s) is formed by the appendages of the fourth abdominal segment which are united at the base but separate distally. These ap- pendages are three-jointed. The united basal seg- ment is termed the manubrium (Fig. 234, ma); the intermediate segments, the denies (Fig. 234, d); and the terminal segments, the mucrones (Fig. 234, mu). In the Entomobryidse the furcula appears to be formed by the appendages of the fifth abdominal seg- ment; but a study of the muscles that move it shows that it really pertains to the fourth segment. In some genera of the Poduridee the furcula is wanting. The order Collembola includes two quite distinct types of insects; in one of these types the body is elongate with distinct segmentation; in the other the body is shortened, the abdomen globose and its segments in part fused. Based on this distinction the order is divided into two suborders as follows : A. Body elongate Suborder Arthropleona. AA. Body globose Suborder Symphypleona. SUBORDER ARTHROPLEONA* In this suborder the body is elongate with dis- tinct segmentation (Fig. 235). The three thoracic and six abdominal segments are distinct as a rule; the exceptions apply only to the last two or three abdominal segments. The heart is furnished with six pairs of ostia. The tracheae are wanting; these insects live in damp situations and apparent- ly breathe through the surface of the body. This suborder includes two families, which can be sep- arated as follows : A. Furcula present or absent; when present clearly ap- pended to the fourth abdominal segment. .Podurid^ AA. Furcula present and apparently appended to the fifth abdominal segment Entomobryid^ Family Podurid^ . — Among the better-known members of this family are the following: The "Snow -flea," Achorfdes nivicola, which occurs abundantly in winter on the surface of snow (Fig. 235); this species is also known as Achorutes socidlis. Achorutes armdtus is often found on fungi. arthron (&p0ov), a joint; pleon, a crustacean's abdomen. Fig. 234.-The furcula of Ta- pir itis: ma, manubrium; d, left dens; mti, left muc- r o. ( A f t e r Lubbock,) Fig. 235.— The snow flea, Achorutes nivi cola. (After Fol som.) *Arthropleona: COLLEMBOLA 229 Anurida marttima occurs abundantly on the seashore chiefly between tide marks; several important embryological and anatomical mono- graphs have been published regarding this species. Podura aqudtica is one of the most abundant members of the Collembola; it occurs on the surface of standing water on the margins of ponds and streams. Family Entomobryid^. — This is the largest family of the Collem- bola, containing many genera and species. In some genera the body is clothed with scales. To this family belongs the genus Orchesella, the only genus in the Collembola in which the antennae consist of six segments. SUBORDER SYMPHYPLEONA* In this suborder the body is shortened; the last two abdominal segments are quite distinct but the other body segments are fused into a globular mass in which the seg- mentation is more or less obliterated (Fig. 236). The heart is furnished with only two pairs of ostia. Trachea? are present in the typical genus, Smintlmms. The external openings of the tracheee are one on each side of the neck, in a vertical fold; spiracles properly speaking are not present (Willem '00). This suborder includes a single family, ^^f ; ,f 36.— Pa^m«5 fuscus- ,, o • iu -J (After Lubbock.) the SmmthuridcB. Family Sminthurid^. — The principal genera of this subfamily are Sminthums, Paphms, and Neelits. Each of these genera is made the type of a separate family in some classifications of the order. These genera can be separated as follows : A. Last segment of the antennas long and divided into subsegments.SMiNTHURUS AA. Last segment of the antennae short, not divided into subsegments. B. Thorax shorter than the abdomen; eversible sacs of the collophore long. Papirius BB. Thorax longer than the abdomen; eversible sacs of the collophore short. Neelus In Sminthurus, trachese are present; in the other genera they are absent or extremely vestigial. The presence of tracheae in Sminthurus enables these insects to live in drier situations than can other Col- lembola. The "garden-flea" Sminthurus hortensis is found upon the leaves of young cabbage, turnip, cucumber, and various other plants. JUW.^ vSCglilCllLO aiC J.UC5CU. *Symphypleona; symphyo, to grow together; pleon, a crustacean's ab- domen. CHAPTER VIII ORDER ORTHOPTERA* Grasshoppers, Crickets, Cockroaches, and others The winged members of this order have two pairs of wings; the fore wings are more or less thickened, hut have a distinct venation; the hind wings are folded in plaits like a fan when at rest; there are many forms in which the wings are vestigial or even wanting. The mouth-parts are formed for chewing. The metamorphosis is gradual (paurometabolous) ; the nymphs are terrestrial. The order Orthoptera includes some of the very common and best- known insects. The most familiar representatives are the long-horned grasshoppers, locusts, crickets, katydids, and cockroaches. With the exception of a single family, the Mantida?, the members of this order are as a rule injurious to vegetation ; and many species are quite apt to multiply to such an extent that their destruction of plant life becomes of great economic importance. The two pairs of wings of the Orthoptera differ in structure. The front wings are leather}^ or parchment-like, forming covers for the more delicate hind wings. These wing-covers have received the special name tegmina. The tegmina usually overlap, at least at the tips, when at rest. The hind wings are thinner than the tegmina and usually have a broadly expanded anal area, which is folded in plaits lilce a fan when at rest. Many Orthoptera have vestigial wings, and many are wingless. In the males of the Saltatorial Orthoptera, the Locustidffi, the Tettigonid^, and the Gr3-llidce, musical organs have been formed by modifications of certain parts of the wings; these have been described in Chapter II. The mouth-parts are of the mandibulate type, that is, they are formed for chewing. The mouth-parts of a locust are figured on page 42. In the Orthoptera the metamorphosis is gradual, paurometabo- lous. In the case of those species in which the wings of the adult are either vestigial or wanting, the adults resemble ver^^ greatly immature insects. It is often important to determine whether a short-winged specimen is an adult or not. Fortunately this determination can usually be made with ease with the Saltatorial Orthoptera, the Locustidas, the Tettigonidae, and the Grsdlidae. In these three families the wing-pads of the nymphs are inverted, as shown by the curving down of the extremities of the wing-veins, instead of up as with the adult; and the rudimentary hind-wings are outside of the tegmina, instead of beneath them. The development of the wings of a locust is described in Chapter IV, p. 175. *0rth6ptera: orthos {6pd6i), straight; pteron {nrepSv), a wing. (230) ORTHOPTERA 231 The segmentation of the abdomen and the development and structure of the genitalia or gonapophyses in the jumping Orthoptera are of especial interest; as, on account of the generalized condition of these parts in these insects, they, can serve as a type with which the corresponding parts in more specialized insects can be compared. In some members of this group of families all of the abdominal segments are preserved more or less distinct, and in nearly all of them the genitalia are well -developed.* The segmentation of the abdomen can be seen best on the dorsal aspect of this region; for in some cases the tergum of a segment is well-pre- served while the sternum is vestigial. Figure 237 Fig. 237.- moved: -Side view of a locust with the wings re- /, tympanum. represents a side view of a female locust with the wings removed in order to show the segmentation of the abdomen. The first eight segments of the abdomen of this insect are very distinct; but the caudal segments are much less so. Figure 238 represents the caudal part of the abdomen of the same insect more enlarged, in order to facilitate the lettering of the parts. In this insect the eighth abdominal tergtim resembles the preceding ones. The ninth and tenth abdominal terga are shorter and are joined together on each side ; but in many other jumping Orthoptera these terga are not thus imited. Caudad of the tenth abdomi- nal tergum there is a shield-shaped part, which is commonly known as the supra-anal plate; this plate is divided into two sclerites by a transverse su- ture; the first of these sclerites is be- lieved to be the tergtmi of the eleventh abdominal segment, and the other the telson (Fig. 23 S, /). Thus all of the abdominal segments are preserved, in part at least, in this insect. The last two abdominal segments, the eleventh and the telson, are even more distinctly preserved in the early instars of some orthopterous insects than they are in the adult (Fig. 239). In many adult Orthop- tera there is no suture between the eleventh tergum and the telson. On each side of the body, in the angle between the supra-anal plate and the lateral part of the tenth tergum, there is a triangular sclerite (Fig. 238, p); this pair of sclerites have long been Fig. 238. — Side view of the caudal end of the abdomen of a female locust: 8, g, 10. 11, the tergites of the eighth, ninth, tenth, and eleventh abdominal segments ; t, telson; p, podical plate; c, cer- cus; d^ i, V, dorsal, inner, and ventral valves of the oviposi- tor. *The genitalia are vestigial in Tridactylus and are entirely wanting in Gryllo- talpa. In these genera the reduction or loss of the genitalia is probably correlated with the subterranean life of these insects, they having no need for an ovipositor. 232 AN INTRODUCTION TO ENTOMOLOGY Fig. 239. — Caudal segments of a nymph of a female locust, dorsal aspect: //, eleventh abdominal segment; /, telson; c, cercus. known as the podical -plates; but they have recently been named the para prods because they are situated one on each side of the anus. They are the sternum of the eleventh abdominal seoment, which is divided on the midventral line, to admit of the expansion of the poste- rior end of the alimentary canal during defecation. In this insect the cerci (Fig. 238, c) project from beneath the caudal border of the tenth tergtmi ; they appear, there- fore, to be appendages of the tenth ab- dominal segment; but it is believed that in all insects where cerci are pres- ent they are appendages • of the elev- enth abdominal segment. This, for example, is obviously the case in the Plecoptera (Fig. 240). The homology of the paraprocts is also well shown in this figure. The ovipositor consists of three pairs of processes or gonapophyses ; these are termed the valves or vahmlce of the ovipositor; they are dis- tinguished as the dorsal, ventral, and inner vahnilae, respectively. In the locust the dorsal valvulse (Fig. 238, d) and the ventral valvulse (Fig. 238, v) are strong, curved, and pointed pieces; the inner valvu- lee (Fig. 238, i) are much smaller. The relation of the gonapophyses to the segments of the abdomen can be seen more clearly in the female of Ceuthophilus (Fig. 241). The ventral valvulse arise from the posterior margin of the eighth sternum and the dorsal and inner valvulas arise from the ninth stemimi. These relations can be seen even more clearly in very young n3niiphs where the rudiments of the gonapophyses are mere tubercles, one pair on the hind margin of the eighth abdominal sternum and two pairs on the ninth sternum (Fig. 242). In the male, as in the female, the form of the caudal end of the abdomen and its appendages dif- fers greatly in different members of this order. Space can be taken here to illustrate these parts in only a single species. For detailed ac- counts of these parts in other mem- Fig. 240. — End of abdomen of Pter- bers of this order, special papers on onarcys dorsata, female, ventral +ViiQ Qiihippf c;br.iilrl hp ponsiilted view: J7, 77, the divided sternum this subject should be consulted. ^f ^he eleventh abdominal segment. Among the more recent and gen- the podical plates; c, c, basal parts erally available of these are those of of the cerci. ORTHOPTERA 233 Crampton ('i8) and Walker ('19 and '22 b). These papers include references to the very extended literature on this subject. Figures 243 and 244 represent the caudal end of the abdomen of the male of the Carolina locust, Dissosteira Carolina. In this insect the ninth and tenth terga are joined together on each side (Fig. 244) and the eleventh tergum is separated from the apical part of the supra-anal plate (Fig. 243, s) by a distinct suture. The ninth sternum is large, is turned upward behind, and bears a large con- ical part (Fig. 244, ex) termed the coxale, which is believed to be united coxites of the ninth segment. There are two genera of rare and remarkable insects, each of which has been placed in the Orthoptera by some writers and each of which Fig. 242. — Ventral view of end of abdomen of Fig. 241.— Side view of end of abdomen of Ceuthophilus young nymph of lapidicola: 7, 8, g, 10, above, tergites of the seventh Conocephalus fas- to the tenth abdominal segments; 7, 8, below, sternites ctatus. (After of the seventh and eighth abdominal segments; b, basal Walker.) segment of the ventral valve of the ovipositor ; c, cercus ; p, podical plate; d,i, v, dorsal, inner, and ventral valves of the ovipositor. (After Walker.) is regarded by others as constituting a separate order; these are Grylloblatta and Heniimerus. These genera are briefly discussed at the close of this chapter. Leaving out of account the two genera named above, the order Orthoptera includes only six families, all of which are represented in the United States. These families can be separated by the following table.* TABLE OF FAMILIES OF ORTHOPTERA A. Hind femora fitted for jumping, i. e., very much stouter or very much longer, or both stouter and longer, than the middle femora; organs of flight of imma- ture forms inverted; stridulating insects. (The Saltatorial Orthoptera.) *The limits assigned to the order Orthoptera in this work are those that have been commonly recognized for a long period and are those adopted in recently published manuals treating of this order, except that in some of them the Der- maptera is included in the Orthoptera. But Handlirsch ('08) in his great work on fossil insects proposed a new classification of insects, which differs greatly from the classification adopted here. In this classification the families Blattidae, Mantidag, and Phasmidae are removed from the Orthoptera and each is made to constitute a distinct order. 234 AN INTRODUCTION TO ENTOMOLOGY B. Antennae long and setaceous, except in the mole-crickets and sand-crickets ; tarsi three- or four-jointed; organs of hearing situated in the fore tibiae; ovipositor elongate, except in the mole-crickets and sand-crickets, with its parts compact. C. Tarsi four-jointed; ovipositor, when exserted, forming a strongly- compressed, generally sword-shaped blade, p. 234 Tettigoniid^ CC. Tarsi usually three-jointed, except in the pigmy mole-crickets where they are reduced; ovipositor, when exserted, forming a nearly cylindrical, straight, or occasionally upcurved needle, except in the Trigonidiinae. p. 242 Grylhd^ BB. Antennae short; tarsi three- jointed; organs of hearing situated in the first abdominal segment; ovipositor short, with its parts separate. p. 252 LocusTiD.*: AA. Hind femora closely resembling those of the other legs, and scarcely if at all stouter or longer than the other femora, i. e., not fitted for jumping; organs of flight in a normal position when immature; stridulating organs not developed. B. Body elongate; head free; pronotum elongate; legs slender, rounded; cerci jointed or without joints; walking insects. C. Front legs simple; cerci without joints, p. 260 Phasmid^e CC. Front legs fitted for grasping; cerci jointed, p. 262. . .Mantid^ BB. Body oval, depressed; head wholly or almost wholly withdrawn beneath the pronotum; pronotum shield-like, transverse; legs coinpressed ; cerci jointed; rapidly running insects, p. 263 Bl.\ttid^ Fig. 243.— Dorsal view of end ---;;=£:£»eS5|^^kWg*^'^'^ of abdomen of Dissosteira 1 r , ■, Carolina, male: 9T, loT, Fig 244.-Side view ot end ot abdomen II T, ninth, tenth, and elev- <^. Dissosteira carolma, male ; lettenng as m enth terga; 5, supra-anal figure 243. plate; p, podical plate, c, cercus; ex, coxale. FAMILY TETTIGONIID^ The Locustidae of Authors* The Long-horned Grasshoppers To this family belong the most attractive in appearance of our common Orthoptera. In many of them the wings are graceful in *The name Locustidae has been commonly appHed to this family. This usage is the result of an erroneous application of the generic name Locusta to certain members of this family. The insects of the genus Locusta, established by_ Lin- naeus, and other insects commonly known as locusts, are members of the farnily to which the common name short-horned grasshoppers is applied and which is properly termed the Locustida. The Tettigoniidae is the Phasgonuridae of Kirby's catalogue. ORTHOPTERA 235 form and delicate in color, and the antenna? are exceedingly long and slender, looking more like ornaments than like organs of practical use. These beautiful creatures are much less frequently seen than are the crickets and locusts because of their protective green color, which renders them inconspicuous in their haunts among foliage or on the blades of grass. Their presence is most often indicated by the chirping of the males. The long-horned grasshoppers are those jumping Orthoptera with long, slender antenna?, longer than the body, in which the tarsi are four-jointed and the ovipositor is sword-shaped. The tegmina of the males are furnished, in nearly all winged species, with stridulating organs; but these occupy a much smaller part of the tegmina than with the crickets. The six plates of which the ovipositor is composed are closely united so that this organ has the appearance of a single sword-shaped blade. The different members of the Tettigoniidse exhibit a great variety of methods of oviposition; some lay their eggs in the ground; some in the pith of twigs ; some singly in the edges of leaves ; some in rows on leaves and stems; and others between the root-leaves and stems of various plants. The Tettigoniidse found in America north of Mexico represent eight subfamilies; these can be separated by the following table, which is based on one by Scudder ('97). A. Body generally winged; tarsi more or less depressed. B. Fore tibiae furnished with auditory tympana; fore wings of male, when present, furnished with stridulating organs. C. First two segments of the tarsi without a lateral groove; the two series of spines on the hind side of the posterior tibias continued to the apex. p. 236. Phaneropterin^ CC. First two segments of the tarsi with a lateral groove; one or both of the two series of spines on the hind side of the posterior tibiae not con- tinued to the apex. D. Fore tibiae without apical spines above. E. The apex of the vertex short, crowded by the prominent antennary fossae; pronotum crossed by two distinct sutures, p. 238 PSEUDOPHYLLIN^ EE. The apex of the vertex extended and free from the not prominent antennary fossae; pronotum without transverse sutures, or with only one. F. Fore and middle femora unarmed beneath ; the vertex terminating in a rounded tubercle, which is hollowed out on the sides, p. 238. CONOCEPH.\LIN^ FF. Fore and middle femora spined beneath, the vertex produced forward into a long sharp cone. p. 239 Copiphorin^e DD. Fore tibiae with an apical spine above on the outer side; usually wingless or with vestigial wings, p. 239 Decticin^e BB. Fore tibiae without auditory tympana; fore wings of male, when present, without stridulating organs, p. 240 GRYLLACRlNiE AA. Body usually wingless; tarsi distinctly compressed. B. Tarsi without pulvilli; inserting' angle of the hind femora situated on the inner side. p. 241 Rhaphidophorin.e BB. Tarsi provided with pulvilli; inserting angle of the hind femora situated on the outer side. p. 242 Stenopelmatin^ Some of the more common and better-known representatives of these families are referred to below. To save space the distinguishing 236 AN INTRODUCTION TO ENTOMOLOGY characteristics of the subfamiHes are not repeated ; these are indicated in the table above. Subfamily PHANEROPTERIN^ The False Katydids To this subfamily belong certain long-horned grasshoppers that have broad leaf-like wings and arboreal habits. In these respects they resemble the well- known katydid whose stri- dent call suggested the pop- ular name. Several of these species have received popu- lar names in which the word katydid enters, as indicat- ed below. These species may be termed collectively the false katydids; the true katydids constitute the next Yig.2^6.-Arnbhcoryphaohlongifolia. (From subfamily. Lugger.) Blatchley ('20) describes twenty species and varieties of the false katydids that are found in northeastern America; these represent eight genera. Among our common species there are representatives of three genera; these can be separated as follows. A. Tegmina broadened in the middle; the extreme point of the vertex much broader than the first segment of the antennae. ORTHOPTERA 237 Fig. 247. — Scudderi septentri- onalis. (From Lugger.) B. Hind femora much shorter than the tegmina; ovipositor short and turned abruptly upward (Fig. 245). p. 237 Microcentrum BB. Hind femora but Httle if any shorter than the tegmina; ovipo-sitor well developed, and curved gradually upward, p. 237 Amblycorypha AA. Tegmina of nearly equal breadth throughout; the extreme point of the vertex but little if any broader than the first segment of the antennae, p. 237. , SCUDDERIA Microcentrum. — Two species of this genus are found in the United States east of the Rocky Mountains ; these are known as the angular- winged katydids. Figure 245 repre- sents the female of the larger angular- winged katydid, Microcentrum rhombi- folium, and the remarkable way in which it deposits its eggs on leaves and twigs. In this species the slightly hol- lowed front of the pronottmi has a very small central tooth, which is lacking in smaller species. The smaller angular- winged katydid, Microcentrum retinerve, is only slightly smaller than the larger one. Amblycorypha. — The three most common species of the genus are the following: The oblong-winged katydid, Amblycorypha oblongi- folia (Fig. 246), is the largest of the three most common species. The tegmina measure from 34 to 37 mm. in length; the ovipositor is less ser- rate and less curved than in the next species. The round-winged katydid, Amblycorypha rotundifolia, is a smaller species ; the tegmina are not more than 30 mm. in length and are wide for their length, as indicated by the specific name; the ovipositor is quite broad, much curved, and roughly serrated. Uhler's katj^did, Amblycorypha iihleri, is our smallest species; the body meas- ures from 14 to 16 mm. in length; the tegmina from 24 to 26 mm.; and the ovipositor about 8 mm. Scuddcria. — Species of this genus are found throughout the United States and in Canada; but the greater nimiber of our species are found east of the Great Plains. One species, Scuddcria mexicdna, is found in Cali- fornia and Oregon. A common eastern species which may serve as an ex- am.ple of the insects of this genus, is the northern bush-katydid, Scuddcria Fig. 248.-Pterophylla camellifo- septenirtonalis.^ Figure 247 represents lia. (After Harris.) the male oi this species, natural size. 238 AN INTRODUCTION TO ENTOMOLOGY Subfamily PSEUDOPHYLLIN^ The True Katydids The best -known representative of this subfamily in the United States is the northern true katydid, Pterophylla camellifolia (Fig. 248). This insect is found throughout the United States east of the Rocky Mountains; but in the North it hves in colonies which occupy quite limited areas. This is the insect whose song suggested the popular name katydid. It differs from members of the preceding subfamily in having the hind wings shorter than the tegmina, and in having the tegmina very convex, so that it has an inflated appearance. Subfamily CONOCEPHALIN^ The Meadow Grasshoppers From the middle of the summer to the autumn there can be found upon the grass in our meadows and moist pastures many light-green long-homed grasshoppers of various sizes; these, on ac- count of the situations in which they are usualh^ found, are termed the meadow-grass hoppers. Our common species represent only two genera ; but each of these includes many species. Orchelimum. — This genus includes the larger and stouter species of meadow grasshoppers pared with other Tettigoniidse. Fig. 249. — Orchelimum (From Lugger.) vidgare, male. but they are of medium size com- In these the ovipositor is usually Cojiocephalns. Fig. 250. — Orchelimum vulgare, female. (From Lugger.) Up-curved. Our most abundant species is the common meadow grasshopper, Orchelimum vulgare. This is found from the Rocky Mountains to the Atlantic Coast. Figure 249 represents the male, natural size; and Figure 250, the female. Conocephalus. — This genus comprises, the smaller and slenderer species of this subfamily. In these the ovipositor is slender, and straight or slightly curved (Fig. 251). Until recently this genus has been generally known as Xiphidium.* *It is unfortunate that according to the rules of nomenclature the name Conocephalus must be applied to this genus instead of to the typical genus of the next subfamily, now known as Neoconocephaliis, with the result that the sub- family name Conocephalinee is applied to the meadow grasshoppers instead of to the cone-headed grasshoppers. ORTHOPTERA Subfamily COPIPHORIN^ 239 The Cone-headed Grasshoppers The cone-headed grasshoppers are so called because the vertex is prolonged forward and upward into a cone. These are much larger insects than the meadow grass- hoppers and are found in trees as well as upon grass. This sub- family is represented in our fauna by four genera; but three of these are found only in the South. All of the northern species belong to the genus N eoconoce phalns , of which eleven species occur in the United States. The most com- mon species in the north, east of 252. — Neoconocephaliis ensiger, male. (From Lugger.) the Rocky Mountains, is the sword-bearer, N eoconocephalus ensiger. Figure 252 represents the male of this species, and Figure 253 the female. Both sexes have very long wings, and the ovipositor of the female is remarkable for its length. Fig. 253. — Neoconocephaliis ensiger, female. (From Lugger.) In most of the species of Neoconocephaliis there are two distinct forms : one pea-green in color and the other of a brownish straw-color. Subfamily DECTICIN^ The Shield-backed Grasshoppers A few members of this subfamily have well-developed wings ; but in most species the wings are small, especially in the female, where they are sometimes even absent. Most of the species bear some resemblance to crickets. They present, however, a strange appear- ance, due to the pronotum extending backward over the rest of the thorax, like a sun-bonnet worn over the shoulders with the 240 AN INTRODUCTION TO ENTOMOLOGY Fig. 254. — Atlanticus testaceus, male. (From Lugger.) back side forward. It was the large size of the pronotum that sug- gested for the group the popular name the shield-hacked grass- hoppers. These insects live in grassy fields or in open woods, where they hop about in exposed posi- tions. Even dn some of the short- winged forms the stridulating or- gans of the tegmina of the males are well developed. The North American species represent twenty genera ; most of these are found west of the Mississippi River; a few species occur in the east; nearly all of these belong to the germs Atlanticus. Figure 254 represents the male of At- lanticus testaceus, and Figure 255 the female of Atlanticus davisi. Most of the species of this subfamily are local or very rare and not of economic im- portance; but species of the genus Anabrus and of Perana- hrus at times invade cultivated areas in the western United States and do immense damage. Many popular names have been applied to these insects; perhaps the one in most general use is the western cricket. A very complete monograph of the North American species of this subfamily has been published by Caudell ('07). Fig. 255. — Atlanticus davisi, female. Subfamily GRYLLACRIN^ The Leaf -rolling Grasshoppers The members of this subfamily agree with the preceding sub- families and differ from the two following in having the tarsi more or less depressed. They agree with the fol- lowing subfamilies and differ from the preceding in the ab- sence of auditory t3Tnpana in the fore tibiae and in the ab- sence of stridulating ^. ^ organs even when the filfS^hW r^^'"'"^"" '''''^'''''''''' ^^"'^^'- ^^'"°"' tegmina are present. Only a single spe- Blatchley.) ORTHOPTERA 241 cies, the Carolina leaf -roller, Camptondtus carolinensis (Fig. 256), occurs in our fauna. This species is wingless; it measures from 13 mm. to 15 mm. in length. Its known range extends from New Jersey west to Indiana and south to Florida. This insect is very remarkable in its habits.which have been de- scribed by Caudell ('04) and McAfee ('08). It makes a nest by rolling a leaf and fastening the roll with silken threads which it spins from its mouth. It remains in its nest during the day and emerges at night to capture aphids upon which it feeds. Subfamily RHAPHIDOPHORIN^ The Cave-Crickets or Camel-Crickets Many common names have been applied to members of this sub- family; among these are cai)g-crz'<:^^/5, because they abound in caves and are found in other dark places; camel-crick- ets, because of the high, arched back of some species (Fig. 257); and stone-crickets, from their habit of hiding beneath stones. This last name is not at all distinctive. These are wingless long-horned grass- hoppers that bear some resemblance to the true crickets (Fig. 258). They have a short, thick body and remark- ably stout hind femora, like a cricket, but are entirely destitute of tegmina and wings, and the females, like other Tettigoniidse. have a sword-shaped ovipositor. The more common species are either of a pale brown or a dirty white color and more or less mottled with either lighter or darker shades. Fig. 257. — Ceuthophilus uhleri, male. (From Blatchley.) Fig. 258. — Ceuthophilus, female. Fig. 259. — Ceuthophilus maculatus, female. (From Lugger.) These insects live in dark and moist places, under stones and rubbish, especially in woods, in cellars, in the walls of wells, and in caves. On one occasion I saw many thousands of them on the roof of a cave in Texas. Caudell ('16) in his monograph of this subfamily lists twelve gen- era including many species that occur in the United States. Most of 242 AN INTRODUCTION TO ENTOMOLOGY our common species in the East belong to the genus Ceuthophilus. Figure 257 represents the male of Cew^/zo^Mws w/z/m, and Figure 259 the female of Ceuthophilus maculdius. Subfamily STENOPELMATIN^ The Sand-Crickets These are large, clumsy creatures with big heads (Fig. 260). They live under stones and in loose soil. They are represented in our fauna by a single genus, Stenopebndtus, several species of which are found in the Far West and pjg_ 260.— Stenopelmatus. especially on the Pacific Coast. Family GRYLLIDAE* The Crickets Although the word cricket forms a part of some popular com- pound names of members of the Tettigoniidae, as "western crickets" and "sand-crickets," when the word is used alone it is correctly ap- plied only to members of this family. In the more typical crickets, the hind legs are fitted for leaping; the antennae are long and slender; the tegmina lie flat on the back and are bent down abruptly at the sides of the body; the ovipositor is spear-shaped; and the tarsi are three-jointed. Wingless forms are common. The more striking departures from these characteristics are the following: in the Tridactylinas the antennae are short; in the Tri- gonidiinse the ovipositor is sword-shaped ; in the Gryllotalpinae and the Tridactylinae the ovipositor is wanting in our species; and in the TridactylinEe the tarsi are reduced. It is evident that one step in the reduction of the number of tarsal segments is the growing together of the metatarsus and the second segment. This is shown in the hind tarsi of Anaxlpha, CEcdnthus, Nemobius, and doubtless others, where the suture between these two segments can be seen although the segments are anchylosed. Tympana are usually present in the fore tibiae, one on each side of each tibia, as in the TettigoniidcC. In some genera one t>Tnpantim of each pair is wanting; this is sometimes the outer and sometimes the inner one; in the wingless, and therefore mute, species, the tympana are wanting; and in the Tridactylinae there are none. "This family is termed the Achetidae by some writers. ORTHOPTERA 243 With most species of crickets the two sexes differ greatly in ap- pearance; the female has a long ovipositor and the venation of the wings is simple, while the male has the horizontal part of the fore wings modified to form musical organs. The structure of these has been described in Chapter II. The Gryllidae includes eight subfamilies, all of which are repre- sented in the United States. These subfamilies can be separated by the following table. A. The next to the last segment of the tarsi distmct, depressed, and heart- shaped. B. Hind tibiae armed with two series of spines without teeth between them. p. 243 TrIGONIDIIN/E BB. Hind tibiae with teeth between the spines, p. 244 ENEOPXERiNiE AA. Tarsi compressed, the next to the last segment minute, compressed. B. Fore legs fitted for walking. C. Hind tibiae without spines except the apical spurs. D. With well-developed wings; hind tibiae with only two very small apical spurs. {Neoxabea.) p. 245 CEcanthin^ DD. Wingless or subapterous; hind tibiae with three pairs of apical spurs. p. 250 MOGOPLISTIN^ CC. Hind tibis armed with two series of spines. D. Body subspherical; wingless; hind femora ovate, very strongly swollen, p. 249 Myrmecophilin^ DD. Body more elongate, usually winged; hind femora more elongate, not exceptionally swollen. E. Hind tibiae with minute teeth between the spines, p. 245 CEcanthin.« EE, Hind tibiae without teeth between the spines, p, 247.Gryllin^ BB. Fore legs fitted for digging. C. Antennae many-jointed; all of the tarsi three-jointed, p. 250 Gryllotalpin.^; CC. Antennae eleven- jointed; fore and middle tarsi two-jointed, hind tarsi one-jointed or wanting, p. 251 Tridactylin^ Subfamily TRIGONIDIIN^ The Sword-bearing Crickets These are small crickets, our species measuring from 4 mm. to 8.5 mm. in length of body. They live chiefly on shrubs and tall grasses and weeds growing in or near water. Their distinguishing features are the following : The next to the last segment of the tarsi is distinct, depressed, and heart-shaped, the hind tibias are slender with three pairs of mobile spines besides the terminal spurs, and with no teeth between these spines ; and the ovipositor of the female is compressed and curved upwards. In the sword-shaped form of the ovipositor these crickets present a striking exception to the characteristics of the Gryllid^. The following are our best-known representatives of this sub- family. Anaxlpha exigua. — This cricket resembles somewhat in general appearance the common small field-crickets {Nemohius) , but unlike 244 ^iV INTRODUCTION TO ENTOMOLOGY them it does not live on the ground. The antennse are ver\' long (Fig. 261); the ovipositor is one half as long as the hind femora; the hind femora of the male are longer than the tegmina; and the stridu- lating area of the tegmina is large. The length of the body is 5-8 mm. There are two forms of this species: in one, the hind wings are wanting and only the t>-mpana on the outer face of the fore tibiae are present ; in the other, long hind wings are present and there is a tympanum on each face of the fore tibiee. This species is found from southern New England west to Minnesota and Nebraska and south to Florida and Texas. Faldcula hehdrdi. — This is a smaller species than the preceding, the body measuring only 4-5 mm. in length. It is uniform pale yellowish brown in color. The hind wings are wanting. The stridulating area is small, confined to the basal fourth of the tegmina. The fore tibia are without visible t\Tnpana. Its range extends from New Jersey south and southwest to Florida and Texas. Cyrtoxipha columhidna. — This is a small, pale green fading to brownish yellow, cricket; it is found on shrubs and small trees, usually near water. The wings are always present and pro- longed in the form of a tail or queue. Tympana are present on both faces of the fore tibiae. The tegmina extend 2-3 mm. beyond the end of the abdomen. The length of the body to apices of Yig. 261.— Anaxipha tegmina is 8.5 mm. Its range extends from extgua. (Prom Lug- Washington, D. C, to Florida and Texas. Phylloscyrtus pidchellus. — This cricket differs from the three preceding species in having the last segment of the maxillary palpi spoon-shaped. The head and the thorax are bright crimson-red; the margin of the thorax is pale yellow; the abdomen is black; and the tegmina are chestnut-brown. The length of the body is 6-7 mm. This species is found throughout the United States east of the Mississippi River, except in the northern portions. Subfamily ENEOPTERIN^ The Larger Brown Bush-Crickets These crickets resemble those of the preceding subfamily in the heart-shaped form of the next to the last segment of the tarsi; but differ in having teeth between the spines of the tibiae, and in the ovipositor being spear-shaped. » ORTHOPTERA 245 Only a few species are found in our fauna, three genera: Orocharis, in which both t^-m- pana of the fore tibia; are present ; Hdpithns, with a tympantmi on the inner face only of the fore tibicc; and TafaUsca, with no tympana and no stridulating organs. The most common species is Orocharis saltator (Fig. 262). This is usually pale reddish brown, but some individuals are grayish. The length of the body is 14-16 mm. It is foimd from New Jersey west to Nebraska and south to Florida and Texas. The only common species of Hapithiis is H. agitator, which is found from Long Island west to Nebraska and south to Florida and Texas. Our only species of TafaUsca is T. hlrida, which is found in southern Florida. Subfamily CECANTHIN.^ These represent Fig 262. — Orocharis saltator. (From Lugger.) The Tree-Crickets These are delicate crickets, many of which are of a light green color, with the body and legs sometimes dusky. Figm-e 263 represents a male; in the females the front wings are more closely wrapped about the body, giving the insect a narrower appearance. They live in more or less elevated positions, varying, according to the species, from among herbaceous plants to the higher parts of fruit and forest trees, hence the name tree-crickets commonly applied to them. Their frequent occurrence among flowers suggested the name of the principal genus, CEcdiithus, implying I dwell in flowers. Two genera of tree-crickets are represented in our fauna, Neoxahea and CEcanthus; these can be distinguished by differ- ences in the armature of the hind tibise. Neoxahea. — -In this genus the hind tibise bear neither teeth nor spines except the apical spurs, and the first segment of the antennas is armed in front with a stout, blunt tooth (Fig. 264, h). Neoxahea hipunctdta is the only species known. In this species the hind wings are almost twice as long as the fore wings; the fore wings of the fe- male are each marked with two rather large blackish spots; the wings of the male are un- marked. The general color is pale pinkish brown. The length of the body is about 16 mm. Q^cdnthus. — In this genus the hind tibiae bear both spines and teeth. Several species occur in the United States and Canada; these differ in the color of the body, in the markings on the first two segments of the antenna;, in their song, and in the Fig. 263. — CEcanthus niveus, male. 246 AN INTRODUCTION TO ENTOMOLOGY elevation above the surface of the ground in which they are usually- found. Most of our species are found east of the Great Plains; one, CEcdnthus calijornicus, occurs in California; and one, CEcanthus & fl I Fig. 264. — Basal segments of antennae of CEcanthus and Neoxabea. (The lettering is explained in the text. (After Lugger and Fulton.) argentlnus, in Texas. The species of eastern North America can be distinguished by the following table, which is copied from a de- tailed account of these insects by B. B. Fulton ('15). A. Basal segment of antennse with a swelling on the front and inner side. First and second segments each with a single black mark. B. Basal antennal segment with a round black spot. (Fig. 264, a) . . CE. niveus BB. Basal antennal segment with a J-shaped black mark. (Fig. 264, b) CE. anguslipennis BBB. Basal antennal segment with a straight club-shaped black mark. (Fig. 264, e) CE. exclamationis AA. Basal antennal segment without a swelling on the front and inner side. First and second antennal segments each with two black marks or entirely- black. Tegmina of males 5 mm. or less in width. B. Head and thorax pale yellowish green or black or marked with both colors. C. First antennal segment with a narrow black line along inner edge and a black spot near the distal end. Body entirely pale yellowish green. (Fig. 264, d) CE. quadripunctatus CC. First antennal segment with black markings similar to above, but broader and usually confluent, sometimes covering the whole segment. Head and thorax often with three longitudinal black stripes; ventral side of abdomen always solid black in life. (Fig. 264, c) . . CE. nigriconiis BB. Head, thorax, and antennae reddish brown. Wings in life with conspicuous green veins. Marks on basal antennal segment broad but seldom con . fluent. (Fig. 264, f) CE. pini AAA. Basal antennal segment without a swelling on the front and inner side. Basal portion of antenna red unmarked with black. (Fig. 264, g). Teg- mina of male about 8 mm. wide CE. latipennis The species of CEcanthus that most often attracts attention is the snowy tree-cricket, CEcanthus niveus (Fig. 263). The pres- ence of this insect, though usually unseen, is made very evident in late ORTHOPTERA 247 summer and in the autumn by the song of the males. This song early in the evening and is continued through- out the night ; it consists of a monotonous series of high-pitched trills rhythmically repeated in- definitely. It is a remarkable fact that all of these crickets that are chirping in any locality chirp in unison. Individual singers will stop to rest, but when they start again they keep time with those that have continued the chorus. Except where the true katydid is heard, this is the most conspicuous insect song heard in the night in the regions where this species occurs. This cricket inhabits chiefly high shrubs and trees; it deposits its eggs singly in the bark or cambitim of trees and bushes. While the presence of the snowy tree-cricket is made evident by its song, there is another species that has attracted much attention by its manner of oviposition; this is Qicanthus nigricdrnis. The female lays her eggs in a longitudinal series in the twigs or canes of various plants (Fig. 265). She selects the rasp- berry more often than any other plant; and as that portion of the cane beyond the incisions made for the eggs usually dies, it often happens that these crickets materially injure the plants. In such cases the dead canes should be cut out and burned early in the spring before the eggs hatch. is begun Fig. 265. — Stem of black raspberry with the eggs of CEcanthus nigricor- nis: c, d, egg enlarged. (From Riley.) Subfamily GRYLLIN^ The Field-Crickets The field-crickets abound everywhere, in pastures, meadows, and gardens; and certain species enter our dwellings. They lurk under stones or other objects on the ground or burrow into the earth. They are chiefly solitary, nocturnal insects; yet many can be seen in the fields in the daytime. They usually feed upon plants but are sometimes predacious. With most species the eggs are laid in the autumn, usually in the ground, and are hatched in the following summer. The greater number of the old crickets die on the approach of winter; but a few survive the cold season. In many of the species there are both short-winged and long-winged forms. This subfamily is represented in our fauna by several genera; but nearly all of our common species are included in the two genera Gryllus and Nemobius. 248 AN INTRODUCTION TO ENTOMOLOGY Gryllns assimilis liicttio- The larger field-crickets, Gryllus. — The members of this genus are dark-colored, thick-bodied insects of medium or large size. In these the hind tibiae are armed with strong fixed spines and the first segment of the hind tarsi is armed with two rows of teeth above. There are two auditory tympana in each fore tibia. The length of the body is rarely less than 14 mm. Many supposedly distinct species of Gryllus have been de- scribed as occurring in our fauna; biit now all of our native forms are believed to be merely varieties of one species, Gryllus assimilis, and the different varieties are distin- guished by subspecific names. Six of these varieties that occur in the East are described by Blatchley ('20). Two of these will serve to illustrate our native forms. Gryllus assimilis luctuosus. — This is one of our more common forms of the genus. It is distinguished by the great length of the ovipositor of the female, which is nearly or fully half as long again as the hind femora (Fig. 266) ; and by the fact that the head of the male is distinctly wider than the front of the pronotum. Gryllus assimilis pennsylvanicus . — In this variety the ovipositor is less than half as long again as the hind femora, and the head of the male is but little if any wider than the front of the pronotum (Fig. 267). In fresh specimens the color is not shining black, but with a very fine grayish pubes- cence. In addition to our native forms of Gryllus, there is an Old World species that has been introduced into this cormtry; this is the house-cricket, Gryllus domesticus. Refer- ences to the "cricket of the hearth" are common in English literature and refer to this species, which is now widely distributed in this country, though it is rarely abundant. It is pale yellowish brown or straw-colored, and slender in form (Fig. 268). The length of the body is 15-17 mm. Our native field-crickets sometimes enter our dwellings in the autumn; but the house-cricket can be easily distinguished from these. The smaller field-crickets, Nemohius. — To this genus belong the little field-crickets, which are the most abimdant of all of our crickets. In these the hind tibiae are furnished with long, mobile, hairy spines. Fig. 267. — Gryllus assim- ilis pennsylv ani- ens. (From Lugger.) ORTHOPTERA 249 and the first segment of the hind tarsi is unarmed above or with only- one row of teeth. There is only one tympanum in each fore tibia. The length of the body is less than 1 2 mm. There are many species and varieties of this genus in our fauna. The following enlarged figures of two of our species will serve to illustrate the form of these insects. (Fig. 269 and 270.) Fig. 268.— Gryllus do- mesticus. (FromLug- ger.) Fig. 269. — Nemo- bius fascial us. (From Lugger.) Fig. 270. — Nemo- bins palustris. (Pom Blatch- ley.) Subfamily MYRMECOPHILIN^ The Ant-loving Crickets The members of this subfamily are very small crickets, which live as guests in the nests of ants. The form of these crickets is very remarkable. The body is ovate, greatly convex above, and wing- less (Fig. 271); the hind femora are ovate and greatly enlarged, the cerci are long; and the ovi- positor is short and stout. Wheeler ('00) states that these crickets feed on an oily secretion covering the surface of the body of the ants; they also obtain this substance from the greasy walls of the ant-burrows. Apparently the ants derive no benefit from the presence of these Fig. 271. — Myrmecopldla pergandei. (From Lugger.) 250 AN INTRODUCTION TO ENTOMOLOGY guests, and destroy them when they can; but the crickets are very agile. These are the smallest of the true Orthoptera. This subfamily includes a single genus, Myrmecophila, of which five species have been described from the United States. Only one species has been found in the East; this is Myrmecophila pergdndei. In this species the length of the body is 3-5 mm. Subfamily MOGOPLISTIN^ The Wingless Bush-Crickets These crickets are found chiefly on bushes or among rubbish under bushes; some are found beneath debris in sandy places. They are small; those found in the United States measure from 5 mm. to 13 mm. in length of body. They are either wing- less or furnished in the male sex with short tegmina, in which the stridulating organs are well developed. The body is covered with translucent, easily abraded scales. Most of the species are tropical or subtropical in dis- tribution; our species are found chiefly in the South and Southwest; but the range of one of them extends north to Fig. 273 {From "Rehn and Long Island. Only four spe- Hebard.) ^-^g j^^ve been described from the East and one of these is restricted to Florida. A few others are known from the western part of our country. A monograph of the North American species was published by Rehn and Hebard ('12). Figure 272 represents the male of Cryptoptilum trigonipdlpuni, a wingless species found from Virginia southward; and Figure 273, the male of Holosphyrum boredle, found in the Southwest. Fig. 272. — Cryptopti- lum trigonipalpum. Holosphy- rum boreale. (From Rehn and He- bard.) Subfamily GRYLLOTALPIN^ The Mole-Crickets The mole-crickets differ greatly in appearance from the more typical crickets, the form of the body and of the fore legs being adapted to burrowing in the ground. The front tibiae, especially, are fitted for digging; they are greatly broadened and shaped some- ORTHOPTERA 251 Fig. 274.— Gryllotal- pa hexadactyla. what like a hand or a foot of a mole; they are terminated by strong, blade-like teeth, termed the dactyls (Fig. 274). Two of the tarsal segments are blade-like and so situated that they can be moved across the dactyls like the cutting blades of a mowing machine (Fig. 275). Sharpe ('95) states that this organ enables the mole-cricket to cut the small roots it meets in digging its burrows; but this is doubted by Morse ('20), who believes that the roots are cut by the powerful mandibles. The antennas of mole-crickets are much shorter than the body; the hind femora are but little enlarged, not well fitted for jumping; and the ovipositor is not visible externally. The name o£ the type genus, Gryllotdlpa, is from Gryllus, a cricket, and talpa, a mole. Two genera of mole-crickets are found in the United States: Gryllotalpa, in which the front tibiee are furnished with four dactyls; and Scap- tertscus, in which each fore tibia bears only two dactyls. Each of these genera is represented in our fauna by several species. Our best -known and most widely distributed species is Gryllotdlpa hexadactyla (Fig. 274). This species has been generally known in this country as Gryllotdlpa horedlis; but this name is now be- lieved to be a synonym. The range of this species extends from British America to the southern part of South America. The length of the body is 20-30 mm. The mole-crickets are not common insects in this country; but occasionally they are found in great numbers in a limited lo- cality. They make burrows in moist places from six to eight inches below the surface of the ground, and feed upon the tender roots of various plants, and also on other insects. The eggs are deposited in a neatly constructed subterranean chamber, about the size of a hen's egg. Subfamily TRIDACTYLIN^ The Pigmy Mole-Crickets The members of this subfamily resemble the mole-crickets in the form of the body and in their burrowing habits; but they are much Fig. 275. — Front leg of a mole-cricket; A, inner aspect; B, outer aspect; e, ear-slit. (From Sharp.) 252 AN INTRODUCTION TO ENTOMOLOGY smaller, the larger species measuring only lo mm. in length; and the hind femora are greatly enlarged, being strongly saltatorial (Fig. 276). The antennae are short and composed of only eleven segments. The fore wings are usually short and never extend to the end of the abdomen; they are homy, are almost veinless, and are not furnished with stridulating organs in the male. The hind wings are much longer, usually extending beyond the end of the abdomen. The fore tibiae lack auditory t^Tmpana. The fore and middletarsi, in our genera, are two-jointed; the hind tarsi are one-jointed or want- ing. The hind tibite are fumishd with movable plates, "natatory lamellae," near the distal end; these are ordinarily closely appressed to the tibia but can be spread out like a fan. It is probable that these plates are used to aid the insect in leaping from the ^ Tactylus api'ca- surface of water upon which they have jumped; /?.?. (From Lug- they may also serve a similar purpose on land, mak- ger.) ing a firm planting of the end of the leg upon the groiuid. The ovipositor is vestigial in our species; but Walker ('19) states that in the exotic genus Ripipteryx there is a well-developed ovipositor, which is remarkably similar to that of the short-horned grasshoppers. These insects apparently have two pairs of cerci ; this is due to the fact that in addition to the true cerci each of the two podical plates is greatly elongated and bears a terminal segment, which appears like a stylus or cercus. These insects burrow rapidly in sand and possess great powers of leaping. They live on and in the damp sand on the shores of ponds and streams. Their burrows extend onl}^ a short distance below the surface of the ground. Only two genera, each represented by a single species, have been found in America north of Mexico. Triddctyhis. — In this genus the hind tibiae are furnished with four pairs of long, slender plates, the "natatory lamellae;" and the hind tarsi are one-jointed. Our species is Triddctylus apicdlis (Fig. 276). Thejength of the body is 6-9.5 ™i^- Ellipes. — In this genus the hind tibis are furnished with a single pair of "natatory lamellae"; and the hind tarsi are wanting. Our species is Ellipes minuta. The length of the body is 4-5 mm. Walker ('19) as a result of his studies of the genitalia of Ripi- pteryx believes that the pigmy mole-crickets are more closely allied to the Locustidae than they are to the Gryllidae, and ranks them as constituting a distinct family, the Tridactylidae. Family LOCUSTID^* The Locusts or Short-horned Grasshoppers The family Locustidae includes the locusts or short-homed grass- *This family is termed the Acrididse by some writers, this name being based on the generic name Acrida of Linnaeus; other writers use the family name Aery- ORTHOPTERA 253 hoppers. These are common and well-lmown insects. They differ from most of the members of the two preceding famihes in having the antenna) much shorter than the body, and consisting of not more than twenty-tive segments. The ovipositor of the female is short and composed of separate plates; and the basal segment of the abdomen is furnished on each side with a t^nnpanum, the external parts of the organs of hearing (Fig. 277, /). It is to these insects that the term 'locust is properly applied; for the locusts of which we read in the Bible, and in other books published in the older countries, are members of this family. Unfortunately, in the United States the term locust has been applied to the Periodical Cicada, a member of the order Homoptera, described later. And, what is more unfortunate, the scientific name Locus- tidas has been applied by many writers to the long-horned grasshoppers. Locusts lay their eggs in oval masses and cover them with a tough substance. Some species lay their eggs in the groimd. The female makes a hole in the ground with her ovipositor, which is a good digging tool. Some species even make holes in fence-rails, logs, and stumps; then, after the eggs are laid the hole is covered up with a plug of gummy material. There is but one generation a year, and in most cases the winter is passed in the egg-state. This family is of great economic importance, as the members of it usually appear in great numbers in nearly every region where plants grow, and often do much damage. With many species of the Locustidse the males are furnished with stridulating organs. These have been described in Chapter II, page 82. There are very many species of locusts in the United States and Canada; these represent four of the subfamilies of the family Locus- tidas, which can be separated by the following table. A. Claws of the tarsi with a small pad (arolium) between them; pronotum ex- tending at most over the extreme base of the abdomen. B. Prosternum armed anteriorly with a distinct conical or cylindrical tubercle- p. 254 LOCUSTIN^ BB. Prosternum without a distinct tubercle; arolium usually small or rather small. C. Head rounded at the union of the vertex and front ; front perpendicular or nearly so. p. 257 CEdipodin.« CC. Vertex and front of head meeting at an acute angle; vertex extending horizontally; front strongly receding, p. 259 Trux.\lin.e AA. Claws of tarsi without an arolium between them; pronotum extending over the abdomen, p. 259 Acrydiin^ diidse, based on the generic name Acrydium of Fabricius; and still others use the family name Acridiidse, based on Acridium, an emended spelling of Acrydium. The oldest name given to this family is Acrydiana, appHed to it by Latreille in 1802; but the group of insects that Latreille used as the type of the family is the Locusta of Linnaeus (1758); for this reason the name given to the family by Latreille has been changed to Locustidae. See also the footnote on page 234. 254 AN INTRODUCTION TO ENTOMOLOGY Subfamily LOCUSTIN^ The Spur-throated Locusts The members of this subfamily are distinguished from other North American locusts by the presence of a tubercle on the pro- sternum. Here belong many of our more com- mon species; and among them are found the most injurious insects of the order Orthoptera. Among our best-known species are the following. The Rocky Mountain Fig. 277. — Side view of a female locust with the wings removed. locust or western grasshopper, Meldnoplus spretus. — The most terrible of insect scourges that this country has known have been the invasions Fig. 278. — Egg-laying of the Rocky Mountain Locust : a, a, a, female in different positions, ovipositing; b, egg-pod extracted from the ground with the end broken open; c, a few eggs lying loose on the ground; d, e, show the earth partially removed, to illustrate an egg-mass already in place, and one being placed; / sho\vs where such a mass has been covered up. (From Riley.) of this species. Large areas of country have been devastated, and the inhabitants reduced to a state of starvation. The cause of all this suffering is not a large insect. It is represented in natural size by Figure 278. It measures to the tip of its wing-covers 20-35 mm., and resembles very closely our common red-legged lo- cust, the most abundant of all our species. It can easily be distinguished from this species by the greater length of the wings, which extend about one-third of their length beyond the tip of the abdomen, and by the fact that the apex of the last abdominal segment in the males is distinctly notched. Fig. 279.- rubrum. -Melanopltts femur- ORTHOPTERA 255 fWr bivittatus. (From The permanent home or breeding grotinds of this species is in the high, drylands on the eastern slope of the Rocky Mountains, extend- ing from the southern limit of the true forests in British America south through Montana, Wyoming, the western part of the Dakotas, and the Parks of Colorado. There are also regions in which the species exists permanently west of the Rocky Mountains in Idaho and Utah. When the food of this insect becomes scarce in its mountain home, it migrates to lower and more fertile re- gions. Its long wings en- able it to travel great dis- tances; and thus the larger part of the region west of the Mississippi River is liable to be invaded by it. Fortunately, the species cannot long survive in the low, moist regions of the valleys. Although the hordes of locusts which reach these sections retain their vigor, and frequently consume every bit of green vegetation, the young, which hatch from the eggs that they lay, perish before reaching maturity. In this way the invaded region is freed from the pest until it is stocked again by another in- cursion. There is, however, a large sec- tion of country lying immediately east of the great area indicated above as the permanent home of this species, which it frequently invades and in which it can perpetuate itself for several years, but from which it in time disappears. This sub-permanent region, as it has been termed, extends east in British America so as to include nearly one-third of Mani- toba; and, in the United States, it em- braces nearly the whole of the Dakotas, the western half of Nebraska, and the northeast fourth of Colorado. The temporary region, or that only periodically visited and from which the Fig. 281. — Melanoplus bivitta- species gen erallv disappears within a vear, (From'uf eO "" ^''"^''^' extends east and south so as to include ugger.j more than half of Minnesota and Iowa, the western tier of counties of Missouri, the whole of Kansas and Oklahoma, and the greater part of Texas. The country lying east of the section thus indicated has never been invaded by this locust, and there is no probability that it will ever be reached by it. 256 AN INTRODUCTION TO ENTOMOLOGY Detailed directions for the control of this pest have been pub- lished in many State and Federal Government reports. Among these methods of control are the plowing of landjin which its eggs have been deposited, the use of poisoned bran- mash as a bait, and catching of the insects Fig. 282.- — Melanoplus differentialis. (From Riley.) \^y machines com- monly known as "hopper dozers." The red-legged locust, Melanoplus femur-ruhrum. — This is the Fig. 283. — Schistocerca americana. (From Riley.) most common short-homed grasshopper throughout the United States, except where Melanoplus spretus occurs. It ravages* our meadows and pastures more than all other species combined. It is found in most parts of North America. The female is represented, natural size, by Figure 279. Melanoplus hivittdtus . — This species is also found from the Atlantic to the Pacific. It is marked with a yellowish stripe, extending along each side from the upper angle of the eye to the tip of the front wing (Fig. 280). The length of the body varies from 23 mm. to 40 mm. This locust is often killed by a para- sitic fungus. Dead fungus-infected in- dividuals are frequently found clinging to weeds, up which they have climbed to die (Fig. 281). Melanoplus differentialis. — This spe- cies is slightly larger than the preceding; and it lacks the prominent yellow stripe (Fig. 282). Schistocerca americana. — This magnifi- cent species occurs in the Southern States pig_ 284^— Brachvstol7 magna ' ' - r . r ,1 ^ (From Riley.) ' and has been foimd as far north as Con- ORTHOPTERA 257 necticut and Iowa. It can be recognized by Figure 283, which rep- resents it natural size. This locust sometimes assumes the migratory habit, and is sometimes injurious to agriculture. The lubber grasshopper, Brachystola magna. — This is a large, clumsy species in which the wings are vestigial (Fig. 284) ; it is confined to the central portion of North America. Leptysma marginicolUs. — In most of the spur-throated locusts the face is nearly ver- tical; but in a few species it is very oblique. This species is a good illustration of this type (Fig. 285); it is fomid in the Southern States east of the Mississippi River. Fig. 285. — Leplysma marginicolUs. Subfamily (EDIPODIN^ The Band-winged Locusts In this subfamily the prosternimi is without a distinct tubercle; the head is rounded at the union of the vertex and the front; and the front is perpendicular or nearly so. In most of our species the hind wings are in part black, and a portion of them yellow or red; this gives them a banded appearance. There are many representatives of this subfamily in our fauna; the following are some of the more common ones. The clouded locust, Encoptolophus sordidus. — -This species (Fig. 286) is very common in the eastern United States during the autumn. It abounds in meadows and pas- tures, and attracts attention by the crackling soimd made by the males during flight. It is of a dirty brown color, mottled with spots of a darker shade. The length of the body of the male is i g- Fig. 2m.— Encoptolophus sordidus. 22 mm. ; of the female, 24-32 mm. The northern green-striped locust, Chortophaga viridifascidta. — This is a very common species in the United States and Canada east of the Rocky Mountains. There are two well-marked varieties. In one, the typical form, the head, thorax, and femora are green, and there is a broad green stripe on each fore wing, extend- 258 AN INTRODUCTION TO ENTOMOLOGY ing from the base to beyond the middle; this often includes two dusky spots on the edge. In the other vari- ety, the ground color is dusky brown. Intergrades occur, in which the head and thorax are of a reddish velvety brown. The length of the body is 17-32 mm. The Carolina locust, Dissostelra Carolina. — Not- withstanding its specific name, this species is com- mon throughout the United States and Canada. It is a large species; the length of the body of the males is 24-33 mm., of the females 33-40 mm. It abounds in highways and in barren r«- " o n- , • 1- fv T ^ places. It takes flight 7^g.287.-Drssosteuacarohna.{VromLngger.) ^^^^.^^^ ^^^ ^^^ ^|^^^ stridulate while in the air. The color of this insect varies greatly, simulating that of the soil upon which it is found. It is usually of a pale yel- lowish or reddish brown, with small dusky spots. The hind wings are black, with a broad yellow margin which is covered with dusky spots at the tip (Fig. 287). Boll's locust, Spharagemon bolli. — This species is widely distributed in the United States and southern Ontario east of the Rocky Mountains. The length of the body of the male is 20-28 mm., of the female 27-36 mm. The hind wings are pale greenish yellow at the base and are crossed by a dark band; the apical third is transparent smoky in color (Fig. 288). The coral-winged locust, Hipptscus apiculdtus. — This is one of the larger of our band-winged locusts (Fig. 289). The length of the body of the male is 25-30 mm., of the female 36-44 mm. The general color is ash-brown. The basal portion of the hind wings is bright coral-red, rarely yellow; this part is bordered without by a dark band. This species is widely distributed east of the Rockv Mountains. Fig. 288. — spharagemon bolli (From Lugger.) ORTHOPTERA 259 Fig. 289. — Hippiscus apicidatus. (From Lugger.) Subfamily TRUXALIN^ The Slant-faced Locusts In this subfamily, as in the preceding one, the prostemum is unarmed but the head is of a different form. In the Truxalinaj, the vertex and the front meet on an acute angle. In some species this angle is a sharp one, the shape of the head being similar to that of Leptysma (Fig. 285). In other species, however, the front is less receding ; this is the case in the fol- lowing species. The sprinkled locust, Chlo'ealtis conspersa. — This is a very abundant species in the northern United Fig. 290. — Chloealtis conspersa, male. (From Lugger.) States and Canada east of the Great Plains. It is brown, with the sides of the pronotum and the first two or three abdominal seg- ments shining black in the male; and with the body and tegmina of the female sprinkled or mottled with darker broAvn. The teg- mina and hind wings are a little shorter than the abdomen in the male (Fig. 290), shorter in the female (Fig. 291). The males measure 15- length; the females, 20-28 mm. Fig. 291. — Chloealtis conspersa, female. (From Lugger.) and mucli 20 mm. in Subfamily ACRYDIIN^ TJie Pigmy Locusts The Acry'diinse includes small locusts of very tmusual form. They differ so much from other locustids that some students of the 260 AN INTRODUCTION TO ENTOMOLOGY Fig. 292.— A pig- my locust.. Fig. 293. — Acrydium graiiulatum. ley, after Kirby.) (From Blatch- Orthoptera believe they constitute a separate family. The most striking character of the subfamily is the shape of the pronotum. This is prolong- ed backwards over the abdomen to or beyond its extremity (Fig. 292). The head is deeply set in the pronotum; and the prostemum is ex- panded into a broad border, which partly envelops the mouth-parts like a muffler. The antennae are very slender and short. The tegmina are vestigial, being in the form of small, rough scales; while the wings are usually well-developed. These locusts differ, also, from all others in having no arolium between the claws of the tarsi. The pigmy locusts are commonly foimd in low, wet places, and on the borders of streams. Their colors are usually dark, and are often pro- tective, closely resem- bling the soil upon which the insects occur. They are very active and pos- sess great leaping powers. Some of the species vary greatly in coloring; this has resulted often in a single species being described under two or more names. This is an exceedingly difficult group in which to determine the species. Figure 293 represents Acrydium granuldtum with its wings spread, and the pronota of two color varieties. Figure 294 represents Acrydium arenosum obscurum, greath^ enlarged, with its wings .. .. „......^ -^ closed. Family PHASMID^* The Walking-Sticks and the Leaf-Insects The Phasmid£e is of especial interest on ac- count of the remarkable mimetic forms of the insects comprising it. In those species that are foimd in the United States, except one in Florida, the body is linear (Fig. 295), wingless, and furnished with long legs and antennse. This peculiar form has suggested the name walking-sticks which is commonly applied *This family is separated from the Orthoptera by Handlirsch ('o6-'o8) and made to constitute a distinct order, the Phasmoidea. Fig. 294. — Acrydium arenosum obscurum. (From Hancock.) ORTHOPTERA 261 to these insects; they are also known as stick-insects. In some exotic species the body has the appearance of being covered with moss or with Hchens, which increases the resemblance to a stick or a piece of bark. While our species are all wingless, except Aplopus mayeri, found in southern Florida, many exotic species are furnished with wings; and with some of these the wings resemble leaves. Among the more remarkable of the leaf-insects, as they are known, are those of the genus Phyllimn (Fig. 296), the members of which occur in the tropical regions of the Old World. In the walking-sticks, the body is elongate and subcylindrical • the abdomen consists of ten segments, but the basal segment is small and usually coalesced with the metathorax and sometimes it is entirely invisible; the legs are all fitted for walking; the tarsi are five-jointed except in the genus Tiniema, where they are three- jointed; the cerci are without joints. These insects are strictly herbivorous; they are slow in their motions, and often remain quiet for a long time in one place. They evidently depend on their mimetic form for protection. In addition to this some species have the power of ejecting a stinking fluid, which is said to be very acrid ; this fluid comes from glands placed in the thorax. The eggs are scattered on the ground beneath the plants upon which the insects feed, the female, unlike most Orthoptera, making no provision for their safety. In our common northern species the eggs are dropped late in the simimer and do not hatch till the following spring, and they often remain till the second spring before they hatch. About 600 species of phasmids have been described; but they are largely restricted to the tropical and subtropical regions. Caudell ('03) in his monograph of the species of the United States enu- merates sixteen species that occur in our fauna; but these are foimd chiefly in the southern part of the coimtry. Our common northern walking-stick is Diapheromera femordta (Fig. 295). The range of this species extends into Canada. It is a quite common insect, and on sev- eral occasions has appeared in such great numbers as to be seriously destructive to the foliage of forest trees; but these outbreaks have been temporary Diapheromera fern- 262 AN INTRODUCTION TO ENTOMOLOGY Among the more striking in ap- pearance of the walking-sticks found in the South axeMegaphasmadentricus, our largest species, measuring from 125 to 150mm. in length, and Anisomorpha buprestoides, a yellowish bro^vn species, about half as long as the preceding, with conspicuous, broad, black stripes extending from the front of the head to the tip of the abdomen. The reproduction of lost legs occurs frequently in this family. Family MANTID^^ The Praying Mantes or Soothsayers The praying mantes are easily rec- Fig. 296.— Phyllium scythe. (From ognized by the unusual form of the Sharp, after Westwood.) prothoraxand of the first pair of legs (Fig. 297). The prothorax is elongate, sometimes nearly as long as the remainder of the body; and the front legs are large and fitted for seizing prey. The coxse of the front legs are very long, pre- senting the appearance of femora; and the femora and tibiae of these legs are armed with spines; the tibia of each leg can be folded back against the femur so that the spines of the two will securely hold any insect seized by the praying mantis. The second and third pairs of legs are simple and similar; the tarsi are five-jointed; and the cerci are jointed. With some species the wings resemble leaves of plants in fomi and coloring. This resemblance is protective, causing the insects to resemble twigs of the plants upon which they are. All of the species are carnivorous, feeding on other insects. They do not pursue their prey but wait patiently with the front legs raised like uplifted hands in prayer, until it comes within reach, when they seize it. This position, which they assume while waiting, gives them most of their popular names, of which there are many. The eggs of the Mantidae are encased in chambered oothecas, which are usually fastened to the stems or twigs of plants (Fig. 298). In the case of the species that occur in the North, there is only one generation in a year and the winter is passed in the egg-state. Most of the members of this family are tropical insects; a few species, probably less than twenty, live in the southern half of *This family is separated from the Orthoptera by Handlirsch ('o6-'o8) and made to constitute a distinct order, the Mantoidea. ORTHOPTERA 263 the United States; and one of our native species, Stagmomdntis Carolina (Fig. 297), is found as far north as Maryland and southern Indiana. Recently two exotic species have been introduced into the Northern States, probably by the importa- tion of o6theca3 on nursery stock, and have become established here. These are the Mantis religiosa of Europe, which was first observed in this comitry near Rochester, N. Y., in 1899, and Paratenodera sinensis of China and Japan, which was first ob- served here at Philadelphia about 1895. Family BLATTID^* The Cockroaches The cockroaches are such well-known insects that there is but little need for a detailed account of their characteristics. As already indicated in the table of families, the body is oval and depressed ; the head is nearly horizontal, and wholly or almost wholly withdrawn beneath the pronotiim; the head is bent so that the mouth-parts project caudad between the bases of the first pair of legs; the antennae are long and bristle-like ; and the pronotimi is shield-like. This family includes only the cockroaches ; but these Fig. 298.— Egg- insects are known in some localities as "black ^^^^^ °^. *^^"^' , ,1 ,, 1 , • • J.1 momantts car- beetles, and our most common species m the ^n^^^ (From northern cities bears the name of Croton-bug. Riley.) *This family is separated from the Orthoptera by Handlirsch ('o6-'o8) and made to constitute a distinct order, the Blattoidea. 264 .4iV INTRODUCTION TO ENTOMOLOGY In the Northern States our native species are usually found in the fields or forests under sticks, stones, or other rubbish. But certain imported species become pests in dwell- ^^^^> /'WSPW^ ings. In the warmer parts of the coimtry, how- ^*-2Si*si< ?*i44ai#tif^ ever, native and foreign species alike swarm in Fig. 299.- Ootheca of a buildings of all kinds, and are very common out cockroach. ^^ ^^^^^ Cockroaches are very general feeders; they destroy nearly all forms of provisions, and injure many other kinds of merchandise. They often deface the covers of cloth-bound books, eating blotches upon them for the sake of the sizing used in their manufacture ; and I have had them eat even the gum from postage stamps. They thrive best in warm, damp situations ; in dwellings they prefer the kitchens and laundries, and the neighborhood of steam and water pipes. They are chiefly nocturnal insects. They conceal themselves during the day beneath furniture or the floors, or within the spaces in the walls of a house; and at night they emerge in search of food. The de- pressed form of their bodies enables them to enter small cracks in the floors or walls. Not only are these insects very destructive to our possessions, but owing to their fetid odor merely the sight of them awakens disgust ; but it is due them to state that they are said to devour greedily bed- bugs. This will better enable us : to abide their presence in our staterooms on ocean voyages, or in our chambers when we are forced to stop at poor hotels. ^; The eggs of cockroaches are enclosed in purse-hke capsules (Fig. 299). These capsules, or ootheca?, vary in form in difl'erent genera, but are more or less bean-shaped. Within, the ootheca is divided into two parallel spaces, in each of which there is a row of separate chambers, each chamber enclosing an egg. The female often carries an ootheca protruding from the end of the abdomen for several days. It has been found that a single female may produce several oothecas. The n^^mphs resemble the adults except in size, and, in the case of winged species, in the degree of develop- ment of the wings. In adults also of some species the wings are reduced, atrophied, or absent; this condi- tion exists more frequently in females than in males (Fig. 300). As in most other insects, the homologies of the wing-veins can be most easily determined by a study of the tracheation of the wings of n\Tnphs; Figure 301 will serve to illustrate this. Experiments conducted by the Bureau of Ento- mology at Washington have shown that one -of the Fig. 300. — A most effective means of ridding premises of cockroaches wingless is dusting the places they frequent with commercial sodium fluorid. Several other substances are used for this purpose; ORTHOPTERA 265 among these are borax, pyrethrum, sulphur, and phosphorus paste. Cockroaches are chiefly inhabitants of warm countries; although nearly one thousand species have been described, few are found in the Fig. 301. — Fore wing of a nymph of a cockroach. temperate regions. Only forty-three species have been found in North America north of the Mexican boimdary, and ten of these are probably introduced species (Hebard '17). The cockroaches that are most often found in buildings are two introduced species, the Croton-bug and the Oriental cockroach, and two native species, the American cockroach and the common wood-cockroach. The adults Fig. 302. — The Croton-bug: a, first instar; b, second instar; c, third instar, d, fourth instar; e, adult; /, adult female with egg-case; g, egg-case, enlarged; h, adult with the wings spread. All natural size except g. (From Howard and Marlatt.) of these four species can be separated by the following table. For tables separating all North American species see Hebard ('17). A. With well-developed tegmina. B. Tegmina extending to or beyond the tip of the abdomen. C. Body about 12 mm. in length The Croton-bug CC. Body 16 mm. or more in length. 266 AN INTRODUCTION TO ENTOMOLOGY D. Margin of the pronotum light in color while the disk is dark. . . The commo?i wood-cockroach, male DD. Pronotum reddish-brown with two blotches of a lighter color. The A merican cockroach BB. Wings not extending to the tip of the abdomen. C. With a light band on each lateral border of the pronotum The common ■wood-cockroach, female CC. With no bands on the pronotum The Oriental cockroach, male AA. Tegmina represented by small ovate pads The Oriental cockroach, female The Croton-bug, Blattella germanica (Fig. 302), is the best-known of all of the cockroaches in our northern cities. It is easily recognized by its small size, about i?, ^—-^ *\ ^ — -^ 12 mm. in length, and ^ by its pale color with two dark, parallel bands on the prono- tum. Its popular name originated in New York City, and was suggested by. the fact that this pest is ^ \/ very abundant, in houses, about water pipes connected with the Croton Aqueduct. This is a species intro- duced from Europe; it has spread to nearly ^ ^^ ^ / oT 1 ^^^ parts of the world, living upon ships, and Fig. 303. — The oriental cockroach: a, female; b, spreading from them. male, ^, side view of female; rf, half-grown sped- -pj^e oriental COck- men. All natural size, (rrom Howard and Mar- , -oj^^, • ,-t latt.) roach, BLatta onentalis (Fig. 303), is also a cosmopolitan species ; its original habitat is supposed to have been in Asia; but it has been distributed by commerce throughout the world except in the colder regions. In this coimtry it is most abun- dant in the central latitudes of the United States ; it has been found in only a few places in Canada. It measures from 18 to 25 mm. in length. It is blackish brown in color. In the male the wings cover about two-thirds of the abdomen; while in the female they are small, ovate-lanceolate, lateral pads. The American cockroach, Periplaneta americdna (Fig. 304), is a native of tropical or subtropical America that has become distributed both in tropical and mild climates over the entire world. This is a large species measuring from 25 to 33 mm. in length. The common wood-cockroach, Parcobldtta pennsylvdnica, is a common species throughout the eastern half of the United States, ORTHOPTERA 267 and its range extends into southern Canada. It is a na- Fig. 304. — The American cockroach. (From Howard and Marlatt.) tive of our woods but is frequently attracted to lights in our houses. The two sexes differ so greatly in appear- ance that they were long believed to be distinct species. In both sexes the lateral margins of the prono- tum are light in color while the disk is dark. In the male the body measures from 15 to 25 mm. in length and the wings extend be- yond the tip of the ab- domen (Fig. 305). The female is smaller and the wings are much shorter than in the male (Fig. 306) Fig. 305. — The common wood-cockroach, male. (From Lugger.) Fig. 306. — The com- m o n wood-cock- roach , female. (From Blatchley.) ORTHOPTEROID INSECTS OF UNCERTAIN KINSHIP Under this head are placed two families of insects the zoological position of each of which has not been definitely determined. 268 AN INTRODUCTION TO ENTOMOLOGY Family GRYLLOBLATTID^ This family was recently established by Dr. E. M. Walker ('14) for the reception of the species described below, which, while showing striking afifinities to the Orthoptera, differs remarkably from all other known members of this order. Some writers who favor the breaking up of the order Orthoptera into several orders, regard this species as the type of a distinct order of insects, the Notoptera. Grylloblatta campodeiformis. — In this the only species of the family known, the body is elongate, slender, depressed, and thysanuriform Fig. 307. — Grylloblatta campodeifonnis. (xAfter Walker.) (Fig. 307). The legs are fitted for running, the tarsi are five-jointed and lack pulvilli. The cerci are long, about as long as the hind tibiae, slender, and eight-jointed. The ovipositor is exserted and resembles that of the Tettigoniidse. The eyes are small and the ocelli are absent. The adult male measures 16.5 mm. in length; the female, 30mm. As yet, this species has been fomid only in the vicinity of Banff, Alberta, and in Pliunas County, California. It is found under stones, at high altitudes, and runs like a centipede. ORTHOPTERA 269 Family HEMIMERID^ This family includes a single genus, Hemtmerus, of which two spe- cies have been found in equatorial West Africa. These are blind, wingless insects, of the form shown in Figure 30S. They are remarkable in that they exhibit an intra-uterine de- velopment. Hansen ('94), whose account is all the information we have on this subject, thinks that the young are connected with the walls of the maternal passages by means of a process from the neck of each ; about six yoimg were found at a time inside the mother, the largest one being next to the external opening. The species described by Hansen was found living on the body of a large rat; it runs rapidly among the hairs and apparently also springs. In an early accoimt of one of the species of Hemtmerus this insect was described erro- neously as possessing two lower lips, and for that reason was placed in a distinct order, the Diploglossata, which is no longer recognized. Although these are exotic insects, they are y ^ „ • mentioned here on account of their exceptional jia^i se n i '^""(From manner of development and mode of life. Hansen.) CHAPTER IX ORDER ZORAPTERA* So little is known regarding the insects of this order, only a single genus having been found, that it would be premature at this time to define definitely the characters of the order. This is well shown by the fact that recent discoveries have greatly modified our views regarding the ordinal characters of these insects. This order was established by Silvestri in 1 9 1 3 . At that time only wingless individuals were known; and it was supposed by this author that the wingless condition was a distinctive ordinal character; he, therefore, proposed the name Zoraptera for the order. But recently Caudell ('20) has described winged individuals of each of the two species found in this coimtry. The name Zoraptera, however, must be retained even though it is inappropriate. Family ZOROTYPID^ The single known genus, Zorotypus, is the type of this family and until other genera are found the characters of this genus must be taken as those of this family and of the order Zoraptera as well. At the time this is written, only six species of Zorotypus have been described. These have been found in widely separated parts of the world, one each in Africa, Ceylon, Java, and Costa Rica, and two in Florida. One of the species from Florida has been found also in Texas. The known species are all minute, the largest measuring only 2.5 mm. in length. In our two species both wingless and winged adults have been found ; and it is probable that these two forms exist in the other species. The winged adults that have been observed are all females; but it would not be wise to conclude that only this sex is winged. Of the wingless form both male and female have been found. As these are social insects, living in colonies of various sizes, it may be that the wingless and the winged adults represent distinct castes, analogous to the castes of termites. Another similarity to termites is that the winged individuals shed their wings as do the winged termites. The wingless adults (Figure 309, 4) resemble in general appear- ance small worker termites ; but they have longer legs and are more active. The legs are formed for running; the tarsi are two-jointed and each bears two claws. The mandibles are strong. The antennae are moniliform and nine-jointed. Compound eyes and ocelli are wanting. The cerci are short, fleshy, and unsegmented. The winged adult female (Fig. 309, 1) has large compound eyes, three ocelli, nine-jointed antennEe, and two pairs of wings. The vena- *Zoraptera: zoros (x£op6i), pure; apterous (fiTrrepos) , without wings. (270) ZORAPTERA 271 tion of the wings is represented in the figure. As the tracheation of the wings of nymphs has not been studied, I will not venture to make any suggestions regarding the homologies of the wing-veins. Fig- 309- — Zorotypus hiihbardi: i, winged adult female; 2, adult female that had shed her wings; 3, nymph of winged form; 4, wingless adult female. 5, An- tenna of adult wingless Zorotypus snyderi. (From Caudell, in Proc. Ent. Soc. Wash., Vol. 22.) 272 AN INTRODUCTION TO ENTOMOLOGY Figure 309, 2, represents an adult female that had shed her wings and Figure 309, 3, a nymph with well-developed wing-pads. The two known American species are Zorotypus huhhardi and Zoroiypus snyderi. Detailed descriptions of each of the forms of each of these species are given by Caudell ('20), and the external anatomy of Zorotypus huhbardi is described by Crampton ('20 a), who also discusses the relationships of the order Zoraptera to the other orders of insects. The colonies of Zorotypus are found under the bark of logs and stumps and frequently near the galleries of termites. For this reason they were formerly believed to live as inquilines in the nests of termites; but recent observations do not support this view. CHAPTER X ORDER ISOPTERA* The Termites or White- Ants The members of this order are social insects, living in colonies like ants. Each species consists of several distinct castes, the number of which differs in different species. Each caste includes both male and female individuals. In most species there are four castes as follows: first, the first reproductive caste, in which the wings become fully de- veloped and are used for a swarming flight and then shed; second, the second reproductive caste, in which the wing-buds remain short; the members of this caste are neoteinic, becoming sexually mature while retaining the nymphal form of the body; third, the worker caste; and fourth, the soldier caste. Except in a single Australian gemis, the two pairs of wings are similar in form and in the more general features of their venation; they are long and narrow, and are laid fiat on the back when not in use. The abdomen is broadly joined to the thorax; the mouth-parts are formed for chewing; the metamorphosis is gradual. The termites or white-ants are chiefly tropical insects; but some species live in the temperate zones. These insects can be easily recognized by the fact that they live in ant-like colonies, by the pale color of the greater nimiber of individuals of which a colony is com- posed, and by the form of the abdomen, which is broadly joined to the thorax instead of being pedunculate as in ants. The termites are commonly called white-ants on account of their color and of a resemblance in form and habits to the true ants. These resemblances, however, are only very general. In structure the termites and ants are widely separated. In habits there is little more in common than that both are social, and the fact that in each the function of reproduction is restricted to a few individuals, while the greater nimiber differ in form from the sexually perfect males and females, and are especially adapted to the performance of the labors and defense of the colony. The cuticula of termites is delicate even in adults; the mature winged forms can withstand exposure to dry air for a limited period, as is necessary during their swarming flight; but other members of a colony quickly become shriveled and die if exposed. It is for this reason that they build tubes constructed of earth and excrement for passage-ways, and only rarely appear in the open, and then m.erely for a brief period. The mouth-parts, which are fitted for chewing, are quite general- ized, resembling somewhat those of the Orthoptera; but in the case of the soldier caste the mandibles are very large and vary greatly in form in the different species. *Is6ptera: isos (f™™^ exudes, which is used as a means of defense and also, I^^g it is said, as a cement in constructing the nest and /^^ the earth-like tubes through which the insects travel (Fig. 314). Such individuals are known as nasuti. In this caste the mandibles are small, differing greatly from those of soldiers. The nasuti are usually smaller than the workers and are pigmented. They have been commonly described as a special type of soldiers ; Fig. 314-— A nas- but it seems better, in order to avoid confusion, to utus. (After regard them as constituting a distinct caste. Among ^^P'^ the North American termites, nasuti are found in the genera Constrictotermes and Nasutitermes, which lack the true soldier caste. In some tropical termites two types of nasuti, large and small, have been foimd. As to the origin of the different castes of termites there has been much discussion and two radically different views are held. The first view was probably suggested by the well-known fact that, in the case of the honey-bee, queens can be developed from eggs or young larvcB that ordinarily would produce workers. According to this view the newly hatched termites are not differentiated into castes; but 278 AN INTRODUCTION TO ENTOMOLOGY this differentiation takes place later as the result of extrinsic factors, such as food, the presence or absence of parasitic protozoa in the alimentary tract, and the care received frorn the older workers. According to the second view the young of the different castes are different and the castes are therefore "predetermined in the egg or embryo by intrinsic factors." Some comparatively recent investigations support the second view. It was found by Thompson ('17 and '19) that although the newly hatched n\Tiiphs are externally all alike, they are differentiated by internal structural characters into two clearly defined types: first, the reproductive or fertile forms, with large brain and large sex organs, and usually a dense opaque body; and second, the worker-soldier or sterile forms, with small brain and small sex organs, and usually a clear transparent body. It was also found by Thompson that later, when the nymphs had become from 2 mm. to 3 mm. in length, they were differentiated into "small-headed" but large-brained reproductive forms, and "large- headed" but small-brained worker-soldier forms. In the case of worker-soldier n\Tiiphs of Eutermes pHifrcus, a Jamaican species, which were 2 mm. long and externally all alike, they were distinguishable, after staining, into worker nymphs with a small vestigial frontal gland, and soldier n\Tnphs with a large frontal gland. In a study of Reticulitermes (Leucotermes)flavipes , Thompson ('17) found that the n\Tnphs of the reproductive forms that are only 1.3 to 1.4 mm. in length are differentiated into two groups by differences in the size of the brain and sex organs. These are early instars of the first reproductive caste and the second reproductive caste, respec- tively. The early instars of the third reproductive caste have not been distinguished from the nymphs of workers. There is space here for but little regarding the nest-building habits of these wonderful insects. In the tropics certain species build nests of great size. Some of these are moimds ten or twelve feet or more in height. Other species build large globular masses upon the trunks or branches of trees or upon other objects. Figure 315 represents such a nest which I observed on a fence in Cuba. Owing to the delicacy of their cuticula and the consequent danger of becoming shriveled if exposed, the termites build covered ways from their nests to such places as they wish to visit, if they are in exposed situations like that shown in the figure. These exposed nests are composed chiefly of the excreted undigested wood upon which the insects have fed. This is molded into the desired form and on drying it becomes soHd. The termites that live in the United States do not build exposed nests; and, as the queens do not lose the power of movement, there is no permanent royal cell, centrally located, in which the king and queen are imprisoned, as is the case with many tropical species. Some of our species mine in the earth, their nests being made imder stones or other objects lying on the ground; some burrow only in I SOFTER A 279 wood; and others that burrow in the ground extend their nests into wood. To the last category belong the species of the genus Reticulitermes , which includes all of the teiTtiites found north of Georgia and east of Nevada. These often infest the foimda- tion timbers of buildings, floor- ing in basements, and other woodwork of buildings and furniture. These pests will feed upon almost any organic matter; books are sometimes completely ruined by them. In infesting anything com- posed of wood, the}^ eat out the interior, leaving a thin film on the outside. Thus a table may appear to be sound, but crumble to pieces beneath a slight weight, entrance having been made through the floor of the house and the legs of the table. While termites infest chiefly dead wood, there are many records of their infesting living plants. I found them common throughout Florida, infesting orange-trees, guava- bushes, pampas-grass, and su- gar-cane. When termites in- fest living plants, they attack that part which is at or just below the surface of the ground. In the case of pampas-grass the base of the stalk is hollowed; with woody plants, as orange-trees and guava bushes, the bark at the base of the tree is eaten and frequently the tree is completely girdled; with sugar-cane the most serious injury is the destniction of the seed-cane. Certain African termites have been found to cultivate fungus- gardens in their nests, similar to those of the well-known leaf-cutting ants. The care of the young and of the queens by the workers in colonies of social insects has attracted the attention and admiration of observ- ers in all times. This care has been quite generally attributed to something resembling the parental feelings of our own species. But the observations of several naturalists in recent years have shown that with the social insects the devotion of the workers to the brood and to the queen is far from being purely altruistic; that it is largely or entirely due to a desire to feed upon certain exudates produced by Fig. 315. — Nest of a Cuban termite. 280 ^A^ INTRODUCTION TO ENTOMOLOGY the individuals that are fed; the feeding of the youiig and the queens being accompanied by a licking of their bodies by the nurses. Among the more important papers on this subject are one on termites by Holmgren ('09) and one on ants by Wheeler ('18). Holmgren shows that all of the castes of termites, but especially the queens, have extensive exudate tissues, consisting of the peripheral layers of the abdominal fat-body, the products of which pass through pores in the cuticula, where they are licked up by other members of the colony; and that the intensity of the licking and feeding of the individuals of a termite colony is directly proportional to the amount of their exudate tissue. Wheeler in his paper on ants shows that the larvae of certain species of ants possess remarkable exudate organs, and proposes for this exchange of nourishment the term trophallaxis* It is believed by the writers quoted above and by others that this exchange of nourishment between those individuals that feed and those that are fed was the source of the colonial habit in social insects. Roubaud ('16) in a paper on the wasps of Africa points out the probable steps by which the social habit was developed in wasps. Beginning with certain solitary etunenids that feed their larvae from day to day and while doing this feed upon saliva exuded by the lar^^se, he suggests that there naturally follows a tendency to increase the number of larvae to be reared simultaneously in order at the same time to satisfy the urgency of oviposition and to profit by the greater abundance of the secretion of the larvae. Now that this explanation of the origin of the social habit has been suggested, it, doubtless, will be much discussed. The student is urged, therefore, to consult the current literature for opinions regard- ing it. The most extended account of the termites of this country is the recently published paper by Nathan Banks and Thomas E. Snyder ('20). In the first part of this paper, Mr. Banks gives a revision of the nearctic termites, in which all of our known species are described, seventeen of them for the first time. This brings the total number of our known species up to thirty-six, representing ten genera. In the second part of this paper, Mr. Snyder brings together the known data regarding the habits and distribution of the termites of the United States; much of which data is based on his personal observations. Many species of insects live in the nests of termites. The relations of the termitophiles, of which several hundred species have been described, to their hosts vary greatly; some are predatory, some are parasites, and others are guests. Among the guests some are indiffer- ently tolerated, while others are true guests which produce exudates that are eagerly devoured by their hosts and in return either receive regurgitated food or manage to prey on the defenseless brood. Among the termitophiles are some that are very remarkable in form, having the abdomen excessively enlarged and being furnished with large exudate organs. *Trophallaxis : trophe (rpo^Tjj, nourishment; allattem {aWdrreiv), to exchange. CHAPTER XI Order NEUROPTERA* The Horned Corydalus, the Lacewing-FUes, the Ant-Lions, and others The members of this order have four wings; these are membranous and are usually furnished with many veins and cross-veins. In most members of the order, the wings have been specialized by the addition in the preanal area of many supernumerary veins of the accessory type. The mouth-parts are formed for chewing. The tarsi are five-jointed. The cerci are absent. The metamorphosis is complete. The order Neuroptera as now restricted differs greatly in extent from the Neuroptera of the early entomologists. Formerly there were included in this order many insects that are no longer believed to be closely related. This has resulted in the establishment of several dis- tinct orders for the insects that have been removed from the old order Neiiroptera. This fact should be kept in mind when consulting the older text-books. The wings of the Neuroptera are membranous and usually fur- nished with many wing-veins. The two pairs of wings are similar in texture and usually in outline ; in some the fore wings are slightly larger than the hind wings, in others the two pairs of wings are of the same size. The anal area is small in both fore and hind wings ; it is rarely folded (Sialidcc), and then only slightly so. A distinct anal furrow is rarely developed. Definitive accessory veins are usually present, and, as a rule, there are many marginal accessory veins. Intercalary veins are never developed. When at rest, with few ex- ceptions, the wings are folded roof-like over the abdomen. In some cases organs for uniting the fore and hind wings are present. Correlated with the extensive development of accessory veins in the Neuroptera, there has resulted in nearly all of the families of this order the production of a pectinately branched radial sector; that is, this vein is so modified that it consists of a supporting stem upon which are borne a greater or less number of parallel branches. This is shown in most of the figures of wings illustrating this chapter, and is a distinctive characteristic of this order; in no one of the other orders of living insects in which accessory veins occur is a well- developed pectinately branched radial sector found. Such a radial sector existed, however, in many of the Paleozoic insects. In certain genera of the Neuroptera a dichotomously branched radial sector has been retained. In many Neuroptera one or more series of cross-veins extend across the wing and form with sections of the longitudinal veins that *Neur6ptera: neuron (vevpov), a nerve; pteron (irrepSv), a wing. (281) 282 AN INTRODUCTION TO ENTOMOLOGY they connect a very regular zigzag line ; such cross-veins are termed gradate veins. Examples of series of gradate veins are well shown in the wings of the Hemerobiidae and in those of the allied families. The mouth-parts are formed for chewing. In several families the larvae suck the blood of their pre}^ by means of their peculiarly modified man- dibles and maxillae. These are very long and those of each side form an organ for piercing and sucking. The mouth-parts of the larva of an ant-lion will serve to illustrate this type of mouth-parts (Fig. 316). In this insect the mandibles (md) are very long, curved at the distal end, fitted for grasping and piercing the body of the prey, and armed with strong spines and setse. On the ventral aspect of each mandible there is a furrow extending the entire length of the mandible; and over this furrow the long and slender maxilla (mx) fits. On the dorsal aspect of the maxilla there is also a furrow. These two furrows form a tube which extends from the tip of the combined mandible and maxilla to the base of this organ where it communicates with the mouth cavity. Through this tube the blood of the prey is conveyed to the mouth. On the middle line of the body, between the mentum (m) and the front margin of the dorsal wall of the head (/), there is a tightly closed slit which is the mouth ; this, however, is not functional, the food being received into lateral expansions of the mouth-cavity at the base of the mandibles and maxillee. For a more detailed account of the struc- ture of the mouth-parts of an ant-lion, see Lozinski (08). The metamorphosis is complete. The larvae that are known are predacious or parasitic and in most cases are campodeif orm ; a few of them are aquatic, Sialidae, Sisyrids, and certain exotic forms, but most of them are terrestrial ; some when full-grown enter the ground and make earthen cells in which they transform, but most of them spin cocoons. The silk of which these cocoons are made, in the case of those in which the silk-organs have been described, is secreted by modified Malpighian vessels and is spun from the anus. The silk-organs of Sisyra will serve as an example of neurojoterous silk-organs ; these were described by Miss Anthony ('02) . Figure 317 is a diagram of a sagittal section of a larva through the median plane. In this larva the posterior fourth of the mid-intestine is merely a Fig. 316. — Head and mouth- parts of a larva of an ant- lion, ventral aspect: c, car- do of the maxilla; e, eye;/, front margin of the dorsal wall of the head, labrum (?); m, mentum; wJ, man- dible, mx, maxilla; p, la- bial palpus; s, stipes of the maxilla. NEUROPTERA 283 solid cord of atrophied cells; the passage from the mid-intestine to the hind -intestine is thus closed. The atrophied part of the mid- intestine ends in the walls of a dilation, the silk-receptacle {sr). Into this receptacle empty the five Malpighian tubes, three of which are attached by both ends and two of which extend posteriorly and end free in the body cavity ; all are modified in their middle portions for the secretion of silk; here the cells are much larger and more irregular in shape than the ordinary Malpighian tubule cells, and show singular, branched nuclei like those characteristic of silk-gland- Fig. 317. — Sagittal section of a larva of Sisyra: a, b-h', c-c'. three silk-glands attached at both ends; d, e, two silk-glands attached at one end; sr, silk- receptacle; sp, spinneret; /, fat-bodies; hr, brain; g, subcesophageal ganglion; r, band of regenerative cells of the stomach; p, point of junction of sucking tubes, s, sucking pharynx; m, muscle attachment of pharynx; o, oesophagus. (From Anthony.) cells of caterpillars and other insects. That part of the hind-intestine extending back from the silk-receptacle is a slender tube for the greater part of its length ; but in the last three abdominal segments it is enlarged, forming a reservoir for accumulated silk {sp), which is spim from the anus when needed for making the cocoon. The pupae of Neuroptera are exarate, that is, their legs and wings are free. In some cases {Chrysopa, Hemerobius, and Mantispa) the pupa crawls about for a time after leaving its cocoon and before changing to the adult. The known Neuroptera of the world represent twenty families; the wings of one or more members of each of these families have been figured by the writer in his "The Wings of Insects." Thirteen of these families are represented in North America; these can be sepa- rated by the following table. TABLE OF THE FAMILIES OF NORTH AMERICAN NEUROPTERA A. Prothorax as long as or longer than the mesothorax and metathorax com- bined. B. Fore legs greatly enlarged and fitted for grasping, p. 289. Mantispid^ BB. Fore legs not enlarged and not fitted for grasping, p. 289. Raphidiid^ AA. Prothorax not as long as the mesothorax and metathorax combined. B. Hind wings broad at base and with the anal area folded like a fan when not in use. p. 284 : Sialid^ BB.Hind wings narrow at base and not/olded like a fan when closed. C. Wings with very few veins and covered with whitiish powder, p. 307. Coniopoterygid^ CC. Wings with numerous veins and not covered with powder. D. Antennae gradually enlarged towards the end or filiform with a terminal knob. 284 AN INTRODUCTION TO ENTOMOLOGY E. Antennae short; wings with an elongate cell behind the point of fusion of veins Sc and Ri. p. 303 Myrmeleonid^ EE. Antennas long; wings without an elongate cell behind the point of fusion of veins Sc and Ri. p. 305 Ascalaphid^ DD. Antennas not enlarged towards the end. E. Male with pectinate antennae; female with an exserted ovipositor, p. 297 Dilarid^e EE. Antenn£E not pectinate in either sex; female without ex- serted ovipositor. F. Radius of the fore wings with apparently two or more sectors. G. Radius of the fore wings with apparently two sectors, one of which is vein R2 +3 and the other veinR4+5. p. 293 SVMPHEROBIID.t GG. Radius of the fore wings with three or more sectors. Veins R4 and Rs arise separately from vein Ri; one or more definitive accessory branches of the radius of the fore wings present, p. 294 Hemerobiid.^ FF. Radius of the fore wings with a single sector. G. Radial sector of the fore wings without definitive accessory veins although marginal accessory veins are present, p. 291 SiSYRiD.t GG. Radial sector of fore wings with definitive ac- cessory veins. H. Transverse veins between the costa and sub- costa simple, p. 299 CHRVSOFiDiE HH. JMany of the transverse veins between the costa and subcosta forked. I. Humeral cross- vein recurved and branch- ed; first radio-medial cross- vein of the hind wings longitudinal and sigmoid. p. 298 POLYSTCECHOTID^ II. Humeral cross- vein not recurved; first radio-medial cross-vein of the hind wings transverse, p. 298 Berothid^ Family vSIALID^* The Sialids The members of the Sialidse differ greatly in size and appearance ; but they agree in having the hind wings broad at the base with the anal area folded like a fan when not in use. In this respect the}' diifer from all other Neuroptera. The type of the wing-venation of the sialids differs greatly in the two subfamilies into which the family is divided, as described below. The larv« are aquatic, predacious, campodeiform, and possess paired, lateral filaments on most or on all of the abdominal segments. They leave the water when full-grown and transform in earthen cells on the banks of the streams or lakes in which they lived as larvee. The eggs are deposited in clusters on any convenient support near the water, in such situations that the yoimg \a.Tx^ can easily find *This family is separated from the Neuroptera by Handlirsch ('o6-'o8) as a distinct order, the Megaloptera. H. W. Van der Weele Cio) also separates it from the Neuroptera, but he associates with it the family Raphidiidae in his order Alegaloptera. NEUROPTERA 285 access to the water. The adults fly but little; they are most often found resting on some support near the water, with the wings folded over the abdomen. The SialidiE of the world have been monographed by H. W. Van der Weele ('lo). The family Sialidaj is divided into two subfamilies; these can be separated as follows : A. Ocelli wanting; fourth tarsal segment prominently bilobed; radial sector not pectinatel}^ branched. Insects rather small, having an expanse of wings of about 25 mm. p. 285 Sialin/e AA. With three ocelli; fourth tarsal segment simple, not bilobed; radial sector pectinately branched. Insects large or moderately large, p. 286 CORYDALIN^ Subfamily STALING The Alder-Flies The alder-flies are so-called because the adults are commonly foiuid on alders on the banks of streams; this name was given to them by English anglers. The subfamily Sialina} includes only two genera, both of which are represented in this cotintry, each by a single species. These genera are distinguished as follows : A. Costal area of the fore wings greatly expanded before the middle (Fig.318). SlALIS AA. Costal area of the fore wings sHghtly expanded before the middle Protosialis A', Fig. 318. — Wings of Sialis infumata. 286 AN INTRODUCTION TO ENTOMOLOGY The smoky alder-fly, Stalis in f urn at a. —This is a small insect hav- ing a wing-expanse of about 25 mm. ; the males are sometimes smaller than this, and the females slightly larger. It is dusky browTiish in color. It can be easily recognized by the form and venation of its wings (Fig. 318). The costal area of the fore wings is greatly expanded before the middle, and most of the wing-veins are stout. A striking feature of these wings, one that is characteristic of the subfamily Sialinffi, is that the radial sector is nearly typical in form; the only modification being the development of one or more marginal accessory veins upon it. These accessory veins, however, are in a quite different position from that occupied by the accessory veins borne by the radial sector in the Corydalinae, where a pectinately branched radial sector has been developed. The larva (Fig. 319) is furnished with the paired lateral filaments characteristic of the larvag of the vSialidfc on the first seven abdominal segments. These filaments are more or less distinctly five-segmented. The last abdominal segment is prolonged into a taper- ing lash-like filament. The larvae are foimd in swiftly flowing streams adhering to the lower side of stones in the bed of the streams and in trashy places filled with aquatic plants in the borders of streams and ponds; they are very active. The larvae transform in earthen cells at some little distance from the water. Two or three weeks after the making of the pupal cell the adult fly emerges. The eggs are laid in patches, each consisting of a single layer of eggs. The females frequently add their eggs to patches of eggs that have been laid by other females. The eggs when first laid are lighter in color than later. Several specific names have been given to what are now believed to be merely varieties of this species. Protosialts americdna.- — In this species the costal area of the fore wings is only slightly expanded before the middle; and the wing- veins are not as stout as in Sialis. The early stages have not been described. Fig. 319. — Larva of Sialis infu- mata. (After Needham.) Subfamily CORYDALIN^ Corydalus and the Fish-Flies The subfamily Corydalinae is represented in this country by the well-known horned corydalus and several smaller species, commonly known as the fish-flies. In these insects there are three ocelli; the fourth tarsal segment is not bilobed; and the radial sector is pec- tinately branched (Fig. 320). The larvae are distinguished by the NEUROPTERA 287 presence of a pair of anal prolegs, each of which bears a pair of hooks. Six species are found in the United States and Canada; these repre- sent four genera, which can be separated as follows. A. Latero-caudal angles of the head with a sharp tooth. Large insects, p. 287 CORYDALUS AA. Latero-caudal angles of the head unarmed. Insects moderately large; the fish-flies. B. Wings somewhat ashj' in color with more or less dusky markings. C. Veins of fore wings marked with dark and light, uniformly alternate. p. 288 Chauliodes CC. Veins of fore wings uniform in color except where dusky markings cross them. p. 288 Neohermes BB. Wings black or brown with white markings, p. 288 Nigronia Corydahts. — The only member of this genus in our fauna is Corydalus cornutus. This is a magnificent insect, which has a wing- expanse of from 100 to 130 mm. Figure 321 represents the male, 3 are even more strange in appear- ance than are those of the preceding family. Here, as in that family, *This family is separated from the Neuroptera by Handlirsch ('o6-'o8) and made to constitute a separate order, the Raphidioidea. 290 AN INTRODUCTION TO ENTOMOLOGY the prothorax is greatly elongated ; but the members of this family can be easily recognized by their re- markable fore legs, which are great- ly enlarged and resemble those of the praying mantes in form (Fig. 325). These legs are fitted for seiz- ing prey; and, in order that they may reach farther forward, they are joined to the front end of the long prothorax. In the adult stage, these insects are predacious; while the larvce, so far as is known, are parasitic. Brauer ('69) described the trans- formations of Mantis pa styriaca, a European species. This insect undergoes a hypermetamorphosis. It was accidentally discovered that the larvae were parasitic in the egg-sacs of spiders of the genus Lycosa. These are the large black Fig. 325. — Mantispa. In the speci- men figured the fore legs were twisted somewhat in order to show the form of the parts. Fig. 326. — Hypermetamorphosis of ikfawrt'ipa. (From Henneguy, after Brauer.) spiders which are common tmder stones, and which carry their egg-sacs with them. Brauer obtained eggs from a female Mantispa kept in confinement. These eggs were rose-red in color, and fastened upon stalks, like the eggs of Chrysopa. The eggs were laid in July; and the larvae emerged 2 1 days later. The young larvffi are campodeiform (Fig. 326, A); they are very agile creatures, with a long, slender body, well-developed legs, and long, slender antennae. They pass the winter without food. In the spring they find their way into the egg- sacs of the above-named spiders. Here they feed upon the yoimg spiders; and the body becomes proportionately thicker. Later the larva molts and undergoes a remarkable change in form, becom- ing what is known as the second larva; in this stage the larva is NEUROPTERA 291 scarabeiform (Fig. 326, B); the legs are much reduced in size; the antennae are short ; and the head is very small. When fully grown this larva measures from 7 to 10 mm. in length. It then spins a cocoon, and changes to a pupa within the skin of the larva. Later the larval skin is cast; and, finally, after being in the cocoon about a month, the pupa becomes active, pierces the cocoon and the egg-sac, and crawls about for a time (Fig. 326, C) ; later it changes to the adult form (Fig. 326, D). The life-history of Symphasis varia, a Brazilian species, is partly known. The larvas of this species live parasitically in the nests o'f wasps; when full-grown each larva spins a cocoon "in one of the cells of the nest. Only a few representatives of this family occur in the United vStates, and all are rare insects. Family SISYRID^ The Spongilla-Flies The Sisyridse in- clude a very limited number of small, smoky brown insects, of the form shoA\Ti in Figure 327. They are called Spongilla-flies because the larvas live ^. as parasites in fresh- ^InihonT.j""'''' ''"'' ^"""^ enlarged. (From water sponges, the typical genus of which is Spongilla. Two interesting features of these insects are the comparative simplicity of the wing-venation of the adults, and the anomalous habits of the larvas. The more striking characteristics of the wings (Fig. 3 28) are the following : The costal area of the fore wings is not greatly broadened; the himieral vein is not recurrent and is not branched. Veins vSc and Ri coalesce near the apex of the wing. The radial sector is pectinately branched; but no definitive accessory veins have been developed; this is the simplest form of pectinately branched radial sector foimd in the fore wings in this order. Marginal accessory veins are present. The larvas are aquatic and live in fresh-water sponges, upon which they feed. The life-history of a representative of each of the two genera, Sisyra and Climacia, which constitute this family, was worked out by Professor Needham ('01); and the anatom}^ and transformations of a species of Sisyra were carefully studied by Miss Anthony ('02). The following notes are based on the accounts published by these authors. Sisyra umbrdta. — The form of the adult is shown in Figure 327; its color is nearly uniform blackish brown. The legs and the apex of the abdomen are dirty 3'ellowish. The length of the male to the tips of the wings is 6 mm ; that of the female, 8 mm. 292 AN INTRODUCTION TO ENTOMOLOGY The larva (Fig. 329) is campodeiform. Its mouth-parts are formed for sucking as in the larvce of ant-lions (see page 282); they 3^^ 2d A J^^^ ^\ III / r-7 Fig. 328. — Wings of Sisyra flaviconiis. are very long; and two sucking organs, each formed of the mandible and maxilla of one side, are closely parallel for the greater part of their length. Each of the first seven abdominal segments bears on the ventral side a pair of jointed filaments which are believed to be tracheal gills. When full-grown, the larva leaves the water and spins over itself, on some object near the water, a hemi- spheric cover of close- ly woven silk, at- tached by its edges to the supporting sur- face, and a complete inner cocoon of con- siderably smaller size, likewise closely woven. The silk-organs of the larva are describ- t:,. t f c- ed on pages 282-3. Fig. 329. — Larva of 5^5 V- ^j" ^ . ,. ^^ rr^,. ra umbrata. (After An- Climana dtctyona— This species resem- thony.) bles the preceding in size and is quite similar Fig. 330. — Cocoon and cocoon-cover of Cli- macia. NEUROPTERA 293 in coloration ; the two can be distinguished by the form of the labia (Fig. 33 1). In the larva of this species the setse on the dorsum of the tho- rax are situated on tubercles; they are sessile in the larva of 5z5;vm. The habits of the larva are similar to those of Sisyra. Cliniacia dictyona; h, Sisyra umbrata. (Af t( Fig. 331. — Labia of Spongilla-flies: Needham.) Before spinning its cocoon this larva spins a hemispheric cover beneath which the cocoon is made, as does the larva of Sisyra. But in the case of Climacia this cocoon-cover is lace-like ; it is a beautiful object (Fig. 330). Excepting the sialids, the larvse of Sisyra and Climacia are the only known aquatic neuropterous larvee found in this country. Family SYMPHEROBIID^ The Sympherobiids This family includes certain insects which were formerly classed with the HemerobiidcC but which exhibit a type of specialization of the wings that is quite different from that which is distinctively characteristic of that family. The distinctive characteristic of the Sympherobiidee is that vein R2+3 of the fore wings has become separated from the remainder of the radial sector and is attached separately to vein Ri. This results in the radius of the fore wing having two sectors, each of which is forked (Fig. 332). In this family the number of the branches of the radial sector has not been increased, this vein being four-branched in both fore and hind wings ; but the tips of all of the branches are forked. The costal area of the fore wing is broad towards the base of the wing ; and the humeral vein is recurved and branched. The North American species of this family represent two genera. 294 AN INTRODUCTION TO ENTOMOLOGY Synipherdbius. — In this ^enus there are two series of gradate veins in the fore wings ; the outer series consists of four cross- veins (Fig. 332). Seven American species have been described. The wing-expanse of these insects ranges from 9 mm. to 12 mm. Fig. 332. — Wings of Sympherobiiis amiculus. Psectra. — In this genus there is only one series of gradate veins in the fore wings. The only species is Psectra diptera. The specific name of this species was suggested by the fact that in the female the hind wings are atrophied. This is a widely distributed species both in this cotmtry and in Europe. Its wing expanse is from 5 nun. to 6 mm. Family HEMEROBIID^ The Hemerobiids The Hemerobiidaj include insects of moderate size; in most of our species the wing-expanse is between 12 mm. and 22 mm.; in one species of Megalomus it is only 6 mm. In most of the species the body is brown or blackish and is often marked with yellow; in some NEUROPTERA 295 the body is pale yellow. The wings are usually hyaline or pale yellowish. This family has been greatly restricted in recent times ; formerly there were included in it the members of the two preceding and the three following families. /2:^r^rrrrr^^mm22Zm^ Fig. 333. — Wings of Hcmerohius humuli. ■ As now restricted this family is composed of a group of genera that are characterized by a distinctive manner of specialization of the radius of the fore wings. This feature is a coalescence of vein Ri and the stem of the pectinately branched radial sector, which results in what I have termed the suppression of the stem of the radial sector. A comparatively simple example of this condition is exhibited by Hemerobius hUmuli; in the fore wings of this species (Fig. sss)' veins R5, R4, and R2+3 arise separately from what appears to be the main stem of the radius but which is really vein Ri and the basal part of the radial sector coalesced. An early stage in the suppression of the stem of the radial sector is shown in the hind wing oi Hemerobius humuli (Fig. 2>2)Z)- Here 296 AN INTRODUCTION TO ENTOMOLOGY vein R2+3+4 is bent forward' near its base and is joined to vein Ri. The extending of the union of veins Ri and R2+3+4 from the point where the}^ now anastomose towards the base of the wing:, so as to obHterate the small cell between them, and also towards the apex of Fig. 334. — Wings of Megalomtis mosstus. the wing for a certain distance, would produce the condition that exists in the fore wing. The wings of Hemerobius represent a comparatively simple type of hemerobiid wings; those of Megalonms mcestus (Fig. 334), a more complicated one. Here there have been developed a larger ntunber of definitive accessory veins and of marginal accessory veins. Under the title "A Revision of the Nearctic Hemerobiidas" Mr.N. Banks ('05) has published an account of this family, the two preceding families, and the three following families, in which all of our species kno^vn at that time are described. NEUROPTERA l flies, other popular names have been applied to them; they are some- times called golden-eyed flies, on account of the peculiar metallic color of their eyes while alive; and as some species, when handled, emit a very disagreeable odor, they have been called stink-flies, an undesirable name for such beautiful insects. The wings of the Chrysopidas are characterized by a very re- markable and distinctive type of specialization, the details of which Fig. 339. — Eggs, larva, cocoon, and adult of Chrysopa. Fig. 340. — Fore wing of Chrysopa nigriconiis: cubitus. JSr, pseudo-media; Cui', pseudo- can be understood only by a study of the tracheation of the wings of the pupae. Such a study has been made by McClendon ('06), Tillyard ('16), and R. C. Smith ('22). A superficial examination of a wing of Chrysopa (Fig. 340) reveals the presence of two longitudinal veins between the radial sector and the inner margin of the wing, one of which appears to be the media and the other vein Cui; but each of these, as is shown later, is a serial vein composed of sections of several veins. NEUROPTERA 301 As it would be impracticable to apply to these serial veins names indicating their composition, they have been termed the pseudo- media or vein M' and the pseudo-cuhitus-one or vein Cu/, re- spectively (Fig. 340, M' and Cu/). Fig. 341. — Tracheation of the wings of a pupa of Chrysopa iiigricornis. An examination of the tracheation of the wings of a pupa of Chrysopa nigricornis reveals the nature of the two serial veins M' and Cui' (Fig. 341). In order to show more definitely the composition of the two serial veins, a diagram of an adult wing is given (Fig. 342), in which the elements of the coalesced veins are represented slightly separated, and the cross-veins connecting the coalesced veins are represented by dotted lines. By comparing this diagram with Figure 340 the homologies of the different veins can be recognized. The larvce of the lacewing-fiies are known as aphis-lions, because they feed upon aphids; they are found on the foliage of plants in- fested by these pests; they also feed upon other small insects and the eggs of insects; they are spindle-shaped (Fig. 339) and are fur- nished with piercing and sucking mouth-parts like those of ant-lions. Nearly all aphis-lions are naked; but a few species cover them- selves with the skins of their victims and other debris, as do the larvcC of Hemerohius. This has been observed by European writers (Sharp 302 ^A^ INTRODUCTION TO ENTOMOLOGY '95); and recently jNlr. R. C. Smith ('21) has found that the larvag of several of our native species have a similar habit. The cocoons are generally found on the lower sides of leaves or on the supports of plants; they are spherical and composed of dense layers of silk. In order to emerge the insect cuts a circular lid from ''''''^+^^rSr^r^ Fig. 342. — Diagram of the wings of Chrysopa nigricomis, showing the coalesced veins slightly separated. one side of the cocoon; this is done by the pupa by means of its mandibles. After emerging from its cocoon, the pupa crawls about for a short time before changing to the adult state. The adults are often attracted to lights at night. A remarkable fact in the life-history of these insects is the way in which the female cares for her eggs. When about to lay an egg she emits from the end of her body a minute drop of a tenacious substance, which is probably a product of the colleterial glands; this she applies to the object on which she is standing and then draws it out into a slender thread by lifting the abdomen ; then an egg is placed on the summit of this thread. The thread dries at once and firmly holds the egg in mid-air. These threads are usually about 12 mm. in length, and occur singly or in groups; a group is represented attached to a leaf in Figure 339. About fifty species belonging to this family have been found in the United States and Canada ; the greater number of these belong to the genus Chrysopa. Fig. 343- — Larva, cocoon with pupa-skin projecting, and adult, of an ant-lion. NEUROPTERA 303 Family MYRMELEONID^ The Ant-Li ons The members of the family Myrmeleonidae are commonly known as ant-lions. This name was suggested by the fact that the larvse of the best-known species, those that dig pitfalls, feed chiefly on ants. The adults are graceful creatures. The body is long and slender (Fig. 343); the antennae are short and en- larged towards the end; the wings are long and narrow and delicate in structure; they are furnished with many accessory veins, both definitive and marginal, and with very many cross-veins. A distinctive feature of the wings of these insects is the presence of an elongated cell behind the point of fusion of veins Sc and Ri (Fig. 344); this characteristic serves to distinguish this family from the closely allied Ascalaphidse. The determination of the homologies of the wing-veins of the Myrmeleonidge was completed only recently. The results of this de- termination are set forth in detail by the writer in his "The Wings of Insects," where they are illustrated by many figures. Our native species, as a rule, are not striking in appearance; the wings are hyaline and are o^ten more or less spotted with black or brown marks ; but certain exotic forms, as those of the genus Pal- pares, are large and have conspicuously marked wings. The larvffi have broad and somewhat depressed bodies which taper towards each end (Fig. 343). The mouth-parts are large and powerful and are of the piercing and sucking type ; they are described on page 282. The pupa state is passed in a spherical cocoon, made of sand fastened together with silk, and neatly lined with the same material (Fig. 343). The silk is spun from the posterior end of the alimentary canal and is secreted by modified Malpighian vessels, as in Sisyra (see page 283.) This is a large family including several hundred described species. In his "Catalogue of the Neuropteroid Insects of the United States," Banks ('07) lists fift^'-eight species of this family known at that time to occur in our fauna; these are distributed among eleven genera. The life-histories of comparatively few of the species are known; but certain species, the larvas of which dig pitfalls in sandy places, have attracted much attention since the earliest days of entomology. 304 AN INTRODUCTION TO ENTOMOLOGY Ant-lions are much more common in the Southern and Southwest- ern States than they are in the North. The pitfalls of the larvae are usually found in sandy places that are protected from rain, as beneath buildings or overhanging rocks. In making these pitfalls the sand is thrown out by an upward jerk of the head, this part of the body Fig. 344. — Wings of Mynncleon. serving as a shovel. The pits differ greatly in depth, according to the nature of the soil in which they are made. Their sides are as steep as the sand will lie. When an ant or other wingless insect steps upon the brink of one of these pits, the sand crumbles beneath its feet, and it is precipitated into the jaws of the ant-lion, which is buried in the sand, with its jaws at the bottom of the pit (Fig. 345). In case the ant does not fall to the bottom of the pit, the ant-lion undermines it by throwing out some sand beneath it. I have even seen an ant-lion throw the sand in such a way that in falling it would tend to hit the ant and knock it down the side of the pit. These larvae can be easily kept in a dish of sand, and their habits watched. The most common ant-lion in the North is Myrmeleon im- maculdtiis; the larva of this species makes a pitfall. The habits of the larvae of Glenurus, Dendroleon, and Acanthdclisis, three genera that are repre- sented in this country, have been described by European writers. These larvae do not dig pitfalls, but partially bury themselves in the sand, from which position they throw themselves quickly upon their victims. Fig. 345. — Pitfall of an ant-lion. NEUROPTERA 305 Family ASCALAPHID^ The Ascalaphids The family Ascalaphidac is quite closely allied to the preceding family; but the members of this family can be easily distinguished from myrmeleonids by the greater length of the antennae (Fig. 346) and by the fact that in the wings there is not an elongate cell behind the point of fusion of veins ScandRi; compare Fig- ures 347 and 344. Fig. T,^6.~-Ululodes hyalina. (From Kellogg, after McClendon.) The adults are pre- dacious ; some species fly in the daytime in bright sunshine, but it is said that others fly in the twilight. Some species resemble myrmeleon- CU2 •-. I rca Fig. 347. — Wings of Uhdodes hyalina. ids in appearance, while others resemble dragon-flies. When at rest they remain motionless on some small branch or stalk, head down, with the wings and antennae closely applied to the branch, and the abdomen erected and often bent so as to resemble a short brown twig or branch (Fig. 346). 306 AN INTRODUCTION TO ENTOMOLOGY The larv£e resemble ant-lions in the form of the body and possess the same type of mouth-parts (Fig. 348). They have on each segment of the body a pair of lateral finger-like appendages, which are clothed with hairs. They do not dig pitfalls, but lie in ambush on the surface of the ground, with the body more or less covered, and wait for small insects to come near them. When a larva is full-grown, it spins a spherical silken cocoon. An account of the life-history of one of our native species, Ululodes hydlina, has been published by McClendon ('02). The Ascalaphidas of the world have been mon- ographed by H. W. Van der Weele ('08). In this monograph more than two hundred species are de- scribed. The members of this family are chiefly p- g T r tropical insects, but a few species occur in the illulodes hyalina. United States ; these represent three genera, which (After McClendon.) Can be separated by the following table. A. Eyes entire Neuroptynx AA. Each eye divided into two parts by a groove. B. Hind margin of wings entire Ululodes BB. Hind margin of wings excised Colobopterus Fig- 349- — Wings of Semidalis aleurodiformis. (After Enderlein.) NEUROPTERA 307 Family CONIOPTERYGID^ The Mealy-winged Neuroptera The Coniopterygidse is a family of limited extent; and it includes only small insects, the smallest of the Neuroptera; the described American species measure only 3 mm. or less in length. They are characterized by a reduced wing-venation (Fig. 349) and by having the body and wings covered by a whitish powder. While the adults resemble very slightly other neuropterous insects, the larvae resemble those of the Hemerobiida^ and allied families in form, in the structure of their mouth-parts, in their predacious habits, and in their metamorphosis. The larvae have been seen to feed upon coccids, aphids, and the eggs of the red-spider; they doubtless feed on other small insects. When full-grown they make a double cocoon consisting of an outer flat layer and an inner spherical case. Mr. Nathan Banks ('07) has published a revision of the species that have been found in our fauna. This includes eight species, representing five genera. CHAPTER XII ORDER EPHEMERIDA* The May-Flies The members of this order have delicate membranous wings, which are triangular in outline and are usually furnished with a considerable number of intercalary veins and with many cross-veins; the hind wings are much small- er than the fore wings and are sometimes wanting. The mouth-parts of the adults are vestigial; those of the naiads are fitted for chewing. The metamorphosis is incomplete. The May-flies or ephemerids are often very common insects in the vicinity of streams, ponds, and lakes; frequently the surface of such bodies of water is thickly strewn with them. They are attracted by lights ; and it is not an uncommon occur- rence in summertime to see hundreds of them flying about a single street-lamp. The May-flies are easily distinguished from other net -winged insects by the shape of the wings and the relative sizes of the two pairs (Fig. 350). The mouth -parts of the adult are vestigial, as these insects eat nothing in are very small; they are composed of Fig. 350— A May-fly. this state. The antennae two short, stout segments s u c- ceededbya slen- der, many-joint- ed bristle. The thorax is robust, with the meso- thorax predomi- nant; the great development of this segment is correlated with the large size of the fore wings. The abdomen is Fig. 351. — Caudal end of abdomen of Siphlurus alternatus, lone soft and ™ale: p, /o, //, abdominal segments; f, cerci; w/, median composed of ten caudal filament ; p, penis ; /, forceps-limbs. (After Morgan.) *Ephemerida, Ephemera: ephemeron (itp-^fj^pov) , a May-fly. (308) EPIIEMERID. 309 visible segments; the eleventh segment, which bears the cerci, is overlapped by the tenth (Fig. 351). The cerci are long, slender, and many-jointed; and in some species there is a median caudal filament, which resembles the cerci inform; these three organs, the two cerci and the median caudal filament, are commonly referred to as the caudal setae. In the male there is a pair of clasping organs placed ventrally at the extremity of the tenth segment; these are usually two-, three-, or four-jointed and are termed the forceps- limbs. Eachvas deferens and each oviduct has a separate opening; in the male these openings are at the caudal end of the body; in the female, between the seventh and eighth stemites. In some May -flies the compound eyes are divided; one part of each, in such cases, is a dav-eve, and the other a night-eve ('seepage 144). As the adult May-fly takes no food, its alimentary canal is not needed in this stage for purposes of digestion, and, instead of serving this function, acts as a balloon, being inflated with air, thus lessening the specific gravity of the bod}^ and aid- ing in flight. In this order a marked cephalization of the flight function has taken place, which has resulted in a great reduction of the hind wings in all living forms. In some cases {Ccsnis et al.), this has gone so far that the hind wings are wanting (Fig. 352); but at least one pair of wings is present in all members of this order. When at rest, the wings are held upright; they are never folded over the abdomen. No anal furrow has been developed. A striking feature of the wings of May-flies is their well-known corrugated or fan-like form, there being a remarkably Fig. 352.— Cams, a t w o- winged May-fly. Fig. 353. — Fore wing of Chirotonetes albonianicatus. perfect alternation of so-called convex and concave veins. Correlated with the development of the fan-like form of the wings has been the development of intercalary veins, that is, veins that did not arise as branches of the primitive veins, but were developed in each case as a thickened fold, more or less nearly midway between two preexisting 310 AN INTRODUCTION TO ENTOMOLOGY veins, with which primarily it was connected only by cross-veins. The veins labeled IMi, IM3, and ICu, in Figures 353 and 354 are good illustrations of this type of veins. The initial I in these designa- tions is an abbreviation of the word intercalary. Thus the intercalary vein between veins Cui and Cu2, i. e., in the area Cui, is desig- nated as vein ICui. Figures 353 and 354 will aid in the determination of the homol- ogies of the wing-veins of May-flies. In these figures convex veins are designated by plus signs and con- cave veins by minus signs. In attempt- ing to determine the homology of a vein in a wing where the venation is reduced, it should first be determined whether the vein is convex or concave, as the corrugations of the wings of May-flies are the most persistent fea- albomanicatus. tures of them. For a more detailed ac- count of this subject, see Chapter X of "The Wings of Insects." The Greek name Ephemeron applied to these insects in the days of Aristotle was derived from ephemeras, signif^dng lasting but a day; and from that time to this, frequent references have been made to the insects that live only a single day. This brevity of the life of these insects is true only of their existence in the adult state. Strictly speak- ing, the May-flies are long-lived insects; some species pass through their life-cycle in a few weeks in midsimmier; but as a rule one, two, or even three years are required for the development of a generation. The greater part of this time is passed, however, beneath the surface of water, and after the insect emerges into the air and assumes the adult form its existence is very brief. With many species the indi- viduals leave the water, molt twice, mate, lay their eggs, and die in the course of an evening or early morning; and although the adults of many genera live several days, the existence of these insects is very short compared with that of the adults of other insects. The females lay their eggs in water. Some short-lived species discharge the contents of each ovary in a mass. Individuals are often found in which there project from the caudal end of the body two parallel subcylindrical masses of eggs, one protruding from each of the openings of the oviducts. "The less perishable species extrude their eggs gradually, part at a time, and deposit them in one or the other of the following manners : either the mother alights upon the water Fig. 354. — Hind wing of Chirotonetes EPHEMERIDA 311 at intervals to wash off the eggs that have issued from the mouths of the oviducts during her flight or else she creeps down into the water — enclosed within a film of air with her wings collapsed so as to overlie the abdomen in the form of an acute narrowly linear bundle, and with her setae closed together- — to lay her eggs upon the under side of the stones, disposing of them in rounded patches, in a single layer Fig- 355- — Metamorphosis of a ATay-fly, Ephemera varia: A, adult; B, naiad. (After Needham.) evenly spread, and in mutual contiguity." (Eaton 'S3.) The metamorphosis of May-flies is incomplete. The wings are developed externally, as in the Orthoptera; the development of the compound eyes is not retarded; but the immature forms, or naiads, are "sidewise developed" to fit them for aquatic life. In most species the form of the body of the naiads is elongate and furnished with two or three long "caudal setfe," that is, the cerci and in some a median caudal filament; in these respects the naiads resemble, to a greater or less degree, the adults (Fig. 355); but except in the early instars the abdomen of a naiad is furnished with tracheal gills (Figs. 355 and 356). The tracheal gills are usually large and prominent; in most species there are seven pairs, borne by the first seven abdominal segments. They vary greatly in form in the different genera. In some each gill is divided into two long narrow branches, which lie in one plane (Fig. 355) ; in others the gills consist of a scoop-shaped covering piece beneath which is a more delicate part consisting of many thread-like branches. A detailed account of the various forms of tracheal gills of May-flies is given by Miss Morgan ('13). The naiads of May-flies are all aquatic; they are very active; and are almost entirely herbivorous, ^. ^ feeding largely on the decaying stems and leaves of ^\'^\ o f ^a aquatic plants, the epidermis of moss and of roots, May-fly. 312 AN INTRODUCTION TO ENTOMOLOGY algae, and diatoms. The variations in the details of their habits are described as follows by Dr. Needham ('i8). "A few, \\]<.& Hexagenia, Ephemera, and Po/jmiVarcv^ are burrowers beneath the bottom silt. A few like Ccenis and Ephemerella, are of sedentary habits and live rather inactively on the bottom, and on silt-covered stems. Alany are active climbers among green vegetation; such are Callibails and Blasturiis; and some of these can swim and dart about by means of synchronous strokes of tail and gills with the swiftness of a minnow. The species of Leptophlebia love the beds of slow-flowing streams, and all the flattened nymphs of the Heptageninae live in swiftly moving water, and manifest various degrees of adaptation to withstanding the wash of strong currents. The form is depressed, and margins of the head and body are thin and flaring, and can be appressed closely to the stones to deflect the current." There are two features of special interest in the structure of the naiads of May -flies: first, the hypopharj-nx bears a pair of lateral lobes, which are believed to be vestiges of paragnatha; and sec- ond, the presence of accessor}^ circulatorv^ organs in the cerci and median caudal filament (Fig. 35 7) • May -flies exhibit a remark- able peculiarity in their develop- ment. After the insect leaves the water and has apparently as- sumed the adult form, that is, after the wings have become fully expanded, it molts again. These are the only insects that miolt af- Fig- 357-— A, caudal end of abdomen of tev they have attained functional Clo'eon dipterum: h, heart; a, acces sory circulatory organs. B, twenty wings. The term stibimago is, ap- ^ -^ - -n -■ plied to the instar between the sixth segment of a cercus : o, orince m ■ -, j w-i_ £ i x -c j-v,^ blood vessel. (After Zimmerman.) naiad and the final fomi of the msect, the adult. With some species the duration of the subimago stage is only a few minutes ; the insect molts on leaving the water; flies a short distance; and molts again. In others this stage lasts twenty-four hours or more. With many species of May-flies there is great uniformity in the date of maturing of the individuals. Thus immense swarms of them will leave the water at about the same time, and in the course of a few days pass away, this being the only appearance of the species until another generation has been developed. The great swarms of "lake- flies," Ephemera smmlans, which appear along our northern lakes about the third week of July, afford good illustration of this peculi- arity. Family EPHEMERID^ The May-Flies The order Ephemerida includes a single family, the Ephemeridas; the characteristics of this family, therefore, are those of the order, which are given above. EPHEMERIDA 313 Comparatively few writers have made extended studies of the classification of the ephemerids ; this is doubtless partly due to the fact that pinned specimens usually become shriveled and are very fragile; consequently this order is poorly represented in most collections of insects. In spite of this, more than one hundred species have been described from the United States. An important paper on the classification of May-flies is that by Dr. Needham (05) in Bulletin_86 of the New York State Museum. Here are given keys for separating the North American genera, one for the adult insects and one for the naiads. CHAPTER XIII ORDER ODONATA* The Dragon-Flies and the Damsel-Flies The members of this order have Jour membranous wings, which are finely netted with veins; the hind wings are as large as or larger than the fore wings; and each wing has near the middle of the costal margin a joint-like structure, the nodus. There are no wingless species. The mouth-parts are formed for chewing. The metamorphosis is incomplete. Dragon-flies and damsel-flies are very common insects in the vicinity of streams, ponds, and lakes; they are well known to all who frequent such places. The dragon-flies, especially, attract attention on account of their largesize(Fig. 358) and rapid flight, back and forth, over the water and the shores ; the damsel-flies (Fig. 359) are less likely to be noticed, on account of their less vigorous flight. The name of this order is evi- dently from the Greek word odous, a tooth; but the reason for applying it to these insects is Fig. 358. — A dragon-fly, Plathemis lydia. (From San- born.) obscure; it may refer to the tusk-like form of the abdomen. In these insects, the head is large; it differs in shape in the two suborders as described below. The compound eyes are large; they often occupy the greater part of the surface of the head ; in many cases the upper facets of the eye are larger than the lower, and in a few forms the line of division between the two kinds is sharpl\' marked. It is probable that the ommatidia with the larger facets are night-eyes, and those with the smaller facets, day-eyes. See pages 142 and 1 43 . Three ocelli are present. The antennte are short ; they consist of from five to eight segments; of these the two basal ones are thick, the others form a bristle-like organ. The mouth- parts are well developed ; the labnrni is prominent ; the mandibles and maxillae are both strongly toothed; and the labium consists of "Odonata: odous {65oCs), a tooth. (314) ODONA TA 315 Fig. 359. —A damsel-fly. three large lobes, which with the labrum nearly enclose the jaws when at rest. The thorax is large. The wings are, as a rule, of nearly similar size and structure ; they are richly netted with veins; and the costal border of each is divided into basal and apical parts by what is termed the nodus (Fig. 364, n). The legs are rarely used for walking, but are used chiefly for perching, and are set far forward ; the tarsi are three- jointed. The abdomen is long, slender, and more or less cylindrical; the caudal end is furnished with clasping organs in the males. A remarkable peculiarity of the order is the fact that the copulatory organs of the male are distinct from the opening of the vasa deferentia; the former are situated on the second abdominal segment, the latter on the ninth. Before pairing, the male conveys the seminal fluid to a bladder-like cavity on the second abdominal segnnent; this is done by bending the tip of the abdomen forward. Except in the subfamily Gomphince, the pair- ing takes place during flight. The male seizes the prothorax or hind part of the head of the female with his anal clasping organs; the female then curves the end of the abdomen to the organs on the second abdominal segment of the male. Pairs of dragon-flies thus united and flying over water are a common sight. The Odonata are predacious, both in the immature instars and as adults. The adults feed on a great variety of insects, which they capture by flight; and the larger dragon -flies habitually eat the smaller ones, but a large part of their food consists of mosquitoes and other small Diptera. The eggs are laid in or near water. All of the damsel-flies and many dragon-flies are provided with an ovipositor, by means of which punctures are made in the stems of aquatic plants, in logs, in wet mud, etc., for the reception of the eggs. The females of those dragon-flies that lack a well-developed ovipositor deposit their eggs in various ways. In some species the female flies back and forth over the surface of the water, sweeping down at intervals to touch it with the tip of her abdomen and thus wash off one or more eggs into it. In other species the eggs are laid in a mass on some object just below the surface of the water; some species do this by alighting upon a water-plant, and, pushing the end of the abdomen below the surface of the water, glue a bunch of eggs to the submerged stem or leaf; in other species the mass of eggs is built up gradually; the female will poise in the air a short distance above the point where the mass of eggs is being laid, and at frequent intervals descend with a swift curved motion and add to the egg-mass and then return to her former position to repeat the operation. Still other species hang their 316 AN INTRODUCTION TO ENTOMOLOGY eggs in long gelatinous strings, on some plant stem at the surface of the water. The metamorphosis is incomplete. The naiads are all aquatic except those of a few Hawaiian damsel-flies, which live on moist soil under the leaves of liliaceous plants. The wings are developed externally, and the development of the compound eyes is not retarded, as it is with larvae. The adaptations for aquatic life differ in the two suborders and are described later. All naiads of the Odonata are predacious. The mouth is furnished with well-developed mandibles and maxillse, all of which are armed with strong teeth. But none of these is visible when the insect is at rest. The lower lip is greatly enlarged, and so formed that it closes over the jaws, concealing them. For this reason it has been termed the mask. But it is much more than a mask; it is a powerful weapon of offence. It is greatly elongated and is jointed in such a way that it can be thrust out forward in front of the head. It is armed at its extremity with sharp hooks, for seizing and retaining its prey (Fig. 360). The order Odonata is divided into three sub- orders. One of these suborders, the Anisozygop- tera, is composed almost entirely of fossil forms, -Underside being represented among living insects by a single of head of a nmad g^^us, Epiophlebia, which is found in Japan. The ?abium"^ unfolded. Other two suborders are well represented in this (After Sharp.) ' country ; one of them consists of the dragon-flies, the other of the damsel-flies. Fig. 360. Suborder ANISOPTERA* The dragon-flies are easily recognized by the relative size of the two pairs of wings, and by the attitude of the wings when at rest (Fig. 361). The hind wings are larger than the fore wings and are of a somewhat different shape ; but the most striking char- acteristic is the fact that the wings are ex- The Dragon-Flies Fig. 361. — A dragon-fly, Lihellula luctuosa. tended horizontally when at rest. *Anis6ptera: anisos {ivuros), unequal; pteron {Trrepov), a wing. ODONA TA 817 The head is large, broad, often semi-globose, and concave behind. The wings are very strong. An important factor in the strengthening Fig. 362. — Wings of naiads of Gomphus descriptus, early stages. (From Comstock and Needham.) of the wings of these insects is the development of a series of corruga- tions, which has resulted in certain veins becoming convex and others concave ; this has progressed so far that there is a very perfect alterna- tion of convex and concave veins. The habits of dragon-flies have been carefully studied by Professor Needham ('18), who writes as follows: "Among the dragon-flies are many superb flyers. The speed on the wing of Trdmea and Anax equals, and their agility exceeds, that of swallows. They all capture their prey in flight ; and are de]:)endent on their wings for getting a living. But the habit of flight is very different in different groups. Only a few of the Fig. 363. — Tracheation of the wings of (After Needham.) grown naiad of Gomphus descriptus. 318 AN INTRODUCTION TO ENTOMOLOGY strongest forms roam the upper air at will. There is a host of beautiful species, the skimmers or Libellulida, that hover over ponds in horizontal flight, the larger species on tireless wings, keeping to the higher levels. The stronger flying ^schni- dae course along streams on more or less regular beats; but the Gomphines are less constantly on the wing, flying usually in short sallies, from one resting place to another, and alighting oftener on stones or other fiat surfaces than on vertical stems." The characters presented by the venation of the wings of the Odonata are much used in the classification of these insects. In general the veins and areas of the wings are designated as in the accounts of the wings of other orders of insects ; but there are certain features in the wings of these insects that are peculiar to them. The most distinctive feature of the wings of the Odonata is the fact that in the course of their development one or more branches, usuallv two, of the medial trachea invade the area of the radial sector. Fig. 364. — Wings of Gomphus descripHis. In the front wing, cells or areas are labeled; in the hind wing, veins. This results in vein Rs occupying a position behind one or more, usually two, of the branches of media. Figure 362 represents the tracheation of the wings of two naiads of Gomphus descnptus; the wing shown at A is of a ver}^ young naiad; that at B is of a somewhat older one. In the wing shown at A, the branches of trachea M are in their typical position; in the wing shown at B, trachea Mi is in front of trachea Rg. Figure 363 represents the tracheation of a full-grown naiad of the same species. In this stage of the development of the wings, both trachese Mi and M2 are in front of trachea Rs; and it is in this position that the veins of the adult wing are developed (Fig. 364). ODONA TA 319 By comparing the figure of the wing of an adult (Fig. 364) with that of the full-grown naiad (Fig. 363), it will be seen that the oblique vein marked o is not a cross-vein but a section of vein Rs ; so too, what appears to be another cross- vein, labeled s n, \s also a section of vein Rs; this section of vein Rs is known as the siibnodus. It will also be seen that what appears to be the base of the radial sector, labeled 6 r, is a secondarily developed vein which connects the radial sector with a branch of media; this secondary vein is known as the bridge. The beginning of the formation of the bridge is shown in Figure 363.* The more important of the other special terms used in descriptions of the wings of dragon-flies are the following : Much use is made in taxonomic work of the two series of cross-veins that are nearest the costal margin of the wing ; those of these cross-veins that are situated between the base of the wing and the nodus are termed the antenodal cross-veins; the first of these two series of antenodal cross-veins ex- tend from the costa to the subcosta; the second from the subcosta to the radius; the antenodal cross-veins are termed the anteciibital cross-veins by some writers. The two series of cross-veins nearest to the costal margin of the wing and between the nodus and the apex of the wing are termed the postnodal cross- veins; the first of the two series of postnodal cross-veins extend from the costa to vein Ri; the second, from vein Ri to vein Mi; the postnodal cross- veins are termed the postcubital cross-veins by some writers. Near the base of the wing there is in dragon-flies a well-marked area of the wing, which is usu- ally triangular in out- line (Fig. 364, t); this . is the triangle; ive-^'f 366.- Exuviae ,1 , , , *. 1 . of a naiad of a drag- quently the triangle is on-fly, Tetr ago- divided by one or neuria. Fig.365.-Hmd-mtestineand part more cross-veins into of the tracheal system of a naiad two or more cells. The area lying imme- oi.^schnacyanea: R, R, R, R,Tec- diatelvin front of the triangle (Fig. 364, tumM anus; /./ dorsal tracheal ^) ^g 1^,-^^^ the super triangle; like the tubes; /z', ventral tracheal tubes- ^. , ^1 • ^ . ^ ' - . , M, Malpighian tubes. (From triangle this area may consist of a single Sharp, after Oustalet.) cell or may be divided by one or more *The conclusions regarding the homologies of the wing-veins given here are based on investigations by Dr. Needham the results of which were published by 320 AN INTRODUCTION TO ENTOMOLOGY cross-veins. Other named areas are the basal anal area (Fig. 364, ha) and the cubital area (Fig. 364, ca). The writer has given in his "The Wings of Insects" an extended discussion of the wings of Odonata, illustrated by many figures, in- cluding a plate in which adjacent veins are represented in different colors, so that the course of each can be easily followed. With the naiads of dragon-flies there is a remarkable modification of the organs of respiration, which fits these insects for aquatic life. The caudal part of the alimentary canal, the rectum, is modified so as to constitute a tracheal gill. It is somewhat enlarged ; and its walls are abundantly supplied with tracheae and tracheoles (Fig. 365). Water is alternately taken in and forced out through the anal opening; by this process the air in the tracheae, with which the walls of the rectiim are supplied, is purified in the same manner as in an ordinary tracheal gill. The rectal tracheal gill of the naiads of dragon-flies is an organ of locomotion, as well as of respiration. By drawing water into the rec- timi gradually, and expelling it forcibly, the insect is able to dart through the water with considerable rapidity. This can be easily observed when naiads are kept in an aquariimi. When the naiad of a dragon-fly is fully grown it leaves the water to transform. The skin of the naiad splits open on the back of the thorax and head, and the adult emerges, leaving the empty skin of the naiad clinging to the object upon which the transformation took place. Figure 366 represents such a skin clinging to the stem of a water plant. The suborder Anisoptera includes two families, the y^schnidae and the Libellulidae ; each of these families is represented in our fauna by many genera and species. These are enumerated in the "Catalogue of the Odonata of North America" by Muttkowski ('10). The two families can be separated by the characters given below. Family ^SCHNID^ The Mschnids In this family the triangle (Fig. 364, t) is about equally distant frorn the arculus (Fig. 364, ar) in the fore and hind wings; and, except in the genus Cordulegdster, there is an oblique brace-vein extending back from the inner end of the stigma (Fig. 364). The seschnids are mostly large species ; among them are the largest, fleetest, and most voracious of our dragon-flies. Some of them roam far from water and are commonly seen coursing over lawns in the evening twilight; but most of them fly over clear water. Comstock and Needham ('gS-'gg) and by Needham ('03). These conclusions have been questioned by Tillyard ('22) and by Schmieder {'22); but I do not feel that it would be wise to modify them before a much more extended investigation of the subject has been made. ODONATA 321 Family LIBELLULID^ The Lihellulids or Skimmers In this family the triangle in the hind wing is much nearer the arculus than is the triangle of the fore wing; and there is no oblique brace- vein extending back from the inner end of the stigma, as in the ceschnids. This is a large family including many of our commonest and best-known species of dragon-flies ; many of them are familiar figures flying over ponds and ditches and by roadsides. Most of them are of well-sustained flight, and are seen continually hovering over the surface of still water; this suggested the common name skimmers which has been applied to them. Fig- 367. — A damsel-fly. Suborder ZYGOPTERA* The Damsel-Flies The damsel-flies differ from the dragon-flies in that the two pairs of wings are similar in form and are either folded parallel with the abdomen when at rest (Fig. 367) or up tilted {Testes). The head is transverse, each eye being borne by a lateral prolongation of the head. The females possess an ovipositor by means of which the eggs are placed in the stems of aquatic plants, sometimes beneath the surface of the water. The name of the suborder probably refers to the fact that the wings are brought together when at rest. Fig. 368. — Wing of Lestes rectangularis: 0, oblique vein; br, the bridge. *Zyg6ptera: zyg07i (^vy6v), yoke; pteron {wrepbu), a wing. 322 AN INTRODUCTION TO ENTOMOLOGY Unlike the dragon-flies, the damsel-flies are comparatively feeble in their flight. They are found near the margins of streams and ponds, in which the immature stages are passed. Most of the features in the venation of the wings of dragon-flies described on earlier pages are also characteristic of the wings of damsel- flies. Figure 368 represents an entire wing of Lestes rectangularis; Fig. 369. — Base of fore wing of Lestes rectangularis: br, the bridge; q, quadrangle; sq, subquadrangle. in this figure o indicates the oblique vein, and br the bridge. In Figure 369 the base of this wing is represented more enlarged, and the principal veins are lettered. In the suborder Zygoptera the cubitus and the first branch, vein Cui, extend in a comparatively direct course from the base of the wing outward (Fig. 369); the abrupt bends in these veins in the region of the triangle, which are so characteristic of the Anisop- tera, are only sHghtly developed here. This results in the areas corresponding to the triangle and the supertriangle of the Anisop- tera being in direct line and forming an area which is often quadrangular; this area is termed the quadrangle (Fig. 369, q). In a large part of this or- der the cross-vein sep- arating the parts of the quadrangle corre- spond ingtothetriangle and the supertriangle of the Anisoptera is lacking, in which case the quadrangle con- sists of a single cell Fig. 370.— Base of wing of Heliocharis. ^""'■"-^ (Fig. 369, q). In some members of this sub- order it is present; in Figure 370, representing the base of a wing of Heliocharis, the two cells of the quadrangle are labeled / and .y to ODONA TA 323 facilitate comparison with figures of wings of Anisoptera. In certain other members of this subor- der the quadrangle is divided into several cells by cross-veins (Fig. 371). The cubital area of the wing is usually quadrangular in outline in the Zygoptera, and is termed the subquad- rangle (Fig. 369, sq). Like the quadrangle, it may con- sist of a single cell or it may be divided by cross-veins (Fig. 371)- The naiads of damsel-flies have three plate-like tracheal gills at the caudal end of the body (Fig. 372). The structure of these gills is illustrated by Figure 373 ; at A is represented an entire gill showing the tracheas; and at B, part of a gill more magnified, showing both tracheae (T) and tracheoles (t). Fig. 371. — Base of wing of Helcerina. Fig. 372.— Naiad of a damsel-fly, Argia. Fig. 373. — Tracheal gill of a damsel-fly: A, entire gill showing the tracheas; B, part of gill more magnified, show- ing both tracheae (T) and tracheoles (t). The suborder Zygoptera includes two families, the Agrionidas and the Coenagrionidae. The genera and species of these families are enumerated by Muttkowski ('10). The two families can be separated as follows. A. Wings with many, at least five, antenodal cross-veins .Agrionid^ AA. Wings usually with only two antenodal cross-veins, rarely with three or four CcENAGRIONIDiE 324 AN INTRODUCTION TO ENTOMOLOGY Family AGRIONID^ TJte True Agrionids In the Agrionidas the wings are furnished with many antenodal cross-veins; and, although the wings are narrow at the base, they are not so distinctly petiolate as in the next family. These insects may be termed the true agrionids, as owing to a misapplication of the generic name Agrion the members of the next family have been incorrectly known as the agrionids. Here belong the most beautiful of our damsel-fiies, whose metallic blue or green colors are sure to attract attention. They are feeble in flight and do not go far from the banks of the pond or stream in which they were developed. There are only two genera of this famih' in our fauna. These are Agrion, whjch has been commonly known as Calopteryx, and HetcB- rina. In Agrion the wings are broad and spoon-shaped. In Hetce- rlna the wings are rather narrow, and in the males the base of one or both pairs is red. Family CCENAGRIONID^ The Stalked-winged Damsel-Flies The members of this famiily are easily recognized by the shape of their wings, which are long, narrow, and very distinctly petiolate (Fig. 368); and by the fact that in each wing there are only twc antenodal cross-veins, except in a few cases where there are three or four. To this family belong the smallest of our damsel-flies; but while our species are of small or moderate size, there exist in the tropics species that are the largest of the Odonata. Some of our species are dull in color; but many are brilliant, being colored with green, blue, or yellow. This family includes the greater number of our damsel-flies. CHAPTER XIV ORDER PLECOPTERA* The Stone-Flies The members of this order have four membranous wings. In some genera the branches of the principal veins are reduced in number and there are comparatively few cross-veins; in others, accessory veins are developed and there are many cross-veins; in most genera the hind wings are much larger than the fore wings, and are folded in plaits and lie upon the abdomen when at rest. The mouth-parts are of the chewing type of structure, btit are frequently vestigial in the adult. The cerci are usually long and many-joi^ited. The metamorphosis is incomplete. Members of this order are common insects in the vicinity of rapid streams and on wave-washed rocky shores of lakes; but they attract httle attention on account of their inconspicuous colors and secretive habits. They are called stone-flies because the immature forms are very abundant under stones in the beds of streams. In the adults the body is depressed, elongate, and with the sides nearly parallel (Fig. 374). The prothorax is large. The antennas are long, tapering, and many-jointed. The mouth-parts are usually greatly reduced. In some genera the mandibles are al- most membranous, but in others they are firm and toothed, being well fitted for biting. The maxillse exhibit variations in the de- gree of their reduction simi- lar to those shown by the mandibles. The maxillary palpi are five-jointed. The labial palpi are three-joint- ed. The legs are widely separated, except the fore legs in the Pteronarcidaj; the tarsi are three-jointed. The hind wings are a little shorter than the fore wings, but usually, owing to the expansion of the anal area, they are considerably larger than the fore wings; in a few genera the hind wings are smaller than the fore wings ; in some species the wings of the male are greatly reduced in size, and in others the males are wingless. When at rest, the wings are folded in plaits and lie upon the *Plec6ptera: plecos {irXiKos), plaited; pleron (jrTepSv), a wing. (325) Fig. 374. — A stone-fly, Pteronarcys dorsata. 326 AN INTRODUCTION TO ENTOMOLOGY abdomen, as shown on the left side of Figure 374. The cerci are usu- ally long and many-jointed; but they are rudimentary in the Nemouridae. The stone-flies are unattractive in appearance; in most of them the colors are obscure, being predominantly black, brown, or gray; but some of them that are active in the da>i:ime and inhabit foliage are green. Their powers of flight are quite limited; they are usually found crawling about on stones or on plants near streams. Several of the smaller species appear in the adult state upon snow on warm days in the latter half of winter. They become more nimierous in early spring and often find their way into our houses. The most common one of these in central New York is the small snow-fly, Cdpnia pygnKsa. It is probable that most adult stone-flies eat nothing; this can be inferred from the reduced condition of their mouth-parts. But it has been shown by Newcomer ('18) that several species of Tceniopteryx, which are equipped with well-developed mouth-parts, feed upon the buds and leaves of plants. One species in particular, T. pactfica, is a serious pest in the Wenatchee Valley, Wash., where it bites into the buds of fruit trees. One of the more striking features of the venation of the wings of the Plecoptera is a lack of uniformity in the number and courses of the subordinate veins. Not only are striking differences in wing-venation to be observed between different individuals of the same species, but frequently the wings of the two sides of an individual will vary greatly in venation. This is especially true as to the number of cross-veins and the branching of the veins in the distal parts of the wings. On the other hand, the characters presented by the trunks of the principal veins are quite constant. There is one characteristic of the wings of the Plecoptera that is so constant that it may be considered an ordinal character. This is the fact that in the wings of the adult the radial sector of the hind wings is attached to media instead of to radius (Fig. 376b). This switching of the radial sector of the hind wings is true only of the venation of the adult. In the wings of naiads the trachea Rs is a branch of trachea R. There are certain features of the wings of Plecoptera, which, although not always constant, occur in so large a portion of the members of the order that they may be considered characteristic; these are the following, all of which are repre- sented in Figure 376/?.- The presence of the radial cross-vein (/-). The absence of cross- veins in cell R and in the basal part of area Ri. (Cross- veins are found in cell R in Pleronarcys.) The strengthening in the fore wings of the area between media and vein Cui and of that between veins Cuj and Cu^ by the development of many cross- veins. The reduction of media to a two-branched condition. The reduction of the radial sector to a two-branched condition. (This reduction of the radial sector is apparent only after an extended study of the wings of stone-flies. In many cases, of which the form represented by Figure 3766 is one, accessory veins have been developed on vein R2 -I-3 which appear to be the primitive branches of the radial sector; but these accessory veins are very inconstant in number and position.) And the unbranched condition of the first anal vein. In concluding this brief summary of the special features of the wings of the Plecoptera it seems desirable to define some terms frequently used by writers on this order. The transverse cord. — In many genera of this order there is a nearly continuous series of cross-veins extending across each wing just beyond the middle of its length; this series of cross- veins is termed the anastomosis by many writers on the Plecoptera. As it is not formed by an anastomosing of veins, the use of the term transverse cord is preferable. PLECOPTERA 327 The pterostigma. — In most members of this order a specialized pterostigma has not been developed; but the term pterostigma is commonly applied to the cell beyond the end of the subcosta and between the costa and vein Rj, even though it is of the same color and texture as the remainder of the wing. The basal anal cell. — A very constant feature of the anal area of the wings of Plecoptera is the presence of a cross- vein near the base of the wing, which extends from the first anal vein to the second. The cell that is closed by this cross- vein is termed the basal anal cell (Fig. 376^, ba). The females drop their eggs in a mass in water. I have taken females of Perla and of Pteronarcys at lights, each with a mass of eggs hanging from the abdomen. The metamorphosis is incomplete. The immature forms are all aquatic. These naiads are common on the lower surface of stones in rapids. They can be found easily by lifting stones from such situations and turning them over quickly, when the na- iads will be found clinging to the stones with their fiat bodies closely appressed to them and their legs, antennse, and cerci ra- diating on the surface of the stone, but they are apt to run away quickly. The naiads of stone-flies live only in well-aerated water ; they are not found in stagnant water or in foul streams. They are said to feed on other aquatic insects, includ- ing smaller individuals of their own species ; but according to the observations of Dr. P. W. Claassen they are largely vegetable feeders. The body is depressed (Fig. 375); the antennge are long, so too are the cerci. Most species possess tracheal gills, situated usually on the ventral side of the thorax just be- hind the base of each leg ; but tracheal gills are found in some species either on the un- der side of the head, on the basal abdom- inal segments, or at the tip of the abdo- men. A large number of the smaller species are destitute of tracheal gills; in these the air supply is absorbed through the thin cuticula of the ventral surface. The colors of naiads are often brighter than those of adults. When full-grown the naiads leave the water and transform on some near-by object. The empty exuvise are often found clinging to stones or logs projecting from water or on the banks of streams. According to a recent classification of this order, that of Tillyard ('21), it includes seven families; but only four of these families are represented in our fauna. A monograph of the North American species of the order is in preparation by Professor J. G. Needham and Professor P. W. Claassen ; this is nearly completed and probably will be published soon. The four families of our fauna can be separat- ed by the following table. Fig- 375- — Naiad of a stone-fly, Acroneura. 328 AN INTRODUCTION TO ENTOMOLOGY A. Anal area of the fore wings with two or more series of cross-veins (Fig. 376a). p. 328 Pteronarcid^ AA. Anal area of the fore wings with not more than a single series of cross- veins, usually with no cross-veins beyond the basal anal cell. B . Media of the fore wings separating from radius gradually, the two forming a sharp angle (Fig. 3766). p. 328 Perlid^e BB. Media of the fore wings separating from radius abruptly, the two form- ing a blunt angle (Fig. 376c). C. Anal area of the fore wings with a forked vein arising from the basal anal cell (Fig. 376a). Cerci vestigial, p. 330. Nemourid^e CC. Anal area of the fore wings with only simple veins arising from the basal anal cell (Fig. 376^). Cerci well developed, p. 330 Capniid^ Family PTERONARCID^ This is a small family which is represented in North America by only two genera and by but few species. Pterondrcys. — This genus includes the largest of our stone-flies. Figure 374 represents a common species. The venation of the wings Fig. 376a. — Wings of Pteronarcella badia. is reticulate ; the reticulation is irregular and extends in the fore wings from the costa through the anal area. A remarkable feature of members of this genus is that vestiges of tracheal gills are retained by the adults. Pteronarcella. — This genus includes smaller species than the pre- ceding one, and the venation of the wings is more regular than in Pteronarcys (Fig. 376a). Family PERLID^ The members of this family differ from the Pteronarcidae in the smaller number of cross-veins in the anal area of the fore wings, PLECOPTERA 329 there being usually no cross-veins beyond the basal anal cells (Fig. 3766); and they differ from the following families in that media of 2d A Fig. 3766. — Wings of Isogeniis sp. Fig. 376c. — Wings of Nemoiira sp. 330 AN INTRODUCTION TO ENTOMOLOGY the fore wings separates from radius gradually, the two forming a sharp angle (Fig. 3766). This is the largest of the families, including a large portion of the genera and species found in our fauna; fourteen genera have been described from this region. Family NEMOURID^ In this and the following family the media of the fore wings separates from radius abruptly, the two forming a blunt angle (Fig. 376c). In this family the second and third anal veins of the fore wings coalesce for some distance beyond the basal anal cell, forming a forked vein (Fig. 376c), and the cerci are vestigial. The family is represented in our fauna by nine genera. Our more common representatives are small, dusky, and grayish species that are found emerging throughout the spring of the year. Family CAPNIID^ In this family, as in the Nemouridae, the media of the fore wings separates from radius abruptly, the two forming a blunt angle (Fig. 376(i) ; but in this family there are in the anal area of the fore wings A'4+5 Fig. 376i^ Neidid/e JJ. Head without transverse incision. K. Membrane with four or five simple veins arising from the base of the membrane, the two inner ones sometimes joined to a cell near the base (Fig. 413). p. 386. LyC'EID^ KK. Membrane with many, usually forked veins, springing from a transverse basal vein (Fig. 414). p. 389. . . . Coreid^ HHH. Hemelytra vestigial; parasitic bugs preying on bats. p. 379 Polyctenid^ DD. Antennae five- jointed.* E. Hemelytra with the clavus similar in texture to the membrane, which is without veins (Fig. 409); small semiaquatic bugs, measuring less than 3 mm. in length (Hebrus). p. 372 Hebrid.'E EE. Hemelytra with the clavus markedly thicker than the membrane. F. Tibia; armed with strong spines, p. 391 CydniD/E FF. Tibige smooth or with small spines. G. Scutellum narrowed behind, only rarely almost cover- ing the abdomen, p. 390 PENTATOMiDiE GG. Scutellum not narrowed as in the Pentatomidas, very convex, nearly or quite covering the ab- domen, p. 392 Scutellerid^ *ln some cases there are minute intermediate joints between the principal joints of the antennas; for the purposes of this table these intermediate joints are not counted. 360 AN INTRODUCTION TO ENTOMOLOGY Fig. 410. — Nabi Fig. 411. — Miridae. Fig. 412. — Pyrrhocoridse. Fig. 413.— Lygagidse. Fig. 414. — Coreidae. Figures 408 to 414. — Diagrams illustrating the types of hemelytra characteristic of several families of Hemiptera. Family CORIXID^* The Water-Boatmen The family Corixidae includes oval, gray-and-black mottled bugs, usually less than half an inch in length, which live in lakes, ponds, and streams, in both stagnant and running water. The characteristic form and markings of these insects are shown in Figure 415. The name of the typical genus of this family, Corixa, is evidently from the Greek word coris, meaning a bug. For this reason many writers have spelled the generic name Corisa and the family name Corisidse. This name was probably given to these insects iDCcause they have an odor like that of the bedbug. The water-boatmen exhibit some striking peculiarities in struc- *Corixidae, Corixa, a misspelling of Corisa: coris (kVO, a bug. IIEMIPTERA 361 ture: the head overlaps the prothorax instead of being inserted in that segment; the beak is ver>^ short and scarcely distinguishable from the face, the opening to the mouth being on the front of the so- called beak; the tarsi of the front legs (termed palce) are flattened or scoop-like in form; each consists of a single se^^ent and bears a comb-like fringe of bristles; the middle legs are long, slender, and end in two claws ; the hind legs are flattened and fringed for swimming ; and, in the males, the abdominal sterna, especially the four caudal ones, are very uns\ mmetrical, being on one side broken into irregular- shaped fragments. The water-boatmen have the body flattened above, and swim upon their ventral surface; they differ in these respects from the members of the next family. They swim with a quick, darting motion ; they use for this purpose chiefly their long, oar-like, posterior legs. When in their favorite attitude, they are anchored to some object near the bottom of the pond or aquarium by the tips of their long, slender, intermediate legs; at such times the fore legs hang slightly folded, and the posterior legs are stretched out horizontally at right angles to the length of the body. The body of these insects, with the air which chngs to it, is much lighter than water; consequently whenever they lose hold upon the object to which they have been clinging, they rise quickly to the surface, unless they prevent it by swimming. They occasionally float on the surface of the water, and can leap into the air from the water and take flight. Fig. 415.— A water-boat- The bodies of these insects, as they swim through the water, are almost completely enveloped in air. The coating of air upon the ventral surface and sides can be easily seen, for it glistens like silver. By watching the insects carefully when they are bending their bodies, the air can be seen to fill the spaces between the head and the prothorax, and between the pro- thorax and the mesothorax. The space beneath the wings is also filled with air. When these insects are in impure water, they must come to the surface at intervals to change this supply of air. But I have demonstrated that in good water it is not necessary for them to do this. The air with which the body is clothed is purified by contact with the fine particles of air in the water ; so that the insect can breathe its coat of air again and again indefinitely. It has been commonly believed that the corixids are carnivorous ; but Hungerford ('19) has shown, by an extended series of experiments, that these insects gather their food supply from the ooze at the bottom of pools in which they live. This flocculent material they sweep into their mouths by means of the flat rakes of their fore tarsi. This material is largely of plant origin ; but the protozoa and other minute animals living on it are also consimied. This author also found that the corixids feed on the chlorophyll of Spirogyra. 362 AN INTRODUCTION TO ENTOMOLOGY In most cases the eggs of corixids are attached to the steins of aquatic plants; but Ramphocorixa acuminata usually attaches its eggs to the body of a cra^Tfish. The males of most of the Corixidas are furnished with stridulating organs. These consist of one or two rows of chitinous "pegs" on the fore tarsi and a roughened area on the inner surface of the fore femora near the base. By rubbing the tarsal comb of one leg over the roughened area of the femur of the opposite leg, a chirping sound is I^roduced. These stridulating organs dififer in form in different species. In addition to the stridulating organs of the fore legs there is in certain species a more or less curry-comb-like organ near the lateral margin of the dorsal wall of the sixth abdominal segment; this has been termed the "strigil." It is situated, when present, on the left side in Corixa and on the right side in several other genera. Its func- tion has not been definitely determined. Both the adults and the eggs of Corixa are used for food for man and for birds in Mexico and in Egypt. The eggs are gathered from water-plants. Glover states that in Mexico the natives cultivate a sedge upon which the insects will deposit their eggs; this sedge is made into bundles, which are floated in the water of a lake until covered with eggs; the bundles are then taken out, dried, and beaten over a cloth ; the eggs, being thus disengaged, are cleaned and powdered into flour. Kirkaldy ('98) reports the importation into England of Corixa mercenaria and its eggs for food of insectivorous birds, game, fish, etc., by the ton; and computes "that each ton of the adults will contain little short of 250 million individuals!! As to the ova, they are beyond computation." The adults are captured at night with nets when they leave the water in swarms. It is difficult to separate the different species of water-boatmen on account of their close resemblance to each other; this is especially true of the females. Fifty-five species are listed in the Van Duzee check-list; these represent six genera. Family NOTONECTID^ The Back-Swimmers The NotonectidcC differ from all other aquatic Hemiptera in the fact that they always swim on their backs; and there is a corresponding difference in the form of these in- sects. The body is much deeper than in the allied families, and is more boat-shaped. The back, from the peculiar attitude of the insect when in the water, ^^S- Y^'^J^I^^f' corresponds to the bottom of a boat, and is sloped nee a un u a a. ^^ ^^ ^^ greatly resemble in form this part (Fig. 416). The eyes are large, reniform, twice sinuated on the outer side, and project a little way over the front margin of the prothorax. Ocelli are absent. The prothorax has the lateral margins shari^ and pro- HEMIPTERA 303. jecting. The legs are all long; the hind ])air are mueh the longest and fitted for swimming. The tarsi consist each of three segments, but the basal segment is so small that it is often overlooked. There is a ridge along the middle line of the venter which is clothed with hairs, and along each side of this a furrow. Along the upper edge of the outside of this furrow and a short distance from the side of the body, there is a fringe of long hairs, and beneath this fringe the abdominal spiracles are situated. The features presented by the ventral side of the abdomen just referred to can be seen on dead specimens; but it is well to examine them on living insects. This can be done by placing a back-swimmer in a glass of water, and, when it is resting at the surface of the water, stud>'ing it b\' means of a lens of low power. Under these conditions it can be seen that the furrow on either side of the venter is an air- chamber, which is enclosed by the two fringes of hairs, one borne by the ridge of the middle line on the body and the other by the outer margin of the furrow. It can also be seen that there is a hole near the tip of the abdomen through which the air passes into the chambers beneath the fringes of hairs. Sometimes when watching an individual under these conditions it will be seen to force the air out of the chambers beneath the fringes of hair, using the hind legs for this purpose, and sometimes an entire fringe will be lifted like a hd. By examining the first ventral abdominal segment of a dead indi- vidual a little furrow can be seen on each side; these are air-passages extending between the chambers on the ventral side of the abdomen to that beneath the wings. Air is also carried among the hairs on the lower side of the thorax, and in the spaces between the head and the prothorax and between the prothorax and the mesothorax; this is probably expired air. In collecting back-swimmers, care must be taken or they will inflict painful stings with the stylets of their beak. The manner of oviposition of these insects differs in different spe- cies. Some merely attach their eggs to the surface of aquatic plants by means of a colorless, water-proof glue; others have a long oviposi- tor by means of which they insert their eggs in the tissue of these plants. The males of some back-swimmers possess stridulating areas; these are located on the femora and tibias of the fore legs and on the sides of the face at the base of the beak. The notonectids of our fauna represent three genera ; these can be separated by the following table : A. Legs dissimilar; hind legs flattened and fringed for swimminp. B. Last segment of the antennas much shorter than the penultimate segment. NOTONECTA BB. Last segment of the antennae longer than the penultimate segment. BUENOA AA. Legs quite similar Ple.\ Notonecta. — To this genus belong the greater number of our species, of which twelve have been described. These are the back- 364 AN INTRODUCTION TO ENTOMOLOGY swimmers that are commionly seen floating at the surface of the water, with the caudal part projecting sufficiently to admit of the air being drawn into the air chambers. When in this position, their long, oar-like, hind legs are stretched outward and forward ready for action; when disturbed they dart away toward the bottom of the pond, carry-^ing a supply of air with them. Buenoa. — This genus, of which six species have been found in this country', is composed of much more slender forms than is the preceding. The habits of two of our species have been studied by Hungerford (' 19) . These insects do not rest at the surface of the water as do some species of Notonecta, but may be seen swimming slowly, or even poising in midwater some distance beneath the surface. They abound in water teeming with Entomostraca, upon which they largely feed. Plea. — The members of this genus are small insects, not exceeding 3 mm. in length. The shape of the body is quite different from that of other back-swimmers, being highly arched behind. They are found in tangles of aquatic vegetation, to the filaments of which they cling when at rest. They feed on small Crustacea. Only one species. Plea striola, has been described from our fauna. Family NEPID^ The Water-Scorpions The members of this family can be distinguished from other aquatic Hemiptera by the presence of a long respiratory tube at the end of the abdomen. This tube consists of two long filaments, each with a groove on its mesal side. By applying these ^^ ^"jjX filaments together the grooves form a tube, which ^^V^/^^ conducts the air to two spiracles situated at the '^'-N^^^^-^ caudal end of the abdomen. By means of this ap- j^HT paratus these insects are able to rest on the bottom ^^^H^S| of a shallow pond, or among rubbish or plants in r H^SP I water, and by projecting this tube to the surface / ^Br \ obtain what air they need. J With regard to the form of the body, two very I different types exist in this family. In one, repre- I sented by the genus Nepa, the body is a long oval, pjg .jy ^gp^ flat, and thin (Fig. 417); in the other, represented apiculata. by the genus Ranatra, the body is almost linear and cylindrical (Fig. 418). An intermediate form, Curicta, represented by two species, is found in Louisiana, Texas, and Arizona. The water-scorpions are carnivorous ; and with them the first pair of legs is fitted for seizing prey. In these legs the coxae are very long, especially in Ranatra; the femora are furnished with a groove into which the tibiee and tarsi fit like the blade of a pocket-knife into its handle. HEMIPTERA 365 Although the Nepidae are aquatic insects, the second and third pairs of legs are fitted for walking rather than for swimming. Of the genus Nepa we have only a single species, Nepa apiculdta. This insect is about i6 mm. in length, not including the respiratory tube, which measures a little more than 6 mm. It lives in shallow water concealed in the mud or among the dead leaves and twigs, lying in wait for its prey. The eggs are inserted in the tissues of decaying plants ; they are an elongate oval and bear near one end a crown of eleven slender fila- ments. Of the genus Ranatra eight American species have been described. These in- sects are found in the same situations as Nepa; where, owing to the linear form of the body and to the dirt with which it is usually covered, it is quite difficult to de- tect their presence. They have also been observed in deep water clinging to the stems of rushes and grasses, with the re- spiratory tube piercing the surface film (Bueno) ; and also upon floating dead leaves and stalks of cat-tail, where they were basking in the sun and entirely dry (Hungerford). Ranatra has stridulating organs; these consist of a roughened patch on the outside of each fore coxa and a rasp on the inner margin of each shoulder of the prothorax ; by means of these organs a squeak- ing sound is produced. The eggs of Ranatra have been described by Pettit; they are elongate oval, about 3.5 mm. in length, and bear at one end a pair of slender appendages, about 4 mm. long; they are embedded in the rotting stems of aquatic plants, from which the appendages of the eggs project. A monograph of the Nepidfe of North America was published by Hungerford ('22). Fig. 418. — Ranatra fusca. Family BELOSTOMATID^E The Giant Water-Fugs The common name "giant water-bugs" was applied to this family because to it belong the largest of the Hemiptera now living; a species that is found in Guiana and Brazil measures from 75 to 100 mm. in length; and the larger of our species exceed in size our other water-bugs. 366 AN INTRODUCTION TO ENTOMOLOGY Fig. 419. — Lethocenis america- nus. The members of this family are all wide and flat-bodied aquatic insects, of more or less ovate outline. The fore legs are raptorial ; the middle and hind legs are fitted for swimming, being flattened and ciliated; this is especially true of the hind legs. At the caudal end of the body there is, in the adult, a pair of narrow, strap-like respiratory appendages, which are re- tractile. These insects are rapacious creatures, feeding on other insects, snails, and small fish. Like other water-bugs, they fly fi om pond to pond and are frequently attracted to lights. This is especially the case where electric lights are used, into which they sometimes fly and are killed by hundreds. On this account they are known in man}' parts of the country as "electric-light bugs." The family Belostomatid^e is repre- sented in this country by four genera. Recent studies of the nomenclature of the genera of this famiily have resulted in the making of changes in some of the generic names. This should be kept in mind when using the older text-books. Our genera are separated by Hungerford ('19) as follows: A. Mesothorax with a strong midventral keel; membrane of the hemelytra re- duced Abedus AA. Mesothorax without a midventral keel; membrane of the hemelytra not reduced. B. Basal segment of the beak longer than the second; base of the wing- membrane nearly or quite straight. Body about 25 mm. or less in length ' Belostoma BB. Basal segment of the beak shorter than the second; base of the wing- membrane sinuous. Body more than 37 mm. in length. C. Anterior femora grooved for the reception of the tibia. ..Lethocercs CC. Anterior femora not grooved for the reception of the tibia.. Benacus Lethocerus: — To this genus and the following one belong our larger members of this family. The appearance of these insects is indicated by Figure 419, which represents Lethocenis americaniis. In this genus the anterior femora are furnished with a groove for the reception of the tibia. Five species have been described from the United States and Canada. In most of the references to these 420. — Belos- insects in our literature the gener- ic name Belostoma is used. p- .^^ —Male of Benacus. — Only a single spe- Abedus, with eggs. Fig. toma flunnnea. IIEMIPTERA 367 ciesoi this genxxs, Bendcus gnseus, is found in our fauna. This close- ly resembles Lethocerus americanus (Fig. 419), but can be distinguish - ed from that species by the absence of the groove in the femora of the fore legs. Belostoma. — To this genus as now recognized belong our more com- mon representatives of the smaller members of this family. These have long been known incorrectly under the generic name Zaitha. Our most common species is Belostoma flummea (Fig. 420). In this genus and the following one the eggs are carried by the males on their backs, where they are placed by the females, sometimes in spite of vigorous opposition on the part of the male. Ahedus. — Five species of this genus have been found in the south- western parts of the United States. Figure 421 represents the male of one of these carrying his load of eggs. Family NAUCORID^ The Creeping Water-^iigs The Naucorida: includes flat-bodied, chiefly oval insects, of moderate size. The abdomen is without caudal appendages. The front legs are fitted for grasping, the femora being greatly enlarged; the middle and hind legs are suited for crawling rather than for swimming. There are no ocelli ; the antennas are very short, and -well concealed beneath the eyes; the beak is three-jointed and covered at the base by the large labnmi ; and the hemely tra are furnished with a distinct embolium. Although these are aquatic insects, they have been comparatively little modified for such a life. They carry air beneath their wings and obtain this air by pushing the tip of the abdomen above the surface of the water. They are predac'ous and are fond of reedy and grassy, quiet waters, where they creep about like the dytiscid beetles, creeping and swimming around and Fig.422.--Pf/- between the leaves and spravs of the submerged plants, oconsfemor- seekmg their prey. Only two genera of this family are represented in our fauna; these are Pelocoris and Ambry sus. In Amhrysus the front margin of the prothorax is deeply excavated for the reception of the head; in Pelocoris this is not the case. Pelocoris. — Only three speciesof thisgenus are found in this country and these are restricted to the eastern half of the United States. The most common one is Pelocoris femordtiis (Fig. 422). It measures about Q mm. in length, and when alive is more or less greenish testa- ceous in color; but after death it is pale yellow or brownish in color, with black or dark brown markings. Ambrysus. — Ten species of this genus have been found in this country; thev are restricted to the Far West. 368 AN INTRODUCTION TO ENTOMOLOGY Family GELASTOCORID^ The Toad-shaped Bugs The GelastocoridcB was formerly known as the GalguHdae; conse- quently most of the references to these insects will be found under the older family name, which has been dropped, as the generic name Galgulus, on which it was based, is not tenable. In these insects the body is broad and short, and the eyes are prominent and projecting; the form of the body and the protuberant eyes remind one of a toad (Fig. 423). Ocelli are present. The an- tennas are short and nearly or quite concealed beneath the eyes. The beak is short, stout, and four-segmented. The fore legs are raptorial. The toad-shaped bugs live on the muddy margins of streams or other bodies of water. Some of them make holes for themselves, and live for a part of the time beneath the ground. They feed upon other insects, which they capture by leaping suddenly upon them. Their colors are protective and vary so as to agree with Fig.423-7-Ge/- -f-j-^g color of the soil on which thev live. Hungerford /a/?/'" "'''' has found that the eggs are buried in the sand. Only five species are known to occur in this country. The most common and most widely distributed representative of the family found in this country is Gelasiocoris oculdtus (Fig. 423). Two other species of Gelasiocoris are found in the Southern and Western States. In this genus the hemelytra are not fused and the fore tarsi are two-clawed. In the genus Mononyx, of which a single species, Mononyxjiiscipes, is found in California, the hemelytra are free, but the fore tarsi are one-clawed. The genus NMhra is also represented in this country by a single species, Nerthra styglea, which is found in Georgia and Florida. In this genus the hemelytra are fused together along a straight suture indicated by a groove. Family OCHTERID^ The Ochterids These are shore-inhabiting bugs, which are closely allied to the preceding family, in which they were formerly classed. They differ from the toad-shaped bugs in having the fore legs slender and fitted for running, and in having the short antennae exposed. They resemble the following family, the Saldidae, in having the beak long, reaching the hind coxae. The eyes are prominent, and two ocelli are present. The family includes a single genus, Ochterus, which, due to an error, has been commonly known as Pelogonus. Only three species occur in the United States; one of these was described from Virginia, one from Florida, and the third is widely distributed from the At- lantic Coast to Arizona. HEMIPTERA 369 The widely distributed species is Ochterns americanus. It measures 5 mm. in length, and is blackish in color sprinkled with golden yellow points. On each side of the prothorax, behind the front angles, there is a bright yellow spot. The members of this family are predacious. Family SALDID^ The Shcre-Fngs With the Saldida? we reach the beginning of the extensive series of families of Hemiptera in which the antennae are prominent and are not concealed beneath the head. In this family the insects are of small size, and of dark colors with white or yellow markings. The head stands out free from the thorax on a cylindrical base. The an- tennae are four-jointed; there are two ocelli; the rostrum is three- jointed and very long, reaching to or beyond the middle coxae. The membrane of the wing-covers is furnished with looped veins, forming four or five long cells placed side by side. Occasionally there is little or no distinc- tion between the corium and the membrane. Two forms sometimes occur in the same species, one with a dis- tinct membrane, and another with the membrane thick- ^^S- 424— A ened and almost as coriaceous as the corium proper. ^'loreoug. The shape of these shore-bugs is shown by Figure 424. These insects abound in the vicinity of streams and other bodies of water, and upon damp soils, especially of marshes near our coasts. Some of the shore bugs dig burrows, and live for a part of the time beneath the ground. They take flight quickly when disturbed, but alight after flying a short distance, taking care also to slip quickly into the shade of some projecting tuft of grass or clod where the soil agrees with the color of their bodies. Thirty-three species belonging to this family have been found in the United States and Canada; these represent eight genera. Family VELIID.^ The Broad-shouldered Water-Striders The Velliidse includes insects which are very closely allied to the following family, the water-striders, both in structure, and in'^habits. In both families the distal segment of the tarsi, at least of the fore tarsi, is more or less bifid, and the claws are inserted before the apex ; these characters distinguish these two families from all other Hemip- tera. In the Veliidje the body is usually stout, oval, and broadest across the prothorax (Fig. 425). The beak is three- jointed; the legs are not extremely long, the hind femora not extending much beyond 370 AN INTRODUCTION TO ENTOMOLOGY the end of the abdomen. In fact, the legs are fitted for running over the water, instead of for rowing, as with the Gerridas. The intermedi- ate legs are about equidistant from the front and hind pairs, except in Rhcgovelia. These insects are dimorphic, both fully winged and short -winged or wingless adults occurring in the same species. About twenty species of this family have been found in America north of Mexico; these represent four genera. The broad-shouldered water-striders are found both on the banks of streams and ponds and on the surface of water. About one-half of our species belong to the genus Microvelia. These are very small, plump-bodied bugs, which are usually black and silvery in color or mottled with brown. They are found at the water's edge but run out on the water when disturbed ; and they are also often found upon rafts of floating vegetation. To the genus Rhagovelia belong somewhat larger forms, which are characteri2ed by the long, deeply split, terminal segment of the tarsi of the middle legs. Our most common species of this genus is Rhagovelia ohesa (Fig. 425). These bugs are found running over the surface of rapidly moving waters in streams. They can also dive and swim well under water. Four species of Rhagovelia are found in this ^. „, ,. , ^ '^ Fig. 42s. — Kliapovelia country. *> -+ o The genus Velia includes the larger members of the family. In these the tarsi of the middle legs are not cleft. Four species of this genus occur in our fauna. They are found on moderately rapid streams or little bogs and eddies connected there- with. The fourth genus occurring in our fauna is represented by a single species, Mocrovelia harrisii, which is restricted to the Far West. Family GERRID^ The Water-Striders This family includes elongated or oval insects which live upon the surface of water. Their legs are long and slender; the hind femora extend much beyond the apex of the abdomen; the middle and hind pairs of legs are approximated and distant from the fore legs; the terminal segment of the tarsi, at least of the fore tarsi, is more or less bifid, and the claws are inserted before the apex. The beak is four-jointed. The antenna are long and four-jointed. The water-striders prefer quiet waters, upon which they rest or over which they skim rapidly; they often congregate in great numbers. There are commonly two forms of adults belonging to the same species, the winged and the wingless; sometimes a third form occurs in which the adult has short wings. These insects are predacious; they feed on insects that fall into the water, and I have seen them jump from the water to capture flies and other insects tliat were flying near them. II KM I PT ERA 371 Twenty species of water-striders ha\^e been found in America north of Mexico; these represent seven genera. These genera are separated by Hungerford ('19) as follows: A. Inner margin of the eyes sinuate behind the middle. Body comparatively long and narrow; abdomen long. (Subfamily Gerrinse). B. Pronotum sericeous, dull; antennae comparatively short and stout. C. First segment of the antennae shorter than the second and third taken together. D. Antennae half as long as the body; sixth abdominal segment of the male roundly emarginate Limnoporus DD. Antennae not half as long as the body, not extending beyond the thorax; sixth abdominal segment of the male doubly emarginate. Gerris CC. First segment of the antennae longer than the second and third taken together Gerris BB. Pronotum glabrous, shining; antenna long and slender. . .Tenagogonus AA. Inner margin of the eyes convexly rounded. Body comparatively short and broad; abomen so short as to appear almost nymjjhal in some forms. (Subfamily Halobatinae). B. First antennal segment much shorter than the other three taken together; not much longer than the second and third taken together, and some times shorter. C. Fourth (apical) segment of the antennas longer than the third. D. Eyes fairly prominent; colors of body black and yellow. .Trepobates DD. Eyes smaller, widely separated; body lead-colored, sericeous. ocean dwellers Halobates CC. Fourth segment of antennae never more than equal to the third; basal segment of anterior tarsi much shorter than the second; hind femur equal to or much shorter than the hind tibia and tarsus taken together Rheumatobates BB. First antennal segment nearly equal to the remaining three taken to- gether, much longer than the second and third; antennas almost as long as the entire body; hind femur twice as long as hind tibia. Metrobates Gerris. — Of the twenty species of water-striders found in this country, nine belong to this genus; a common species in the East is Gerris conformis (Fig. 426). Fig. 426. — Gerris conformis. Limndporus.- — We have only a single species of this genus, L. rii- Joscutilldtus. Tenagogonus. — Three species are listed from our fauna, only one of which has been found in the North; this is T. gillettei, which is reported from Ohio. The others are found in Florida and California. Metrobates.- — Our only species, M. hesperius, is found in Ontario and the eastern part of the United States. 372 AN INTRODUCTION TO ENTOMOLOGY Trepobates. — This genus is represented only by T. ptctus. This is a beautiful vellow and black species, which is quite widely distribut- ed. Rheumatobates. — Three species of this genus have been described . The males are remarkable for the strange form of the posterior femora, which are strongly bent, and the shape of the antennse, which are fitted for clasping. Halobates. — These are truly pelagic insects, living on the surface of the ocean, often hundreds of miles from land. They are most abundant in the region of calms near the equator; they feed on the juices of dead animals floating on the surface, and probably attach their eggs to floating sea-weed (Sargassum) . H. micans is found off the coast of Florida and H. sericeus off the coast of California. Family MESOVELIID.'E The Mesoveliids This is a small family of which only two species have been found in North America. These are the following. Mesovelia mulsdnti. — This is a small bug, measuring only 4 or 5 mm. in length; it is of a pale yellow color marked with brown. The antennae are long, filiform., and four-jointed; the beak is three- jointed; the legs are moderately long and slender; and the tarsi are three-jointed. This species is dimorphic, the adults being either winged or wingless. In the winged form, the membrane of the hemelytra is without veins. This species lives on the surface of quiet waters and on rafts of floating vegetation and is predacious. It is furnished with an ovi- positor and embeds its eggs in the stems of aquatic plants. Mesovelia douglasensis . — This is a smaller species than the pre- ceding; the length of the female is 2.1 mm., of the male 1.8 mm. It is olive-brown in color. It was recently discovered and described by Professor Hungerford ('24). It was found near Douglas Lake, Michi- gan. Family HEBRID^ The Hebrids This family includes very small plump-bodied bugs, measuring less than 3 mm. in length. The antenna are either four-jointed or five- jointed; the beak is three-jointed; and the tarsi are two-jointed. Ocelli are present. The head and thorax are sulcate beneath. The clavus of the hemelytra is similar in texture to the membrane, which is without ^1/S;r^^™'''^'''°" °^ ^'^'"^ ^^'S- 427)- Two genera of this family ^ '^"■^' are found in the United States. HEMIPTERA 373 Hebrus.- — In this genus the antennae consist of five segments, not counting a minute segment at the base of the third. The adults are always winged. Four species occur in our fauna. These bugs are found on moist earth at the margins of pools and run out upon the water when disturbed; they are also found on floating vegetation. Merragdta. — In this genus the antennae are four-jointed not count- ing the small segment at the base of the third. The adults are dimor- phic, short-winged and long-winged forms occcurring in the same species. These insects inhabit still and stagnant waters and often descend beneath the surface; at such times the body is surrounded by a film of air. Only two species have been found, as yet, in this country. Family HYDROMETRID.-E The Water-Measurers The members of this family are very slender insects, with linear legs and antennae (Fig. 428) . The head is as long as the entire thorax, although this region is long also. The eyes are round, projecting, and placed a little nearer the base than the tip of the head. Ocelli are absent. The antenna are four-jointed; the beak is three- jointed; and the tarsi are three-jointed. These insects creep slowly upon the surface of the water; they carry the body considerably ele- vated, and are found mostly where plants are growing in quiet waters. It was probably their deliberate gait when walking on water that sug- gested the generic name Hydrometra, or water- measurer. In this country these insects have been commonly known under the generic name Limnobates, or marsh-treaders ; but Hydrometra is much the older name. Only three species have been found in the United States. One of these, Hydrometra martini Fig. 428. — Hydrome- (Fig. 428), is widely distributed. The other two, tra martini' Hydrometra australis and Hydrometra wileyi, are found in the South. These insects are dimorphic both winged and wingless forms occurring in the same species. Descriptions of the three species are given by Hungerford ('23). The egg of Hydrometra martini is remarkable in form ; it is figured on page 167. Family SCHIZOPTERID^ The Schizopterids This family and the following one, the Dipsocoridae, constitute a quite distinct superfamily, the members of which are most easily rec- 374 AN INTRODUCTION TO ENTOMOLOGY ognized by the form of the antennae (Fig. 429, b). These are four- jointed; the first two segments are short and thick; the third and fourth segments are long, slender, and clothed with long hairs; the third segment is thickened toward the base. In these two families ocelli are present; the beak is three- jointed; the legs are quite slender, and the tarsi are three-jointed. The species are small or very minute. The vSchizopteridae is distinguished from the following family by the shape of the head and the form of the cavities in which the front legs are inserted. The head when viewed from above is wider than long and is strongly defiexed; the fore coxal cavities are very prominent and tumidly formed. The beak is short. Fig. 429.~Glyptocombussaltator: The Schizopteridas is represented in a, dorsal aspect; b, antenna, our fauna by a single species, Glyptocom- (After Heidemann.) bus saltdtor "(Fig. 429). This is a minute bug, measuring only 1.2 mm. in length and .6 mm. in width. The known specimens were taken on Plimimers Island, Md. The describer of this species, Mr. O. Heidemann, states: "This species is most difficult to collect and is only to be found by sifting fallen leaves, rubbish and earth. The collector must watch patiently until the minute insect makes its presence known by jumping, and even then it takes a skillful hand to secure it in a vial." Family DIPSOCORID^ The Dipsocorids This family is closely allied to the preceding family; the dis- tinguishing features common to the two families are indicated in the account of that family. In the Dipsocoridce the head is extended horizontally or slightly defiexed, and the fore coxal cavities are not at all prominent. The beak is long. This family is represented in our fauna by a single genus, Cera- tocombtis, of which two or three species have been found in New Mexico; and one of these is doubtfully reported from Florida. These measure less than 2 mm. in length. Family ISOMETOPID^ The Tsometopids This is a family of limited extent, there being very few species known in the entire world. It includes ver\^ small bugs, those found in this country ranging from 2 mm. to 2.6 mm. in length. HEMIPTERA 375 The Isometopickc is closely allied to the followinj^; famih-, the Mirida;; by some writers it has been classed as a subfamil\' of that family. In both families the antennae are four-jointed; the beak is four-jointed; the hemelytra are composed of cla\ais, corium, cuneus, and membrane; at the base of the membrane there are one or two cells; otherwise the membrane is with out veins. The Isometopidse is dis- tinguished from the following family by the presence of ocelli, two in number. Only four species of this family have been found in our fauna; one in Texas, one in Arizona, and two in the East. The Eastern species are Myiomma cixii- formis, which is dull black in color with a narrow white band across the base of the cuneus; and Isometopus pulchellus, which is easily recognizable by its contrasting colors of dark brown and yellowish white (Pig. 430). Both are exceedingly rare in- sects. Family MIRID^ The Leaf-Bugs Fig. 430. — Isometopus pulchel- lus. (After Heidemann.) This family, which has been known as the Capsidae, is more large- h' represented in this country than any other family of the Hemiptera. Van Duzee in his "Catalogue of the Hemiptera North of Mexico" lists 398 species, which represent 129 genera. The species are usually of medium or small size. The form of the body varies greatly in the different genera, which makes it difficult to characterize the family. The most available char- acter for distinguishing these insects is the structure of the hemelytra. These are almost always complete, and com- posed of clavus, corium, cuneus, and membrane. At the base of the membrane there are one or two cells; otherwise the membrane is without veins (Fig. 431). Other characters of the family are as follows: the ocelli are wanting; the beak and the antennas are each four-jointed ; the coxae are subelongate; and the tarsi are three-jointed. It is impracticable to discuss here the divisions of this family; reference can be made to only a few of the more common species. The four-lined leaf-bug, Pcecilocapsus lineatus. — This is a bright Pcedlocapsus 376 AN INTRODUCTION TO ENTOMOLOGY yellow bug, marked with black. It measures about 8 mm. in length. There are four longitudinal black lines which extend over the prothoraxand the greater part of the hemeMra (Fig. 432). There is in man}^ individuals a black dot on the cuneus of each hemelytron; and the membrane is also black. This insect infests various plants, but abounds most on the leaves of currant, gooseberry, mint, parsnip, Weigela, Dahlia, and rose. It punctures the young and tender leaves, causing small brown spots; but these are sometimes so nimierous and closely placed that the leaves become completely withered. It is a widely distributed species, its range extending from Canada to Georgia and westward to the Rocky Alountains. There is only one generation a year. The eggs are laid in the terminal twigs of currant and other bushes in midsummer and hatch the following spring. They are laid in clusters, each containing six or eight eggs; these egg-clusters are forced out of the stem somewhat by the growth of the surrounding plant tissue; and as the projecting part of the egg is white, they can be easily found. The methods of control are the pruning and burning of twigs containing egg-clusters, and, early in the season, ^fuolat>s' ^^^ destruction of the nymphs by the use of kerosene lineatus. emulsion or some one of the tobacco extracts. The tarnished plant-bug, Lygus pratensis. — The tarnished plant-bug is a very common species which is found through- out the United States and in Canada. It is smaller than the preceding species, measuring 5 mm. in length and 2.5 mm. in its greatest width. It is exceedingly variable in color and markings ; its color varies from a dull bark -brown to a greenish or dirty yellowish brown. In the more typical forms the prothorax has a yellowish margin and several longitudinal yellowish lines; there is a V-shaped yellowish mark on the scutellum; the distal end of the corium is dark; and the cuneus is pale, with a black point at the apex. This pest is a very general feeder; it has been recorded as injuring about fifty species of plants of economic value; its injuries to the buds of Aster, Dahlia, and Chrysanthemum, and to the buds and blossoms of orchard -trees, and to nursery stock, are well-known. As yet no practical method of control of this pest has been found. The apple-redbug, Heterccordylus malinus. — This species and the following one are sometimes a serious pest in apple orchards. They cause spotting of the leaves; but, what is far more serious, they punc- ture the young fruit, which results either in the dropping of the fruit or in its becoming badly deformed so as to be unmarketable. The eggs are inserted into the bark of the smaller branches late in June or early in July; they hatch in the following spring soon after the opening of the leaves of the fruit-buds. The n) mphs are tomato- red in color. They first attack the tender leaves, but as soon as the fruit sets they attack it. The young nymphs can be killed by an IIEMIPTERA 377 application of "black leaf 40" tobacco-extract diluted at the rate of. I pint in 100 gallons of water; the efficiency of this spray is increased by the addition of about 4 pounds of soap to each 100 gallons. Two applications of the spray should be made: the first, just before the blossoms open; the second, just after the petals fall. The spraying should be done on bright warm days, for in cool weather many of the nymphs hide away in the opening leaves. The adult apple-redbug is about 6 mm. long. The general color varies from red to nearly black. Usually the thorax is black in front and red behind. The wings are red. usually black along the inner edge and with a pointed ovate black spot near the outer margin. The scutellum, legs, and antenn£e are black. The entire dorsal sur- face is sparsely covered with conspicuous white, flattened, scale-like hairs. The false apple-redbug, Lygideamendax. — This species resembles the preceding one in general appearance and in habits. The nymphs can be distinguished by their brighter red color, b^ the absence of dusky markings on the thorax, and by having the body clothed with fine, short, black hairs. The adult of this species is lighter- colored and lacks the scale-like hairs on the dorsal surface. The above account of these two species is an abstract of one pub- lished by Professor C. R. Crosby ('11). The hop-redbug, Paracalocoris hawleyi. — The leaves of hop plants are sometimes perforated and the stems stunted and deformed by the nymphs of this species, which are red with white markings. The adult is 6 mm. long, black, with hemelytra hyaline or pale yellowish, and the cuneus reddish. For a detailed account see Hawley ('17). Family TERMATOPHYLID^ The Termatophylids This family is closely allied to the following one, the Anthocorida?, but differs in that the beak is four-jointed and ocelli are wanting. The hemelytra are well developed, furnished with an embolium, and usually with a single large cell in the membrane. The tarsi are three- jointed and are not furnished with an arolium. The Termatophylidffi is a very small family, but it is world-wide in its distribution. A single very rare species has been found in this country. This is Hesperophylum heidemdnni, which has been taken in New Hampshire and Arizona. Only the female of this species has been described. It is dark brown with the scutellum yellowish white; the cell in the membrane of the hemelytra is semicircular ; the length of the body is 4 mm. Family ANTHOCORID^ The Flower-Bugs This family is closely allied to the following one; but in the flower-bugs ocelli are present, though sometimes difficult to see. 378 AN INTRODUCTION TO ENTOMOLOGY and the hemelytra are almost always fully developed and are furnished with an embolium (Fig. 433). As in the following family, the beak consists of three segments; the antenna}, of four; and the tarsi, of three. The species are small. The}^ are found in a great variety of situations, often upon trees and on flowers, sometimes under bark or rubbish. They are predacious. -Hemelytron of Triphelps. Thirty-six Species have been catalogued in our fauna; these represent thirteen genera. The following species will serve as an example. The insidious flower-bug, Triphelps insididsns. — -This is perhaps the best -known of our species. It is a small black bug, measuring only 2 mm. in length; the hemelytra are yellowish white on the coritmi, at the tip of which is a large, triangular, blackish spot; the membrane is milk}'- white. This species is widely distributed; it is common on flowers, and is often found preying upon the leaf -inhabit- ing form of the grape Phylloxera; it is also often found in company with the chinch-bug, upon which it preys and for which it is some- times mistaken. Family CIMICID^ The Bedbug Family The members of this family are parasitic bugs, which are either wingless or possess only vestigial hemelytra. In these insects the ocelli are absent, the antennae are four-jointed, the beak is three- jointed, and the tarsi are three-jointed. Only four species belonging to this family have been found in America north of Mexico. These can be separated by the following table, which is based on a more detailed one given by Riley and Johannsen ('15). A. Beak short, reaching to about the anterior coxs. B. Pronotum with the anterior margin very deeply sinuate. The genus Cimex. C. Body covered with very short hairs; second segment of the antenna; shorter than the third; hemelytra with the inner margin rounded and shorter than the scutellum. The common bedbug. . .C. lectuldrius CC. Body covered with longer hairs; second and third segments of the an- tennas of equal length; hemelytra with the inner margin straight and longer than the scutellum. Species found on bats. . .C.pilosellus BB. Anterior margin of the pronotum very shghtly sinuate or nearly straight in the middle. Species found in swallows' nests .. .Qictacus vicdrius AA. Beak long, reaching to the posterior coxae. Infests poultry in southwest United States and in Mexico Hamatoslphon inodorus The common bedbug, Clmex lectuldrius. — The body is ovate in outline and is very fiat (Fig. 434) ; it is reddish brown in color, and is 4-5 mm. long by 3 mm. broad when full-grown. This pest is a noc- HRMIPTERA 379 Fig.434.— Cme.v lectulanus. turnal insect, hiding by day in cracks of furniture and beneath various objects. Ordinarily it is found only in the dwellings of man; but it has been known to infest chicken houses. The means commonly employed to destroy this pest is to wet the cracks of the bedstead and other places in which it hides with corrosive sublimate dissolved in alco- hol. This is sold by druggists under the name of bedbug poison. As this substance is a virulent poison, it should be used with great care. In case a room is badly infested, it should be thoroughly cleaned; fumigated with sulphur or with hydro- cyanic acid gas; the walls repapered, kalsomined, or whitewashed ; and the woodwork repainted. Detailed directions for the use of gases against household insects are given by Herrick ('14). In traveling, where one is forced to lodge at places in- fested by this insect or by fleas, protection from them can be had by sprinkling a small quantity of pyrethrum powder between the sheets of the bed on retiring. The other members of this family found in this country can be distinguished from the com- mon bedbug by means of the table given above. Family POLYCTENID.-E The Many-combed Bugs The Polyctenidffi includes a small number of very rare species of bugs that are parasitic upon bats. Until recently it was not known to be represented in America north of Mexico; but Ferris ('19) records the finding of one species, Hesperoctenes longi- ceps, on the bat Eumops calif orni- cus, near San Bernardino, Cali- fornia. Figure 435 is a reduced copy of a figure of this insect by Ferris. The left half of the figure represents the dorsal aspect of this insect; the right half, the ventral aspect. This carefully made figure renders a detailed description unnecessary. The length of the body of the female is 4.5 mm.; of the male, 3.8 mm. Fig. 4^,5. —Hesperoctenes longiceps: A, female, left half dorsal, right half ven- tral; B, posterior tarsus; C, anterior tarsus; D, dorsal aspect of second an- tennal segment, distal end upward. (After Ferris.) 380 AN INTRODUCTION TO ENTOMOLOGY Hemelytron of Nabis ferns. In this family the hemelytra are vestigial and the hind and middle tarsi are four-jointed. The name of the typical genus, Polyctenes, was probably suggested by the presence of several comb-like series of spines on the body. Family NABIDtE The Nabids In this family the body is oblong and somewhat oval behind. The beak is long, slender, and four-jointed. The hemelytra are longer than the abdomen, or are very short . Some species are di- morphic, being represented by both long-winged and short-wing- ed forms. In the forms with long wings the membrane is usually furnished with four long veins bounding three discal cells, which are often open ; from these discal cells diverge veins which form several marginal cells (Fig. 436). The fore tibiae are armed with spines and are capable of being closed tightly upon the femora, which are stout; they are thus fitted for grasping prey. Nearly all of our common species belong to the genus Nabts; in fact this genus includes twenty-six of the thirty-one species found in this country. Due to an error made long ago, this genus has been commonly known as Coriscus; and most of the references to these insects are under this name. Nobis ferus. — This is one of our most common species. It measures about 8 mm. in length. It is pale yellow with numerous minute brown dots; the veins of the membrane are also browrlish. This species is distributed from the Atlantic Coast to the Pacific. It secretes itself in the flowers or among the foliage of various herbaceous plants, and captures small insects upon which it feeds. Ndbis subcoleoptrdtus. — The short-winged form of this species is another very common insect (Fig. 437). This is of a shining jet-black color, with the edge of the abdomen and legs >-ellowish. The hemelytra barely extend to the second abdominal segment. The long-winged form of this species is not common; it is much narrower behind, and the hemelytra and the ab- domen are rather dusky, or piceous, instead of jet-black. Family REDUVIID^ The Assassin-Bugs The Redu\didae is a large family, including numerous genera of diverse forms. AIan\' of the members of it are insects of considerable HEMIPTERA 381 size, and some are gayly colored. They are predacious, living on the blood of insects. In some cases they attack the higher animals; and, occasionally, even man suffers from them. Fig. 438. — Arilus cristatus. (From Glover.) In this family the beak is short, three-jointed, attached to the tip of the head, and with the distal end, when not in use, resting upon the presternum, which is grooved to receive it. Except in a few spe- cies, ocelli are present in the winged forms. The anten- nas are four-jointed. More than one hundred species occur in our fauna; these represent forty-four genera. The following species will serve to illustrate the great diversity in form of members of this famHy. The wheel-bug, Arilus cristatus. — The wheel-bug is so called on account of the cogwheel-like crest on the prothorax (Fig. 438). It is a common insect south of New York City, and is found as far west as Texas and New Mexico. The adult, a cluster of eggs, and several nymphs, are represented in the figure. The nymphs when young are blood-red, with black marks. The masked bedbug-hunter, Rediivius persondtus. — The adult of this species is represented by Figure 439; it measures from 15 to 20 mm. in length, and is black or ver}' dark brown in color. 382 ^A^ INTRODUCTION TO ENTOMOLOGY There are two marked peculiarities of this species that have caused it to attract much attention: first, in its immature instars the body is covered with a viscid substance which causes particles of dust and fibers to adhere to it; not only the body, but the legs and antennse also, are masked in this way; in fact the nymph resembles a mass of lint, and attracts attention only when it moves; second, this species infests houses for the sake of preying upon the bedbug. It feeds also upon flies and other insects. The big bedbug, Tridtoma sangtiisuga. — Closely allied to the masked bedbug-hunter is a large bug which insinuates itself into beds for a less commendable purpose than that of its ally, for it seeks human blood at first hand. This insect measures 25 mm. in length; it is black marked with red; there are six red spots on each side of the abdomen, both above and below. It inflicts a most painful wound. This is one of several species of the Reduviida? that received the name of "kissing-bug" as a result of sensational newspaper accounts which were widely published in the summer of 1899 and which stated that a new and deadly bug had made its appearance, which had the habit of choosing the lips or cheeks for its point of attack on man. It is found from New Jersey south to Florida and west to Illinois and Texas. The genus Triatoma was renamed Conorhinns and most of the references to this species are under this generic name. The thread-legged bug, Emesa hrevipennis, — This is our most common representative of one of the subfamilies of the Redu- viidcC in which the body is ver}" slenderandthemiddle and hind legs are thread-like (Fig. 440). The front legs are less thread- like, and are fitted for grasp- ing ; they suggest by their form the front legs of the Mantidas; the coxa is greatly elongated, more than four times as long as Fig. 440. — Emesa hrevipennis. thick; the femur is spined; and the tibia shuts back upon the femur. In Figure 440 they are represented beneath the thread- like antennae. Emesa hrevipennis measures about 33 mm. in length; it is found upon trees, or sometimes swinging by its long legs from the roofs of sheds or barns. A monograph of the Reduviida? of North America has been pub- lished by Fracker ('12). Family PHYMATID^ The Ambush- Bugs The Ph^TTiatidas is poorly represented in this country but some of the species are very common. Here we find the body extended IIEMIPTERA 383 laterally into angular or rounded projections, suggesting the name of the typical genus. But the most striking character which dis- tinguishes this group is the remarkable form of the front legs. These are fitted for seizing prey. The coxa is somewhat elongated ; the femur is greatly thickened, so that it is half or two thirds as broad as long; the tibia is sickle-shaped, and fits closely upon the broadened and curved end of the femur; both tibia and femur are armed with a series of close-set teeth, so that the unlucky insect that is grasped by this organ is firmly held between two saws ; the apparently useless tarsus is bent back into a groove in the tibia. Another striking character is presented by the antennas, the terminal segment being more or less enlarged into a knob. Under the lateral margin of the pronottun in Phymata there is on each side a groove into which the antenna fits. Only two genera are represented in our fauna, each by six species. These are Phymata and Macrocephahis. In Phymata the scutellum is of ordinary size; in Macro- cephalus it is very large and extends to the tip of the abdomen. Our most common species is Phymata erosa (Fig. 441). It is a }ellow insect, greenish when fresh, marked with a broad black band across the expanded part of the abdomen. It conceals itself in the flowers of various plants, and captures the insects which come to sip nectar. It is remarkable what large insects it can overcome and destroy; cabbage butterflies, honey-bees, and large wasps are over- powered by it. Family ENICOCEPHALID^ "m Fig. 441. Phymata ffsa. The Unique-headed Fugs In this family the hemelytra are wholly mem- branous and provided with longitudinal veins and a few cross-veins (Fig. 442). The head is constricted at its base and behind the eyes, and is swollen between these two constrictions. This is a form of head not found in any other Hemip- tera. Ocelli are present. The antennae are four- jointed; the first, second, and third segments are each followed by a small ring-joint. The beak is four-jointed. The front tarsi are one-jointed, the middle and hind tarsi two-jointed. The front legs are fitted for grasping prey, the fore tarsi being capable of closing upon the end of the broad tibiae. This is a small family; but few species are known from the entire world, and only two have been described from America north of Mexico. These are Enicrcephalus formtciua, found in California, and Systelloderus biceps, which has been found from New York to Utah. Fig. 442. — Systello- derus biceps. (Af- ter Johannsen.) 384 AN INTRODUCTION TO ENTOMOLOGY But little has been published regarding the habits of these insects. It is evident, from the structure of their fore legs, that they are predacious. Professor Johannsen ('09 b) found Systelloderus biceps {Henicocephalus cuUcis) flying in small swarms near Ithaca, N. Y. Their manner of flight resembled that of chironomids. They were obser\^ed repeatedly from July 5 to the last week in August, always in the latter part of the afternoon. This species measures 4 mm. in length. The type genus of this family was first named Enicocephalus ; this name was later emended to Henicocephalus; but the older form of the name, though incorrectly formed, is now used. Family TINGIDtE The Lace-Bugs The Tingidae are doubtless the most easily recognized of all Hemip- tera. The reticulated and gauze-like structure of the hemelytra, usually accompanied by expansions of the pro- thorax of a similar form, gives these insects a characteristic appearance which needs only to be once seen to be recognized in the future. Figure 443 represents one of these insects greatly enlarged, the hair-line at the side indicating the natural size of the insect. They are generally verv small insects. But they occur in great numbers on the leaves of trees and shrubs, which they puncture in order to suck their nourishment from them. In this family the ocelli are wanting; the beak and antennas are four- jointed; the scu- tellum is usually wanting or vestigial, replaced by the angular hind portions of the pronotiim; and the tarsi are two-jointed. About seventv-five species of lace-bugs, representing twenty-three genera, are now listed from this country. There are two well-marked subfamilies. Subfamily TINGING Fig. 443. — Corythitcha arcuata. This division includes nearly all of the known species. Here the scutellum is usually covered by an angular projection of the pronotum ; and the hemelytra have no distinction between the clavus, corium, and membrane. The following species will serve as an il- lustration of this subfamily. The hawthorn lace-bug, CorythUcha arcuata. — This is a widely distributed species, which punctures the under surface of the leaves of different species of Cratcegus. The infested leaves have a brown and sunburnt appearance. Eggs, n>Tnphs, and adults are found together. The adult is represented, much enlarged, in Figure 443. HEMIPTERA 385 In Figure 444 the eggs and a nymph are shown. The eggs are covered by a brown substance, which hardens soon after oviposition. Subfamily PIESMIN^ In this subfamily the scutellum is not covered; the hemelytra have a distinct clavus, with a well-marked claval suture; the clavus is furnished with one, and the corium with three, longitudinal veins which are much stronger than the network of veins between them. In long- winged individuals the tip of the membrane lacks the network of veins and appears like the mem- brane in other families. As yet but a single American species has been described. The ash-gray Piesma, Piesma cinerea.- — This species measures about 3 mm. in length, and is of an ash-gray color. The prothorax is deeply pitted, so that it presents the same appearance as the base of the wing-covers. The head is deeply bifid at tip, and there is a short robust spine be- tween the eye and the antenna on each side. This species sometimes infests vineyards to an injurious extent, destroying the flower-buds in early spring. Family PYRRHOCORID^ Fig. 444.— Eggs and nymph of Cory- ihucha arcuata. The Cotton-Stainer Family In this family the antennee are four-jointed; the beak is also four-jointed; ocelli are absent; and the hemelytra are not furnished with a cuneus. The members of the family are stout and heavily built insects, and are generally rather large and marked with strongly contrasting colors, in which red and black play a con- spicuous part, in this respect re- sembling some of the larger species of the following family. The Pyrrhocoridae can be dis- tinguished from the Lygasidae by the absence of ocelli, and by the venation of the membrane of the hemelytra (Fig. 445). At the base of the membrane there are two or three large cells, and from these arise branching veins. Only twenty-two species, representing five genera, have been found in our fauna, and these are restricted to the Southern and Western States. Our most important species, from an economic standpoint, is the red-bug or cotton-stainer, Dysdercus suturellus (Fig. 446). It is Fig. 445. — Hemelytron of Euryopthal- mus succincttis. 386 ^.V INTRODUCTION TO ENTOMOLOGY oblong-oval in form, of a red color; the hemeh-tra and an arc on the base of the prothorax, and also the scutellum, are pale brown. The hemeh^ra have the costal margin, a narrow line bordering the base of the membrane and continuing diagonally along the outer margin of the clavus, and also a slender streak on the inner margin of the clavus, pale yellow. It varies much in size, ranging from lo mm. to 1 6 mm. in length. The young bugs are bright red with black legs and antennae. From time immemorial this has been one of the worst pests with which the cotton-planters of Florida and the West Indies have had to contend. It does much damage by piercing the stems and bolls with its beak and sucking the sap ; but the principal injury to the crop is from staining the cotton in the opening boll by its excrement. It is also injurious to oranges; it punctures the rind of the fruit with its beak; and soon decay sets in, and the fruit drops. These insects can be trapped in cotton-fields by laying chips of sugar-cane upon the earth near the plants ; in orange-groves small heaps of cotton-seed will be found useful, as well as pieces of sugar-cane. The insects that collect upon these traps can be destroyed with hot water. The species whose range extends farthest north is Euryophthdlmus succindtus. This is found from New Jersey south to Florida and west to Arizona. It is brownish black, with the lateral and Fig. 446. — Dys- dercus suturellus. hind margins of the prothorax, elytra, and the edge of the abdomen, margined with orange or red. It measures about 15 mm. in length. Family LYG^ID^ The Chinch-Biig Family the costal margin of the hem- Fig. 447. — Hemelytron of Lygceus kalmii. The Lygaeidae is one of the larger families of the Hemiptera. It includes certain forms which closely resemble members of the pre- ceding family in size, form, and strongly contrasting colors. But the great majority of the species are of smaller size and less brightly col- ored ; and all differ from that family in presenting distinct ocelli. The membrane of the hemelytra is furnished with four or five simple veins, which arise from the base of the membrane ; sometimes the two inner veins are joined to a cell near the base (Fig. 447). Nearly two hundred species belonging to this family have been found in our fauna; these represent fifty-five genera and seven subfamilies. Although these insects feed on vegetation, they have attracted but little attention as pests of cultivated plants excepting the following species. HEMIPTERA 387 The chinch-bug, BUssus leucopterus. — This well-known pest of grain-fields is a small bug, which when fully grown measures a little less than 4 mm. in length. It is blackish in color, with conspicuous, snowy white hemelytra. There is on the costal margin of each hemelytron near the middle of its length a black spot ; from each of these spots there extends towards the head a some- what Y-shaped dusky line. The body is clothed with nimierous microscopic hairs. In Figure 448 this insect is represented natural size and enlarged. The species is dimorphic, there being a short -winged form. There are two generations of the chinch -bug each p^g ^_^8 — BUsstis year. The insects winter in the adult state, hiding leucopterus. beneath rubbish of any kind; they even penetrate forests and creep under leaves, and into crevices in bark. In early spring they emerge from their winter quarters and pair; soon after, the females begin to lay eggs; this they do leisurely, the process being carried on for two or three weeks. The eggs are yellowish ; about 500 are laid by a single insect; they are deposited in fields of grain, be- neath the ground upon the roots, or on the stem near the surface. The eggs hatch in about two weeks after being laid. The newly hatched bugs are red; they feed at first on the roots of the plant which they infest, sucking the juices; afterwards they attack the stalks. The bugs become full-grown in from forty to fifty days. Before the females of this brood deposit their eggs, they leave their original quarters and migrate in search of a more abundant supply of food. About this time the wheat becomes dry and hard; and the migration appears to be a very general one. Although the insects sometimes go in different directions, as a general rule the masses take one direction, which is towards the nearest field of oats, com, or some other cereal or grass that is still in a succulent state. At this time many of the bugs have not reached the adult state ; and even in the case of the fully winged individuals the migration is usually on foot. In their new quarters the bugs lay the eggs for the second or fall brood. The methods of control of this pest that are used are the fol- lowing: the burning in autumn of all rubbish about fields, in fence comers, and in other places where the bugs have congregated to pass the winter; the stopping of the marching of the spring brood into new fields by means of a furrow or ditch with vertical sides, and with holes like post -holes at intervals of a few rods in the bottom of the furrow or ditch, in which the bugs are trapped; the use of a line of gas-tar on the ground to stop the marching of the spring brood ; in some cases kerosene emulsion has been used to advantage ; the sowing of decoy plots of attractive grains in early spring, and the later plowing under of the bugs and their food and harrowing and rolling the ground to keep the bugs from escaping; and the artificial dissemination of the fungus Sporotrichum globulifenmi, which is the QQUse of a contagious disease of the chinch-bug. 388 AN INTRODUCTION TO ENTOMOLOGY Family NEIDID^ The Stilt-Bugs The family Neididag consists of a small nimiber of species, which on account of their attenuated forms are very striking in appearance (Fig. 449) . The body is long and narrow; the legs and antennas are also long and extremely slender. There is a transverse incision in the vertex in front of the ocelli. The antennae are four-jointed, elbowed at the base of the second segment, and with I/>\^//\, the tip of the first segment enlarged. The y \J/ Y_ beak is four-jointed; and the membrane r — Jh^~^ r of the hemelytra is furnished with a very / /BX 1 few veins, r/ / I \ • W i Only eight species of this family have been found in our fatma ; but these repre- sent six genera. Only two of the species are widely distributed in the United States and Canada. These are sluggish insects, found in the undergrowth of Fig. ^4g.~jalysus spinosus. woods and in meadows and pastures. Jalysus spindsus. — This is the best- known member of this family. It is distributed from the Atlantic to the Pacific in both the United States and Canada. It is as slender as a crane-fly (Fig. 449) and of a pale tawny color. The front of the head tapers off to an almost acute, upturned point. An erect spine projects form the base of the scutellum, and another from each side of the mesopleura, just in front of the posterior coxae. The body is about 8 mm. in length. Jalysus perdavatus .■ — This is one of the southern members of the family, but it has been found in New Jersey and the District of Columbia. It is smaller than the preceding species; the length of the male is 5 mm., of the female 6 mm. There is an erect spine be- tween the bases of the antennae ; and the last segment of the antennas is shorter and thicker than in /. spinosus. Neides mUticus .—LUke Jalysus spinosus, this species is found from the Atlantic to the Pacific in both the United States and Canada. It lacks the spines of the scutellum and thorax; and the front of the head is bent down, in the form of a little horn. The other representatives of this family in our fauna are found in Florida, Arizona, New Mexico, and California. Family ARADID^ The Flat-Bugs The members of this family are very flat insects; in fact they are the flattest of all Hemiptera. They live in the cracks or beneath # HEMIPTERA 389 the bark of decaying trees; and the form of the body is especially adapted for gliding about in these cramped situations. They are usually dull brown or black ; sometimes they are varied with reddish or pale markings. The hemelytra are usually well developed, with distinct corium, clavus, and mem- brane; but they are reduced in size, so that when folded they cover only the disk of the abdomen (Fig. 450). Ocelli are lacking ; the antennae are four-jointed ; the tarsi are two-jointed; and the beak is four-jointed, but often apparently three-jointed. Fig. 450. — Ar- These insects are supposed to feed upon fungi or adus acutus. upon the juices of decaying wood and bark. The family is well represented in this country; fifty-nine species, repre- senting nine genera, are now known, and doubtless many remain to be discovered. Family COREID^ The Squash-Bug Family The members of this family vary greatly in form. Some of the species are among the most formidable in appearance of all of our Hemiptera ; while others are comparatively weak and inconspicuous. The family is characterized as follows: the antennas are insert- ed above an ideal line extending from the eye to the base of the rostrum, and are four-jointed; the vertex is not transversely im- Fig. 451.— Hemelytron of Leptocoris pressed; the ocelli are present; trivittatus. the beak is four-jointed; the scutellum is small or of medium size; the hemelytra are usually complete and composed of clavus, corium, and membrane; the membrane is furnished with many veins, which spring from a transverse basal vein, and are usually forked (Fig. 451); the tarsi are three-jointed. This is a large family; one hundred and twenty- four species, representing forty-eight genera, have been found in our fauna. It contains both vegetable feeders and carnivorous forms ; in some cases the same species will feed upon both insects and plants. The most common and best-known species is the following. The squash-bug, Anasa trlstis. — The form of the body of the adult insect is represented in Figure 452. In this stage the insect appears blackish brown above and dirty yellow beneath. The ground color is really Fig.452.— ^wa^a ochre-yellow, darkened by numerous minute black tristis. punctures. Upon the head are two longitudinal black stripes; the lateral margins of the prothorax are yellow, owing to the absence of the punctures along a narrow 390 AN INTRODUCTION TO ENTOMOLOGY Space; and the margin of the abdomen is spotted with yellow from a similar cause; the membrane of the hemelytra is black. This species winters in the adult state. In early simimer it lays its eggs in little patches on the young leaves of squash and allied plants. The young bugs are short and more rounded than the adult insects. There are several generations of this /""^■MMOii^^^ species each year. JP^k ^\ This is one of the most annoying of ^^^|f«W V^ the many pests of the kitchen-garden; .J> liMiim T9 and, unfortunately, no satisfactory meth- od of control has been devised. The egg masses are conspicuous and can be col- lected and destroyed ; the young nymphs can be killed by spraying with io% kerosene emulsion; the adults can be trapped under bits of boards and stones; and many n\Tnphs can be killed by de- stroying the vines as soon as the crop is harvested. Acanthocephala femordta (Fig. 453) will serve as an example of one of the larger members of this family. This species is distribut- ed from North Carolina to Florida and Texas. It has been known to destroy the cotton-worm, and is said to injure the fruit of the cherry by puncturing it with its beak and sucking the juices. Fig. 453.- — Acanthocephala femorata. (From Glover.) Family PENTATOMID^ The Stink-Btig Family With the Pentatomidas we reach a series of families, three in ntimber, in which the antennae are usually five-jointed, differing in this respect from all of the preceding families. The form of the body presented by the great majority of the members of the Pentatomidae is well shown by Figure 454. It is broad, short, and but slightly convex; the head and prothorax form a triangle. The scutellum is narrowed behind ; it is large and in a few forms nearly covers the abdomen. The tibias are unarmed or are furnished with very fine short spines. As with the Coreidae, the members of this family vary greatly in their habits; some are injurious to vegetation; others are predacious; while some species feed indifferently upon animal or vegetable matter. Some species are often found on berries and have received the popular name of pentatomid. HEMIPTERA 391 Stink-hugs on account of their fetid odor, which they are apt to impart to the berries over which they crawl. This nauseous odor is caused by a fluid which is excreted through two openings, one on each side of the lower side of the body near the middle coxae. The harlequin cabbage-bug, Murgantia histronica. — Among the species of the Pentatomidae that feed upon cultivated plants, the harlequin cabbage-bug or "calico-back" is the most important pest. It is very destructive to cabbage and other cruciferous plants in the Southern States and on the Pacific Coast. It is black, with bands, stripes, and margins of red or orange or yellow. Its bizarre coloring has suggested the popular names given above. The full-grown bugs live through the winter, and in the early spring each female lays on the under surface of the young leaves of its food-plants about twelve eggs in two parallel rows. The eggs are barrel-shaped and are white banded with black. The young bugs are pale green with black spots. They mature rapidly ; and it is said that there are several generations in one season. This is an exceedingly difficult species to contend against. Much can be done by cleaning up the cabbage stalks and other remnants as soon as the crop is harvested, and, in the following spring, trapping the bugs that have hiber- nated by placing turnip or cabbage leaves in the in- fested gardens or fields, or by planting trap-crops of mustard or other cruciferous plants. The bugs that are not collected by these methods and their eggs should be collected by hand; this can be easily done Fig- 455 -^"J- as both the bugs and their eggs are conspicuous. ^m/nWFrom As if to atone for the destruction caused by their Glover.) relative, the harlequin cabbage-bug, there are many members of this family that aid the agriculturist by destroying noxious insects. The species of the genus Podisus have been reported often as destroying the Colorado potato-beetle, currant worms, and other well-known pests. Figure 455. represents a member of this genus, Podisus maculiventris. Family CYDNID^ The Burrower-Bugs and the Negro-Bugs The Cydnidas is the second of the series of families in which the antennae are five-jointed. In this family the outline of the body is more generally oval, rounded, or elliptical, and the form more convex, than in the Pentatomidae. The scutellum is large but varies greatly in size and in outline. Each lateral margin of the scutellimi is furnished with a furrow into which the margin of the hemelytron of that side fits. In this respect the Cydnid^e agrees with the preceding family and differs from the following one. The tibiae are armed with strong spines. The family includes two well-marked subfamilies. 392 AN INTRODUCTION TO ENTOMOLOGY Subfamily CYDNIN^ The Burrower-Bugs The subfamily Cydnina? includes the greater number of the mem- bers of the Cydnidffi found in the United States and Canada ; of these there are twenty-nine species now listed, representing nine genera ; most of these are restricted to the South and the Far West. In this subfamily the scutellum is either broad and bluntly rounded, or triangular with the apex pressed down. The species are generally black or very dark brown. They are found burrowing in sandy places, or on the surface of the ground beneath sticks and stones, or at the roots of grass and other herbage. A European species is said to suck the sap from various plants near the ground. It is desirable that further observations be made upon the habits of this subfamily. Figure 456 represents Cyrtomenus mirabilis, a species found in the South and the Southwest. Subfamily THYREOCORIN^ The Negro-Fugs The subfamily Thyreocorinas is represented in our fauna by a single genus, Thyreocoris, of which sixteen species have been found in this country. They are mostly black and beetle-like in appearance, some have a bluish or greenish tinge, and all are very convex. The body is short, broad, and very convex, in fact almost hemispherical. The scutellimi is very convex and covers nearly the whole of the abdomen. These insects infest various plants, and often in- Fig. 457-— jure raspberries and other fruits by imparting a dis- ^rirZer agreeable, bedbug-like odor to them. A common and widely distributed species is Thyreocoris ater (Fig. 457). Another species often found on berries is T. pulicdrius; this species is some- times a serious celery pest. It is shiny black and has a white stripe • on each side of the body; it measures 3 mm. in length. A Family SCUTELLERID^ The Shield-hacked Bugs 'The members of this family are turtle-shaped bugs; that is, the HEMIPTERA 393 body is short, broad, and very convex. The scutellum is very covering nearly the whole of the abdomen. The lateral margins of the scutellum are not furnished with grooves for receiving the edges of the hemelytra as is the case in the two preceding families. The tibise are smooth or furnished with small spines. Figure 458 represents Eurygaster alterndhis somewhat enlarged, and serves to illustrate the typical form of members of this family. The family is represented in this country by fourteen genera including twenty-six species. I have met no account of any of our species occurring in sufficient numbers to be of economic importance. large, CHAPTER XXI ORDER HOMOPTERA* Cicadas, Leaf-Hoppers, Aphids, Scale-Bugs, and others The winged members of this order have four wings, except in the family CoccidTnphs leave the trees on which the eggs were deposited and migrate to succulent weeds. The early life of the adult is spent on the weeds ; but later the females migrate to trees for egg-laying. The two-horned tree-hopper, Ceresa dtceros. — This species re- sembles the buifalo tree-hopper in size and form. It is a pale dirty yellow, spotted with brown; the lateral and caudal aspect of each horn is brown; the caudal tip of the prothorax, and a large spot midway between the tip and the horns, are also brown. The insect is densely clothed with hairs. It is common on black elder, Sambucus canadensis. Funkhouser followed the life-history from the egg to the adult on this plant. The eggs are laid about the middle of August in the second-year stems, and hatch about the middle of May. The two-marked tree-hopper, Enchendpa binotdta. — In this spe- cies the pronotum is prolonged in an upward- and forward- projecting horn (Fig. 471). This insect is very abundant on trees, shrubs, and vines. It is gregarious, and both adult and immature forms are found clustered together. The eggs are usually laid in frothy masses, which are very white and appear like wax. Funkhouser states that a variety of this species found on butternut lays its eggs in the buds and does not cover them with the heavy froth. The specific name of this species refers to the fact there are two yellow spots on the dorsal line of the pronotiim. Another very common species, and one that is closely allied to the preceding, is Campylenchia latipes. This is brownish, unspotted, and has a rather longer horn than that of the two-marked tree-hopper; but it varies much in color and in the length of the pronotal horn. This is a grass-inhabiting species and is common in pastures and especially on alfalfa. It is often taken by sweeping. Telamdna. — To this genus belong our humpback Fig. 471.— £«- chenopa bi- notata. Fisf. 472 amona. -Tel- 406 AN INTRODUCTION TO ENTOMOLOGY forms (Fig. 472), of which about thirty species have been found in our fauna. They Hve chiefly on oaks, hickories, basswood, and other forest trees. The adults generally rest singly on the limbs and branches of the trees ; the}' are strong flyers and are difficult to capture. The immature forms keep together in small groups. Figure 473 represents a front view of several membracids in our collection. Family CICADELLID^* The Leaf-Hoppers This family is a very large one, and it is also of considerable economic importance; for it includes a number of species that are very injurious to cultivated plants. The members of it are of small or moderate size. The antennge are inserted in front of and between the eyes; the pronotum is not prolonged above the abdomen; and the hind tibiae are nearly or quite as long as the abdomen, curved, and armed with a row of spines on each margin. The form and armature of the hind tibise are the most salient characters of this family. The form of the body is commonly long and slender, often spindle-shaped; but ^. some are plump. ^%elis exiti- These insects are able to leap powerfully; and, as osus. they are more often found on the leaves of herbage and on grass than elsewhere, they have been named leaf -hoppers. They infest a great variety of plants; some of them are important pests in gardens, orchards, and vineyards; but they are most destruc- tive as pests of grains and grasses. Although this is true, much less attention has been paid to injuries caused by them to grains and grasses than to those inflicted upon vineyards and rose bushes. More than seven hundred species, representing about seventy genera, have been found in the United States and Canada. Among the more important members of the family from an economic standpoint are the following. The destructive leaf-hopper, Euscelis exitiosus, which is repre- sented, greatly enlarged, in Figure 474, sometimes infests winter wheat to a serious extent. It is a widety distributed species, its range including nearly the whole of the United States. It is a small, active, brownish insect, which measures with its wings folded about 5 mm. in length. It injures grass or grain by piercing the midrib of the leaf and sucking the juices from it. The grape-vine leaf -hopper, Erythroneura comes, is a well-known pest which infests the leaves of grape, in all parts of this country where this vine is grown. It is a little more than 3 mm. in length, and has the back and wings marked in a peculiar manner with yellow and red. In the winter the darker markings are a dark orange-red, but after feeding has been restmied for a short time in the spring they change to a light lemon-3'ellow. The darker markings on the *This family has been commonly known as the Jassidae, but Cicadellidae is the older name. HO MOP T ERA 407 adults vary so much that eleven distinct varieties are now recognized ; two of these are represented at b and c in Figure 475. The rose leaf-hopper, Empoa roses, is a well-known pest of the rose. Swarms of these insects may be found, in various stages of growth, on the leaves of the rose-bush through the greater part of the summer, and their nu- merous cast skins may be seen adhering to the low- er sides of the leaves; in fact attention is most fre- quently called to this pest by these white ex- uviae. The adult meas- ures less than 3 mm. in length. Its body is yel- lowish white, its wings are white and transpar- ent, and its eyes, claws, and ovipositor are brown. The apple leaf-hop- per, Empodsca mali. — Al- though this species is named the apple leaf- hopper, it infests to an in- jurious extent man}'- dif- ferent plants, both cultivated and wild. Slingerland and Crosby ('14) state that it infests apple, currant, gooseberry, raspberry, potato, sugar-beets, beans, celery, grains, grasses, shade trees, and .weeds. The adult insect measures about 3 mm. in length, and is of a pale yellowish green color with six or eight distinguishing white spots on the front margin of the pronotum. The genus Drceculacephala includes grass-green or pale green, spindle-shaped species, in which the head as seen from above is long and triangular. One of the species, D. reticulata, sometimes greatly injures fields of grain in the South. The genus Oncometopia includes species in which the head is more blunt than in the preceding genus and is wider across the eyes. than the thorax. 0. unddta (Fig. 476) is a common. /~\W' species. Its body, head, fore part of the thorax, scutel- vwv him, and legs are bright yellow, with circular lines of /W\ black on the head, thorax, and scutellum. The fore ®i wings are bluish purple, when fresh, coated with whitish powder. It measures 12 mm. in length. It is said to lay its eggs in grape canes, and to puncture with its beak the stems of the bunches of grapes, causing the stems to wither and the bunches to drop off. One division of this family, the subfamily Gyponinas, includes forms which resemble certain genera belonging to the Cercopidaeby their Fig. 475. — Erythronetira comes: a and b, female and male of the typical comes variety; c, the vitis variety. (From Slingerland.) Fig. 476. —On- cometopia tindata. 408 A N INTROD C UTION TO ENTOMOLOG Y pltunp proportions. Among these are Penthima americdna, which is a plump, short-bodied insect, resembHng a Clastoptera; and the genus Gypona includes a large nimiber of species, some of which resemble very closely certain species of Aphrophora. A glance at the posterior tibiae of these leaf-hoppers will enable one to distinguish them from the cercopids, which they so closely resemble. Methods of combating leaf-hoppers. — Leaf-hoppers, being sucking insects, are fought with contact insecticides. But it is difficult to destroy the adults, for they are so well-protected by their wings that applications strong enough to kill them are liable to injure the foliage of the host-plant; and, too, they are very active and fly away when approached. The most effective remedial measures are those directed against the nymphs. These consist of the use of some spray, as a ten- per-cent. kerosene emulsion or a soap solution made by dissolving one pound of soap in six or eight gallons of water, or a solution made of one ounce of "black leaf 40" tobacco extract and six gallons of water in which has been dissolved a piece of soap the size of a hen's egg. The application should be so applied as to wet the lower surface of every leaf. Family FULGORID^ The Lantern-Fly Family This family is remarkable for certain exotic forms which it includes. Chief among these is the great lantern-fly of Brazil, Laterndria pJios- phorea. This is the largest species of the family and is one of the most striking in appearance of all insects (Fig. 477). It has immense wings, which expand nearly six inches; upon each hind wing there is Fig. 477. — The lantern-fly, Latertiaria phosphorea. a large eye-like spot. But the character that makes this insect es- pecially prominent is the form of the head. This has a great bladder- like prolongation extending forward, which has been aptly compared to the pod of a peanut. Maria Sibylla Alerian, a careful observer, who wrote more than two hundred years ago (1705), stated that this prolongation of the head is limiinescent. This statement was ac- cepted by Linnseus without question ; and he made use of names for this and some allied species, such as laternaria, phosphorea, candelar- ia, etc., to illustrate the supposed light-producing powers of these insects. The common name lantern-fly is based on the same belief. HOMOPTERA 409 Fig. 478. — Antenna of Megamehis notula. (Aftei Hansen.) Fig. 479. Scolops. The Brazilian lantern-fly has been studied by many more recent observers, and all have failed to find that it is luminescent. It may be that the individuals observed by Madame Merianwere infested by Itmiinescent bacteria, as has been observed to be the case occasionally in certain other insects. No member of this fam- ily is known to be lumi- nescent. The Chinese candle- fly, Fulgoria caiideldria, is another very promi- nent member of this family, which is commonly represented in col- lections of exotic insects and is often figured by the Chinese. This too has been reputed to give light. Certain fulgorids found in China excrete large quantities of a white, flocculent wax, which is used by the Chinese for candles and other purposes. There does not seem to be any typical form of the -body characteristic of this family. The different genera dift'er so greatly that on superficial examination they appear to have very little in common. The most useful character for recognizing these insects is the form and position of the antennse. These are situated on the side of the cheeks beneath the eyes; the two proximal segments, the scape and pedicel, are stout (Fig. 478) ; the clavola consists of a small, nearly pear-shaped basal segment and a slender, segmented or un- segmented, bristle-like ter- minal part. The pedicel is provided with numerous sense-organs. So far as numbers are concerned this family is well represented in our fauna, three hundred fifty- seven species and seventy- seven genera having been listed; but our species are all small compared with the exotics mentioned above. The following of our native genera will serve to illustrate some of the variations in form represented in this country. The species all feed on the juices of plants. Scolops. — In this genus the head is greatly prolonged (Fig. 479), as with the Chinese candle-fly. Our more common species, however, measure only about 8 mm. in length. Otiocerus.- — In this genus the body is oblong; the head is com- pressed, with a double edge both above and below. Otiocerus coque- hertii (Fig. 480) is a gay lemon-yellow or cream-colored species, with Otiocerus coquehertii. (From Uh- 410 AN INTRODUCTION TO ENTOMOLOGY Fig. 481. — Ormenis sep- tentrionalis. wavy red lines on the fore wings. It measures about 8 mm. to the tips of the wings, and lives upon the leaves of grape-vmes, oaks, and hickors'. Ormenis. — In our common representatives of this genus the wing -covers are broad, and closelv applied to each other in a vertical position; they are more or less truncate, and give the insects a wedge-shaped outline. 0. septentriondlis (Fig. 481) is a beautiful, pale green species powdered with white, which feeds on wild grape-vines, drawing nourish- ment from the tender shoots and midribs of the leaves, during its young stages. Family CHERMID^* The Jumping Plant-Lice The jumping plant-lice are small insects; many of them measure less than 2 mm. in length ; and the larger of our species, less than 5 mm. They resemble somewhat the winged aphids; but they look more like miniature cicadas (Fig. 482). They differ from aphids in the firmer texture of the body, in the stouter legs, in having the hind legs fitted for jumping, and in the antennse being ten-jointed or rarely nine- or eleven-jointed. The terminal segment of the antennge bears two thick setee of unequal length. Both sexes are winged in the adult. The front wings are ample, and, while often transparent, are much thicker than the hind wings. The homologies of the wing-veins of the fore wings of Psyllia floccosa are indi- cated in Figure 483 . Tig. 483. — The venation of a fore wing of Psyllia floccosa. (After Patch.) The beak is short and three-jointed. The basal segment of the beak is held rigidly between the fore coxae. *This family has been quite commonly known as the Psyllidae, a result of an incorrect application of the name Chermes to a genus of the Phylloxeridse. HOMOPTERA 411 The jumping plant-lice are very active little creatures, jumping and taking flight when disturbed; but their flight is not a prolonged one. They subsist en- tirely upon the juices of plants; some species form galls; but it is rare that any of the species appear on cultivated plants in sufficient num- bers to attract attention, except in case of the pear- tree Psylla. The family Chermi- dcB is of moderate size; in our latest list one- hundred thirty-seven species representing twenty-four genera, are enumerated from our fauna. The two fol- lowing species will serve to illustrate variations in habits of these insects. Pachypsylla celtidis- ntdmma. — This is a gall- making species which in- fests the leaves of hack- berry {Celtis occidentdlis). Figure 484 represents an infested leaf with galls, and a single gall and a nymph enlarged. The adult insect (Fig. 485) has a wing expanse of about 6 mm. The pear-tree psyllia, Psyllia pyricola. — This is our most impor- Fig. 484. — Gall of Pachypsylla celtidis- mamma: a, leaf with galls, from under-side; b, section!' of gall enlarged and insect in cavity; c, nymph, enlarged. (From Riley.) Fig. 485. — Pachypsylla celtidis-mamma. (From Packard.) Fig. 486. —Psy Ilia pyricola. tant species from an economic standpoint, being a serious enemy of the pear. It is a small species (Fig. 486) ; the summer generations 412 AN INTRODUCTION TO ENTOMOLOGY measure to the tips of the folded wings from 2.1 mm. to 2.8mm., the hibernating form 2>-?) mm. to 4 mm. The general color is light orange to reddish brown, with darker markings. The eggs are laid early in the spring in the creases of the bark, in old leaf-scars, and about the base of the terminal buds. The }-oung n^-mphs migrate to the axils of the leaf petioles and the stems of the forming fruit; later they spread to the under side of the leaves. They secrete large quantities of honey-dew, upon which a blackish fungus grows; this is often the first indication of the presence of the pest. There are at least four generations each year. Badly infested trees shed their leaves and yoimg fruit in midsimimer. In some cases orchards have been so badly injured by this pest that they have been cut down b}- their owners. The methods of control that are recommended are the following: the scraping off of the rough bark from the trunks and larger branches of the trees and burning it, in order to destroy the hibernating adults; and thorough spraying of the trees with kerosene emulsion or "black leaf 40" tobacco extract when the petals have fallen from the blossoms, in order to destroy the newly hatched nvTnphs; this spra}^- ing should be repeated in three or four days; later sprayings are not so effective on account of the protection afforded the insects by the expanded leaves and by their covering of honey-dew. A monograph of the North American species of this family has been published by Crawford ('14). SUPERFAMILY APHIDOIDEA The Plant-Lice or Aphids and their Allies The plant-lice or aphids are well-known insects; they infest nearly all kinds of vegetation in all parts of the country. Our most common examples are minute, soft -bodied, green insects, with long legs and antennas, which appear on various plants in the house and in the field. Usually, at least, in each ^. ^^^^^/^^ species there are both winged and wingless ^^^ ^^^^^^v forms (Fig. 487). There are many species ^^^^ ^^^^ of aphids, nearly all of which are of small Fig. 487. — A group of size; some measure less than i mm. in aphids. length; and our largest species, only 5 or 6 mm. The body in most species is more or less pear-shaped. The winged forms have two pairs of delicate, transparent wings. These are furnished with a few simple or branched veins ; but the venation is more extended than in either of the two following families. The fore wings are larger than the hind wings; and the two wings of each side are connected by a small group of hamuli. The wings are usually held roof -like when at rest (Fig. 488, ah) , but are laid flat on the abdomen in some genera. The beak is four-jointed and varies greatly HOMOPTERA 413 in length; in some species it is longer than the body. The antennas consist of from three to six segments; the last segment is usually provided with a narrowed prolongation (Fig. 488, aa). The first two segments of the antennas are always short, but the other segments show a great specific variation in length and are therefore very useful as systematic characters. Excepting the first two, the seg- ments of the antennee are usually provided with sense-organs, the sensoria, which vary in number and shape in different species and are Fig. 488. — The melon aphis, Aphis gossypi: a, winged agamic female; aa, en- larged antenna of same; ab, winged agamic female, with wings closed, sucking juice from leaf; b, young nymph; c, last nymphal instar of winged form; d, wingless agamic female. (From Chittenden.) much used in the classification of these insects. On the back of the sixth abdominal segment there is, in many species, a pair of tubes, the cornicles, through which a wax-like material is excreted. In some genera these organs are merely perforated tubercles, while in still other genera they are wanting. It was formerly believed that the honey -dew excreted by aphids came from the cornicles; for this reason they are termed the honey-tubes in many of the older books. The honey-dew of aphids is excreted from the posterior end of the alimentary canal. It is sometimes produced in such quantities that it forms a glistening coating on the leaves of the branches below the aphids, and stone walks beneath shade-trees are often densely spotted 414 AN INTRODUCTION TO ENTOMOLOGY with it. This honey -dew is fed upon by bees, wasps, and ants. The bees and wasps take the food where they find it, paying httle if any attention to its source ; but the ants recognize in the plant-Hce useful auxiharies, and often care for them as men care for their herds. This curious relationship is discussed later, under the head of Ants. In addition to honeydew, many aphids excrete a white waxy sub- stance. This may be in the form of powder, scattered over the Sc*R^M+Cu,+ lstA Fig. 489. — The wings of Eriosoma americana. (From Patch.) surface of the bod>' , or it may be in large flocculent or downy masses; even' gradation between these forms exists. The superfamily Aphidoidea includes two families, the Aphididas and the Phylloxeridas. These two families differ in the life-histories of their species and in the venation of the wings of the winged forms, as follows: A. Only the sexually perfect females lay eggs; the parthenogenetic forms give birth to developed young, which, however, in some cases, are each enclosed in a pellicle. The radius of the fore wings is branched; and the outer part of the stigma is bounded behind by vein Ri (Fig. 489) Aphidid^ ^A. Both the sexually perfect females and the parthenogenetic forms lay eggs. Vein R, of the fore wings is wanting; and the outer part of the stigma is bounded behind by the radial sector (Fig. 490) Phylloxerid^ Se.Zl-K.Cu-'»*^ Sc Fig. 490. — The wings of Adelges. (From Patch.) HOMOPTERA 415 Family APHIDID^ The Typical Aphids To this family belong the far greater number of the genera and species of the Aphidoidea. The distinctive characters of this family are given under A in the table above. For a detailed discussion of the wing-venation of these insects, see Patch ('09). In the Aphididas there exists a remarkable type of development known as heterogamy or cyclic reproduction. This is characterized by an alternation of parthenogenetic generations with a sexual generation . And within the series of parthenogenetic generations there may be an alternation of winged and wingless forms. In some cases the reproductive cycle is an exceedingly complicated one, and differ- ent parts of it occur on different species of food plants. In those cases where different parts of the reproductive cycle occur on different food-plants, the plant on which the over-wintering fertilized egg is normally deposited and upon which the stem-mother and her immediate progeny develop is termed the primary host; and that plant to which the migrants fly and from which a later form in the series migrates to the primary host is known as the secondary host. Different species of aphids differ greatly in the details of their development; it is difficult, therefore, to make generalizations re- garding this matter. The following account will serve to indicate the sequence of the forms occurring in the reproductive cycle of a migrat- ing aphid, one in which the different parts of the cycle occur on different food-plants. This account refers to what occurs in the North, where the winter interrupts the production of young, and eggs are developed which continue the life of the species through the inclement season. In hot climates also, where there is a wet and a dry season, eggs are produced to carry the species over the period when succulent food is lacking. And in some cases in the North, on ex- hausted vegetation the non-migratory species produce eggs during the simimer months. The stem-mother: — In the spring there hatches from an over- wintering egg a parthenogenetic, viviparous female, which lives on the primary host. As this female is the stock from which the summer generations spring, she is known as the stem-mother or fundatrix. The stem-mother is winged in some species of one of the tribes (Callipterini) ; but usually she is wingless. The wingless agamic form. — In most species the stem -mother gives birth to young which do not develop wings and which are all females. These reproduce parthenogetically and are known as the wingless agamic form or spurice aptercB* These reproduce their kind for a variable number of generations and then produce the next form. All of these generations live on the primary host. In a few species the wingless agamic form rarely appears if at all. *Spuri(Z (New Latin, fern, pi.); Lat. spurius, an illegitimate or spurious child. 416 AN INTRODUCTION TO ENTOMOLOGY The winged agamic form.- — After a variable number of generations of the wingless agamic form have been developed and the food-plant has become overstocked by them, there appears a generation which becomes winged and which migrates to the secondary host. These are all parthenogenetic, viviparous females. They are known as the winged agamic form or spurice alatae or migrants or migrantes. In some species, the second generation, the offspring of the stem-mother, are winged migrants. When the migrating winged agamic form becomes etablished on the secondary host, it produces young which are all females of the wingless agamic form. After a variable number of generations of this form have been developed, there is produced a generation of winged agamic females which migrate from the secondary host to the primary host. The two forms developed on the secondary host, the wingless and the winged agamic forms, may closely resemble the corresponding forms previously developed on the primary host or may differ markedly from them. The members of the last generation of the series of partheno- genetic forms, which produce the males and the oviparous females, are termed the sexuparas. In some non-migrating species this genera- tion is wingless. The males and the oviparous females. — The winged agamic females that have migrated from the secondary host to the primary one, here give birth to true sexual forms, male and female. These pair, and each female produces one or more eggs. These are sometimes designated as gamogenetic eggs to distinguish them from the so-called pseudova developed in agamic females. See note on page 191. The males and the oviparous females are termed collectively the sexuales; and some writers refer to the oviparous females as the ovipara. (Note that ovipara is a plural noun.) The sexuales differ greatly in form and habits in the different tribes of aphids. In the more generalized aphids the ovipara of some species are winged, and the males are very commonly winged; both sexes have beaks and feed in the same way as do the other forms ; and each female produces several eggs. In some of the more specialized aphids the sexuales are small, wingless, and beakless; consequently the}' can take no food. Each female produces a single egg, which in some cases is not deposited but remains throughout the winter within the shriveled body of the female. In some cases the young produced by the agamic females are each enclosed in a pellicle when born; this is soon ruptured and the young aphid escapes from it. The young thus enclosed are termed pseudova by many writers. The foregoing account, omitting exceptions and variations, can be simimarized as follows: A. DIFFERENT TYPES OF INDIVIDUALS IN THE APHIDID^ First type. — The stem-mother or fundatrix, which is hatched from a fertilized egg, is usually wingless, and reproduces parthenogenetically. Second type. — The parthenogenetically produced wingless agamic females. HO MOP T ERA 417 Third type. — The parthenogenetically produced winged agamic females. Fourth type. — The sexual forms, males and oviparous females. B. SEQUENCE OF GENERATIONS IN A MIGRATING SPECIES Only the first of a series of similar generations is counted. First generation. — The stem-mother. Second generation. — Windless agamic females. There may be a series of generations of this form here. Third generation. — Winged agamic females. These migrate to the secondary host. Fourth generation. — Wingless agamic females. There may be a series of generations of this form here. Fifth generation. — Winged agamic females. These migrate to the primary host and are the sexuparas. Sixth generation. — Males and oviparous females. The females produce the fertilized eggs from which the stem-mothers are hatched, thus completing the life- cycle. A remarkable fact that has been demonstrated by several ob- servers is that the number of generations of the wingless agamic form may be influenced by the conditions under which the aphids live. In an experiment conducted under my direction by Mr. Slingerland, in the insectary at Cornell University, we reared 98 generations of the wingless agamic form without the appearance of any other form. The experiment was carried on for four years and three months without any apparent change in the fecundity of the aphids, and was discontinued owing to the press of other duties. As the aphids were kept in a hothouse throughout the winters, seasonal influences were practically eliminated ; and as members of each gen- eration were placed singly on aphid-free plants and their young re- moved as soon as bom, there was no crowding. In order to determine the influence of crowding, members of the sixtieth generation were placed on separate plants and their young not removed. At the end of three weeks the winged agamic form ap- peared, evidently in response to need of migration to less densely populated plants ; while in other cages where the young were removed promptly, no migrants appeared up to the end of the experiment. The family Aphididae includes a very large nimiber of genera and species. The genera are grouped into tribes and these into subfamilies in various ways by different authors. Recent classifications by American authors are those of Oestlund ('18) and Baker ('20). Four subfamilies are recognized by Baker. The characters of these sub- families given below are largely compiled from this author. Subfamily APHIDIN^ To this subfamily belong most of the species of aphids that are commonly seen living free {i. e., not in galls) upon the foliage of plants. But while most of the species feed on foliage, some of them attack stems and roots. Their attacks on foliage in some cases merely cause a weakening of it ; in other cases, the leaves become curled or otherwise distorted; such distortions are termed psendigalls. True galls formed by aphids are described in the accounts of the last two subfamilies. 418 AN INTRODUCTION TO ENTOMOLOGY In the Aphidinae the males and the oviparous females are com- paratively generalized; they are furnished with functioning mouth- parts and feed as do the other forms; the females lay several eggs; in a few species the oviparous females are winged ; and winged males are common. Wax-glands are not abundant in members of this sub- family; and the antennal sensoria are oval or subcircular. The following are a few of the more common representatives of the Aphidinae. These are selected to illustrate some of the more striking differences in habits exhibited by the different species. a. BARK-FEEDING APHIDINv^. The following species will serve as an example of the bark-feeding species belongings to this subfamily, and also of the maximum size reached by any aphid. The giant hickory -aphid, Longistigma caryce. — This is a very large species, one of the largest aphids known, measuring to the tip of the abdomen 6 mm., and more than lo mm. to the tips of the wings (Fig. 491). It can be distinguished by the shape of the stigma of the fore wings, which is drawn out at the tip to an acute point extending Fig. 491.— Longi- aknost to the tip of the wing. The top of the thorax sHgma caryce. ^^^ ^^^ veins of the wings are black and there are four rows of little transverse black spots on the back. The body is covered with a bluish white substance like the bloom of a plum. This is a bark-feeding species; it is found clustered on the under side of limbs in summer. It infests hickory, maple, and several other forest trees. The oviparous female is wingless; the male, winged. 0. LEAF-FEEDING APHIDIN^. Examples of the leaf-feeding species belonging to this subfamily can be found on a great variety of plants. Among those most easily observed are the species infesting the leaves of fruit trees, and especially the following. The apple-leaf aphis. Aphis pomi. — This is a bright green species, the entire life-cycle of which is passed on the apple. The migrants fly to other parts of the infested tree or to other apple-trees. As a result of the attacks of this species the leaves of the apple are often badly curled and sometimes drop off the tree. The rosy apple-aphis, Anuraphis roseus. — The common name of this species refers to the fact that the agamic females are usually of a pinkish color; but they may vary in color to a light brown, slaty gray, or greenish black, with the body covered with a whitish coating. This species is most common on apple; but it infests also pear, white thorn, and three species of Sorbus. It is a migrating spe- cies; but its secondary host is unknown. HOMOPTERA 419 The apple-bud aphis, Rhopalos'iphitm pninifdlia. — This is the species that most commonly infests the opening apple-buds, often nearly covering them. It also infests pear, plum, quince, and many other plants. It is a migrating species ; various species of grain serve as its secondary host. C. ROOT-FEEDING APHIDIN^. The corn-root aphis, Anuraphts maidi-radtcis . — This is a serious pest of corn throughout the principal corn-growing States, sometimes totally ruining fields of com. Broom-corn and sorghimi are the only other cultivated crops injured by it ; but it infests many species of weeds that grow in corn-fields. Our knowledge of this species is largely the result of investigations of Professor S. A. Forbes, who has published several detailed accounts of it in his reports as State Entomologist of Illinois. This author found that this aphid is largely dependent on a small brown ant, the corn-field ant {Ldsius americdnus) , the nests of which are common in corn-fields. The ants store the winter eggs of the aphids in their nests and care for them throughout the winter. In the spring, when the stem-mothers hatch, they are trans- ferred by the ants to the roots of the weeds upon which they feed. As soon as corn-plants are available, the ants transfer the aphids to the roots of the corn, the ants digging burrows along the roots of the com for this purpose. The ants in return for their labors derive honey-dew from the aphids. One can understand how these ants that attend aphids that are excreting honey-dew should learn to drive away the enemies of the aphids, as is often done ; but is it not wonderful that Lasiiis americanus should recognize the importance of preserving the eggs from which their herds are to develop ! The strawberry -root aphid. Aphis forhesi. — The winter eggs of this species are found upon the stems and along the midribs of the green leaves of strawberry plants. The stem-mothers and one or more generations of the offspring feed upon the leaves in the early spring. But "a little later in the season the corn-field ant appears and transfers the aphids to the roots of the strawberry, where it cares for them in the same way that in corn-fields it cares for the corn-root aphis. This ant is entirely responsible for the infesting of the roots by the aphids; and it is here that the greatest injury to the plants is done. Subfamily MINDARIN.^ This subfamily was established by Baker ('20) for the reception of the genus Mindarus, which can be distinguished from all other living aphids by the venation of the wings. In this genus the radial sector of the fore wings separates from vein Ri at the base of the 420 AN INTRODUCTION TO ENTOMOLOGY long, narrow stig- ma (Fig. 492). In all other living aphids the origin of the ra- dial sector is much nearer the tip of the wing ; but in many of the fossil aphid wings it is as in Mindarus . The males and the oviparous females are small and wing- less; but they retain the beak, at least in most individuals, and feed. The female lays several eggs. Only one species, Mindarus abietinus, is known. This lives free upon the twigs of spruce and other conifers, which become somewhat distorted and are often killed by the attack of the insects. When disturbed this insect secretes large quantities of honeydew. The life-cycle of this species usually includes only three genera- tions, the stem-mother, the winged agamic females {sexuparce), and the sexual forms. Sometimes there is a generation of wingless agamic females. This species was redescribed by Thomas as Schizoneura pinicola. Fig. 492. — Wings of Mindarus. (After Patch.) Subfamily ERIOSOMATIN^ This subfamily includes those genera of aphids in which the males and the oviparous females are greatly specialized by reduction. They do not have functioning mouth -parts; some have a beak when born but lose it at the first molting; in others the beak is vestigial at birth. As they cannot feed, they remain small. Both sexes are wingless. The oviparous females produce each a single sgg, which in some species is not laid but remains throughout the winter in the shriveled body of the female. In this subfamily, the cornicles are much reduced or are wanting; wax-glands are abundantly developed ; and the antennal sensoria are prominent. These are often annular. The members of this subfamily that are most likely to attract attention can be grouped under two heads: a, the woolly aphids; and 6, the gall-making Erisomatinge. These groups, however, do not represent natural divisions of the subfamily and do not include all members of it. They are merely used for convenience in the present discussion. a. THE WOOLLY APHIDS The woolly aphids are the most conspicuous members of the Aphidida;, on account of the abundant, white, waxy excretion that HOMOPTERA 421 covers colonies of them. The three following species are widely dis- tributed and are common. The woolly apple aphis, Eriosoma lanlgera. — This plant-louse, on account of its woolly covering and the fact that it is a serious pest of the apple, is known as the woolly apple aphis, although the apple is its secondary host. This insect not only has a complicated series of generations but the life-cycle is subject to variations ; its usual course is as follows : The winter-eggs are deposited in crevices of the bark of elm. From these eggs stem-mothers hatch in the spring and pass to the young leaves, where they produce either the well-known leaf-curl of the elm or, when a group of terminal leaves are affected, what has been termed a rosette, which is a cluster of deformed leaves. Within these pseudogalls the second generation is produced; this consists of wingless agamic females. The offspring of these, the third generation, become winged and migrate from the elm to the apple. Here they produce the fourth generation, the members of which live on the water-shoots or the tender bark of the apple, and are wingless. The fifth generation also consists of wingless agamic females. Some of these develop on the bark of the branches, which apparently ceases to grow at the point of attack but swells into a large ridge about the cluster of plant-lice, leaving them in a sheltered pit ; the aphids also frequently congregate in the axils of the leaves and the forks of the branches. Other members of this generation pass to the roots of the tree, where they produce knotty swellings on the fibrous roots. The sixth generation consists, in part, of winged agamic females which migrate from the apple to the elm, where they produce the seventh generation. This generation, the last in the series, consists of the males and oviparous females, both of which are beakless and wing- less. These pair and each female produces a single egg, which is found in a crevice of the bark with the remains of the body of the female. The course of events outlined above may be modified in two ways : first, it is said that the sexual forms are sometimes produced on the apple; and second, some members of the sixth generation do not develop wings and migrate, but are wingless and produce young that hibernate on the apple. This species infests also mountain ash and hawthorn, as secondary hosts. The elm-feeding generations of this species that cause the leaf- curls and rosettes have been known as Schizoiteura americdna. And there are also found during the summer aphids on tender elm bark which are believed to belong to this species and which have been described under the name Schizoneura rileyi. In the Pacific Coast States there is another species of aphid that produces leaf curl on elm. This is Schizoneura Ulnii, a European species, which in Europe has been found to migrate to Rihes. The alder-blight, Prociphilus tesselldtus. — A woolly aphid that is found in dense masses on the branches of several species of alder is known as the alder-blight. Colonies of this species are easily found 422 AN INTRODUCTION TO ENTOMOLOGY in the regions where it occurs, as their covering of flocculent excretion renders them very conspicuous. These colonies are of especial in- terest, as within them is found the predacious larva of the wanderer butterfly, Feniseca tarquinius, which feeds on the aphids. In the late stmmier or early autumn the last generation of wingless agamic females bring forth young, which winter among the fallen leaves at the base of the alder and return to the branches in the spring. From this there appears to be no need of an alternate host. But it was found by Dr. Patch that at the same time that the form that hibernates at the base of the alder is produced, winged migrants appear and fly to maple trees, where they give birth, in the crevices and rough places in the bark, to males and oviparous females. Each of these females produces a single egg. From these eggs there hatch in the spring aphids which pass to the lower side of the leaves of the maple, where they become conspicuous on account of their abundant and long woolly excretion. In this period of its existence this species is the well-known pest of the maple that has long been known as Pemphigus acerfolii, which name must now be regarded as a synonym of Proctphilus iesselldtus, the older name. In July winged migrants are developed on maple which fly to alder. The alder-blight excretes honeydew abimdantly; the result is that the branches infested by this insect, and those beneath the cluster of aphids, become blackened with fungi that grow upon this excretion. There is also a curious fungus which grows in large spongy masses immediately beneath the cluster of plant-lice; this is known to bot- anists as Scorias spongiosa. It is evidently fed by the honeydew that falls upon it. The beech-tree blight, Proctphilus imbricdtor.- — This infests both twigs and leaves of beech. Like the preceding species it occurs in clusters of individuals, each of which is clothed with a conspicuous downy excretion. These clusters often attract attention by the curious habit which the insects have of waving their bodies up and down when disturbed. When an infested limb is jarred, the aphids emit a shower of honeydew. Owing to the abundance of this excretion, the branches and leaves of an infested tree become blackened by growths of fungi, as with the preceding species. The life-cycle of this species has not been determined. b. THE GALL-MAKING ERIOSOMATIN^ Certain members of this subfamily cause the growth of remarkable galls, resembling in this respect certain members of the following subfamily. Among the gall-making Eriosomatinag that are most likely to attract attention are the following. The cockscomb elm-gall colopha, Colopha ulmtcola. — There are two species of aphids that make similar galls on the leaves of elm. These galls are commonly known as cockscomb elm-galls on account of their shape. Those made by the two species of aphids are so similar that a description of one will apply to the other. In each case HO MO PT ERA 423 the gall is an excrescence resembling a cock's comb in form, which rises abruptly from the upper surface of the leaf (Fig. 493, a). It is com'pressed, and has its sides wrinkled perpendicularly and its siimmit irregularly gashed and toothed. It opens on the under side of the leaf by a long slit-like orifice. The winter eggs can be found during the winter in the crevices of the bark of the elm; each egg is usually enclosed in the dry skin of the oviparous female (Fig. 493, 6). In the spring the stem-mothers -=C:^ Fig. 493. — Colopha ulmicola: a, leaf showing galls from above and beneath; h, fertilized egg surrounded by the skin of the female; c, newly born young of the second generation; h, its antenna; d, full-grown nymph of the second genera- tion; e, adult of second generation; /, antenna of migrant ; g, antenna of stem- mother. (From Riley.) pass to the leaves and each causes by its attack the growth of a gall. The second generation is produced within the gall; it consists of winged agamic females (Fig. 493, e). These migrants can be dis- tinguished from those of the other cockscomb elm-gall aphid by the fact that in this species vein M of the fore wings is forked. The migrants of this species pass from the elm to certain grasses, among them species of Eragrostis and Panicum. The forms found on these secondary hosts have been described under the name Colopha. eragrostidis, but this is a much later name than Colopha ulmtcola. 424 AN INTRODUCTION TO ENTOMOLOGY The cockscomb elm-gall tetraneura, Tetraneura gramlnis. — The life-cycle of this species is quite similar to that of the preceding one. The prim^ary host is elm. The stem-mothers cause the growth of cockscomb-like galls; and the migrants produced in these galls pass to grasses. These migrants differ from those of the preceding species in that vein M of the fore wings is not forked. This species was first described from individu- als found on the second- ary hosts and was named Tetraneura gramlnis. Lat- er, forms found on elms were named Tetraneura colophoides. For a detailed ac- count of the gall-aphids of the elm, see Patch Cio). The poplar-leaf gall- aphid, Thecdhius populi- caulis. — This aphid is common on several spe- cies of poplar. It makes a swelling the size of a small marble on the leaf at the junction of the petiole with the blade. This gall is of a reddish tint, and has on one side a slit-like opening. In the early part of the season each gall is occu- pied by a single wingless female, probably the agamic stem-mother, which by midsummer becomes the mother of numerous progeny. These are winged and probably migrate to some other host -plant; but the life-cycle of this species has not been determined. The vagabond gall-aphid, Mordwilkdja vagabiinda. — This species infests the tips of the twigs of several species of poplar; here it causes the growth of large corrugated galls, which resemble somewhat the flower of the double cockscomb of our gardens. The galls are at first bright green, but later turn black, become woody, and remain on the "trees during the winter (Fig. 494). Very little is known regarding the Jife-cycle of this species. Fig. 494. — The vagabond poplar-gall. Walsh and Rilev.) (From Subfamily HORMAPHIDIN^ The members of this subfamily are usually gall-makers, resembling in this respect certain members of the Eriosomatinae, and also re- sembling them in that the antennal sensoria are annular. But in this subfamily the sexual forms are not so specialized by reduction :as in the preceding one. In the Hormaphidinse, although the males .and the oviparous females are small and wingless, they possess HOMOPTERA 425 beaks, they feed, and the oviparous female lays more than one egg. In this subfamily great specialization of wax-producing organs occurs. In many species some of the agamic generations become greatly modi- fied in form so that they do not resemble the more typical aphids. In some species these modified forms have the appearance of an Aleyrodes; in other species, that of a coccid. Our best -known representatives of this subfamily are two species of gall-makers, each of which infests alternately witch-hazel and birch. The life-histories of these were very carefully worked out by Fig. 495. — The witch-hazel cone-gall: a, natural size; &, section of gall, enlarged. (From Pergande.) Pergande ('01); the following accounts are greatly condensed from that author. The witch-hazel cone-gall aphid, Hormaphis hamamelidis. — The winter- egg is deposited on the branches and twigs of witch-hazel and hatches early in the spring. The stem -mother, which hatches from this egg, attacks the lower surface of the leaf, causing the growth of a conical gall on the upper surface of the leaf with a mouth on the lower surface (Fig. 495). The second generation, the offspring of the stem-mother, consists of many individuals; these are pro- duced within the gall, which becomes crowded with them. These are agamic females, which become winged, leave the gall, and mi- grate to birches, where they deposit their young on the lower side of the leaves. The first instar of the third generation, the off.spring of the migrants, is broadly oval, with the entire margin of the body 426 AN INTRODUCTION TO ENTOMOLOGY ^^\,\\u,- 1, ■^■'Ly^ '' /~vJ2SuLs-jZII^^ Studded with short and stout excretory tubercles (Fig. 496) ; from each of these there issues a short, glassy, beautifully iridescent, waxy rod. The second and third instars of this generation are marked by a reduction of the antennae, beak, and legs. The fourth instar, which is found about the middle of June, is aley- rodiform (Fig. 497). The fourth and fifth generations resemble the third, there be- ing three aleyrodiform gen- erations. The members of the sixth generation become winged and are the return migrants. These fly to witch-hazel, where they give birth to the seventh genera- tion, which consists of males and oviparous females. These pair and the females lay the winter eggs; each (From' Pergande!) female produces from five to ten eggs. The males and In this species the antennas Fig. 496. — Hormaphis hamamelidis, first instar of the third generation the oviparous females are both wingless of the winged forms are three-jointed. Later experiments by Morgan and Shull ('10) indicate that this species can complete its life-cycle on the witch-hazel. According to these authors there are only three genera- tions: first, the stem-mother, which causes the growth of the cone-gall; second, the winged forms, which are developed in the gall and which spread to the leaves ; and third, the males and oviparous females. No aleyrodiform individuals were found on the witch- hazel. The spiny witch-hazel-gall aphid, Hamameltstes spinosus. — The winter eggs of this species are commonly de- posited near the flower-buds of witch- hazel, late in June or early in July, but they do not hatch till May or June of the following year. The stem-mother attacks the flower-bud. which becomes transformed into a large gall of the form shown in Figure 498. Within this gall the stem-mother produces the second generation ; these crowd the gall and develop into winged migrants, which leave the gall, from July to late fall, and fly to birches. The Fig. 497. — Hormaphis hamamel- idis, fourth instar of the third generation. (After Pergande.) HOMOPTERA 427 young of the migrants, the third generation, feed a short time and then settle close to the leaf-buds, where they hibernate; the last in- Fig. 498. — The spiny witch-hazel gall: a, mature gall; b, section of gall. (From Pergande.) Star of this generation resembles a coccid (Fig. 499). The fourth generation is produced early in the spring ; the young of this genera- tion move to the young and tender leaves of the birch, which, as a Fig. 499. — Hamamelistes spinosus, last instar of the third generation, much enlarged: a, dorsal view; b, lateral view; c, ventral view; d, antenna; e, f, g, legs. (From Pergande.) result of the attack, become corrugated, the upper surface bulging out between the veins, and the folds closing up below. In these 428 AN INTRODUCTION TO ENTOMOLOGY pseudogalls the fifth generation is produced; the members of this generation become winged and migrate to witch-hazel in early summer, where they produce the seventh and last generation of the series, the males and oviparous females. These pair and the females soon lay their eggs. Both sexes are wingless. The winged migrants of this species can be distinguished from those of the preceding species by their five- jointed antennae. Family PHYLLOXERID^ The Adelgids and the Phylloxerids The members of this family differ from the typical aphids in that both the sexually perfect females and the parthenogenetic forms lay eggs, in lacking vein Ri of the fore wings, and in that the outer part of the stigma is bounded behind by the radial sector (Fig. 500). sc.n^u^Cii^^'*^ Fig. 500. — Wings of Adelges. (From Patch In this family the cornicles are always wanting; and the males and sexualh' perfect females are dwarfed and wingless. This family includes two subfamilies, which can be separated by the following table. These subfamilies are regarded as distinct families bv some writers. A. The wingless agamic females excrete a waxy flocculence. The winged forms have five-jointed antennae, the last three segments of which bear each a single sensorium. The wings are held roof-like when at rest. The free part of vein Cu of the fore wings is separate from vein ist A (Fig. 500). The sexual forms have a beak. The alimentary' canal is normal, producing a fluid excrement. The species infest only conifers Adelgin^e AA. The wingless agamic females do not secrete a waxy fiocculence, but in the genus Phylloxerina they excrete a waxy powder. The winged forms have three-jointed antennas, the second segment of which bears two sensoria. The wings when at rest are laid fiat upon the abdomen. The free parts of veins Cu HO MOP T ERA 429 and 1st A of the fore wings coalesce at base (Fig. 501). The sexual forms have no beak. The anus is closed. The species do not infest conifers Phylloxerin^ Sc+R+31: Fig. 501. — Wings of Phylloxera. (From Patch Subfamily ADELGIN^ The Adelgids This subfamily includes those insects found on conifers that have been quite generally known under the generic name Chermes. But it has been determined that this name should be applied to certain jumping plant-lice of the family Chermidae, formerly known as the Psyllidae. The necessity of this change is very unfortunate, as much has been published regarding members of the Adelginae and in most of these accounts they are described under the name Chermes. All the species of this subfamily infest conifers; and in all cases in which the sexual generation is known, this generation lives on spruce. The secondary host may be either larch, pine, or fir. Much has been written regarding the life-histories of these insects. It has been found that what may be regarded as the typical life-cycle of an Adelges or ''Chermes'' is a very complex one, including the developing of two parallel series of forms differing in habits ; that in one of these series a single host-plant, spruce, is infested and the life- cycle is completed in one year; while in the other series the life-cycle extends over two years and is passed in part upon spruce and in part upon larch or some other host-plant. In this typical life-cycle, beginning with the individual that hatches from a fertilized egg, there are developed five generations, the members of which differ in either form or habits or both from those of the other generations, before the cycle is completed by the production again of fertilized eggs. The actual nimiber of generations may be greater than this, owing to the fact that in a part of the cycle there may be a series of similar generations only the first of which is counted in this enumeration. 430 AN INTRODUCTION TO ENTOMOLOGY This indicating of a typical life-cycle is an effort to outline as simply as possible the life-history of these insects. In some species it is much more complicated; thus, for example, Borner ('08) in his account of the life-history of Cnaphalodes strobilobius recognizes seven parallel series of forms. The distinctive characters of the five differing generations in the typical life-cycle are indicated below .^ A. GENERATIONS ON SPRUCE {Piceo) A one-year cycle or the first year of a two-year cycle. First generation. — This consists of the true stem-mother (fundatrix vera), a wingless agamic female. In the case of those supposed parthenogenetic species which do not migrate to another host-plant and which complete their life-cycle in one year, this form is the offspring of the second generation, an agamic form; in the case of species that migrate to a secondary host-plant, and where there are two parallel series, the stem-mother is the offspring of either the second generation or the fifth generation, the sexual forms. The stem-mothers hatch in the autumn ; they hibernate immature in crevices at the bases of buds, complete their growth in the spring, and by their attack upon the buds cause the beginning of the growth of galls. Each stem-mother lays a large number of eggs. Sec 0 fid generation. — The members of this generation hatch from the eggs laid by the stem-mothers, and by their attack upon the buds cause the completion of the growth of the galls. The galls are formed by the hypertrophy and coalescence of the spruce-needles. The members of this generation have been termed the gallicola, because they inhabit the galls. They reach the last nymphal instar within the galls. When this stage is reached, the galls open and the nymphs emerge and soon molt, becoming winged agamic females. As to their habits, there are two types of gallicolae: first, the non-migrants, which remain on the spruce and lay the eggs from which the stern-mothers of the one-year cycle are hatched; and second, the migrants, which fly to a secondary host-plant, which is not spruce, and where they lay many eggs, but not so many as are laid by the stem-mothers. B. GENERATIONS ON A SECONDARY HOST Part of the second year of a two-year cycle. The secondary host may be a species of either larch {Larix), pine (Pinus), or fir {A bies) ; but no galls are produced on any of these. Third generation. — The members of this generation hatch from eggs laid by migrants of the second generation that have flown from spruce to larch or other secondary host and laid their eggs there. The young that hatch from these eggs hibernate in crevices in the bark and comolete their growth in the spring, becom- ing wingless agamic females. The members of this generation and of similar generations which follow immediately but which are not numbered here, are termed colonici, because they are settlers in a new region, or exstdes, that is, exiles. Some writers term the first of this series of generations false stem-mothers {fimdatrices spurice) to distinguish them from the true stem-mother, which is the beginning of the two-year cycle. The members of the third generation resemble those of the first generation, but usually lay fewer eggs and do not cause the growth of galls. The offspring of the third generation are all wingless agamic females, which reproduce their kind. Of these there may be a series of generations, which are not numbered in this generalized statement; and there may be among these several parallel series of generations, differing in the life-cycle but all reproducing parthenogenetically on the secondary host. The secondary host may be thus infested throughout the year; while the primary host, if there is not an annual series, will be free during the interval between the migration of the second genera- tion and the return migration of the fourth generation. HOMOPTERA 431 Among the oflfspring of the third generation two types are recognized by Marchal ('13): first, nymphs which remain undeveloped for a time, the sislens type; and second, nymphs which develop at once into wingless agamic females, the progrediens type.* Fourth generation. — The members of this generation are produced by indi- viduals of the progrediens type of the third generation. They develop into winged agamic females. The adults migrate to spruce and there lay a small number of eggs. Since their oflfspring are the sexual forms, this generation is known as the sexuparcB. C. A GENERATION ON SPRUCE The completion of the second year of a two-year cycle. Fifth generation. — From eggs laid by the sexuparas that have migrated from the secondary host to spruce, there are developed males and sexually perfect females, termed the sexuales; both of these forms are wingless. They pair and each female lays a single egg. These eggs hatch in the autumn; the young hibernate and become the true stem-mothers. Thus is completed the two- year life-cycle. Omitting the annual series, the typical two-year life-cycle includes the follow- ing series of generations, which are described above. First. — The wingless agamic stem-mother. Second. — The winged agamic migrants. Third. — The wingless agamic colonici or exsules. (a) The sistentes, several generations. (b) The progredientes, several generations. Fourth. — The winged agamic sexuparas. Fifth. — The wingless sexuales, males and sexually perfect females. Each female produces a single fertilized egg, from which hatches a stem-mother, thus completing the life-cycle. In the case of some species, which have been studied very carefully by different observers, only an annual series, consisting of the first and second generations described above, is knov^^n. It should be noted that in a life-cycle of this kind there are no sexual forms and that although a winged form appears it is not known to migrate. These facts indicate that either some members of the winged generation migrate to a secondary host-plant which has not been discovered, or that the species in question have become, by adaptation, purely par- thenogenetic. Which of these alternatives is true has been much dis- cussed. The following species are some of the more common of our repre- sentatives of this subfamily. The pine-leaf adelges, Adelges pinijdlics.- — Our knowledge of the life-history of this species is still fragmentary. In one part of its life- cycle it infests the leaves of white pine (Ptnus strohus). The genera- tions found here are winged agamic females. These attach them- selves firmly to the pine-needles, each with its head directed towards the base of the needle. Within each there are developed about one hundred eggs, which are not extruded. After the death of the female, the mass of eggs remains adhering to the leaf, covered over and *Sistens, Latin sisto, to stand; progrediens, Latin pro, forth, gradior, to go. 432 AN INTRODUCTION TO ENTOMOLOGY protected by the remains of the body and closed wings of the dead insect. It has been determined that these plant- Hce infesting the pine leaves are specifically identical with those that issue from a cone- like gall found on several species of spruce (Fig. 502). The spruce-inhabiting form has been known as Cherntes abiettcolens ; but pinifoUcB is the older specific name and should be used for all forms of this species. It is probable that this species has a two- year life-cycle and that spruce is its primar\^ host and pine its secondary host. The green-winged adelges, Adelges able- tis. — This species causes the growth of pine- Fig. 502. — Gall of Adelges apple-shaped galls on several species of pinifoHcB on spruce. spruce (Fig. 503). It is a European species and its life-history has been the subject of much controversy. It is held by Bomer ('08) that it has a typical life-cycle in which there are two parallel series: first, an annual series on spruce alone; and second, a two-year series in which larch is used as a secondary host. On the other hand, Cholodkovsky ('15) maintains that it is a parthenogenetic species; that its life- cycle includes only two generations, the agamic hibernating stem-mothers and the gallicolae; and that the form with a typical life-cycle is a distinct species {Chermes vlridis). Dr. Patch ('09) has studied Adel- ges ahietis in Maine and has found only the parthenogenetic forms, the hibernating stem- mothers and the gallicolae ; thus confirming the conclusion that it may have become a parthenogenetic species. The pme-bark adelges, Adelges pinicorti- cis. — This species infests several species of pine, but especially white pine. The trunks and larger limbs of the infested trees often appear as if whitewashed ; this is due to the woolly excretion which covers the bodies of the insects. But little is known regarding the life-cycle of the species. Wingless females, which are doubtless agamic as they lay many eggs, hibernate on the pine and feed on the bark in the spring. They lay their eggs in April ; these soon hatch and the young develop into winged agamic females in May. These soon dis- appear and the pine is said to be free from the pest during the svmimer. Return migrants to the pine have not been observed; but there must be a generation of these, the parents of the wingless hibernating Fig. 503- abietis. -Gall of Adelges HOMOPTERA 433 generation, if, as stated, the pines are free from the pest during Riimmpr Subfamily PHYLLOXERIN^ The Phylloxerids The distinguishing characters of this subfamily are given under AA in the table on page 428 and need not be repeated here. It in- cludes two genera. Phylloxera and Phylloxerina. The genus Phylloxerina is distinguished by the fact that the wingless agamic females excrete a waxy powder, which gives them, the appearance of mealy-bugs. Species of this genus have been found in this country on poplar, willow, and sour-gum. The genus Phylloxera is represented by the grape Phylloxera and thirty or more described species that infest forest-trees— hickory, oak, and cnestnut. Most of these are found on hickory. Those on hickory cause the growth of galls either on the leaves or on the tender twigs and petioles. Other species produce either pseudogalls or white or yellowish circular spots on the infested leaves. The species infesting forest-trees were monographed by Pergande ('04). Although in this subfamily there is a generation of winged mi- grants in the life-cycle of each species, few if any of them have a secondary host. The migrants fly to other parts of the infested plant or to other plants of the same species. So far as is known, the life-cycle of the species infesting forest -trees is a comparatively simple one. The stem-mother hatches in the spring from an over-wintering, fertilized egg and causes the growth of a gall; she develops within the gall and produces unfertilized eggs. From these eggs hatch young that develop into winged agamic females. These produce eggs of two sizes; from the smaller eggs hatch males; and from the larger ones, females. The sexes pair and each female lays a single fertilized egg. In some species these eggs are laid in June and do not hatch till the following April. The grape Phylloxera, Phylloxera vastdtrix. — From an economic standpoint this species is the most important member of the Phyl- loxerina^; millions of acres of vineyards have been destroyed by it.* The most extensive ravages of this pest have occurred in France and in California. This species is a native of the eastern United States, where it infests various species of wild grapes. It does not injure these seriously; but when it was introduced into France it was found that the European grape, Vitis vinifera, is extremely sus- ceptible to its attack. The great injury to the vineyards of California is due to the fact that it is the European grape that is chiefly grown there. The presence of this insect is manifested by the infested vines in two ways: first, in the case of certain species of grapes, there *"The Phylloxera when at its worst had destroyed in France some 2,500,000 acres of vineyards, representing an annual loss in wine products of the value of $150,000,000." (Marlatt '98.) 434 AN INTRODUCTION TO ENTOMOLOGY Fig. 504. — Leaf of grapewith galls of Phylloxera. (From Riley.) appear upon the lower surface of the leaves galls, which are more or less wrinkled and hairy (Fig. 504), which open upon the upper surface of the leaf, and each of which contains a wingless, agamic plant-louse and her eggs; second, when the fi- brous roots of a sickly vine are examined, we find, if the disease is due to this insect, that the minute fibers have become swollen and knotty ; or, if the disease is far ad- vanced, they may be en- tirely decayed (Fig. 505, c). Upon these root-swellings there may be found wing- less, agamic, egg-laying plant-lice, the authors of the mischief. The life-history of this species is a complicated one, due to the fact that parallel series of generations with different life-cycles may be developed at the same time. While a fertilized winter egg may be considered a part of the typical life-cycle, some of the agamic females hibernate on the roots of the vine and form a part of a series of agamic generations that apparently may continue indefinitely year after year. The typical life-cycle, that one in which males and sexually perfect females form a part, extends over two years and includes four forms as follows : The gallicolcB. — From an over-wintering fertilized egg, there hatches in the spring a wingless agamic stem-mother, which passes to a leaf and by her attack causes the growth of a gall, within which she passes the remainder of her life. She reaches maturity in about fifteen days, fills the gall with eggs, and soon dies. The young that hatch from the eggs laid by the stem-mother resemble her in being wingless agamic females ; they escape from the gall, spread over the leaves, and in turn cause the growth of galls. Six or seven generations of this form (Fig. 506) are developed during the simimer. They are termed the gallicolcB. The radicicolce or colonici. — On the appearance of cold weather, young hatched from eggs laid by the gall-inhabiting form pass down the vines to the roots, where they hibernate. This completes the first year of the two-year cycle. In the following spring these colonici, that is, settlers in a new region, attack the fibrous roots, and cause the growth of knotty swellings on them (Fig. 505, b, c) and ultimately their destruction. This is the most serious injury to the vine caused by this species. There is a series of generations of the root-inhabiting HOMOPTERA 435 form all of which are wingless agamic females. This form (Fig. 507) differs somewhat in appearance from the gallicolfe. The migrants or scxitparcc. — During the late summer and fall there are hatched from eggs laid by some individuals of the root-inhabiting Fig. 505. — Phylloxera, root-inhabiting form: a, shows a healthy root; b, one on which the Hce are working, representing the knots and swellings caused by their punctures; c, a root that has been deserted by them, and where the rootlets have commenced to decay; d, d, d, show how the lice are found on the larger roots; e, agamic female nymph, dorsal view; /, same, ventral view; g, winged agamic female, dorsal view; h, same, ventral view; i, magnified antenna of winged insect; j, side view of the wingless agamic female, laying eggs on roots; k, shows how the punctures of the lice cause the large roots to rot. (From Riley.) form, young that develop into winged agamic females (Fig. 505, g, h). These come forth from the ground, fly to neighboring vines, and lay eggs in cracks in the bark or under loose bark. They lay only a few eggs, from three to eight. 436 AN INTRODUCTION TO ENTOMOLOGY Fig. 506. — Phylloxera, gall-inhabiting form: a, b, newly batched nymph, ventral and dorsal views ; c, egg; d, section of gall; e, swelling of tendril; /, g, h, mother gall-louse, lateral, dorsal, and ventral views; i, her antenna; j, her two-jointed tarsus. Natural sizes indicated at sides. (From Riley.) The sexuales. — The eggs laid by the winged migrants are of two sizes ; from the smaller eggs there hatch males; and from the larger eggs, sexually perfect fe- males. These pair and each female pro- duces a single egg, which is laid in the fall on old wood. Here it remains over winter, and from it in the fol- lowing spring a stem- mother is hatched. This completes the two-year life-cycle. Control.- — Owing to the great injury that this species has done to vineyards, hundreds of memoirs have been published regarding it ; but, as yet, no satisfactory means of destroying it that can be generally used has been discovered. Where the soil conditions are favor- able it can be destroyed by the use of carbon-bi- sulphide, but this is an expensive method ; where the vineyards are so situ- ated that they can be submerged with water at certain seasons of the year, the insect can be drowned ; and it has been found that vines growing in very sandy soil are less liable to be seriously in- jured by this pest. While it is usually im- practicable to destroy this pest in an infested vineyard, there is a pre- ventative measure that has given good results. Fig. 507. — Phylloxera, root-mhabitmg form: a, roots of Clinton \me showmg the relation of swellings to leaf-galls, and power of resisting de- composition; b, nymph as it appears when hibernating; c, d, antenna and leg of same; e, f, g, forms of more mature lice; h, granulations of skin; i, tubercle; j, transverse folds at border of joints; k, simple eyes. (From Riley.) HO MO PT ERA 437 -An aleyrodid. Fig. 509. — Aleurochiton for- besii. Certain varieties of American grapes are not seriously injured by the root-form of the Phylloxera. By growing these varieties, or by using the roots of them as stocks on which to graft the susceptible European varieties, the danger of injury by this pest is greatly reduced. Family ALEYRODID^ The Aleyrodids or White Flies The members of this family are small or minute insects; our more common species have a wing-expanse of about 3 mm. In the adult state both sexes have four wings, differing in this respect from the Coccidas, with which they were classed by the early entomologists. The wings are transparent, white, clouded or mottled with spots or bands. The wings, and the body as well, are covered with a whitish powder. It is this character that suggested the name of the typical genus,* and the common name white flies. In the immature stages, these insects ^'^Z- 5o8. are scale-like in form and often resemble somewhat certain species of the genus Lecanium of the family Coccidas. Except during the first stadium, the larvas remain quiescent upon the leaves of the infested plant and in most species are sur- rounded or covered by a waxy excretion. In Figure 508 there is represented one of the many forms of this excretion. Here it consists of parallel fibers, which ra- diate from the margin of the body, and its white color contrasts strongly with the dark color of the insect. In some species the fringe of excretion is wanting; and in others, the excretion from the margin of the body, in- stead of extending laterally and forming a fringe, is di- rected toward the leaf upon which the insect rests, and Fig. 510. — -Wings of Udamoselis. (After En- derlein, with changed lettering.) *Aleyrodes {aXevpudrjs), like flour. 438 .4^ INTRODUCTION TO ENTOMOLOGY thus the body is Hfted away from the leaf and is perched upon an exquisite pahsade of white wax (Fig. 509). The members of this family feed exclusively on the leaves of the host-plants. With few exceptions they are not of economic impor- tance ; and also with few exceptions, the injurious species are not wide- ly distributed over the world as are many aphids and coccids. This is probably due to the fact that as they live exclusively on leaves they are not so liable to be transported on cuttings and nursery stock. They are most abundant in tropical and semi-tropical regions. The adults present the following characters : The compound eyes are usually constricted in the middle and in some species each eye is completely divided. In some cases the facets of the two parts of a divided eye are different in size; it is probable that in such cases one part is a day-eye and the other part a night-eye (see page 1 44) . The ocelli are two in number; each ocellus is situated near the anterior margin of a compound eye. The antenna are usually seven-jointed. The labium is composed of three segments. The fore wings are larger than the hind wings; when at rest the wings are carried nearly horizontally. The venation of the wings is greatly reduced; the maximum number of wing-veins found in the family is in the fore wings of the genus Udamoselis (Fig. 510). The three pairs of legs are similar in form; the tarsi are two-jointed; and each tarsus is furnished with a pair of claws and an empodium or paronychiimi. The anus opens on the dorsal wall of the abdomen at some distance from the caudal end of the body and within a tubular structure, which is termed the vasiform orifice. A tongue-like organ, the lingula, projects from the vasiform orifice; and at the base of the lingula there is a broad plate, the operculum; the anus opens beneath these two organs. In this family the type of metamorphosis corresponds quite closely with that known as complete metamorphosis; consequently the term larva is applied to the immature instars except the last, which is designated the pupa. The eggs are elongate-oval in shape and are stalked. The larvse during the first stadium are active, after which they remain quiescent. There are four larvil and one pupal instars. The wings arise as histoblasts in the late embryo, and the growth of the wing-buds during the larval stadia takes place inside the body-wall. The change to the pupal instar, in which the wing-buds are external, takes place beneath the last larval skin, which is known as the pupa- case or puparium. In many descriptions of these insects only three larval instars are recognized, the fourth being described as the pupa. As the change to a pupa takes place beneath the last larval skin, the puparium, and as the adult emerges through a T-shaped opening in the dorsal wall of the puparium, the pupa itself is rarely observed. Parthenogenesis occurs in this family; but according to the observations of Morrill, unfertilized eggs produce only males. As with the adults, the anus of the immature forms opens in a vasiform orifice on the dorsal aspect of the body at some distance HOMOPTERA 441 from the caudal end of the body. The excrement is in the form ot honey-dew, of which much is excreted. Formerly all the members of this family were included in a single genus, Aleyrodes; consequently, except in comparatively recent works, the various species are described under this generic name. In later days, very extended studies have been made of the family; and the Fig. 511. — Asterochiton vaporariorum: a, egg; b, larva, first instar; c, puparium, dorsal view; d, puparium, lateral view; e, adult. (After Morrill.) genus Aleyrodes has been divided into many genera, which are now grouped into three subfamilies. The most complete systematic works on the family are those of Quaintance and Baker ('13 and '17). The following species are among our more common representatives of the family. The greenhouse white fly, Asterochiton vaporariorum. — One of the most important of the greenhouse pests is this insect, which infests very many species of plants that are grown under glass; and some- times it is a serious pest in the open on tomato and other plants that are set out gfter the weather is warm. The adult measures about 1.5 mm. in length, and like other aleyrodids is covered with a white, waxy powder. The eggs are only .2 mm. in length, and are suspended from the leaf by a short stalk (Fig. 511, a). In the first instar the larva is flat, oval in outline, and with each margin of the body furnished with eighteen spines (Fig. 511, b), of which the last is much the longest. In the second and third instars there are only three pairs of marginal spines, a very small pair near the cephalic end of the body and two somewhat larger ones near the caudal end. The marginal fringe of wax is ■J AN INTRODUCTION TO ENTOMOLOGY narrow. The puparium is box-like, the body of the insect being elevated on a palisade of vertical wax rods (Fig. 511, d). There are other rods of wax represented in the dorsal view of the puparium (Fig. 511, c). The most successful means of destroying this pest is by fumigation of infested greenhouses with hydrocyanic acid gas. The strawberry white fly, Asterochiton packardi. — This species is closely allied to the greenhouse white fly, but differs in minute char- acters presented by the spines and wax rods of the immature forms. It infests strawberry plants, and is a hardy species, passing the winter in the egg state out of doors. The citrus white fly, Dialeurodes cUri. — This is a well-known pest in the orange-growing sections of our country, and is also found in greenhouses in the North. It infests all citrus fruits grown in this country and is found on several other plants. This insect injures its host in two ways : first directly, by sucking the sap from the leaves; and second indirectly, by furnishing nourish- ment, in the form of honeydew.to a fungus, the sooty mold {Meliola camellia:), which forms a dark -brown or black membranous coating on the leaves and fruit, and thus interfering with the functioning of the leaves, retarding the ripening of the fruit, and decreasing the yield of the fruit. There are from two to six generations of this species in a year. An extended account of it is given by Morrill and Back ('11). The maple white fly, Aleurochiton forhesii. — Figure 509 represents this species, which is fairly common on maple, but rarely in sufficient numbers to do serious injury. Family COCCID^ The Scale-Insects or Bark-Lice, Mealy-Bugs, and others The family Coccidce includes the scale-insects or bark-lice, the mealy-bugs, and certain other insects for which there are no popular names. To this family belong many of the most serious pests of horticulturists ; scarcely any kind of "fruit is free from their attacks ; and certain species of scale-insects and of mealy-bugs are constant pests in greenhouses. Most of the species live on the leaves and •stems of plants; but some species infest the roots of the host -plants. The great majority of the species remain fixed upon their host during a part of their life-cycle, and can thus be transported long distances while yet alive, on fruit or on nursery stock ; this has resulted in many species becoming world-wide in distribution. Most of the species are minute or of moderate size ; but some members of the family found in Australia measure 25 mm. or more in length. While the economic importance of this family is due chiefly to the noxious species that belong to it, it contains several useful species. 'The most important useful species at this time is the lac-insect, Tachdrdia Idcca. The stick-lac of commerce, from which shell-lac HOMOPTERA 441 or shellac is prepared, is a resinous substance excreted by this species, which lives on the young branches of many tropical trees, most of which belong to the genus Ficus, the figs. In the past, several coccids have been important as coloring agents. The bodies of the lac-insects, which are obtained from stick-lac in the manufacture of shellac, are the source of lac-dye. Another coccid, Kermes Uicis, which lives on a species of oak in southern Europe, has been used as a dye from very early times. And the well-known Fig. 512. — Chionaspis furfura: 7, scales on pear, natural size; /a, scale of male , lb, adult male, ic, scale of female, enlarged. cochineal is composed of the dried bodies of a coccid, Coccus cacti, which lives on various species of cactus. Recently these dyes have been largely supplanted by those obtained from coal-tar. China-wax is also produced by a coccid. It is the excretion of an insect known as pe-la, Ericerus pe-la, and was formerly much used in China in the manufacture of candles, before the introduction of paraffin. In the adult state, the two sexes of coccids differ greatly in form. The males are usually winged (Fig. 512); in a few species they 442 AN INTRODUCTION TO ENTOMOLOGY are either wingless or have vestigial wings. The fore wings are usually large, com- pared with the size of the body ; the hind wings are alwa}'s greatl\' reduced in size; usually they are a pair of club-shaped hal- teres, but in a few forms they are more or less wing - like. Each hind Fig. 5I3-— Wing of Pseudococcus. (From Patch.) ^-^^ -g famished with a bristle, which is hooked at the end and fits into a pocket or fold on the inner margin of the fore wing of the same side ; in a few spe- cies there are two or three or more of these hamuli. The venation of the fore wings is greatly reduced; a wing of Pseudococcus (Fig. 513) will serve to illustrate the usual type of wing- venation found in this family. The legs are wanting in many adult females, having been lost during the metamorphosis. In adult males they are of ordinary form; except in a few species, the tarsi are one-jointed, and each is furnished with a single claw. Accompanying the tarsal claw there are often a few long, clubbed setcC, the digitules (Fig. 514) ; these are tenent hairs ; some of the digi- tules arise from the tip of the tarsus, and some from the claw. The caudal end of the ab- domen of the male usuallv ^. .,,.-. bears a slender tubular pro- ^ig- ^^--Leg of a female Lecamum: d, cess, the stylus. In some spe- ^^^ ^ ^^" cies the stylus is as long as or even longer than the abdomen ; in others it is short, and in some it is apparently wanting. The stylus serves as a support for the penis, which is protruded from it and in some species is very long. The female coccid is always wingless, and the body is either scale- like or gall-like in form, or grub-like and clothed with wax. The waxy covering may be in the form of powder, of large tufts or plates, of a continuous layer, or of a thin scale, beneath which the insect lives. The eyes of coccids exhibit varying degrees of degeneration and retardation of development. The extreme of degeneration is found in the females, where there is only a single simple eye on each .side of the head; this is probably a vestige of a compound eye. In the adult males of the more generalized forms, compound eyes are present ; and in some of these forms, there are also ocelli, two in some and three in others. When compound eyes are present the facets are usually large, and not closely associated. In the more specialized forms, instead of compound eyes there are on each lateral half of the head from two to eight widely separated simple eyes, which may be scattered vestiges of compound eyes. HOMOPTERi 443 Fig. 515. — A depigmented "acces- sory eye" of Pseudococcus de- structor: c, cornea; h, corneal hypodermis; i, iris cell; r, reti- nal cells; n, nerve. The structure and develoj^ment of the eyes of the male of the common mealy- bug, Pseudococcus (Dactylopius) destructor, was studied by Krecker ('09). In this insect there is on each side of the head a very small eye; since these are the only eyes posses.«ed by the young nymphs, they were termed by Krecker the primary eyes. In the adult, in addition to the primary eyes, there are two pairs of eyes, one pair on the dorsal aspect of the head, and a second pair on the ventral aspect; these he termed the accessory eyes. The so-called primary eyes are very de- generate, in the adult at least. There is a lens below which there are a few retinal cells; but there is no corneal hypodermis, no rhab- doms, and no iris. The development of the so-called acces- sory eyes is greatly retarded. The histo- blasts from which they are developed appear in the latter part of the second nymphal stadium or in the beginning of the third; these are thickenings of the hypodermis. When fully developed as seen in the adult, the accessory eyes (Fig. 515) have a large circular cornea, followed by a comparatively thin layer of corneal hypodermis, encircling which is a single row of large iris cells. Below the corneal hypodermis there is a crescent- shaped area of polygonal rods (rhabdoms), which are terminally situated upon the ret- inal cells. From the proximal end of the retinal cells extend the nerve fibrils which join to form the optic nerve, which follows the contour of the head to enter the brain lateral- ly. Reddish brown pigment fills the retina, the iris, and also a ridge surrounding the eyes. There are no cells which function as pigment cells alone. The antennas of the males are lon^ and slender, and consist of from six to thirteen segments; in some of the A/Targarodinc-e they are branched or fiabellate. The antennae of adult females exhibit great variations in structure; they may be well developed and consist of as many as eleven segments; or they may be greatly reduced in size and in the number of segments; in some species they are either vestigial or entirely wanting in adult females. The mouth-parts are situated on the hind part of the ventral aspect of the head, and often extend caudad of the first pair of legs. In front of the beak there is a densely chitinized area, which includes the civ pens, ^'^- 516.— Mouth-parts of a thelabrum,and themandibularandmaxillarv chiSni^ed'area m f^oS^f sderites. In cleared specimens there can be the beak; B, the beak; /, seen withm this area a complicated endo- labrum; 0, oesophagus; skeleton (Fig. Si6, A). s, loop of mandibular and 'phg labium' (Fig. 516. B), which is com- Sumen? '^(Ste^ Ber^^^o^^' termed the beak or rostrum, consists lese.) ' of three segments in a few forms found in 444 AN INTRODUCTION TO ENTOMOLOGY New Zealand, but usually it is more or less reduced, consisting either of two segments or of only one; in a few subfamilies it is wanting in the adult. The mandibular and maxillary setae are wanting in the later nymphal instars of some forms, in some adult females, and in all adult males. These setae, when present, are usually long, frequently longer than the body, and in some species sev- eral times as long. When not exserted, they are coiled within a pouch, termed the crumena, only their united tips extending to the labium. The cnmiena is a deep invagination of the body-wall, which extends far back into the body-cavity. Its walls are delicate, and not easily observed ; but the coiled setas within it can be easily seen in cleared specimens (Fig. 516, s). In the classification of coccids, the characters most used are those presented by the female, although those of the male are used to some extent . The most available characters of the female are the following : first, the general form of the body; second, the form of the waxy excretions; third, the structure of the caudal end of the body; and fourth, the form and position of the pores through which the wax is excreted. To study the third and fourth classes of characters listed above, it is necessary to remove the wax, to clarify the body, and, in some cases, to stain it. The method most commonly used for removing the wax and clarifying the body is to boil the specimen in a ten per cent, aqueous solution of caustic potash. For staining the body. Gage ('19) found that a solution of saurefuchsin was most satisfactory; his formula for the preparation of this solution is as follows : Saurefuchsin 0.5 gr. Hydrochloric acid, 10% 25.0 c.c. Distilled water 300.0 c.c. The cleaned and stained specimens are usually mounted in Canada balsam for micro- scopic examination. Within the family Coccidas there are to be found most re- markable variations in struc- [/( WWJfll \ 1 ture; this is especially true of the form of the caudal end of the body and of the form of the parts through which the wax and other excretions are exud- ed. These characters have been described by many authors; but, unfortunately, there is a great lack of uniformity in the Fig. 517. — Caudal end of female of Eriococ- terminology used by them. cus araucaricB: r, anal ring; s, anal-ring j^ ^^jg place, only sufficient setae; /, anal lobe; as, anal seta. Be- ^ „„ 1 ^ j-„i,„„ 4-^ /i^^^^ tween the bases of the anal-ring seta, space can be taken to define there are openings of wax-glands. the more important struc- HO MO PT ERA 445 tures, using the terms that are more generally applied to them. The anal ring. — In the mealy-bugs, the tortoise-scales, and the lac-insects, and in the nymphs of some others, the anus is surrounded by a well-defined ring, the anal ring (Fig. 517, r). The anal-ring setce. — The anal ring bears several, from two to thirty but usually six, long and stout setse, the anal-ring setcB (Fig. 517. -j)- The anal lobes. — -In many coccids, the caudal end of the body is terminated by a pair of lobes, the anal lobes (Fig. 517, /). The anal setce.- — Each anal lobe bears one or more prominent setas, the anal setce (Fig. 517, as). The anal plates. — In the subfamily Lecaniinae, the abdomen of the female is cleft at the caudal end, and, at the cephalic end of the cleft, there is a pair of tri- angular, or sometimes semi-cir- cular plates, the anal plates (Fig. 518, ap). The pygidium. — In the sub- family Diaspidinas, the abdo- men of the adult female is ter- minated by a strongly chi- tinizedunsegmented region, which consists of four co- alesced segments (Fig. 519); this region is termed the pygid- ium by writers on the Coccidae. This application of the term pygidium is quite different from that used in descriptions of other insects, where it refers only to the tergite of the last abdominal segment. A more detailed account of the charac- ters presented by the pygidium of the Diaspidinas is given later. The spines and the setce. — The position and number of spines and of setae are often indicated in specific descriptions. Care should be taken to distinguish between these two kinds of structures. A seta can be recognized by the cup-like cavity in the cuticula, the alveolus, within which it is jointed to the body; while a spine is an outgrowth of the cuticula that is not separated from it by a joint. See figure 42, page 32. The writer in his early works on the Coccids ('81, '82, '83) termed certain spine-like setae spines. The outlets of wax-glands . — In the Coccidse there are many minute openings in the cuticula through which wax is excreted; these vary greatly in form, in position on the body, and in the structure of the part of the cuticula through which they open. As the characters presented by these openings are much used in the classification of coccids, a very elaborate terminology referring to them has been developed. Unfortunately different authors use quite different terms Fig. 518. — A Lecanium, enlarged :a^, anal plates. Fig. 519. — Adult female Lepidosaphes: p, py- gidium. 446 AN INTRODUCTION TO ENTOMOLOGY and, therefore, it is necessary to learn the terms used by an author in order to understand his descriptions. The most detailed and sys- tematic terminology that has been proposed is that of MacGillivray ('21). Some of the many terms adopted by this author are defined below. The ceratubce. — In the Diaspidinae and in some species of several other subfamilies, the terminal portion of the outlet of some of the wax-glands is an invaginated cuticular tube. The inner end of this tube is truncate, and, in the Diaspidinae, bears a perforated knob. This invaginated cuticular tube is termed a ceratuba. The ceratubse vary greatly in length and in shape; in some the greater part of the O^^^ _ _ tube is reduced to a fine thread, /qC3\ ^^^k ^^?^!?\ with a bulb-like inner end. A Sp<^§ V V t^^S::;p few ceratubae are represented in a ^^ ^^ \j^j^ diagram given later (Fig. 522). 0^\. .^"W -^f^ .j0!!^ ^^^ openings of most ceratubae Cj JC^ ^^a ^^3 ^^^ ^^^^ ^'^^^ ^^^ body-wall, but Vi«^r \/TSr ^^m9 some of them open through plates in the marginal fringe. The dif- Fig. 520. — Several types of openings of ferent types of ceratubas have re- cerores. ceived distinguishing names formed by combining a prefix with the word ceratubas. The cerores. — The various types of outlets of the wax-glands in which the cuticula is not invaginated so as to form a ceratuba are termed cerores. The openings of cerores through the cuticula vary Fig. 521. — Diagram of a pygidium of a diaspid: a, anus showing through the body; d, densariae; g, genacerores; i, incisions; /, first pair of lobes; pe, pectinae; pi, plate; s, setag; v, vagina. greatly in form; several types of these openings are represented in Figure 520. While in most cases the openings of cerores are flush with the general surface of the cuticula, in some coccids (Ortheziinae) the cerores open through spines. There are also variations in the grouping of the cerores. Each of the various types has received a technical name formed by combining a prefix with the word cerores. HOMOPTERA 447 Thus, for example, the cerores that occur in four or five groups about the genital opening in many of the Diaspidinae (Fig. 52 1 , g) are termed genacerores. The features oj the pygidium.- — The pygidia of adult female diaspids present characters that are much used in distinguishing the species of this subfamily; among these are the following. Fig. 522. — A composite diagram of a pygidium: a, anus; b, marginal ceratubae, with elongated openings; d, ceratubas opening through plates; e, linear ceratubae; /, /, I, lobes; the lobes of the second and third pairs are divided. The position of the anus, which opens on the dorsal aspect of the pygidium at varying distances from the end of the body (Fig. 522, a). The opening of the vagina, on the ventral aspect of the pygidium (Fig. 521, ^). The presence or absence of groups of genacerores (Fig. 521, g), the number of these groups when present, and the number of cerores in each group. The difi^erent groups are distinguished as the median group (mesogenacerores) , the cephalo-lateral groups, one on each side (pre gnacer ores), and the caudo-lateral groups, one on each side (postgenacerores) , respectively. These all open on the ventral aspect of the pygidium. Each genaceroris has several openings. The position and number of openings of ceratubae, and the types of ceratubae that are present (Fig. 522). The number of pairs of lobes borne by the margin, the shape of the lobes, and whether they are divided or not (Fig. 522, /, /, /). The pairs of lobes are numbered, beginning with the pair at the end of the body; in some species this pair is represented by a single lobe. The number of pairs of incisions {incisurce) in the margin of the pygidium (Fig. 521, z). The presence or absence of thickenings of the margins of the incisions {densaricE); these are thickenings of the ventral wall (Fig. 521, d). 448 AN INTRODUCTION TO ENTOMOLOGY The presence or absence of club-shaped thickenings of the dorsal wall (paraphyses) that extend forward from near the bases of the lobes (Fig. 523, ;^). The presence or absence of a thickening of the lateral margin of the pygidinm cephalad of the region in which the lobes are situated, and resembling the lobes in structure (Fig. 523, m). The nimiber and shape of the thin projections of the margin, known as plates. Two quite distinct types of plates can be dis- tinguished: in one they are broad and fringed (Fig. 521, pe); the plates of this type have been termed pectince; in the other type they are spine-like in form (Fig. 521, pi); some writers restrict the term plate to this type, and use pectinaz for the first type. Each plate contains the outlet of a wax-gland. Fig. 523. — Part of the pygidium of Chrysomphalus tenehricosus , ventral aspect, with the paraphyses (pp) of the dorsal wall showing through: /, /, /, lobes; m, thickened margin; s, spine-like setas. The metamorphosis of coccids. — In this family the two sexes are indistinguishable during the first nymphal stadium. Both are fur- nished with legs, antenncC, and functional mouth-parts. It is dttring this period that the sedentary species spread over the plants that they infest. In their subsequent development the sexes differ greatly; hence the metamorphosis of each can be best discussed separately. The females never become winged. Some, as the mealy-bugs and Orthezia, continue active throughout their entire or almost entire life; but most forms become sedentary early in life and remain fixed upon their host. Many species lose their legs and antennae when they assume the quiescent form ; and in some the mandibular and maxillary setae are wanting in the adult. The number of nymphal instars in females varies from two to four; the smaller number occurs in the more specialized subfamilies. In the males there are usually four nymphal instars. During the latter part of the nymphal life the male is quiescent, having formed a cocoon or a scale within or beneath which it remains till it emerges as an adult. The stage of development at which the quiescent HOMOPTERA 449 period begins varies greatly. Thus, while in the mealy-bugs the cocoon is made during the second stadium, in Icerya it is not made till near the end of the third. In the Diaspidinas the formation of the scale begins either at the close of the first stadium or imniediately after the first molt. With the molt at the beginning of the quiescent period the male loses its legs, antennae, and mandibular and maxillary setse. The setae are not replaced; and, consequently, the adult males can take no food. The legs and antennae of the adult are developed from histoblasts, as in insects with a complete metamorphosis; the wing- buds appear in the last nymphal stadium; but they are developed externally, as in insects with a gradual metamorphosis. The type of metamorphosis of the male coccid is, therefore, neither strictly com- plete nor gradual. This illustrates the difficulty of attempting to make sharp distinctions; for in nature all gradations exist between the different types of structure and of development. The classification of the Coccidce. — The different writers on the Coccidas have grouped the genera into a variable number of sub- families. In the classification by MacGillivray ('21), this author recognizes seventeen subfamilies, and gives two tables for separating them, one based on the characters presented by the first nymphal instar, and one on those of adult females. Tables are also given for separating the genera and species of the different subfamilies. The following are a few of the better-known representatives of this family found in this country. Several subfamilies not mentioned here are represented in our fauna. Subfamily MONOPHLEBIN^ The Giant Coccids The common name of this family was suggested by the large size of many of the exotic species. The best-known species found in North America is of moderate size ; this is the cottony-cushion scale, Icerya pUrchasi (Fig. 524). The adult fe- male measures from 4 to 8 mm. in length, is scale-like, dark orange- red, and has the dorsal surface more or less covered with a white or yel- lowish white powder. It secretes a large, longitudinally ribbed egg-sac, which is white tinged with yellow. This beautiful insect was at one time the most dangerous insect pest in California, and did a great amount of _ injury. It is an introduced Austra- pjg. ^^^.-Icerya purchasi: females, lian species, and has been subdued adults, and young on orange. 450 AN INTRODUCTION TO ENTOMOLOGY to a great extent by the introduction of an Australian lady-bug, Roddlia cardindlis. Subfamily COCCIN^ The Cochineal Coccids This subfamily is of especial interest because it includes the cochineal insect, Coccus cacti. This is a native of Mexico, but occurs in the southern United States. It feeds upon various species of the Cactacese. It has been extensively cultivated in India, Spain, and other countries. The adult female bears some resemblance to a mealy-bug, but differs in lacking anal lobes and an anal ring. It excretes a mass of white cottony threads, within which the eggs are laid. The dye-stuff consists of the female insects, which, when mature, are brushed off the plants, killed, and dried. The entire insect is used. Cochineal is now being superseded by aniline dyes, which are made from coal-tar. Subfamily ORTHEZIIN.E Fig. 525. — Orthezia, larged. greatly en The Ensign Coccids Members of this subfamily occur not uncommonly on various weeds. They are remarkable for the s^tti- metrically arranged, glistening, white plates of excretion with which the body is clothed. Figure 525 represents a nymph; in the adult female, the ex- cretion becomes more elongated pos- teriorly, and forms a sac containing the eggs mixed with fine down. Later, when the young are bom, they excrete a sufficient amount of the lamellar excretion to cover them. In many species the egg-sac is held in a more or less elevated position; this fact suggested the common name ensign- coccids for these insects. Most of our species belong to the genus Orthezia, Subfamily ERIOCOCCIN^ The Mealy-Bugs This subfamily includes many genera and species ; the best -known members of it are certain mealy-bugs, which are the most common and noxious of greenhouse pests. These insects have received the HO MO PT ERA 451 Fig. 527. — Pseudococciis citri. Fig. 526. — Pseudococcus longispinosus. name mealy-hugs because their bodies are covered with a fine granular excretion, appearing as if they had been dusted with flour. The females are active nearly throughout their entire life. The males make a cocoon early in their nymphal life in which they remain till they emerge as adults. Figure 526 represents Pseudococcus longispinosus, a common species in greenhouses; and Figure 527, Pseudococcus citri, another species that is ilH^V ^IBIf' Mlilillliii"% f/ found in greenhouses in the North. The latter species is also a well-known pest of orange trees in the South. Several species of mealy- bugs of the genus Ripersia are found in the nests of ants of the genus Lasius. Subfamily LECANIIN^ The Tortoise-Scales The tortoise-scales are so named on account of the form of the body in many species. Fig. 528. — Lecanium hesperidum, adult fe- males, natural size. 452 AN INTRODUCTION TO ENTOMOLOGY The most striking characteristic of this subfamily is that the abdomen of the female is cleft at the caudal end, and at the cephalic end of this cleft there is a pair of triangular or semicircular plates, the anal plates (Fig. 518). This is a large subfamily including many genera and species. While the various forms agree in the distinguishing characteristics given above, there are great differences in the appearance of the adult females. Many of them excrete very little wax, the body being practically naked, and the eggs, or the young in the viviparous species, Fig. 529. Saissetia olece: enlarged. /, adult females on olive, natural size; la, female, are deposited beneath the body; in other species, although the body is nearly naked, the adult female excretes a large, cottony egg-sac; and in still others the body is deeply encased in wax. The three following species will serve as examples of those in which the body is naked and which do not form an egg-sac. The soft scale, Lecdnium hesperidum. — This is the commonest and most widely spread member of this subfamily ; it infests a great variety of plants; in the North, it is very common in greenhouses; in the warmer parts of the country it lives out of doors. The adult female is nearly fiat (Fig. 528), and is viviparous. HOMOPTERA 453 The black scale, Saissetia olecB. — This is a well-known pest, es- pecially in California, where it infests various kinds of fruit-trees and other plants. The adult fe- male is dark brown, nearly black, in color; nearly hemi- spherical in form (Fig. 529), often, however, quite a little longer than broad. There is a median longitudinal ridge on the back, and two transverse ridges, the three forming a raised surface of the form of a capital H. The hemispherical scale, Saissetia hemisphcerica. — -The adult female is nearly hemi- spherical in form, with the edges of the body flattened (Fig. 530). This species is found in conservatories every- where, and in the open air in warmer regions. Pulvindria. — Those mem- bers of this subfamily in which the adult female is nearly naked but excretes a large cottony egg-sac beneath or be- hind the body, are represented in this country by the genus Pulvinaria, of which we have many species. Our best -known species are the two following. The cottony maple-scale, Pulvindria vitis. — This species is common on maple, osage orange, grape, and other plants. Figure 531 represents several adult females with their egg-sacs on a cane of grape. The maple-leaf pulvinaria, Pulvindria acertcola . — This species is also found on maple. It differs from the preceding Fig. 531. — Pulvinaria vitis. species in that the egg- sac is much longer than the body of the female, and is formed on the leaves instead of on the stem of the host. Ceroplastes. — -In this genus the body of the female is covered with thick plates of wax. More than sixty species have been described, MaTxAl Fig. 530. — Saissetia hemisphcerica: 3, adult females on orange, natural size; ja, adult female, enlarged. 454 AN INTRODUCTION TO ENTOMOLOGY several of which are found in the southern United States ; the follow- ing will serve as an example of these beautiful insects. The barnacle scale, Ceropldstes cir- ripediformis. — Several individuals of this species are represented natural size, and one enlarged, in Figure 532. It infests orange, quince, and many other plants. Subfamily KERMESIIN^ The Pseudogall Coccids This subfamily includes only one genus, Kermes. Species of this genus are common on oaks wherever they grow. These insects are remarkable for the wonderful gall-like form of the adult females. So striking is this re- semblance, that they have been mis- taken for galls by many entomologists. Fig. 533 represents a species of this genus upon Quercus agrifolia. The gall- like bodies on the stem are adult fe- males, the smaller scales on the leaves are immature males. Subfamily DIASPIDIN^ The Armored Scales Fig. 532.—Ceroplastes cirripedi- a>i, r^- -a- ■ ^ a ^u formis. The Diaspidmse mcludes those coc- cids that form a scale, composed in part of molted skins and partly of an excretion of the insect, beneath which the insect lives. It is on account of this covering that these scale-insects are named the armored scales. The Diaspidinse are also characterized by a coalescence of the last four abdominal segments so as to form what is known as the pygidium; this peculiar structure is described on an earlier page. The formation of the scale begins immediately after the close of the active period of the first nymphal instar. At this time the young insect settles and begins to draw nourishment from its host. Soon after, there exude from the body fine threads of wax, the commence- ment of the formation of the scale. At the close of the first stadiimi, the molted skin is added to the scale and forms a part of it. This is also true, except as noted below, of the second molted skin of the female (Fig. 534, 2b and 2c). In the formation of the scale of the male only the first molted skin is added to the scale (Fig. 534, 2d). The scales of males can be distinguished by this fact, and, too, they are much smaller than the scales of females. HOMOPTERA 455 In a few genera the female does not molt the second exuviae* ; the body shrinks away from it, and transforms within it. In such cases is it termed a puparium. Figure 535 represents the scale of Fionnia fiormice; here the pupariiim can be seen through the trans- parent scale. Fig- 533- — Kermes sp. on Quercus agrifolia: adult females on the stem; immature males on the leaves. The shape of the scale, and the position of the exuviae on it, fur- nish characters that are very useful in the classification of the Diaspidins. To this subfamily belong some of the most serious pests of shrubs and trees, as, for example, the San Jose scale and the oyster-shell scale. The following are a few of the many well-known species of this very important subfamily. *The term exuvice is a Latin word which had no singular form, the plural noun being used as is in English the word clothes. Some recent writers use the term exuvia for a single molted skin. 456 AN INTRODUCTION TO ENTOMOLOGY The purple scale, Lepidosaphes pinncBjormis. — This scale-insect is well known in the orange-growing sections of this and of other JttKiS. Fig. 534. — Chionaspis pinifolicE: 2, scales on Pinus strobiis, natural size, leaves stunted; 2a, leaves not stunted by coccids; 2b, scale of female, usual form, enlarged; 2C, scale of female, wide form, enlarged; 2d, scale of male, enlarged. countries. It is one of the two most common scale-insects found on citrus trees in Florida. The scales of this species are represented in Figure 536; they are represented natural size on the leaf, and greatly enlarged in the other figures. The scale of the female §is long, more or less curved, and widened posteriorly (Fig. 536, la and ih) ; the first of these two figures repre- sents the dorsal scale, and the second the ventral scale, which is well developed in this species. Some eggs can be seen through a gap in the ventral scale. The scale of the male (Fig. 536, ic) is usually straight or nearly so. @ At about one-quarter of the length of the scale from the posterior extremity, the scale is thin, forming a hinge which allows the posterior part of it to be lifted by the male as he emerges. While this insect is chiefly known as a pest of citrus trees, it has been found on several other, species of plants. It has been described under several different names; for a long time it was known as Mytildspis citrlcola. Tig. 535— -F"*- orinia fiorimcB HOMOPTERA 457 Glover's scale, Lepidosaphes gloverii. — This is the second of the two most common species of scale-insects found on citrus trees in Florida. In this species the scale of the female is much narrower than that of the preceding species. This species is widely distributed over the warmer parts of the world. The oyster-shell scale, Lepidosaphes ulmi. — This is a northern rep- resentative of the genus to which the two preceding species belong. It is closely allied to the purple scale; in fact Figure 536 would serve to illustrate this species except that it does not occur on orange and that it is found chiefly on the trunk of its host. The two species differ in the characters presented by the pygidium. The oyster-shell scale is Fig- 536- — Lepidosaphes pinnceformis : i, scales on orange, natural size; la, scale of female, dorsal view, enlarged; ib, scale of female with ventral scale and eggs, enlarged; ic, scale of male, enlarged. a cosmopolitan insect, and it infests very many species of shrubs and trees. In the North it is the commonest and best-known scale-insect infesting fruit-trees and various ornamental shrubs. It is discussed in all of our manuals of fruit-insects ; in some of them it is described under the name Mytildspis pomorum. The scurfy scale, Chiondspis furftira. — This, like the preceding species, is a very common pest of the apple and various other trees and shrubs; but usually it is not very destructive. In this species the scale of the female is widened posteriorly, and bears the exuviae at the anterior end (Fig. 5 1 2 , /c) . The scale of the male is very small, being only .75 mm. in length, narrow, and tricarinated (Fig. 512, la). 458 AN INTRODUCTION TO ENTOMOLOGY The pine-leaf scale, Chionaspis pinifolicB: — This is a very common pest of pine, spruce, and other coniferous trees, throughout the United States and Canada. It infests the leaves of its various hosts. The scale of the female is snowy white in color, with the exuviae light yellow; it is usually long and narrow, as represented in Figure 534, 2h; but on the broader-leaved pines it is often of the form shown Fig. 537. — Aulacaspis rosce: i, scales on rose, natural size; la, scale of female, enlarged; ib, scale of male, enlarged. at 2c in the figure ; this is the typical form of the scale of the female in the genus Chionaspis. The rose-scale, Aulacaspis rosce. — This species infests the stems of roses, blackberry, raspberry, dewberry, and some other plants. The infested stems often become densely coated with the scales. The scale of the female is circular, snowy white, with the exuviae light yellow and upon one side (Fig. 537, la). The scale of the male is also white; it is long, tricarinated, and with the exuviae at one end (Fig. 537, ih); it measures 1.25 mm. in length. The San Jose scale, Comstockaspis perniciosa. — The San Jose scale was first described by the writer in 1881, under the name Aspidiotus perniciosus. It has since been made the type of a new genus, Com- stockaspis, by MacGillivray ('21). At the time it was described it was known only in Santa Clara County, California. But in describing HOMOPTERA 459 it, notwithstanding its limited distribution, I stated: "From what I have seen of it, I think that it is the most pernicious scale-insect known in this country." Since that time it has become widely dis- tributed. Slingerland and Crosby write of it as follows: "The San Jose scale has attained greater notoriety, has been the cause of more legislation, both foreign and interstate, and has demonstrated its capabilities of doing more injury to the fruit interests of the United States and Canada than any other insect." This species infests various fruit-trees and ornamental shrubs ; it infests the bark, leaves, and fruit of its hosts, and usually causes reddish discolorations of the bark and of the skin of the fruit. This species can be distinguished from the other scale-insects that are important pests of our fruit-trees by the form of the scales. The scale of the female is circular and flat, with the exuviae central, or nearly so. The scale is gray, excepting the central part, that which covers the exuviae, which varies from a pale yellow to a reddish yellow. It measures 2 mm. in diameter. The scale of the male is black, and is somewhat elongate when fully formed. The exuviae is covered with secretion; its position is marked by a nipple-like prominence which is between the center and the anterior margin of the scale. Control of scale-insects. — The extensive damage that has been done by scale-insects to fruit-trees and to cultivated shrubs has led to many experiments in the destruction of these insects. The results have been quite satisfactory ; with proper care, it is now possible to keep in check the ravages of these pests. Detailed accounts of the methods to be employed are given in many easily available publications, and especially in bulletins of experiment stations. In the case of deciduous trees and shrubs, the best time to destroy scale-insects infesting them is during the winter, when the trees are bare and in a dormant state. At this time the entire tree can be reached with sprays, without the interference of leaves; and, too, certain sprays can be safely used that are liable to injure the trees during the growing season. This is especially true of the lime-sulphur mixture, which is very widely used for the destruction of scale-insects, and is very effective. Among the other insecticides used for this purpose are kerosene emulsion and dilute miscible oils. For summer spraying, whale-oil soap, one pound dissolved in four or five gallons of water, can be safely used. In the case of trees that are constantly clothed with foliage, the effective use of sprays is more difficult. In the orange-growing sections of California the trees are fumigated with hydrocyanic acid gas, the tree to be treated being first covered with a large tent. CHAPTER XXII ORDER DERMAPTERA* The Earwigs The winged members of this order usually have four wings; but in some of them the hind wings are vestigial or wanting; the fore wings are leathery, very small, without veins, and when at rest meet in a straight line on the back; the hind wings, when well developed, are large, with radiating veins, and when at rest are folded both lengthwise and crosswise. The mouth-parts are formed for chewing. The caudal end of the body is furnished with a pair of appendages, the cerci, which resemble forceps. The metamorphosis is gradual. This order includes only the earwigs. These are long and narrow insects, resembling rove-beetles in the form of the body and in having short and thickened fore wings, which, when at rest, meet in a straight line on the back (Fig. 538); but the earwigs are easily distinguished from rove-beetles by the presence of a pair of forceps-like appendages at the caudal end of the body. The common name, earwig, was given to these insects in England, and has reference to a widely spread fancy that these insects creep into the ears of sleeping persons. Other similar \/ fl ^m I names are applied to them in Europe, Ohr- •*' y JHbLs Wurm in Germany and perceoreille in France. ^ ^/iflBi '^■^^ earwigs are rare in the northeastern " ^H™ 1 United States and Canada, but are more often found in the South and on the Pacific Coast. In Europe they are common, and often trouble- some pests, feeding upon the corollas of flowers, fruits, and other vegetable substances. Al- though they are probably chiefly herbivorous, some species are carnivorous, feeding on other insects, and some are probably scavengers, as they have been found with rove-beetles about decaying animal matter. They are nocturnal, hiding in the day-time among leaves and in all kinds of crevices, and coming out by night; sometimes they are attracted to lights. Earwigs are small or of moderate size; the living species measure from 2.5 to 37 mm. in length. The body is narrow and flat. The mouth-parts are fitted for chewing, and resemble in their more general features those of the Orthoptera ; minute but distinct parag- natha are present ; and the second maxillae are incompletely fused. *Dermaptera: derma (d4pfj.a), skin; pteron {Trrepdv), a wing. (460) Fig. 538.— An Labia minor, male. earwig. DERMAPTERA 461 The compound eyes are rather large; but the ocehi are wanting. The antennas are slender, and consist of from ten to thirty-five seg- ments; the second segment is always small. The fore wings are leath- ery, very short, without veins, and when at rest meet in a straight line on the back. This pair of wings is commonly termed the tegmina or the elytra. The hind wings, when fully developed, are large, with radiating veins, and when at rest are folded both lengthwise and crosswise. The folded hind wings project a short distance behind the fore wings (Fig. 538). The radiating veins of the hind wings extend from a point near the middle of the length of the wing (Fig. 539). When the wing is not in use, that part over which the radiating veins extend is folded in plaits like a fan, after which the wing is folded twice crosswise. This part of the wing is the greatly expanded anal Fig. 539. — Hind wing of an earwig: nf, nodal furrow. area. The preanal area is much reduced and contains only two longitudinal veins ; this area is quite densely chitinized. The trachea- tion of the hind wings has been described and figured by the writer (Comstock '18). The wings vary much in size and development even in the same species ; and there are many species that are wingless. The legs are similar in form, and the tarsi are three-jointed. The most distinctive feature of earwigs is the form of the cerci, which are forceps-like, and usually very prominent. A similar form of cerci is found, however, in the genus Japyx of the order Thysanura. The size and shape of the forceps of earwigs differ in the different species and in the two sexes of the same species; they are usually more highly developed in the male than in the female; they are used as organs of defense and offense, in pairing, and are sometimes used as an aid in folding the wings. 462 AX INTRODUCTIOX TO ENTOMOLOGY ? ->/^- / Fig. 541. — Pro- lahia pidchella hurgessi,ra2\Q. (From Rehn and Hebard.) Certain ean\-igs possess stink-glands, which open through tuber- cles situated one on each side near the hind margins of the second and third visible abdominal segments; from which, it is said, they can squirt a foul-smelling fluid to a distance of three or four inches. These tubercles are represented in Figure 543. The sexes can be distinguished by . .^_^ the smaller size of the forceps of the ^/^:^^\ female, and by the fact that in the •^'Kr^--^N female there are distinctly visible only six abdominal sterna, while in the ^ . I |^^» male there are eight. /^/«rR\^ In some earwigs the two efferent ducts of the reproductive organs open^. separately. The metamorphosis is gradual, the yotmg resembling the adult in form, and the wings developing externally. The female is said to brood over the eggs, but to abandon the young soon after the} are hatched. Fig. 540.— LoWa The order Dermaptera was estabHshed by minor, female, Latreille in 1 83 1, and again by Westwood in 1839 and end of ab- i^^er the name Euplexoptera. This later name has maS'^ %rom been used by many authors, including the writer; but Lugger.) the older name should be adopted. The species of the world have been monographed by Burr ('11). Ear\\-igs are cosmopolitan insects, and are easily transported by commerce; consequently exotic species are liable to be found near seaports; and some such species have become established in this country. The order is a comparativeh" small one ; only about four himdred living species have been described, and these are mostly tropical or semi-tropical. The native and the exotic species that have become established in America north of Mexico number together only fifteen; among these are the following. Theseaside earwig, Anisolabis mariiima . — In this species both pairs of wings are wanting, the antennae are 24-jointed, and the length of the body is from 18 to 20 mm. This earwig is fotind along the coast from Maine to Texas. The ring-legged earwig, Anisolabis anntllipes. — This is also a wingless species. It differs from the preceding in that the antennas are only 15- or i6-jointed, the body is about half as long, and the legs are ringed with fuscous. Its range does not extend as far north as that of the seaside eans'ig, but it extends farther inland. The little ean%-ig. Labia minor. — In this species the body is thickly clothed with fine yellowish pubescence. It is a small species, the body measuring only from 4 to 5 mm. in length. Figure 538 represents the male, natural size and greatly enlarged; and Figure 540, the female, DERMAPTERA 463 with the end of the abdomen of the male below. This species is widely distributed in the United States and is the only species estabhshed in Canada. The handsome earwig, Proldbia pulchella. — This species is widely distributed over the southern United States; it is found under the bark of dead trees. The body is dark chestnut-brown, shining and glabrous. It measures from 6 to 6.5 mm. in length. This species is dimorphic; in one form, known as burgessi (Fig. 541), the hind wings are shorter than the tegmina. This is one of our few native species. The spine-tailed earwig, Doru aculedtum. — In the genus to which this species belongs, the pygidium of the male is armed with a distinct Fig. ^^2.—Doni acii- leatum, male. (From Blatchley.) Fig. 543. — Forficula aiiricularia: A, male with short forceps; B, forceps of female; C, long type of forceps of male. (After Morse.) tubercle or spine (Fig. 542) . This species is dark chestnut-brown, with the palpi, legs, edges of pronotum, and the outer two-thirds of the tegmina yellow. The hind wings are usually aborted. The length of the body is 7.5 to 11 mm. The range of tliis species extends from New Jersey and southern Michigan west and south to Nebraska, Georgia, and Louisiana. The common European earwig, Forficula auriculdria. — In this species and in the preceding one as well, the second tarsal segment is lobed and prolonged beneath the third ; but the two species can be distinguished by the shape of the forceps of the male (Fig. 543). The males of this species are dimorphic; in one form the forceps average about 4 mm. in length, in the other about 7 mm. This common European species appeared in great numbers at Newport, Rhode Island, about 191 2. CHAPTER XXIII ORDER COLEOPTERA* The Beetles The winged members of this order have Jour wings; but the first pair of wings are greatly thickened, forming a pair of "wing-covers'' or elytra, beneath which the membranous hind wings are folded when at rest. The elytra meet in a straight line along the middle of the back and serve as armor, protecting that part of the body which they cover. The mouth- parts are formed for chewing. The metamorphosis is complete. The order Coleoptera includes only the beetles. These insects can be readily distinguished from all others except the earwigs by the structure of the fore wings, these being homy, veinless "wing-covers" or el\i:ra, which meet in a straight line along the middle of the back (Fig. 544); and they differ from ear- wigs in lacking pincer-like appendages at the caudal end of the body. Beetles also differ from earwigs in having a complete metamorphosis. Only a few modifications of the typical characteristics exist in this order; among the Fig. $^.—Desmocerus pal- ^nore familiar of these are the following : in liatus. some of the Meloidas the elytra do not meet in a straight line ; in many of the Carabidae, Curculionidse, et al., the hind wings are wanting, and in some of these the elytra are grown together ; in a few females of the Lampyridae and Phengodidae both pairs of wings are wanting. The different mouth-parts are ven^ evenly developed; we do not find some of them greatly enlarged at the expense of others, as in several other orders of insects. The upper lip, or labrum, is usually distinct; the mandibles are powerful jaws fitted either for seizing prey or for gnawing; the maxillas are also well developed and are quite complicated, consisting of several distinct pieces; the maxillary palpi are usually prominent; and the lower lip, or labium, is also well developed and complicated, consisting of several parts and bearing prominent labial palpi. Detailed figures of the maxillas and labiiim of beetles are given in Chapter II. In the classification of beetles much use is being made of the variations in form of the ventral and lateral sclerites of the thorax. Figure 545 will serv^e as an illustration of these sclerites. One feature merits special mention: the coxae of the hind legs are flattened and immovably attached to the thorax so that they appear to be a part of the thorax instead of the basal segment of an appendage. Coleoptera: coleos {hoKebs), a sheath; pteron {irrepby), a wing. (464) COLEOPTERA 465 Almost the only use that has been made of the characteristics of the wings has been restricted to certain features of the elytra, those that can be seen with- out spreading the wings. These are the shape of the elytra, the presence or ab- sence of strise, the pres- ence or absence of punctures and their distribution when present, and the pres- enceor absence of sets, pubescence, or scales on the surface of the elytra. A beginningha s been made, however, to make use of the venation of the hind wings; this, as yet, is restricted to an indi- cation of the type of wing-venation charac- teristic in each case of the superfamilies. The venation of the wings of the Cole- optera has become greatly modified, and, consequently, the de- termination of the ho- mologies of the wing- veins is a difficult mat- Fig- 545- — Ventral aspect of a beetle, Enchroma gigan- ter. The transforma- /^a." ^, prothorax; 5, mesothorax; C, metathorax; tion of the fore wintrc ^' ^' ^' ^°^^' ^^' ^^' ^^' epimera; es, es, es, epis- tion Ol tne lOre wmgs ^^^^^. ^_ ^_ ^^ sterna; /, /, trochantins; x, elytrum; mtO elytra has result- y^ antecoxal piece of metasternum. ed in a great reduction of' their venation; and the foldings of the hind wings interrupt the veins and cause distortions in their courses. It is only recently that extended studies of the wing-venation of the Coleoptera have been made, and the conclusions reached by the different investigators are not fully in accord. But much progress has been made, and so much interest is being shown in the subject that we can confidently expect that conclusions will soon be reached that can be generally accepted. Among the recent studies of the subject is an extended one by Dr. Wm. T. M. Forbes ('22 b), in which the venation of the hind wings of more than fifty species of beetles are figured. The accompanying figures (Figs. 546-547), copied from Dr. Forbes' paper, will serve to illustrate his conclusions regarding the homologies of the wing-veins 466 AN INTRODUCTION TO ENTOMOLOGY of beetles. Another recent paper in which the venation of the wings of many beetles is figured is that of Graham ('22). Fig. 546. — Tracheation of wing of imago of Calosoma. (From Forbes.) arc-^ *hum fthA, - - 3dA; Fig. 547. — Tracheation of wing of imago of Dysliscus verticalis. (From Forbes.) Beetles undergo a complete metamorphosis. The larvag, which are commonly called grubs, var}^ greatly in form; some are campodeiform, others are scarabeiform, and some are vermiform. In some members of the order there is a hypermetamorphosis, the successive larv^al instars representing different types of larvae; this is true of members of the Meloidae and Micromalthidffi. Oc- casionally individuals of Tenehrio molitor are found in which the wings are developed externally. The pupse are exarate, that is, the limbs are free (Fig. 548). These insects usually transform in rude cocoons made of earth or of bits of wood fastened together by a viscid substance excreted by the larvae. Many wood-burrowing species transform in the tunnels made bv the larva? ; and some of the Dermes- Fig. 548.— Pu- pa of a bee- tle. COLEOPTERA 467 tidce as well as some of the Coccinellidse transform in the last larval skin. Both larvae and adults present a very wide range of habits. While the majority of the species are terrestrial, the members of several families are aquatic ; and while some feed on vegetable matter, others feed upon animal matter. The vegetable feeders include those that eat the living parts of plants, those that bore in dead wood, and those that feed upon decaying vegetable substances. Among the animal feeders are those that are predacious, those that feed on dried parts of animals, and those that act as scavengers, feeding on decaying animal matter. Viewed from the human standpoint, some species are very beneficial, others are extremely noxious. The Coleoptera is a very large order; in the "Catalogue of the Coleoptera of America, North of Mexico" by Leng ('20), 18,547 species are listed; these represent 109 families. The order is divided into two suborders, the Adephaga and the Polyphaga. In each of the suborders the families are grouped into superfamilies, two in the Adephaga and twenty in the Polyphaga; and in the suborder Polyphaga the superfamilies are grouped into seven series of superfamilies. Students of the Coleoptera are not fully agreed as to some of the details of this classification ; but as this catalogue will doubtless serve, for a long time, in this country, as a guide for the arrangement of collections, it seems best to follow it in this introductory text-book. Some of the places where there is a lack of agreement among the authorities are indicated in the conspectus on page 38 of the Catalogue. SYNOPSIS OF THE COLEOPTERA {Tables for determining the families are given below) I. SUBORDER ADEPHAGA This suborder includes the first seven families, the Cicindelidas to the Gyrinidae inclusive, pages 476 to 484. The family Rhysodidse (page 508) is also included in this suborder by some writers. II. SUBORDER POLYPHAGA This suborder includes all but the first seven families, or the first eight if the Rhysodidae be included in the Adephaga. The families of this suborder are grouped into seven series, as follows: — SERIES I. — THE PALPICORNIA This series includes a single family, the HydrophilidjE ; page 485. SERIES II. — THE BRACHELYTRA This series includes fifteen families, the Platypsyllidse to the Histeridse, in- clusive, pages 486 to 490. SERIES III. — THE POLYFORMIA This series includes forty-three families, the Lycidae to the Nosodendridas, inclusive, pages 491 to 508. SERIES IV. — THE CLAVICORNIA This series includes thirty families, if the Rhysodidae be placed here instead of in the suborder Adephaga; these are the families Rhysodidae to Cisidas, in- clusive, pages 508 to 215. 468 AN INTRODUCTION TO ENTOMOLOGY SERIES V. — THE LAMELLICORNIA This series includes four families, the Scarabaeidae, theTrogidae, the Lucanidae, and the Passalidce, pages 515 to 524. SERIES VI. — THE PHYTOPHAGA This series includes three families, the Cerambycidae, the Chrysomelidae , and the Mylabridae, pages 524 to 535. SERIES VII. — THE RHYNCHOPHORA This series includes six families, the Brentidas to the Scolytidae, inclusive, pages 536 to 542. TABLES FOR DETERMINING THE FAMILIES OF THE COLEOPTERA TABLE I.— THE SUBORDERS AND THE SERIES OF SUPERFAMILIES A. Ventral part of the first segment of the abdomen divided by the hind coxal cavities, so that the sides are separated from the very small medial part. Suborder Adephaga; see Table II, below. AA. Ventral part of the first segment of the abdomen visible for its entire breadth. Suborder Polyphaga. Fig. 549. — Head of Harpalus, ven- tral aspect: a, antenna; g, g, gula; ga, galea or outer lobe of the maxilla; gs, gular suture; Ip, labial palpus; m, m, mandibles; mp, maxillary palpus; s, submen- tum. Fig. 550. — Prothorax of Harpalus, ventral aspect: c, coxa; em, epi- merum ; es, episternum ; /, femur ; n, pronotum; s, s, 5, prosternum. B. Head not prolonged into a narrow beak, palpi always flexible; two gula sutures at least before and behind (Fig. 549) ; sutures between the prosternum and the episterna and epimera distinct (Fig. 550) ; the epimera of the pro- thorax not meeting on the middle line behind the prosternum (Fig. 550). C. Abdomen with at least three corneous segments dorsally, and exposed more or less by the short elytra. Hind wings with simple, straight veins; antennffi variable, but never lamellate. Series Brachelytra, See Table III, below. CC. Abdomen with at most two corneous segments dorsally, usually com- pletely covered by the elytra; hind wings with veins in part connected by recurrent veins. D. Antennae clubbed or not, but if clubbed not lamellate. E. Tarsi usually apparently four-jointed, the real fourth segment being reduced in size so as to form an indistinct segment at the base of the last segment, with which it is immovably united (Fig. 551, A); the first three segments of the tarsi dilated and brush-like beneath; the third segment bilobed. In two genera, Parandra and COLEOPTERA 469 Spondylis, the fourth segment of the tarsus, although much reduced and immovably united with the fifth, is distinctly visible, the first three Fig- 551- — Tarsi of Phytophaga: ^.typical; B, Spondylis; C, Parandra. segments are but slightly dilated, and the third is either bilobed, Spondylis (Fig. 551, 5), or not, Parandra (Fig. 551, C). Series Phytophaga. See Table VI, below. EE. Tarsi varying in form and in the number of the segments, but when five-jointed not of the type described under E above, the joint be- tween the fourth and fifth segments being flexible. Series Palpicornia, Polyformia, and Clavicornia. See Table IV, below. DD. Antennas with a lamellate club. Series Lam- ellicornia. See Table V, below. BB. Head either prolonged into a beak or not; palpi usually short and rigid; gular sutures confluent on the median line (Fig. 552, gs); prosternal sutures wanting; the epimera of the prothorax meeting on the middle line behind the prosternum (Fig. 552, em). Series Rhynchophora. See Table VII, below. TABLE II.— THE FAMILIES OF THE SUB- ORDER ADEPHAGA Fig. 552. — Head and prothorax of Rhyn- chophorus: gs, con- fluent gular su- tures; s, proster- num; em, epime- rum; c, coxa; /, fe- mur. . Metasternum with an antecoxal piece, separated by a well-marked suture reaching from one side to the other and extending in a triangular process between the hind coxag. B. Antennae eleven-jointed; hind coxse mobile, and of the usual form; habits terrestrial. C. Antennae inserted on the front above the base of the mandibles, p. 476. ClCINDELID^ 470 AN INTRODUCTION TO ENTOMOLOGY CC. Antenna arising at the side of the head between the base of the mandi- bles and the eyes. D. Beetles of a round convex form in which the scutellum is entirely concealed, p. 481 Omophronid^ DD. Not such beetles, p. 478 Carabid^ BB. Antennce ten- jointed; hind coxae fixed and greatly expanded so as to conceal the basal half of the hind femora and from three to six of the ab- dominal segments; habits aquatic, p. 481 Haliplid^ AA. Metasternum either with a very short antecoxal piece, which is separated by an indistinct suture and which is not prolonged posteriorly between the cox£B, or without an antecoxal piece. B. Metasternum with a very short antecoxal piece, p. 481 .Amphizoid^ BB. Metasternum without an antecoxal piece. C. Legs fitted for swimming. D. With only two eyes. p. 482 Dytiscid^ DD. With fotir eyes, two above and two below, p. 484. .Gyrinid^ CC. Legs fitted for walking, p. 508 Rhysodid^* TABLE IIL— THE FAMILIES OF THE BRACHELYTRA A. Elytra short, leaving the greater part of the abdomen exposed; the suture between the elytra when closed straight; wings present, and when not in use folded beneath the short elytra; the dorsal part of the abdominal segments en- tirely horny. B. Abdomen flexible, and with seven or eight segments visible below, p. 488. Staphy-linid^ BB. Abdomen not flexible, and with only five or six ventral segments visible. C. Antennas with less than six joints, p. 490 Clavigerid^ CC. Antennas eleven-jointed, rarely ten-jointed, p. 489.. Pselaphid^ AA. Elytra usually long, covering the greater part of the abdomen; when short the wings are wanting, or, if present, may or may not be folded under the short elytra when at rest; the dorsal part of the abdominal segments partly membranous. B. Hind tarsi five-jointed. C. Antennae elbowed, and clavate. p. 490 Histerid.'E CC. Antennae rarely elbowed, and then not clavate. D. Abdomen with not more than five ventral segments. E. Antennae capitate, the last three segments forming an abrupt club. p. 490 SPH^RITID^t EE. Antennas but slightly clavate if at all. p. 490.. . .Scaphidiid^ DD. Abdomen with six or more ventral segments. E. Anterior coxae flat. p. 486 Platypsyllid^ EE. Anterior coxae either globular or conical. F. Anterior coxae globular, p. 487 Leptinid.*; FF. Anterior coxae conical. G. Posterior coxae widely separated. H. Eyes wanting or inconspicuous, p. 487 Silphid^ HH. With well-developed eyes. I. Elytra covering the abdomen, p. 488 . . . Scydm^nid^ II. Elytra not covering the entire abdomen, p. 490 SCAPHIDIIDiE GG. Posterior coxae approximate. H. Posterior coxas laminate, p. 488 Clambid^ HH. Posterior coxas not laminate. *The Rhysodidae is a very aberrant family, and its affinities have been much discussed. The form of the ventral part of the first abdominal segment is similar to that characteristic of the Adephaga; hence, according to Table I, this family should be placed in this suborder. But other characters led Leconte and Horn ('83) to place it in the Clavicornia, in which view they are followed by recent writers. fSee also p. 508, the Nitidulidae of the series Clavicornia. COLEOPTERA 471 I. Eyes with large facets, p. 486 Brathinid/E II. Eyes with small facets, p. 487 Silphid^ BB. Hind tarsi either only three-jointed or four-jointed, but apparently three- jointed, the third segment being small and concealed in a notch at the end of the second segment. (See also BBB and BBBB.) C. Abdomen with six or seven ventral segments. D. Tarsi four-jointed, the third segment small and concealed in a notch at the end of the second segment, p. 488 Corylophid^ DD. Tarsi three-jointed, p. 490 Trichopterygid^ CC. Abdomen with only three ventral segments, p. 490. Sph^riid/E BBB. All tarsi four-jointed. (See also BBBB.) C. Hind coxae contiguous and with plates covering the femora entirely or in part. p. 487 Silphid^ CC. Hind coxae separate and not covering the femora, p. 488 Corylophid^ BBBB. Hind tarsi with only four segments; the fore tarsi, and almost always the middle tarsi also, with five segments, p. 487 Silphid^ TABLE IV.— THE FAMILIES OF THE PALPICORNIA, POLYFORMIA AND CLAVICORNIA It is impracticable to separate these three series of families in these tables, owing to the fact that characters sharply separating them have not been found. A. Hind tarsi five-jointed. B. Maxillary palpi as long as or longer than the antennae, p.485 Hydrophilid^ BB. Maxillary palpi much shorter than the antennae. C. Tarsal claws very large; the first three abdominal segments grown together on the ventral side. D. Abdomen with more than five ventral segments; anterior coxae with very large trochantin. p. 503 Psephenid^ DD. Abdomen with five ventral segments. E. Anteriorcoxae transverse, with distinct trochantin. p.504.DRYOPiDyE. EE. Anterior coxs rounded, without trochantin. p. 504...Elmid^ CC. Tarsal claws of usual size; ventral abdominal segments usually free,, sometimes (Buprestidae) the first two grown together. D. Abdomen with not more than five ventral segments. E. Femur joined to the apex or very near the apex of the trochanter. F. Antennae inserted upon the front, p. 514 Ptinid^ FF. Antennae inserted before the eyes. G Tibia; without spurs, p. 514 Anobiid^ GO. Tibiae with distinct spurs. H. First ventral segment scarcely longer than the second. -, P- 515. Bostrichid^ JrlH. First ventral segment elongated, p. 515 Lyctid^ EE. Femur joined to the side of the trochanter. F. Anterior coxs globular or transverse, usually projecting but little from the coxal cavity. G. Anterior coxae transverse, more or less cylindrical. H. Posterior coxa; grooved for the reception of the femora. I. Legs stout, retractile; tibiae dilated, usually with a furrow near the outer end for the reception of the tarsi; tibial spurs distinct. J. Antennae inserted at the side of the head. K. Head prominent, mentum large, p. 5o8.Nosodendrid^ KK. Head retracted, mentum small, p. 5o8.Byrrhid.«; J J. Antennae inserted on the front; head retracted, p. 506. Chelonariid^ II. Tibia; slender, with small and sometimes obsolete terminal spurs, or without spurs. J. Head constricted behind; eyes smooth, p. 494.CuPESlD^. J J. Head not constricted behind ; eyes granulated. 472 AN INTRODUCTION TO ENTOMOLOGY K. Anterior coxae with a distinct trochantin. p. 505. Dascillid^ KK. Anterior coxae without trochantin. L. Lacinia of the maxillae armed with a terminal hook. p. 505 EUCINETID^ LL. Lacinia not armed with a terminal hook. p. 505. Helodid.« HH. Posterior coxae flat; not grooved for the reception of the femora. I. Tarsi more or less dilated, first segment not short. J. Antennae eleven-jointed, terminated by a three-jointed club. p. 508 NlTIDULID^ JJ. Antennas ten-jointed, club two-jointed, p. 508 Rhizophagid,^ II. Tarsi slender, first segment short, p. 508 . . Ostomid^ GG. Anterior coxae globular. H. Presternum with a process which extends backward into a groove in the mesosternum. I. The first two abdominal segments grown together on the ventral side. p. 502 Buprestid^ II. Ventral segments free. J. Prothorax loosely joined to the mesothorax; front coxal cavities entirely in the prosternum. K. Posterior coxae laminate; trochanters small. L. Antennae somewhat distant from the eyes, their in- sertion narrowing the front, p. 502 Eucnemid.'E LL. Antennae inserted under the margin of the front. M. Antennas arising near the eyes. p. 499.Elaterid^ MM. Antennae arising at a distance in front of the eyes (Perothops). p. 502 Eucnemid.'E KK. Posterior coxae not laminate; trochanters of middle and posterior legs very long. p. 499. . . .Cerophytid^ JJ. Prothorax firmly joined to the mesothorax; front coxal cavities closed behind by the mesosternum. p. 502 Throscid^ HH. Prosternum without a process received by the mesoster- num, although it may be prolonged so as to meet the meso- sternum. I. Posterior coxas contiguous, p. 511 Phalacrid^ II. Posterior coxae separated. J. Body depressed; middle coxal cavities not closed ex- ternally by a meeting of the mesosternum and meta- sternum. p. 509 CucujiD^ JJ. Body more or less convex; middle coxal cavities en- tirely surrounded by the sterna. K. Prosternum not prolonged behind, p. 510. . . Mycetophagid^ KK. Prosternum prolonged, meeting the mesosternum. L. Anterior coxal cavities open behind, p. 510.. . . Cryptophagid.-e LL. Anterior coxal cavities closed behind, p. 509 Erotylid^ T'F. Anterior coxae conical, and projecting prominently from the coxal cavity. G. Posterior coxae dilated into plates partly protecting the femora, at least at their bases. H. Antennas serrate or flabellate. p. 499 Rhipicerid/E HH. Antennae with the last three segments forming a large club. I. Tarsi with second and third segments lobed beneath, p. .SIC Byturid^ II. Tarsi simple, p. 506 Dermestid^ COLEOPTERA 473 HHH. Antennas with the last three segments somewhat larger than the preceding, but not suddenly enlarged, p. 510. DERODONTID.E GG. Posterior coxse not dilated into plates partly protecting the femora. H. Posterior coxae flat, not prominent, covered by the femora in repose. I. Tarsi with the fourth joint of normal size. p. 493.Clerid^ II. Tarsi with the fourth joint very small, p. 493.Corynetid^ HH. Posterior coxas conical and prominent. I. Anterior coxae with distinct trochantins. p. 493.Melyrid^ II. Anterior coxae without trochantins. p. 493.Lymexylid^ DD. Abdomen with six or more ventral segments. E. Anterior coxas globular. F. Tibial spurs well developed, p. 499 Cebrionid/E FF. Tibial spurs very delicate and short, p. 499. . . Plastocerid^ EE. Anterior coxae conical. F. Posterior coxae not prominent, flat, covered by the femora in repose. G. Tarsi with the fourth joint of normal size. p. 493. . . .Clerid^ GG. Tarsi with the fourth joint very small, p. 493. CoRYNETiDiE FF. Posterior coxae more or less conical and prominent at least in- ternally, not covered by the femora in repose. G. Anterior coxae long, with distinct trohacntins. H. Abdomen with seven or eight ventral segments. I. Middle coxae contiguous; epipleurse distinct. J. Episterna of metathorax sinuate on inner side, epi- oleiiTce usually wide at the base. K. Head more or less covered; antennas approximate or moderately distant; metathoracic epimera long. p. 491. Lampyrid^ KK. Head exposed; antennae distant; metathoracic epimera wide. o. 492 Phengodid^ JJ. Episterna of metathorax not sinuate on the inner side; epipleurae narrow at the base. p. 492 Cantharid^ II. Middle coxae distant; epipleurae wanting, p. 491.LYCID/E HH. Abdomen with only six ventral segments, p. 493.MELYRiDiE GG. Anterior coxae without trochantins. H. Elytra entire; length of body 10 mm. or more. p. 493. . Lymexylid^ HH. Elytra shorter than the abdomen; length of body less than 3 mm. p. 494 Micromalthid^ AA. Hind tarsi either only three- jointed, or four-jointed but apparently only three- jointed, the third joint being small and concealed in a notch at the end of the second joint. (See also AAA and AAAA.) B. Wings fringed with long hairs. A minute aquatic species from S. Cal. and Ariz. (Hydroscapha) . p. 485 Hydrophilid^ BB. Wings not fringed with hairs. C. Tarsi with second segment dilated. D. Tarsal claws appendiculate or toothed; first ventral abdominal seg- ment with distinct curved coxal lines, p. 51 1 .CoccinelliD/E DD. Tarsal claws simple; first ventral abdominal segment without coxal lines, p. 51 1 Endomychid^ CO. Tarsi with second segment not dilated. D. Elytra entirely covering the abdomen; ventral abdominal segments nearly equal, p. 511 Lathridiid^ DD. Elytra truncate, the first and fifth abdominal segments longer than the others. E. Maxillae with galea distinct; anterior coxae small, rounded, p. 509. MONOTOMID^ EE. Galea wanting, anterior coxae subtransverse. p. 5o8.Nitidulid^ 474 AN INTRODUCTION TO ENTOMOLOGY AAA. All tarsi four-jointed- (See also AAA A.) B. The first four abdominal segments grown together on the ventral side. C. Tibias dilated, armed with rows of spines, and fitted for digging, o. 505. Heterocerid^ CC. Tibiae neither dilated nor fitted for digging. D. Antennae inserted tmder a distinct frontal ridge; anterior coxae distant from the metasternum. p. 510 Colydiid^ DD. Antennae inserted on the front ; anterior coxae inclosed behind by the metasternum. p. 511 Murmidiid^ BB. Ventral segments of abdomen not grown together. C. Anterior coxae transverse, p. 511 Mycet^id^ CC. Anterior coxae either globose or oval. D. Anterior coxae globose. E. Tarsi slender, p. 51 1 Endomychid^ EE. Tarsi more or less dilated and spongy beneath, p. 509. Erotylid^ DD. Anterior coxae oval. E. Anterior coxae separated by the horny prosternum. F. Body depressed; head free. p. 510 Mycetophagid^ FF. Body cylindrical; thorax prolonged over the head. p. 515. CiSIDyE EE. Anterior coxae contiguous ; prosternum semimembranous, p. 505. Geory'ssid^ AAAA. Hind tarsi with only four segments; the fore tarsi, and almost always the middle tarsi also, with five segments. B. Anterior coxal cavities closed behind. C. Tarsal claws simple. D. Abdomen with five ventral segments. E. Ventral abdominal segments in part grown together. F. Next to the last segment of the tarsi spongy beneath, p. 514. Lagriid^ FF. Penultimate segment of tarsi not spongy, p. 513. Tenebrionid^ EE. Ventral abdominal segments free. F. Anterior coxal cavities confluent, p. 498 Othniid^ FF. Anterior coxal cavities separated by the prosternum. G. Elytra truncate; tip of abdomen exposed, p. 5o8.Rhizophagid^ GG. Elytra entire, p. 515 Sphindid^ DD. Abdomen with six ventral segments, p. 498 Eurystethid^ CC. Tarsal claws pectinate, p. 512 Alleculid^ BB. Anterior coxal cavities open behind. C. Head not strongly and suddenly constricted at base. D. Middle coxae not very prominent. E. Antennae received in grooves, p. 514 Monommid^ EE. Antennae free. F. Prothorax margined at the sides. G. Middle coxal cavities entirely surrounded by the sterna, p. 510. Cryptophagid^ GG. Epimera of mesothorax reaching the coxae. H. Metasternum long; epimera of metathorax visible, p. 514. Melandryid^ HH. Metasternum quadrate; epimera of metathorax covered. p. 509 CucujiD^ FF. Prothorax not margined at the sides, p. 498 Pythid^ DD. Middle coxae very prominent, p. 494 CEdemerid^ CC. Head strongly constricted at base. D. Head prolonged behind and gradually narrowed, p. 494.Cephaloid^ DD. Head suddenly narrowed behind. E. Prothorax with the side pieces not separated from the pronotum by a suture. F. Prothorax at base narrower than the elytra. G. Hind coxae not prominent or but slightly so. H. Anterior coxae globular, not prominent, p. 509.CucujiD^ COLEOPTERA 475 HH. Anterior coxce conical, prominent. I. Abdomen composed of five free segments; tarsi with the penultimate joint lobed beneath. J. Neck wide; eyes large, finely faceted, and generally emarginate. p. 498 " Pedilid^ JJ. Neck narrow, eyes not emarginate. K. Eyes large, oval, rather finely faceted, p. 498.Pedilid^ KK. Eyes small, rounded, generally coarsely faceted, p.498. Anthicid^ II. Abdomen composed of four free segments, the first formed of two united, with the suture sometimes indicated; tarsi with the antepenultimate joint lobed beneath, p. 499.. EuGLENID^ GG. Hind coxse large, prominent. H. Tarsal claws simple; head horizontal. p.498.PYROCHROiDyE HH. Claws cleft or toothed, front vertical, p. 495.Meloid^ FF. Prothorax at base as wide as the elytra, p. 494. .Rhipiphorid^ EE. Lateral suture of prothorax distinct; base of prothorax as wide as the elytra. F. Antennas filiform. G. Hind coxae plate-like. p. 494 Mordellid^ GG. Hind coxae not plate-like. p. 514 Melandryid^ FF. Antennae flabellate in the male, subserrate in the female, p. 494. Rhipiphorid^ TABLE v.— THE FAMILIES OF THE LAMELLICORNIA A. Plates composing the club of the antennae flattened and capable of close apposition. B. Abdomen with six visible ventral segments, p. 515 Scarab^id^ BB. Abdomen with five visible ventral segments. C. Epimera of mesothorax attaining the oblique coxae, p. 5I5.Scarab^iD/E CC. Epimera of mesothorax not attaining the coxae, p. 522 . . Trogid^ AA. Plates composing the club of the antennae not capable of close apposition, and usually not flattened. B. Mentum deeply emarginate, ligula filling the emargination. p. 524.. ■.••••. Passalid^ BB. Mentum entire, ligula covered by the mentum or at its apex. p. 523. LUCANID^ TABLE VI.— FAMILIES OF THE PHYTOPHAGA This series includes three families, which are so connected by intermediate forms that it is not easy to separate them. The following table will aid the student in separating the more typical forms. A. Body elongate; antennas almost always long, often as long as the body or longer. The larvae are borers, p. 524 Cerambycid^ AA. Body short and more or less oval; antennae short. B. Front prolonged into a broad quadrate beak; elytra rather short so that the tip of the abdomen is always exposed. The larvas live in seeds, p. 535. Mylabrid^ BB. Front not prolonged into a beak; usually the tip of the abdomen is covered by the elytra. Both larvae and adults feed on the leaves of plants, p. 530 Chrysomelid^ TABLE VII.— THE FAMILIES OF THE RHYNCHOPHORA {Compiled from Blatchley and Leng) A. Beak rarely absent, usually longer than broad; tibiae never with a series of teeth externally. 476 AN INTRODUCTION TO ENTOMOLOGY B. Antennas straight without a distinct club, though with the outer joints often more or less thickened; beak present at least in the female and pointing directly forward ; form usually very slender and elongate, p. 536..Brentid^ BB. Antennae straight or elbowed, always with a distinct club. C. Palpi flexible; antennal club rarely compact; beak always short and broad; labrum present; thorax with a transverse raised line which is either ante-basal or basal, p. 536. . . Platystomid^ CC. Palpi rigid and labrum wanting except in the subfamilyRhinomacerinae antennal club usually compact; beak variable in length, often long and ctirved downwards, p. 537 Curculionid^* AA. Beak absent or extremely short and broad ; tibiae with a series of teeth ex- ternally, or, if these are wanting, with a prominent curved spine at apex; an- tennae short, but little longer than the head, always elbowed, and with a com- pact club except in Phthorophcelus where the club is lamellate; palpi rigid; body short, subcylindrical or rarely oval. B. Anterior tarsi with the first segment longer than the second, third and fourth together, p. 541 — Platypodid^ BB. Anterior tarsi with the first segment shorter than the second, third, and fom-th together, p. 542 Scolytid^ Suborder ADEPHAGAf The name of this suborder, Adephaga, was suggested by the pre- dacious habits of its members. These beetles are distinguished from other Coleoptera by the presence of a suture on each side of the pro- thorax separating the pleurtim from the notum, and by the fact that the ventral part of the first segment of the abdomen is divided by the hind coxal cavities so that the sides are separated from the very small medial part (Fig. 553). The Adephaga differ from other Coleoptera in that the nutritive cells of the ovaries alternate with the egg- chambers. The larvae are campodeiform, and differ from all other beetle larvae in that their legs are six- jointed except in a single exotic species; this is one more segment than is found in the legs of other beetle larvae. The legs are usually whereas the legs of other coleopterous /si A Fig. 553. — Ventral aspect of part of thorax and abdomen of Galerita janus: ist A, first abdominal seg- ment ; 2d A, second abdominal seg- ment. furnished with two claws, larvae are one-clawed. f-This suborder is represented in North America by seven families these can be separated by Table II, page 469. Family CICINDELID^ The Tiger-Beetles The graceful forms and beautiful colors of the greater number of the tiger-beetles, those of the genus Cicindela, have made the *Since this table was published by Blatchley and Leng, the family Belidae has been separated from the Curculionidae. See page 537. fAdephaga: adephagous {dd-ncpdyoi) , voracious. COLEOPTERA 477 Fig. 555- Fig- 554- family one of the favorites of students of Coleoptera. Their popular name is sug- gestive of their predacious habits, and of the stripes with which many are marked. They are usually a metallic green or bronze, banded or spotted with yellow. Some are black; and some that live on white sand are grayish white, being ex- actly like the sand in color. Figure 554 represents a common species of Cicindela. A useful character for distinguishing the members of this family is the fact that the terminal hook of the maxilla (the digitus) is united to this organ by a movable joint (Fig. 555, h). The sexes of the tiger-beetles can be distinguished, except in Amhlycheila, by the sixth abdominal segment of the males being notched .so as to expose a small seventh segment; while in the females only six segments are visible. In the males, the first three segments of the anterior tarsi are usually dilated and densely clothed with hair beneath. The tiger-beetle larvae (Fig. 556) are as ugly and ungraceful as the adults are beautiful. The two have only one habit in common — their eagerness for prey. The larvae live in vertical burrows in sandy places or in beaten paths. These burrows occur also in ploughed fields that have become dry and hard . They often extend a foot or more in depth . The larva takes a position of watchfulness at the mouth of its burrow. Its dirt-colored head is bent at right angles to its lighter-colored body and makes a neat plug to the opening of the hole. Its rapacious jaws extend upward, wide open, ready to seize the first un- wary insect that walks over this living trap, or near it; for a larva will throw its body forward some distance in order to seize its prey. On the fifth segment of the abdomen there is a hump, and on this hump are two hooks curved forward. This is an arrangement by which the little rascal can hold back and keep from being jerked out of its hole when it gets some large insect by the leg, and by which it can drag its struggling prey down into its lair, where it may eat it at leisure. It is interesting to thrust a straw down into one of these burrows, and then dig it out with a trowel. The chances are that you will find the indignant inhabitant at the remote end of the burrow, chewing savagely at the end of the intruding straw. One hundred and fourteen species of tiger-beetles are now listed in our fauna; these represent four genera, which can be separated as follows : A. Posterior coxae contiguous; eyes large, prominent. B. Third joint of the maxillary palpi shorter than the fourth. . .Cicindela BB. Third joint of the maxillary palpi longer than the fourth Tetracha AA. Posterior coxas separated; eyes small. Fig. 556. 478 AN INTRODUCTION TO ENTOMOLOGY B. Sides of the elytra widely inflexed ; thorax scarcely margined. Amblycheila BB. Sides of the elytra narrowly inflexed; thorax distinctly margined. ..Omus Cicindela. — To this genus belong the greater number of our tiger- beetles; seventy-six species and many varieties occur in our fauna; excepting the two species of Tetracha, all of the tiger-beetles found in the East belong to the genus Cicindela. The members of this genus, unlike most other members of the family, are diurnal in habit. They are found on bright, hot days in dusty roads, in beaten paths, and on the shores of streams. They are the most agile of all beetles; and they are not merely swift of foot, but are also able to fly well. When approached, they remain still until we can see them well but are still out of reach ; then like a flash they fly up and away, alighting several rods ahead of us. Before alighting they usually turn so that they face us, and can thus watch our movements. They hide by night and in cloudy or rainy weather in holes in the ground or beneath stones or rubbish. The beetles have been found hibernating, each in a separate burrow extending under a stone. I have seen them in September digging burrows in a hillside; these descended slightly and were about five inches deep. The beetles kicked the dirt out behind them as they dug, so that it lay in a heap at the opening of the hole. Tetracha. — Two species of this genus are widely distributed in the United vStates. They are rather large, metallic-green beetles. Figure 557 represents Tetracha Carolina, which can be distinguished by the apical portion of the elytra being yellow. Our only other species is Tetracha virgmica. These beetles are nocturnal, hiding during the day and hunting by night. Amblycheila.— The best-known representative of this genus is Amblycheila cylindriformis, which is ig-557- found in Kansas, Colorado, Arizona, and New Mexico. It is a very large species, measuring 3 5 mm. in length. It is nocturnal, hiding in holes during the day and coming forth at night to capture its prey. Two other species of this genus have been described from Arizona and Utah. Omus. — Thirty-three species of this genus have been found on the Pacific Coast, nearly all of them in California. They are nocturnal insects, hiding under rubbish during the daytime. Family CARABID^ The Ground-Beetles The ground-beetles are so called because they are very common on the surface of the ground, lurking under stones or rubbish, where they hide by day. At night they roam about in search of their prey. Our more common species are easily recognized by their shining black color and long legs. On the Pacific Coast, however, the darkling beetles (Family Tenebrionidae) , which are also black and have long legs, abound under stones and fragments of wood on the ground. COLEOPTERA 479 But the two families can be easily distinguished by the fact that in the ground-beetles all the tarsi are five-jointed, while in the darkling beetles the hind tarsi are only four-jointed; and the darkling beetles do not run rapidly as do the ground-beetles. With the ground-beetles, the antennse are thread-like, tapering gradually towards the tip, and each segment is of nearly uniform thickness throughout its length ; the legs are fitted for running, and the antenna are inserted between the base of the mandibles and the eyes. Although most of the species are black, there are those that are blue, green, or brown, and a few that are spotted. The wing- covers are almost always ornamented with longitudinal ridges and rows of punctures. Most members of this family are predacious, feeding upon other insects, which they spring upon or capture by chase. A few species use vegetable food; but their depredations are rarely of economic importance. As there are more than two thousand described North American species, and as many of the species are very common, this family may be considered the most important family of the pre- dacious insects. The larvae of ground-beetles are generally long, with the body of nearly equal breadth throughout (Fig. 558). They have sharp projecting mandibles; and the caudal end of the body is usually furnished with a pair of conical bristly appendages. They pjg erg. live in the same obscure situations as the adult insects, but are more shy, and are consequently less frequently seen. Like the adults, they are predacious. Among the more common ground-beetles are the following. The searcher, Calosdma scrutator. — This is one of the larger and more beautiful of our ground -beetles ; it has green or violet wing-covers margined with reddish, and the rest of the body is marked with violet-blue, gold, green, and copper (Fig. 559). This beetle and the two follow- ing have been known to climb trees in search of caterpillars. Calosdma sycophanta, a common species in Europe, has been introduced and success- fully colonized in New England, as a means of combating the gipsy-moth and the brown-tail moth. This species is somewhat smaller than the preceding, and lacks the reddish band on the margins of the elytra. The fiery hunter, Calosdma cdlidum, is easily recognized by the rows of reddish or Fig. 559. copper-colored pits on the wing-covers (Fig. 560). The bombardier-beetles, Brachlnus. — There are many species of beetles that have at the hind end of the bodv little sacs in which 480 AN INTRODUCTION TO ENTOMOLOGY Fig. 560. is secreted a bad-smelling fluid, which is used as a means of defence. These beetles spurt this fluid out onto their enemies when attacked. But in the case of the bombardier-beetles this fluid changes to a gas, which looks like smoke as soon as it comes in contact with the air, and is ejected with a sound like that of a tiny pop- gun. When some larger insect tries to capture one of these insect-soldiers, and gets very near it, the latter fires its little gun into the face of its enemy. The noise astonishes the pursuer, and the smoke blinds him. By the time he has recovered from his amazement, the little bombardier is at a safe distance. These beetles have quite a store of ammunition; for we have often had one pop at us four or five times in succession, while we were taking it prisoner. The bombardier-beetles belong to the genus Brachinus, of which we have in this country twenty-seven species. They are ver>^ similar in appearance; the head, prothorax, and legs are reddish yellow, and the wing-covers are dark blue, blackish, or greenish blue (Fig. 561). There is a common beetle which resembles the bom- bardier-beetles quite closely in size and color, but whi may be distinguished by the comb-like form of the tarsal claws; this is Lehia grandis (Fig. 562). It has been reported more often than any other insect as destroying the Colorado potato-beetle. Galerlta jdnus is still another species that bears some Fig. 561. resemblance to the bombardier-beetles. But it is much larger, measuring 16 mm. in length, and has only the prothorax and legs reddish yellow, the head being black; the prothorax is only about *half as wide as the wing-covers. What is perhaps the most com- mon type of ground -beetle is illus- trated by Hdrpalus caliginosus, which is represented natural size in Figure 563. It is of a pitchy black color, and is one of the most commonof our larger species. There are one hundred and thirty -six de- scribed species of Harpalus in this country. Most of them are smaller than this one, are flattened, and have the prothorax nearly square. The beetles of the genus Die celus are quite common; and some of the larger species resemble Harpalus caliginosus quite closely. They can be distinguished by a prominent keel- shaped ridge which extends back upon each wing- cover from near the comer of the prothorax. Fig. 564. Dm- \ /^ lich vVy rsal y^kT leen />^^C\ Fig. 563- Fig. 562. — Lebia grandis, natu- ral size and enlarged. COLEOPTERA 481 The most common of all ground-beetles, in the Northeastern States at least, is Pcecihis lucublandus. In this species (Fig. 564) the nar- row, flat margin on each side of the prothorax is widened near the hind angle of this segment. The family AMPHIZOID^ is represented in our fauna by two species of Aniphizoa, which occur in California, Vancouver, and Alaska, clinging to logs or stones under the surface of streams. In these beetles the metasternum is truncate behind, not reaching the abdomen, and has a very short antecoxal piece. The familv OMOPHRONID^ consists of a single genus, Oiuophron, the members of which are remarkable for their round form and the fact that the scutellum is entirely concealed. They measure about 6 mm. in length, and are found in holes in wet sand near the margins of streams and ponds. They are found from the Atlantic to the Pacific; fourteen species have been described. Family HALIPLID^ The Crawling Water-Beetles This family includes a few species of small aquatic beetles, which are oval, more or less pointed at each end, and very convex; our larger species measure from 3.5mm. to 5 mm. in length, but some are much smaller. The wing-covers have rows of punctures, and the hind cox« are greatly expanded so as to conceal the basal half of the hind femora and from three to six of the abdominal segments. The anterior and middle tibiae and the tarsi of all of the legs are fur- nished with long, swimming hairs. These beetles are found in ponds and streams, but most frequently in spring-fed pools that do not dry up during the summer, and contain filamentous algse and other aquatic plants. They swim poorly but crawl over the stems of aquatic plants. Little is known regarding the feeding habits of the adults. Matheson ('12) found that several species feed on the contents of the cells of A^ite//a and the softer portions of Chara and other filamentous algae. He observed also that two species of Peltodytes attach their eggs to aquatic plants, mainly Nitella and Chara, while Haliplus ruficollis places its eggs within the dead cells of Nitella. The larvae are aquatic, living in the same pools as the adults. The body is slender; each segment except the head is furnished on the back with fleshy lobes with spiny tips (Fig. 565), which vary greatly in size in different species; in the larv£e of Peltodytes each of these spines bears a long, jointed filament, which is a tracheal gill. The larvffi of this genus have no spiracles ; but the larvae of Haliplus possess both thoracic and Fig. 565. abdominal spiracles. The larvae of the Haliplidae feed on filamentous algae; when mature, they leave the water and each makes a cell in the damp earth in which the pupa state is passed. About forty species of the Haliplidae have been found in our fauna; these represent three genera. In Brychius, which is represented 482 AN INTRODUCTION TO ENTOMOLOGY by two species in California, the prothorax is quadrate; in the other genera it is narrowed in front. In Haliplus the last segment of the palpi is small and awl-shaped ; in Peltodytes it is longer than the third segment, and conical. The last two genera are widely distribu- ted. Family DYTISCID^ The Predacious Diving-Beetles If one will approach quietly a pool of standing water, there may be seen oval, flattened beetles hanging head downward, with the tip of the abdomen at the surface of the water. Such beetles belong to this family. The predacious diving-beetles are usually brownish black and shining, but are often marked indefinitely with dull yellow They can be distinguished from the water scavenger-beetles, which they resemble in general appearance, by the thread-like form of the antennae. The hind legs are the longest and are fitted for swimming, being flattened and fringed with hair. The middle and the hind pair of legs are widely separated. This is due to the very large hind coxae which cover the greater part of the lower surface of the thorax. In the males of certain genera the first three segments of the fore tarsi are di- lated and form a circular disk, upon the under side of which are little cup- like suckers (Fig. 566); these serve as clasping organs. In a few cases the middle tarsi are dilated also. The fe- males of some species exhibit an inter- Fig. 566. Fig. 567. esting dimorphism in that some of the individuals have the elytra fur- nished with a number of deep furrows (Fig 567 j, while others of the same species have them smooth. The diving-beetles abound in our streams and ponds, but they are more often found in standing water than in streams. When at rest they float in an inclined position, head downward, with the tip of the hind end of the body projecting from the water. The spiracles open on the dorsal side of the abdomen beneath the elytra. By lifting the elytra slightly a reservoir is formed for air, which the beetle can breathe as it swims through the water. When the air becomes impure the beetle rises to the surface, forces it out, and takes a fresh supply. These beetles are very voracious. They destroy not only other insects, but some of them will attack larger animals, as small fish. When kept in aquaria they can be fed upon any kind of meat, raw or cooked. They fly from pond to pond, and are often attracted to light at night. Many of the species make sounds, both under the water and in the air. In some cases this is done by rubbing the abdominal segments upon the elytra; in others, by rubbing the hind legs upon a rough spot on the lower side of the abdomen. COLEOPTERA 483 The females deposit their eggs singly in punctures in the tissues of living plants. The larvae are known as water-tigers, because of their blood-thirsti- ness. They are elon- gated, spindle-form Fig. 568. grubs (Fig. 568). The . head is large, oval or rounded, and flattened; the mandibles are large and sickle-shaped; in each there is a slit-like opening near the tip; from this opening a canal leads along the inner surface to a basal opening on the upper surface, which communicates with the corner of the mouth when the mandible is closed. The central part of the mouth, between the mandibles, is closed, the upper and lower lips being locked together by a dovetail joint. The mandibles are ad- mirably fitted for holding prey and at the same time sucking juices from its body. The thorax is furnished with six well-developed legs. The abdomen is teiTninated by a pair of processes; at the tip of the abdomen there is a pair of large spiracles, which the larva protrudes into the air at intervals, in order to breathe. When a larva is fully grown it leaves the water, burrows into the ground, and makes a round cell, within which it undergoes its trans- formations. The pupa state lasts about three weeks in summer; but the larvse that transform in autumn remain in the pupa state all winter. This is the largest of the families of water-beetles; more than three hundred North American species are known. Thebest way to obtain specimens is to sweep the vegetation grow- ing on the bottom of a quiet pool with a dip-net. The larger of our common species belong to CyMster, Dytlscus, and allied genera. In Cybister the little cups on the vmder side of the tarsal disks of the male are similar, and arranged in four rows. In Dytiscus and its allies the cups of the tarsal disks vary in size. Figure 569 represents a common species of Dytiscus. The most common of the diving-beetles which are of medium size belong to the genus Acllius. In this genus the elytra are densely pimctured with very fine punctures, and the females usually have Fig- 569- four furrows in each wing-cover (Fig. 567). There are also common di v^ing-beetles which are of about the same size as the preceding, but which have the wing- covers marked with numerous very fine transverse striae; these be- long to the genus Colymbetes. Of the smaller diving-beetles, measuring less than 6 mm. in length, many species can be foimd in almost any pond. These represent many genera. 484 AN INTRODUCTION TO ENTOMOLOGY Family GYRINID^ The Whirligig-Beetles As familiar to the country rover as the gurgling of the brook or the flecks of foam on its "golden -braided centre," or the trailing ferns and the rustling rushes on its banks, are these whirligigs on its pools. Around and around each other they dart, tracing graceful curves on the water, which vanish almost as soon as made. They are social fellows, and are almost always fotmd in large numbers, either swimming or resting motionless near together. They rareh^ dive, except when pursued; but are so agile that it is extremely difficult to catch them without a net. Man}^ of them when caught exhale a milky fluid having a very disagreeable odor. They feed upon small flies, beetles, and other insects that fall into the water, and are furnished with well-developed wings, with which they fly from one body of water to another. This is one of the most easily-recognized families of the whole order Coleoptera. The members of it are oval or elliptical in form (Fig. 570), more or less flattened, and usually of a very brilliant bluish black color above, with a bronze metallic lustre. The fore legs are very long and rather slender; the middle and hind legs are short, broad, and very much flattened. These insects are remarkable for having the eyes completely divided b} the margin of the head, so that they appear to have four eyes — a pair upon the upper surface of the head with which to look into the air, and a pair upon the under side for looking into the water. The antennae are very short and peculiar in form. The third segment is enlarged, so as to resemble an ear-like appendage, and the following ones form a short spindle- shaped mass. They are inserted in little cavities in front of the eyes. The eggs of these insects are small, of cylindrical form, and are placed end to end in parallel rows upon the leaves of aquatic plants. The larvae (Fig. 571) are long, narrow, and much flattened. Each abdominal segment is furnished with a pair of tracheal gills, and there is an additional pair at the caudal end of the body. The elongated form of the body and the con- spicuous tracheal gills cause these larv^se to resemble small centipedes. When a larva is full-grown it leaves the water and spins a gray, paper-like cocoon attached to some object near the water. The pupa state of those species in which it has been observed lasts about a month. Fig. 571. The family is a small one. At present only forty-one North American species are known. These represent three genera. The genus Gyretes is distinguished by having the last ventral segment of the abdomen elongated and conical. It is represented by two species. In the other two genera the last ventral segment is flattened and roimded at the tip. In DineHtus the scutellum is invisible; there are thirteen species of this genus. In Gyrlnus the scutellum is visible; of this genus we have twenty-six species. COLEOPTERA 485 Family HYDROPHILID^ The Water -Scavenger Beetles The water-scavenger beetles are common in quiet pools, where they may be found swimming through the water, or crawling among the plants growing on the bottom. They can be easily taken by sweep- ing such plants with a dip-net. They are elongated, elliptical, black beetles, resembling the pre- dacious diving beetles in appearance; but they are usually more convex, and differ also in having club-shaped antenna and very long palpi. As the antennae are usually concealed beneath the head, it often happens that the inexperienced student mistakes the long palpi for antenna?. These beetles are supposed to live chiefly upon the decaying vege- tation in the water ; but a number of species have been known to catch and eat living insects. They breathe by carrying a film of air on the lower surface of the body. This film gives them a silvery appearance when seen from below. They obtain the air by bringing the head to the surface of the water and projecting the an- tennae, which they again fold back with a bubble of air when they descend. The female makes a case for her eggs out of a hardened silk-like secretion. Some species deposit as many as a hundred eggs in one of these water-proof packages (Fig. 572). The egg- cases in some instances are fastened beneath the leaves of aquatic plants ; in others they are provided with floats and let loose in the water; and in still other species the cases are carried by the mother underneath her body and steadied with her hind legs. Frequently some of the young larva devour their companions; in this way the size of the family is decreased before it escapes from the egg-case. Later they live upon insects that fall into the water, and upon snails. These larvae resemble somewhat those of the Dytiscida; but the body is much more plimip, and the mandibles are of moderate size. The family Hydrophilidae is represented in North America by one hundred and ninety species. The largest of our common species is Hydrous triangularis (Fig. 573). In the genus Hydrous the metasternum is prolonged back- ward into a spine between the hind legs, and the sternum of the prothorax bears a deep furrow. The beetles of the genus Tropisternus agree with Hydrous in the form of the prostemum and metasternum, but differ in size, our species measuring less than 12 mm. in length. The most common species in the East is Tropisternus glabra, and on the Pacific Coast T. calif ornicus . Fig- 572. Fig- 573- 486 AN INTRODUCTION TO ENTOMOLOGY Next in size to Hydrous are several species of Hydrophilus. In this genus the metasternum is prolonged somewhat, but does not form a long, sharp spine as in Hydrous and Tropisternus, and the sternum of the prothorax bears a keel-shaped projection. Our most conunon species is Hydrophilus obtusdhts; this measures about 1 5 mm. in length. Some of the sm.aller species of this family are not aquatic, but live in moist earth and in the dung of cattle, where, it is said, they feed on dipterous larvae. Suborder POLYPHAGA* In the suborder Polyphaga the ventral part of the first segment of the abdomen is visible for its entire breadth (Fig. 574); the first three ventral segments are immov- ably united (except in the Cupesidas), and the notum of the prothorax is not separated from the pleura by distinct sutures. So far as known, the nutritive cells of the ovaries are massed to- gether in the terminal chamber of each ovarian tube in all members of this suborder. The larvse vary greatly in form; Fig. 574.-Ventral aspect of part of some are campodeiform, " some are thorax and abdomen of Enchro- scarabeiform, and others are vermi- ma gigantea: ist .4, first abdom- form; in none are the legs more than mal segment. five-jointed, and in none are the legs two-clawed. This suborder includes all but the seven preceding families of the Coleoptera ; the families included in it are grouped into seven series ; see synopsis, page, 467. Family PLATYPSYLLID^ The Beaver-Parasite Only a single representative of this family is known; this is Platypsylla castoris, which lives parasitically on the beaver. This beetle is about 2.5 mm. in length; the body is ovate, elongate, and much flattened; the wing-covers are short, about as long as the prothorax, and leave five abdominal segments exposed; the eyes and wings are wanting. Specimens of this remarkable insect are most easily obtained by beating over a sheet of paper the dried skins of beavers, which can be found in fur-stores. The family BRATHINID^ is composed of the genus Brathinus, of which three species are described, two from the East and one from California. These beetles are somewhat elongate, with the outline *Polyphaga: polyphagus, eating many kinds of food. COLEOPTERA 487 of the prothorax and of the elytra elliptical; they measure from 3.6 mm. to 5 mm. in length. The Cahfomian species was found living in wet moss, darkly overshadowed by bushes, at the margin of a mountain stream. Family LEPTINID^ The Mammal-Nest Beetles This family is represented by only three species in North America. One of these, Lepthms testdceus, is a European species, but is widely distributed in this country. It lives in the nests of mice and other small rodents and insectivora, and also in the nests of bumble-bees. Whether it is a parasite or merely a guest has not been definitely de- termined ; but it seems probable that it feeds upon the eggs and young of mites and other small creatures found in these nests. This beetle is oblong-oval and much depressed in form, and pale yellow in color; it measures from 2 mm. to 2.5 mm. in length. Specimens can be obtained by shaking a nest of a mouse over a sheet of paper. The other two species are LeptinUlus vdlidus, found in Hudson Bay territory, and LeptinUlus aplodonttce, found in California on a rodent (Aplodontia) . Family SILPHID^ The Carrion-Beetles The carrion-beetles are mostly of medium or large size, many species attaining the length of 35 mm. while the smaller species of the more typical genera are nearly 12 mm. in length; some members of the family, how- ever, are minute. The segments near the tip of the antennae are usually enlarged so as to form a compact club, which is neither comb- like nor composed of thin movable plates; sometimes the antennae are nearly filiform. These insects usually feed upon decaying animal matter; some, however, feed upon fungi ; some on vegetables ; and a few species have been known to be predacious when pressed by hunger, destroying living snails and insects, even members of their own spe- cies ; while a few occur only in the nests of ants . It is easy to obtain specimens of these in- sects by placing pieces of meat or small dead pjg ^^^ animals in the fields and examining them daily. There are several other families of beetles the members of which can be attracted in this way. The larvae also live upon decaying flesh and are found in the same situations as the adults. We have in this country more than one hundred species of this family. Our larger and more familiar species represent two genera, Necrophorus and Silpha. The burying-beetles, Necrophorus. — To this genus belong the larger members of the family. The body is very stout, almost cylin- drical (Fig. 575). Our common species have a reddish spot on each i88 AN INTRODUCTION TO ENTOMOLOGY end of each wing-cover; these spots are often so large that they appear as two transverse bands. In some species the prothorax and the head are also marked with red. These insects are called burying-beetles because they bury carrion. When a pair of these beetles discover a dead bird, mouse, or other small animal, they dig beneath it, removing the earth so as to allow the carrion to settle into the ground. This they will continue until the object is below the surface of the groimd. Then they cover it with earth, and finally the female digs down to it and lays her eggs upon it. The larvae that hatch from these eggs feed upon the food thus provided for them. There are many accoimts of exhibitions of remarkable strength and sagacity by burying-beetles. A pair of these insects have been known to roll a large dead rat several feet in order to get it upon a suitable spot for burying. The members of the genus SUpha are very much «f flattened (Fig. 576). The prothorax is round in outline, with very thin edges which overlap the wing-covers \ somewhat. The body is not nearly as stout as that of \ a burying beetle, being fitted for creeping under { dead animals instead of for performing deeds requiring great strength. SUpha bituberosa, which is known as Fig- 576. -thg spinach carrion-beetle, feeds on spinach, beets, and other plants, in the West. In some of the minute members of this family the body is nearly hemispherical. The family CLAMBID^ consists of very minute species, measur- ing about I mm. in length. They live in decomposing vegetable matter. The edge of the hind wings is fringed with long hairs. For other characters, see table, page 470. Only six species, representing three genera, occur in our fauna. The family SCYDM^NID^ includes very small insects found under bark or stones, in ants' nests, or near water. They are small, shining, usually ovate but sometimes slender insects, of a brown color, and more or less clothed with erect hairs. Other characters are given in the preceding table of families. About one hundred seventy-five North American species are known. The family CORYLOPHID^ includes minute beetles found under damp bark and in decaying fungi and other vegetable matter. The body is oval or rounded, and in many species is clothed with a grayish pubescence. The wings are wide, and fringed with long hairs. Some of our common species measure less than i mm. in length. Fifty- seven North American species have been described. Family STAPHYLINID/E The Rove-Beetles The rove-beetles are very common about decaying animal matter, and are often found upon the groimd, imder stones or other objects. COLEOPTERA 4 89 They are mostly very small insects; a few species, however, are of larger size, measuring 12 mm. or more in length. Their appearance is very characteristic, the body being long and slender, and the wing-covers very short (Fig. 577). The wings, however, are fully developed, often exceeding the ab- domen in length; when not in use the wings are folded beneath the short wing-covers. The abdominal seg- ments are freely movable. It is interesting to watch one of these insects fold its wings; frequently they find it necessary to make use of the tip of the abdomen or of one of the legs in order to get the wings folded beneath the wing-covers. Fig. 577. The rove-beetles can run quite swiftly; and they have the curious habit, when disturbed, of raising the tip of the abdomen in a threatening manner, as ii they could sting. As some of the larger species resemble wasps somewhat in the form of the body, these threatening motions are often as effective as if the creatures really had a sting. William Beebe states {Atlantic Monthly, October 19 1 9) that when some rove-beetles were attacked by ants they raised their tails and ejected a drop or two of a repellent fluid which drove the ants away. This observation indicates the probable explanation of the actions of these beetles when disturbed. As these insects feed upon decaying animal and vegetable matter, they should be classed as beneficial. The larvae resemble the adults in the form of the body and are found in similar situations, about decaying animal and vegetable matter, beneath bark and in fungi. Some species are guests in the nests of ants, and others in the nests of termites. Nearly three thousand North American species of rove-beetles have been described. The great majority are small and exceedingly difficult to determine. Among the large species that are common are the following. Creophilus maxillosus. — This species varies from 12 mm. to nearly 25 mm. in length. It is of a shining black color, spotted with patches of fine gray hairs. There is a conspicuous band of these across the middle of the wing-covers, and another on the second and third abominal segments; this abdominal band is best marked on the lower side of the body. Staphyllnus maculosus is a larger species, which often measures fully 25 mm. in length. It is densely punctured, and of a dull brown color, with the scutellimi black, and a row of obscure, square, blackish spots along the middle of the abdomen. Staphylhius vulplnus resembles the preceding somewhat,^ but it has a pair of bright yellow spots at the base of each abdominal segment. Ontholestes cinguldtus is of about the same size as the preceding. It is brown, speckled with brownish black spots, and the tip of its abdomen is clothed with golden hairs. The family PSELAPHID^ includes certain very small beetles, the larger ones not exceeding 3 mm. in length. They resemble rove- 490 AN INTRODUCTION TO ENTOMOLOGY beetles in the shortness of the wing-covers and in having the dorsal part of the abdominal segments entirely hom}^; but they differ from them in that the abdomen is not flexible, and in having fewer abdominal segments, there being only five or six on the ventral side. The species are chestnut -brown, dull yellow, or piceous, and are usually slightly pubescent. The antennae are usually eleven-jointed, rarely ten-jointed. The elytra and abdom.en are convex and usually wider than the head and prothorax. These beetles are usually found imder stone and bark, or flying in the twilight; a few species have been found in the nests of ants. There are three hundred and fifty- five described North American species. The family CLAVIGERID^, or the ant-loving beetles, includes a small number of beetles that resemble the Pselaphids in the char- acters given above except that the antennae are only two-jointed. These beetles live in the nests of ants. They excrete from small tufts of hairs, on the three basal abdominal segments, a fluid of which the ants are very fond. The ants caress the tufts of hairs with their antennae, causing the exudation of the fluid, which they greedily swallow. The ants are said to feed the beetles and to allow them to ride about on their backs, when the beetles wish to do so. Only seven North American species are described. The family TRICHOPTERYGID^, or the feather-wing beetles, includes the smallest beetles that are known; most of our species are less than i mm. in length. The most striking feature of the typical forms is the shape of the wings, which are long, narrow, and fringed with long hairs, being feather-like in appearance; but in some species the wings are wanting. Some species live in rotten wood, muck, manure, and other decaying organic matter; few have been found in ants' nests. There are about eighty described species in our fauna. The family SCAPHIDIID^E, or shining fungus-beetles, includes small, oval, very shining beetles, found in fungi, rotten wood, dead leaves, and beneath the bark of logs. The elytra are broadly tnuicate behind, not covering the tip of the conical abdomen. But little is known regarding their life-history. There are fifty described North American species. The family SPH^RITID^ is represented in our fauna by a single species, Sphcerltes glabrdtus, which has been found in Alaska and California. This beetle is very similar in appearance to those of the genus Hister. For distinguishing characters, see table, page 470. The family SPH^RIID^ includes a single genus, SphcErius, which is represented in North America by only three known species. They are very minute beetles, measuring about .5 mm. in length; they are very convex, and may be found walking on mud or under stones near water. The family HISTERID^ includes certain easily recognized beetles which are foimd about carrion and other decomposing sub- stances. They are mostly small, short, rounded or somewhat square- shaped beetles, of a shining black color, with the wing covers marked COLEOPTERA 491 by lines of fine punctures and truncate behind, leaving two segments of the abdomen exposed (Fig. 578). In some species the wing-covers are marked with red. There are nearly four \u / hundred described North American species. )^l The family LYCID^ includes certain 'Hl\ beetles that were formerly classed in the ^ ^ fire-fly family; but they differ from the Fig. 578. Lampyridae in having the middle coxae distant, and in that the elytra lack epi- pleurae. The elytra are usually furnished with several longitudinal ribs and a network of fine elevated lines. The members of this family are diurnal in habits ; they are found on the leaves of plants, where they seek and feed upon other insects. A common species is Calopteron reticuldtum (Fig. 579). Family LAMPYRID^ The Firefly Family During some warm, moist evening early in our northern June we are startled to see here and there a tiny meteor shoot out of the darkness near at hand, and we suddenly realize that summer is close upon us, heralded by her mysterious messengers, the fireflies. A week or two later these little torch-bearers appear in full force, and the gloom that overhangs marshes and wet meadows, the dusk that shrouds the banks of streams and ponds, the darkness that haunts the borders of forests, are illumined with myriads of flashes as these silent, winged hosts move hither and thither under the cover of the night. The fireflies are soft -bodied beetles of medium or small size, with slender, usually eleven-jointed, saw -like antennae. The prothorax is expanded into a thin projecting margin, which in most cases com- pletely covers the head (Fig. 580). The wing-covers are rather soft, and never strongly embrace the sides of the abdomen, as with most other beetles. The fireflies are nocturnal insects and are sluggish by day. The property of emitting light is possessed by adults of both sexes and by larvae. The latter and the wingless females of certain species are known as glow-worms. The light-organs of the winged adults are situated on the lower . side of one or more of the abdominal segments; but they ^^' are lacking in some genera. There have been many speculations as to the usefulness of the light-producing power of various organisms to the organisms them- selves; and as regards many of these photogenic creatures no definite conclusions have been reached. But there is considerable evidence to show that in the case of adult lampyrids it serves to enable these insects to find their mates. It has been found that females enclosed in a perforated opaque box do not attract males, while those enclosed # 492 ^A^ INTRODUCTION TO ENTOMOLOGY in a glass vial do; thus showing that it is the light emitted by the female, and not its odor, that attracts the male. It has also been shown that in some cases at least there are specific differences in the method of flashing which enables the insects to distinguish at a distance their proper mates. More than fifty species of the Lampyridas have been found in this country. The family PHENGODID^ includes a small number of species that were formerly included in the firefly family. In this family theprothorax, though rounded in front, does not cover the head, which is exposed. The antennas are usually pltimose or flabellate in the males. The females of some species, at least, are glow-worms, re- sembling the larv£e in form, and are photogenic. Only twenty -three American species have been described ; most of these are found in California, Texas, and Arizona, but some occur in the East. Family CANTHARID^ The Soldier-Beetles and others The family Cantharidae includes those genera that were formerly included in the family Lampyridse as the subfamily Telephorinas. For the distinctive characters separating this from the allied families, see the table, page 473. The application of the name Cantharidge to this family is the result of one of those unfortunate changes in generic names rendered necessary by our code of nomenclature. In this case the change is especially unfortunate, as the generic name Cantharis has been com- monly applied to certain blister-beetles and is used in that sense in many medical works and in most text-books of entomology. The change is sure to result in much confusion. The most common members of this family are the soldier-beetles, Chauliopnathus. These are very abundant in late summer and autumn on various flowers, but especially on \ y those of goldenrod. The most com- mon species in the East are the Penn- sylvania soldier-beetle, Chauliognathus pennsylvanicus, which is yellow, with a black spot in the middle of the pro- thorax and one near the tip of each wing-cover (Fig. 581); and the mar- gined soldier-beetle, C. margindtus. ig- 5 I- 'pj^^g species (Fig. 582) can be dis- tinguished from the former by the head and lower parts of the femora being orange. The beetles of this genus are remarkable for having an extensible, fleshy filament attached to each maxilla. These fila- ments are probably used in collecting pollen and nectar from flowers. This family is represented in our fauna by nine genera which in- clude more than one hundred and fifty species. COLEOPTERA 493 The family MELYRID^ is composed chiefly of small or very small beetles, some of which are found on flowers, and others on the groimd in low, moist places. They are said to be carnivorous. They var\' greatly in form, but bear a general resemblance in structure to the preceding four families, from which they can be distinguished by the presence of only six ventral abdominal segments. Some members of the family are furnished with soft, orange- colored vesicles, which they protrude from the sides of the body and which are supposed to be scent organs for defence. One of our most common representatives is Collops quadrimaculdtus , which is yellow -orange, with Fig. 583. the top of the head and four spots on the elytra bluish black (Fig. 583). This species is found on grasses in damp localities. The family is represented in our fauna by more than three hundred species. The family CLERID^, or the checkered beetles, includes a con- siderable ntmiber of predacious species which are foimd on flowers and on the trunks of trees. Many of them are beautifully marked with strongly contrasting colors; this has suggested the common name checkered beetles for them. Frequently they are more or less ant-like in form, the prothorax being in these cases narrower than the wing-covers, and slightly narrower than the head. The abdomen has either five or six ventral" segments; the anterior coxae are conical, prominent, and contiguous, or very slightly separated; the hind coxae are transverse, not prominent, and covered by the femora in repose; the legs are slender ; and the tarsi are five-jointed. In the larval state these insects are usually camivo- trous, living imder bark and in the burrows of wood-boring insects, upon which they prey; some are found in the nests of bees; and still others feed on dead animal matter. The family is represented in our fauna b}^ nearly two p. „ hundred species. Figure 584 represents one of our more common species, Trichodes nutialli. The family CORYNETID^ has recently been sep- arated from the Cleridae, which they closely resemble. In this family the fourth joint of the tarsi is atrophied; this character distinguishes these beetles from the Clerids. About forty American species have been described. To this family belongs the red-legged ham-beetle, Necrohia riifipes. This is a small steel-blue beetle with reddish legs; it measures from 3.5 mm. to 6 mm. in length. It is foimd about dead animal matter in fields and in other situations. It sometimes invades storehouses and seriously infests hams. The family LYMEXYLID^ includes elongated, narrow beetles, with short serrate antennae. Only two species have been foimd in this country and these are rare. To this family belongs the ship- timber beetle, Lymexylon navdle, of northern Europe. The larv^a of this species was at one time a very serious pest in ship-yards, on account of its habit of drilling cylindrical holes in the timber. The 494 AN INTRODUCTION TO ENTOMOLOGY method of control by immersing the timber during the time of o\'i- position of the beetle was suggested bv Linnaeus. The family MICROMALTHID^ includes a single species, Micromalthus dehilis. This is a small beetle, measuring only 2.2 mm. in length. It is elongate, piceous, shining, with the antennas and legs yellow. This species is of great interest on account of its remarkable life-history, only a part of which is yet known. Two papers on this subject have been published by Mr. H. S. Barber ('13a, '13b). Briefl3^ this author's observations indicate that eggs are produced by larvae as well as by the adult females ; that there are seven or eight forms of larvae; that the two sexes of adults are developed through two distinct lines of larv^s; and that viviparous as well as oviparous paedogenesis occurs in the life-cycle. The larA'^e are foimd in decaying oak, chestnut, and pine logs, where they make burrows in the decay- ing wood, on which they feed. The family CUPESID^E includes only four American species. These are foiind imder the bark of decaying trees, and sometimes in houses. The body is covered with small scales ; other characteristics are given in the table of families, page 471. The family CEPHALOID^ is a small family of which only eight American species have been described. See table, page 474, for dis- tinctive characters. The family CEDEMERID^ is composed of beetles of moderate size, with elongate, narrow bodies. The head and prothorax are somewhat narrower than the wing-covers; the antennae are long, nearly filiform, sometimes serrate; the anterior coxal cavities are open behind, and the middle coxae are very prominent. Less than fifty North American species have been described. They are generally foimd on plants, but some live on the ground near water. The lar\^ae live for the most part in decaying wood. ^^ The family MORDELLID^ includes a large number >4H^ of small beetles which are easily recognized by their pe- f^—^ cuhar form (Fig. 5S5). The body is arched, the head Fio-. 585. being bent do\^m; and the abdomen is usually prolonged into a slender point. Our most common species are black; but many are variegated, and all are pubescent. The adults are usualh' found on flowers ; the larv^ae live in rotten wood and in the pith of various plants, upon which they are supposed to feed. Nearly one hundred fiftv American species have been described. The family RHIPIPHORID^ includes a small num- ber of beetles, which are very remarkable in structure and habits. The wing-covers are usually shorter than the ab- domen, and narrowed behind (Fig. 586); sometimes they are ver>^ small, and in one exotic genus they are wanting p- .gg in the female, which lacks the wings also and resembles a larva in form. The antennae are pectinate or flabellate in the males, and frequently serrate in the females. The adult insects are foimd on flowers. The larv^se that are known are parasites, sorne in the nests of wasps, and some on cockroaches. COLEOPTERA 495 Family MELOID^ The Blister -Beetles The blister-beetles are of medium or large size. The body is com- paratively soft; the head is broad, vertical, and abruptly narrowed into a neck; the prothorax is narrower than the wing-covers, which are soft and flexible ; the legs are long and slender ; the hind tarsi are four-jointed, and the fore and middle tarsi are five-jointed. These beetles are found on foliage and on flowers, on which they feed in the adult state; some of the species are very common on goldenrod in the autumn; and several species feed on the leaves of potato. The blister-beetles are so called because they are used for making blister-plasters. The beetles are killed, dried, and pulverized, and the powder thus obtained is made into a paste, which when applied to the skin produces a blister. The species most commonly used is a European one, commonly known as the Spanish-fl}'; but our Ameri- can species possess the same blistering property. The postembryonic development of those blister-beetles of which the complete life-history is laiown is a very remarkable one; for it has been found that in each of these cases there is a complicated hypermetamorphosis. The food of the larva consists, in some species, of the eggs of short-horned grasshoppers, in others of the egg and the food stored in the cell of some solitary bee. The female blister-beetle lays her eggs in the ground; a large number of eggs are laid by a single female ; this fact is doubtless correlated with the difficulties to be overcome by the larvee in their search for their proper food, in which comparatively few are successful. The newly hatched larva is campodeiform (Fig. 587, A), and is known as the triungulin, a term applied to the first instar of blister-beetle larvae. This term was sug- gested by the fact that in this instar the tarsi appear to be three- clawed; but in reality each tarsus is armed with a single claw, on each side of which there is a claw-like seta. The triungulins are very active. In the case of those that feed on the eggs of short -homed grasshoppers, they run over the groiuid seeking a place where one of these insects has deposited its egg-pod; if a triungulin is successful in this search it bores its way into the egg- pod; if more than one find the same egg-pod, battles occur till only one is left. In the case of those species that develop in the nests of bees, the triiuigulin, instead of hunting for a nest, merely climbs a plant, and remains near a flower till it has a chance to seize hold of a bee visiting the flower; it then clings to the bee until she goes to her nest, then, letting go of the bee, it remains in the cell and is shut up there with the egg of the bee and the store of food which she provides for her young. The triungulin first devours the egg; after which it molts and undergoes a change of form, becoming a clumsy creature, which feeds upon the food stored in the cell. Several other changes in form occur before the beetle reaches the adult stage ; these changes are quite similar to those undergone by the larva of £/?i'caM^a. described below. 496 AN INTRODUCTION TO ENTOMOLOGY The wonderful instinct by which the triunguHns of these bHster- beetles find their way to the nests of soHtary bees has not yet reached perfection ; for many of them attach themselves to flies, wasps, honey- bees, and other flower-visiting insects, and merely gain useless trans- portation thereby. The life-history of Epicauta vittdta, which was worked out by Mr. C. V. Riley ('77), will serve to illustrate the hypermetamorphosis of blister-beetles. The adult beetle is yellowish or reddish above, with the head and prothorax marked with black and with two black stripes on each wing-cover (Fig. 587, F). It feeds on the leaves of potato, and is sometimes a serious pest. The female lays her eggs in Fig. 587. — Hypermetamorphosis of Epicauta vittata. (From Sharp, after Riley.) the ground in loose, irregular masses of about 130 each; several such masses are laid by a single female. She prefers for purposes of ovi- position the very same warm, sunny locations chosen by the locusts for laying their eggs. The triungulins that hatch from the blister- beetle eggs (Fig. 587, A) are very active; when one of them finds an egg-pod of a locust it penetrates it, and in the course of several days devours two of the eggs; a period of rest follows during which it molts. The second instar (Fig. 587, B) differs greatly in form from the triungulin, and is known as the caraboid larva. A second molt takes place after about a week, but it is not accompanied by any very great change of form, though the larva is now curved, less active, and in form like the larva of a scarabasid beetle. About a week later, the third molt occurs; the change in form at this molt is not great, the fourth instar (Fig. 587, D) like the third being scarabaeoid in form ; these two instars can be distinguished as the first scarabceoid /art)a and the second scarabceoid larva respectively. The second scara- COLEOPTERA 497 baeoid larva grows apace, its head being constantly bathed in the rich juices of the locust eggs, which it rapidly sucks or more or less com- pletely devours. In another week it forsakes the remnants of the locust egg-mass and forms a smooth cavity in the soil a short distance from it. The larva then molts; the skin is not shed entirely, but remains attached to the caudal end of the body (Fig. 587, C). The new skin of the larva becomes rigid and of a deeper yellow color, reminding one of a puparium of a dipterous insect; this instar, the fifth, is termed the coarctate larva. The insect has the power of re- maining in this coarctate larval condition for a long time, and gen- erally thus hibernates. At the fifth molt the larva becomes active again, and burrows about in the ground; it now resembles in form the second scarabaeoid larva except that it is smaller and whiter; this, the sixth instar, was termed by Riley the scolytoid larva. In the cases observed by Riley, the scolytoid larvae did not feed but transformed to pupae (Fig. 587, E) in the course of a few days. The pupa state lasted five or six days. More than two hundred species of blister-beetles have been found in this country; but by far the greater number of these are confined to the western half of this region. Our most com- mon species in the East belong to the genus Epicauta. These insects feed in the adult state on the leaves of various plants, but especially those of potato, and upon the pollen of goldenrod; the larvee, so far as is known, are parasitic in the egg-pods of locusts (Melanoplus). In addition to Epiciuta vittdta, discussed above, our more corrmion species are the Pennsylvania blister-beetle, Epi- cauta pennsylvdnica, which is of a uniform black color (Fig. 588) ; and Epicauta cinerea, which is sometimes clothed throughout with an ash-colored pubescence, and sometimes the wing-covers are black, except a narrow gray margin; the two varieties were formerly considered distinct species ; the first is commonly known as the gray blister-beetle, the last as the margined blister-beetle. Closely allied to the beetles mentioned above are those of the genus Macrobasis. The most common species of this genus found in the East is Macrobasis unlcolor. This beetle measures from 8 mm. to 15 mm. in length ; it is represented, enlarged, in Figure 589; it is black, but rather densely clothed with grayish hairs, which give an ashen hue to the upper surface; it is known as the ashy-gray blister-beetle. The beetles of the genus Meloe present an exception to the characters of the Coleoptera in that the wing-covers, instead of meeting in a straight Fig. 5«8. 498 AN INTRODUCTION TO ENTOMOLOGY line down the back, overlap at the base (Fig. 590). These wing- covers are short, and the hind wings are lacking. These beetles are called oil-beetles in England, on account of the yel- lowish liquid which oozes from their joints when they are handled. Our most common species is the butter- cup oil-beetle, Meloe angusticollis . It is found in meadows and pastures feeding on the leaves of vari- ous species of buttercups. The species of the genus Nemognatha and some allied forms are remarkable for having the maxillse developed into a long sucking-tube, which is some- times as long as the body, and which resembles some- what the sucking-tube of a butterfly. The family EURYSTETHID^ includes only "three American species, one found in Alaska and two found in California. One of the latter, Eurystethus subopdcus, was found by Professor VanDyke on the seashore, in crevices of inter-tidal rocks. The farnily OTHNIIDyE is represented in our territory by five species of Othnius, one from the East and four from the Far West. They are small beetles, which are found running actively on the leaves of trees, and are probably predacious. In this family the anterior coxal cavities are closed behind, and none of the abdominal segments are grown together on the ventral side. The family PYTHID^ includes less than a score of North American species. Some of these live under bark, and are said to prey on bark-beetles ; others are found under stones. See table, p. 474, for distinctive characters. The family PYROCHROID^ includes a small number of beetles, which are from 8 mm. to 18 mm. in length. The body is elongate; the head and prothorax are narrower than the wing- covers; the antennae are serrate or subpectinate in the females and usually fiabellate in the males (Fig. 591). The beetles are found about decaying trees, beneath the bark of which the larvae live. The family PEDILID^.— In this and in the fol- lowing family the abdomen is composed of five free segments, and the tarsi have the penultimate joint lobed beneath. In this family the eyes are large, finely ^^§' 59i- faceted, and usually emarginate. These beetles are arboreal in habits. There are about fifty described species in our fauna. The family ANTHICID^. — In this family, as in the preceding one, the abdomen consists of five free segments, and the penultimate joint of the tarsi is bilobed. But in this family the eyes are small, rounded, usually coarsely faceted, and emarginate. These are active ground beetles of predacious habits. Among our more com- mon species are those of the genus Notoxus, in which the prothorax is prolonged over the head into a horn. There are nearly two hundred described species of this family in our fauna. \^ COLEOPTERA 499 The family EUGLENID^E is composed of small or minute beetles, found on leaves and flowers; many of them are less than 2 mm. in length. They resemble the members of the two preceding families; but differ in having the antepenultimate segment of the tarsi bilobed, instead of the penultimate, and in having the abdomen composed of only four free ventral segments, of which the first is formed of two, firmly united but with the suture sometimes evident. There are about forty described North American species. The family CEROPHYTID^ includes only two rare species of Cerophytum, one found in California and one in Pennsylvania. These were formerly included in the Elateridas; but they differ from that family in that the posterior coxee are not laminated, and the trochanters of the middle and posterior legs are very long. The family CEBRIONID^ includes a few species foimd in the South. They were formerly included in the Elaterid^; but they differ from that family in that the abdomen consists of six or more ventral segments. This family dift'ers from the following one in hav- ing the tibial spurs well developed. The family PLASTOCERID^ includes about a score of species found in the South and in California. It is closely allied to the pre- ceding family, but differs in having the tibial spurs short and very delicate. The family RHIPICERID^, or cedar-beetles, is represented in this country by a very small number of species, which are most com- monly found on cedars. The antennse are serrate in the females, frequently flabellate in the males. The anterior and middle coxse are conical and prominent, the former with large trochantins; the posterior coxae are transverse, and dilated into a small plate partly covering the femora. Family ELATERID^ The Click-Beetles or Elators There is hardly a coimtry child that has not been entertained by the acrobatic performances of the long, tidy-appearing beetles called snapping-bugs, click-beetles, or skip-jacks (Fig. 592). Touch one of them and it at once curls up its legs, and drops as if shot; it usually lands on its back, and lies there for a time as if dead. Suddenly there is a click, and the insect pops up into the air several inches. If it comes down on its back, it tries again and again until it succeeds in striking on its feet, and then it runs oft\ Our common species of click-beetles are mostly small or of medium size, ranging from 2.5 mm. to 18 mm. in length. A few species are larger, some reaching the length of nearly 50 mm. The majority of the species are of a uniform brownish color; some are black or grayish, and some are conspicuously spotted 500 AN INTRODUCTION TO ENTOMOLOGY ^^^ ^A (Fig. 593). The body is elongated, somewhat flattened, and tapers more or less toward each end ; the antennae are moderately elongated and more or less serrate; the first and second ab- dominal segments are not grown together on the ventral side; and the hind coxae are each furnished with a groove for the reception of the femur. The ability to leap into the air when placed on their back, which is possessed by most members of this family and by a few members of the following ^i g.- 5 93 ---A family, is due to two facts: first, the prostemum is 4 ^Id r' prolonged into a process which extends into a groove natural size and ^^ ^he mesosternum; and second, the prothorax is enlarged. loosely joined to the mesothorax, so that it can be freely moved up and down. When preparing to leap, the beetle bends its body so as to bring the prosternal process nearly out of the groove in the mesosternum; then it suddenly straightens its body, with the result that the prosternal process descends violently into the groove ; the blow thus given to the meso- thorax causes the base of the elytra to strike the supporting surface, and by their elasticity the whole body is propelled upward. Adult elaters are found on leaves and flowers, and are exclusively phytophagous; the larvas live in various situations; most of them are phytophagous, but some species are carnivorous. The larvae are long, narrow, worm-like creatures, very even in width, with a very hard cuticula, and are brownish or yellowish in color (Figs. 594 and 595). They are Fig. ^g^. commonly known as wire-worms, a name suggested by the form and hardness of the body. Some wire-worms live under the bark of trees and in rotten wood ; but many of them live in the ground, and feed on seeds and the roots of grass and grain. In fact there is hardly a cultivated plant that they do not infest, and, working as they do beneath thesurface of the ground, it is extremely difficult to destroy them. Not only do they infest a great variety of plants, but they are very apt to attack them at the most susceptible period of their growth, before they have attained sufficient size and strength to withstand the attack; and often seed is destroyed before it is germinated. Thus fields of com or other grain are ruined at the outset. The appearance of these insects when in the grormd, as seen through the glass side of one of our root-cages, is shown in Fig. 596. There is a vast number of species of click-beetles ; more than five hundred have been described from North America alone. It is quite difficult to separate the closely allied species, as there is but little variation in shape and color. The larvas also show comparatively little variation in the general form ; but in this stage the shape of the parts of the head and its ap- COLEOPTERA 501 pendages, and the structure of the caudal end of the body, afford useful characters. The value of these characters in indicating the principal divisions of the family is pointed out by Hyslop ('17). An extended series of experi- ments were con- ducted by Com- stock and Slin- gerland ('91) in an ciiort to discover a practicable method of preventing the ravages of wire-worms. In those species that we bred, it required several years for the larva to complete its growth. In these species the full-grown larva changes to a pupa in the latter part of the summer, in a little cell in the ground; the pupa soon afterwards changes to an adult ; but the adult remains in the cell formed by the larva till the following spring. Although we tried an extensive series of experiments, extending over several years, we were unable to find any satisfactory way of destroying the larvae infesting field crops. But we foimd that if the cells containing pupfe or recently-transformed adults were broken, the insects perished. We conclude, therefore, that much can be done towards keeping these insects in check by fall-ploughing; for in this way many of the cells containing pupse or young adults would be broken. The eyed el- ater, Alaus ocu- /aiM5.- Although most of our click- beetles are of moderate size, we have a few species that are large. The most common of these is the eyed elater. This is the great pepper-and-salt-colored fellow that has two large, black, velvety, eye-like spots on the pro- thorax (Fig. 597). These are not its eyes, how- ever. The true eyes are situated one on each side of the head near the base of the antenna. This Fig. 596. — ^A corn-plant growing in a root-cage infested by wire-worms and click-beetles. (From a speci- men in the Cornell Insectary.) 502 A N INTROD UCTION TO ENTOMOLOG Y insect varies greatly in size, some individuals being not more than half as large as others. The larvse live in decaying wood, and are often found in the trunks of old apple trees. It was formerly believed that they fed on the decaying wood; but they have been found to be carnivorous. The larger larvae are about 60 mm. in length. There is an elater quite similar to the preceding that differs in having the eye-like spots less distinctly marked; this is Alaus myops. This species is not as common as the preceding one. The family EUCNEMID^ was formerly regarded as a subfamily of the Elaterida?. It differs from the Elateridas, as now restricted, in having the labrum concealed, and in that the antennse are some- what distant from the eyes, and their insertion narrowing the front. The adults are found under bark or on the leaves of plants ; most of the species are rare. "The larvae have a striking resemblance to those of the family Buprestidae, both in form and habits, being abruptly enlarged in front, and usually occurring in wood which has just begun to decay." (Blatchley '10.) The family THROSCID^ includes a few small species which resemble the elaters and buprestids in having the prostermun pro- longed behind into a process, w^hich is received in the mesosternum. They differ from the elaters in having the prothorax firmly joined to themesothorax, and the front coxal cavities closed behind by the meso- sternum instead of by the prosternum; and from the buprestids in having the ventral abdominal segments all free. The adult beetles are found on flowers. Family BUPRESTIDS The Metallic Wood-Eorers or Buprestids The buprestids resemble the click-beetles somewhat in form, being rather long and narrow; but they are easily recognized by their metallic coloring. Their bodies are hard and inflexible, and usually appear as if made of bronze ; but some species exhibit the brightest of metallic colors. The antennae are serrate; the first and second abdominal segments are grown together on the ventral side ; and these beetles do not have the power of springing when placed on the back. The adults are found upon flowers and upon the bark of trees, basking in the hot sunshine. Some of them fly ver\^ rapidly, with a loud buzzing noise; and some drop to the ground when disturbed, and feign death. Most of the larvae are borers, feeding beneath bark or within solid wood. In such species the body is of a ver\^ characteristic form, which is commonly designated as "flat -headed." The flattened portion, however, is composed largely of the segments immediately following the head. The first thoracic segment is very wide and flat; the next two or three segments are also flattened, but are successively smaller; while the rest of the body is quite narrow and cylindrical. COLEOPTERA 503 These "flat -headed" larvas are legless, and have been compared to tadpoles on account of their form. Their burrows are flattened, corresponding with the shape of the larger part of the body. In some of the smaller species the larvte are cylindrical, and are furnished with three pairs of legs. These are leaf -miners; and in the adult state the body is much shorter than in the more typical species. This family is represented in our fauna b\^ nearly three hundred species; among the more important of those that infest cultivated plants are the following. The Virginian buprestid, Chalcophora virginica. — -This is the larg- est of our common buprestids (Fig. 598). It is copper-colored, often almost black, and has its upper surface roughened by irregular, lengthwise furrows. This bee- tle appears late in spring in the vicinity of pine-trees. The larvffi bore in the wood of pine, and are often very injurious. Dicer ca divaricdta is 18 mm. or more in length, copper- colored or brassy above, with the wing-covers marked with square, elevated, black spots. The wing-covers taper very much behind, and are separated at the tips (Fig. 599). va bores in peach, cherry, beech, and maple. The flat-headed apple-tree borer, Chrysohothris femordta. — This is one of the most injurious of all buprestids. The adult (Fig. 600) is about 12 mm. long, and is very dark green above, with bronze re- flections, especially in the furrows of the wing-covers. It appears during June and July, and lays its eggs upon the trunk and limbs of apple, peach, oak, and other trees. The larvae at first bore into the bark and sap-wood, and later into the solid wood. The transforma- tions are completed in one year. To prevent the ravages of this pest, the trees are rubbed with soap during June or July, or cakes of soap are placed in the forks of the trees, so that the rains will dissolve the soap and wash it down over the trunks. This is supposed to prevent the beetles from deposit- ing their eggs on the trees. After a tree is once infested, the larvas should be cut out with a gouge or a knife. Nursery stock that is infested should be promptly burned. The red-necked agrilus, Agrilus ruficolHs. — This beetle (Fig. 601) is about 7.5 mm. long. Its body is narrow and nearly cylindrical. The head is of a dark bronze color, the prothorax of a beautiful coppery bronze, and the wing- covers black. The larva bores in the stems of raspberry and blackberry, causing a large swelling, known as the Fig. 601. raspberry gouty-gall. These galls should be collected and burned in early spring. The family PSEPHENID^ includes only the genus Psephenus, of which we have four species, one found in the East and three in •504 AN INTRODUCTION TO ENTOMOLOGY California. This genus was formerly included in the following family ; but it differs from the Dryopidas in having more than five ventral ab- dominal segments. Our eastern species is Psephenus lecontei. These beetles are found in the vicinity of running water, and often, in the heat of the day-, collect on stones that project from the water; they fly swiftly when disturbed. The body is oval, subdepressed, nar- rowed in front, and clothed with fine, silken hairs, which retain a film of air when the insect goes beneath water. The females deposit their eggs in a layer on the under side of submerged stones in shallow brooks. The beetles measure from 4.5 mm. to 6 mm. in length. The larva is found clinging to the lower surface of stones in rapid streams, and I have found it in muck near a spring. It is very fiat, circular in out- line (Fig. 602), and measures about 7 mm. in length . It breathes by five pairs of branched tracheal gills on the ventral side of the abdomen. It is rarely recognized as an insect by the young collector; in fact it was originally described as a crustacean under the generic name Fluvicola. I have suggested the common name water-penny for the larva. When mature the larva leaves the water, and pupates under the last larval skin, beneath a stone or other object in a damp situation. The family DRYOPID^ as now restricted includes only the sub- family Paminas of the old family Parnidce, in which were included the preceding family and the following family. The Dryopidae differ from the Psephenidae in that the members of it have only five ventral abdominal seg- ments, and from the Elmidae in that in the Dryopidae the anterior coxge are transverse, with a distinct tro- chantin. This family includes small water-beetles in which the legs are not fitted for swimming. They are found most often in swift-running water, where they cling to stones, logs, or aquatic plants. The body is clothed with fine, silken hairs, which retain a film of air when the insect is beneath the water. They feed on decaying matter in the water. The larvae are also aquatic Fig. 602. Fig. 603. The larva of Helichus lithophilus (Fig. 603) resembles somewhat the water-penny {Psephenus), except that the body is more elongate and is deeply notched between the segments. Seventeen species of this family have been found in our fauna . The family ELMID^ includes beetles that are closely allied to the preceding family in structure and in habits; but in this family the anterior coxae are rounded and without a trochantin, and the body is less densely pubescent than in the Dryopidas. COLEOPTERA 505 Fig. 604. The larvae of some exotic species are said to live in damp earth; but the larva of Stenelmis bicarindtus , which was described by Professor Matheson ('14) is aquatic. This larva (Fig. 604) differs greath^ in form from the representatives of the two preceding families figured above, being long and slender. The family HETEROCERID^, or the variegated mud-loving beetles, includes only the genus Heterocerus, of which eleven species have been found in our fauna. In this family all of the tarsi are four-jointed; the first four ab- dominal segments are grown together on the ventral side ; and the tibias are dilated, armed with rows of spines, and fitted for digging. These beetles are oblong or sub-elon- gate, oval, densely clothed with short, silky pubescence, very finely punctate, and of a brown color, with the elytra usually variegated with undulated bands or spots of yellow color. They live in galleries which they excavate in sand or mud at the margins of bodies of water, and, when dis- turbed, run from their galleries and take flight. The family GEORYSSID^, or the minute mud-loving beetles, includes only the genus Georyssus, of which only two species have been found in the United States. They are very minute, rounded, convex, roughly sculptured, black insects, found at the margin of streams, on wet sand; they cover themselves with a coating of mud or fine sand, so that they can be detected only when they move. The family DAvSCILLID^ includes certain beetles that live on plants, usually near water. The legs are short, with slender tibias; The tarsi are five-jointed; the anterior coxse bear a distinct trochan- tin; the posterior coxae are transverse, and dilated into a plate partly covering the femora ; and the abdomen has five free, ventral segments, the fifth rounded at the tip. Sharp ('99) states that the larva of Z)a5c^//M5 cervlnus is subterra- nean, and is believed to live on roots; in form it is somewhat like a lamellicom larva, but is straight, and has a large head. Only twenty-one species of this family have been described from our fauna; but these represent fifteen genera. The family EUCINETID^ has recently been separated from the Dascyllidse. In the Eucinetidae the anterior coxae do not bear a trochantin; the posterior coxse are dilated into immense oblique plates, concealing the hind legs in repose; and the internal lobe of the maxillae is armed with a terminal hook. Only eight species of this family occur in our fauna; seven of these belong to the genus Eucinetus. The larva of a European species of Eticinetus lives on fungoid matter on wood. The family HELODID^E includes small beetles, less than 6 mm. in length, found on plants near water. As in the preceding family, the anterior cox« are without a trochantin; but the lacinia of the maxillae is not armed with a terminal hook; and the cuticula of the 506 AN INTRODUCTION TO ENTOMOLOGY body is usually soft and thin. Sharp ('99) states that the larvee are aquatic, and are remarkable for possessing antennae consisting of a great many joints. Our fauna includes thirty-two described species of this family. The fami"ly CHELONARIID^E is represented in our fauna by a single species, Chelondrium lecontei, found in Florida. See table, page 471, for distinguishing characters. Family DERMESTID^ The Dermestids There are several families of small beetles that feed on decaying matter, or on skins, furs, and dried animal substances. The most important of these is the Dermestidas, as several species belonging to this family destroy household stores or goods. The dermestids can be distinguished from most of the other beetles with similar habits by the fact that the wing-covers completely cover the abdomen. They are chiefly small beetles, although one of the common species measures 8 mm. in length. They are usually oval, plump beetles, with pale gray or brown markings, which are formed of minute scales, which can be rubbed off. These beetles have the habit of pretending that they are dead when they are disturbed; they will roll over on their backs with their legs meekly folded and lie still for a long period. The larvae do much more damage than the adults. They are ac- tive, and are clothed with long hairs. These hairs are covered throughout their entire length with microscopic barbs. This family is represented in our fauna by about one hundred thirty species; the following are some of the more important of these. The larder-beetle, Dermestes lardarius. — This pest of the larder is the most common of the larger members of this family. It measures from 6 mm. to 7.5 mm. in length, and is black except the basal half of its wing-covers, which are pale buff or brown- *ish yellow. This lighter portion is usually crossed by a band of black spots, three on each wing-cover (Fig. 605). The larva feeds on dead animal matter, as meat, skins, feathers, and cheese. It is often a serious pest where bacon Fig- 605. Qj. i^^j^ -g s^Qj.g(j_ When full-grown it is about 12 mm. in length, dark brown above, whitish below, and rather thickly covered with long, brown hairs. It is said that these insects can be attracted by baits of old cheese, from which they may be gathered and destroyed. The carpet -beetle, Anthrenus scrophuldrim. — This is a well-known household pest. It is an introduced European insect, which was first recognized as a serious joest in this country about 1874. It feeds in its larval state on carpets, woollens, furs, and feathers; and for a considerable period was exceedingly destructive. In recent years its ravages have been greatly reduced by the more general use of rugs instead of carpets. As rugs are taken up and cleaned frequently, the COLEOPTERA 507 insect does not have a chance to breed as it does under carpets which are tacked to the floor and taken up only once or twice a year. The larva is well known to many housekeepers as the buffalo-moth. It is a short, fat grub, about 5 mm. in length when full-grown, and densely clothed with dark brown hairs. It lives in the cracks of floors, near the edges of rooms, and beneath furniture, where it eats holes in the carpet. It also enters wardrobes and destroys clothing. The adult is a pretty little beetle which may be found in infested houses, in the spring, on the ceilings and windows. It measures from 2.2 mm. to 3.5 mm. in length and is clothed with black, white, and brick-red scales. There is a whitish spot on each side of the prothorax, and three irregular, whitish spots on the outer margia of each wing- cover; along the suture where the two wing-covers meet, there is a band of brick-red scales, which is widened in several places. It is worth while to learn to know this beetle ; for a lady-bug which often winters in our houses is frequently mistaken for it. The carpet-beetle in its adult state feeds on the pollen of flowers. Sometimes it abounds on the blossoms of currant, cherry, and other fruits. The best way to avoid the ravages of this pest is to use rugs instead of carpets, and to trap the larvae by placing woollen cloths on the floors of closets. By shaking such cloths over a paper once a week, the larvae can be captured. The change from carpets to rugs is a very desirable one; for carpets that are tacked to the floor and taken up only once or twice a year are unwholesome. The change need not be a very expensive one. As carpets wear out they may be replaced with rugs; and good carpets can be made over into rugs. If the floors are not polished, as is usually the case where it was planned to cover them with carpets, they can be made presentable by filling the cracks with putty and painting the boards where they are to be exposed. The museum pests, Anthrenus verhdsci and Anthrenus nntseomm. — There are two minute species of this family that are a constant source of annoyance to those having collections of insects. The adult beetles measure from 2 mm. to 3 mm. in length, and are very convex. They deposit their eggs on specimens in our collections; and the larvae feed upon the specimens, often destroying them. In order to preserve a collection of insects it is necessary that they should be kept in tight cases, so that these pests cannot gain access to them. Specimens should not be left exposed except when in use. And the entire collection should be carefully examined at least once a month. The injury is done by the larvae, which are small, plump, hairy grubs. Their presence is indicated by a fine dust that falls on to the bottom of the case from the infested specimens. These larvcC can be destroyed by pouring a small quantity of carbon disulphide into the case, and keeping it tightly closed for a day or two. Benzine poured on a bit of cotton in the box will cause the pests to leave the specimens, when they may be taken from the box and destroyed. But we have found carbon bisulphide the better agent for the destruction of these pests. 508 AN INTRODUCTION TO ENTOMOLOGY The family BYRRHID^, or the pill-beetles, are short, very con- vex beetles of small or moderate size; some, however, are 12 mm. in length. The body is clothed with hair or minute scales. The legs can be folded up verv^ compactly, the tibia usually having a furrow for the reception of the tarsus. These beetles are found upon walks and at the roots of trees and grass; a few live under the bark of trees. Nearlv one hundred species hoxe been found in this countrv. The family NOvSODENDRID^ includes two species of Noso- dendron, one found in the East and one in California. They were formerly included in the Byrrhidffi, but differ from that family in having the head prominent and the mentum large. These beetles live under the bark of trees. The family RHYSODID^ includes only four species, two from each side of the continent. They are elongate, somewhat flattened beetles, with the head and prothorax deeply furrowed with longi- tudinal grooves; and the abdomen with six ventral segments, the first broadly triangular, widely separating the coxte. They are found under bark. See footnote, page 470. The family OSTOMID^ includes oblong, somewhat flattened beetles, of a black or reddish black color. Most of them live under bark; but some are found in granaries, and have been widely dis- tributed by commerce. The larva of a species found under bark has been observed to feed on the larva of the codlin-moth. One well-known species, Tenebroides mauritanicus, infests gran- aries. It is a shining brown beetle measuring about 8 mm. in length; it is commonly known as the cadelle. Both adult beetles and larvae feed on grain, but are also predacious, feeding on other insects infest- ing grain. The larvae when full-grown burrow into the sides of the bins, where they transform. The family NITIDULID^ comprises small, somewhat flattened beetles. With many species the prothorax has wide, thin margins, and the wing-covers are more or less truncate, so as to leave the tip of the abdomen exposed; but sometimes the elytra are entire. The tarsi are usually fi\^e-jointed, with the fourth segment very small; they are more or less dilated; the posterior coxae are flat, not sulcate; the anterior coxae are transverse; and the abdomen has five free ventral segments. Most species of this family feed on the juices of fruits and ferment- ing sap that exudes from trees ; a few are found on flowers, and others on fungi or carrion. About one hundred thirty species are known tfrom North America. One of the most common species is Glischrochms dps) fascidtus (Fig. 606). This is a shining black species, with two conspicuous, interrupted, reddish bands across the wing-covers, p. ^^^ The family RHIZOPH AGIDyE includes only the genus ^^' ■ i?/iZ2;o^/mgM5, of which there are fourteen North American species. These are small, slender, elongate species, which live beneath bark. This genus was formerly included in the preceding family; it differs from that family in that the antennae are only ten-jointed, and the club of the antennae is two-jointed. COLEOPTERA 509 The family AIONOTOMID^ is composed of small, depressed beetles, found mostly under the bark of trees, but some species live in the nests of ants. The wing-covers are truncate behind, leaving the last abdominal segment exposed. There are nearly forty described North American species. Family CUCUJIDtE The Cucujids The insects of this family are very fiat and usually of an elongate form; most of the species are brown, but some are of a bright red color. As a rule they are found under bark and are believed to be carnivorous both in the larval and adult states; but some feed in grain. There are nearly one hundred species in our fauna. The most conspicuous of our common species is Cucujus cldvipes (Fig. 607). This insect is about 12 mm. in length and of a bright red color, with the eyes and an- tennae black and the tibiae and tarsi dark. The most important member of this family is the corn Fig- 607. silvanus, Silvamis surinamensis, which is one of the small beetles that infest stored grain. This species is readily distinguished from other small beetles with similar habits by its flattened form and the saw-like edges of the prothorax. Besides grain it often infests dried fruits and other stores. It measures from 2.5 mm. to 3 mm. in length. The larva as well as the adult feeds on grain. It differs from the larva of the granary -weevil (Calendra) in the more elongate form of its body and in the possession of three pairs of legs. Family EROTYLID^ The Erotylids The members of this family are usually of moderate or small size; but some species are quite large, measuring 18 mm. or more in ^ Fig. 608. Fig. 609. length. Some of our more common species are conspicuously marked with shining black and red. To the genus Megalodachne belong two common, large species, which are black, with two dull red bands extending across the 510 AN INTRODUCTION TO ENTOMOLOGY wing-covers. M. heros (Fig. 608) is 16 mm. or more in length. M. fascidta is about 12 mm. in length. The genus Languria includes long, narrow species, which resemble click -beetles in form. Figure 609 represents Languria mozdrdi. greatly enlarged. This is a reddish species with dark blue wing- covers; the larva bores in the stalks of clover. It has not become a serious pest as the larvse are destroyed whenever clover is cut at the proper time. The larvae of some species of this family feed on fungi. The family DERODONTID^ includes only five American species, two found in the East and three in the Far West. They are small brown or dull brownish yellow beetles, having the head deeply impressed, with a small, smooth tubercle on each side inside the eye. These beetles are found on fungi. The family CRYPTOPHAGID^ includes insects of small size, usually less than 2.5 mm. in length, and of variable form but never very flat. The thorax is nearly or quite as wide as the wing-covers, and the first ventral abdominal segment is somewhat longer than the others. They are generally of a light yellowish brown color, and live on fungi and decomposing vegetable matter. The family BYTURID^ includes only the genus Bytilrus, of which there are five species in our fauna. This genus was formerly . included in the Dermestidae, but it differs from that family in having the second and third segments of the tarsi lobed beneath, the front coxal cavities closed behind, and the tarsal claws armed with a large basal tooth. The following is a well-known species. The raspberry fruit -worm, Byturus unicolor. — The fruit of the red raspberry is often infested by a small white worm, which clings to the inside of the berry after it is picked. This is the larva of an oval, pale, dull yellow beetle, which is densely clothed with short, fine, gray hairs. The beetle is repre- sented enlarged in Figure 610; it measures from 3.7 to t, 4.5 mm. in length. This insect is also injurious in the adult state, as it feeds on the buds and tender leaves of the raspberry and later attacks the blossoms. Fig. 610. The family MYCETOPHAGID^, or the hairy fungus-beetles, is composed of small, oval, rarely elongate, moderately convex beetles. They are densely punctured and hairy, and are usually prettily marked insects. They live on fungi and under bark. There are about thirty species in our fauna. The family COLYDIID^ is composed of small insects which are usually of an elongate or cylindrical form, and are found under bark, in fungi, and in earth. Some of the species are known to be carniv- orous, feeding on the larvae of wood-boring beetles. The tarsi are four-jointed; the tibiae are not fitted for digging, and the first four abdominal segments are grown together on the ventral side. More than eighty North American species are known. i COLEOPTERA 511 The family MURMIDIID^ includes five introduced species representing five genera. They are very small, oval beetles, differing from the Colydiids in having the antennas inserted on the front, and in having the anterior coxae inclosed behind by the metasternum. The family LATHRIDIID^ includes very small beetles which are found chiefly under bark and stones or in vegetable debris, es- pecially decaying leaves. They are oblong; the wing-covers are usu- ally wider than the prothorax and entirely cover the abdomen. There are about one hundred species in our fauna. The family MYCET^ID^ includes only four American species, which have recently been separated from the following family; they differ from the Endomychidse in having the tarsi distinctly four- jointed. The family ENDOMYCHID^ includes a small number of species, whch are found chiefly in fungus, in decaying wood, or be- neath logs and bark. They are small, oval or oblong beetles. The antennae are about half as long as the body; the prothorax is nearly square, and usually has a w^ide, thin margin, which is slightly turned upwards at the sides. The family PHALACRID^, or the shining flower-beetles, in- cludes very small, convex, shining black beetles; they are found on flowers and sometimes under bark. The larvae live in the heads of flowers, especially in those of the Compositas. More than one hundred North American species have been described. Family COCCINELLID^ The Lady-Eugs These insects are well-known to nearly^ every^ child under the popular name given above. They are more or less nearly hemi- spherical, generally red or yellow, with black spots, or black, with white, red, or y^ellow spots. The larvae occur running about on foliage ; they are often spotted with bright colors and clothed with warts or with spines (Fig. 6ii). When ready- to change to a pupa the larva fastens itself by its tail to any convenient object, and the skin splits open on the back. Sometimes the pupa state is passed within this split skin, and some- times the skin is forced back and remains in a little wad about the tail (Fig. 612). With very few exceptions, the lady-bugs are Fig. 611. Fig. 612. predacious, both in the larval and adult states. They feed upon small insects and upon the eggs of larger species. The larvae of certain species are known as "niggers" by hop-growers, and are greatly prized by^ them ; for they- are very destructive to the hop-louse. On the Pacific Coast lady-bugs are well known as the most beneficial of all insects to the fruit-growers. In addition to the native species found there, several species have been introduced as a means of combating scale-insects. One of these, Rodolia cardindlis, which ft a2 AN INTRODUCTION TO ENTOMOLOGY has been incorrectly known as Veddlia cardtndhs, has proved of very great value in subduing the cottony-cushion scale (Icerya purchasi). This lady-bug was introduced from Australia. The larva of Brachyacautha is found in the nests of ants. It is covered with dense tufts of delicate white wax; its food probably consists of the eggs of coccids living in the nests. A very common lady-bug in the East is Addlia hipunctdta. This species is reddish yellow above, with the middle of the prothorax black, and with a black spot on each w4ng-cover. It frequently passes the winter in our dwellings, and is found on the walls and windows in early spring. Under such circumstances it is often mis- taken for the carpet -beetle, and, unfortunately, destroyed. The nine-spotted lady-bug, Coccinella novemnotdta, has yellowish wing-covers, with four black spots on each, in addition to a common spot just back of the scutellvim (Fig. 613). Although almost all of the Coccinellidae are predacious, there are some that are herbivorous. One of these is -p- f. found in the East. This is the squash -ladybird, Epildchna ^^' ^^' boredlis. This beetle and its larva (Fig. 614) feed on the foliage of various cucurbitaceous plants, but prefer that of the squash. The adult is yellow- ^ \ "* 'T f] ^sh' with large, ,W:n ' ^'/ black spots. The larva is yellow and is clothed with forked spines. A pupa is shown in the figure near the upper right-hand corner. The bean- ladybug, Epi- Idchfia corrupta, which is found in the South and Southwest, is an- other herbivo- rous species. The familv ALLECULI- DJE , or the comb-clawed bark-beetles, includes brownish beetles, without spots, which are found on leaves and flowers and under bark. The body is usually elongate, elliptical, quite convex, and clothed above with minute hairs, which give a silken gloss to the surface. They are most easily distinguished from allied families by the tarsal claws being pectinate, and the anterior coxal cavities closed behind. The larvae of some of our species at least live in rotten wood and resemble wire- COLEOPTERA 513 worms in appearance. There are more than one hundred described North American species. Family TENEBRIONID^ The Darkling Beetles The darkhng beetles are nearly all of a uniform black color, although some are gray, and a few are marked with bright colors. The different species vary greatly in size and in the form of the body. The hind tarsi are four-jointed, and the fore and middle tarsi are five-jointed. For other characters, see table, p. 474. These insects occur chiefly in dry and warm regions. Thus while we have comparatively few species in the northeastern United States, there are many in the Southwest. Most of the species feed on dry vegetable matter, and often on that which is partially decomposed; some live in dung, some in dead animal matter, others in fungi, and a few prey upon larvae. More than eleven hundred species occur in this country. The three following will serve to ilhistrate the variations in form and habits. The meal-worm, Tenebno molitor.- — This is a well-known pest in granaries and mills. The larva is a hard, waxy yellow, cylindrical worm, which measures when full-grown 25 mm. or more in length, and closely resembles a wire-worm ; it feeds on flour and meal. The beetle is black and about 15 mm. in length, (Fig. 615). The larvse and pupae are used for bird-food and are grown in quantity by bird-supply houses. TheiovkQ6.hxng\xs-heet\e,Boletotheruscornutus, is common in the northeastern United States and ^'S- Fig- in Canada about the large toadstools {Poly poms) '^' which grow on the sides of trees. The surface of the body and wing- covers is very rough, and the prothorax bears two prominent horns (Fig. 616). The larva lives within the fungi referred to above. The pinacate-bugs. — Several species of Eleddes are abundant on the Pacific Coast, where they are found under stones and pieces of wood lying on the ground. They are apt to congregate in large numbers under a single shelter, and are clumsy in their move- ments. They defend themselves when disturbed by elevating the hinder part of the body and discharging an oily fluid from it. They present an absurb appear- ance, walking off clumsily, and carrying the hind end of the body as high as possible. The most common Fig. 617. species are large, smooth, club-shaped beetles (Fig. 617), and are commonly known as pinacate-bugs. These beetles and those belonging to several closely allied genera lack hind wings. yellow, cylmdrical m 514 AN INTRODUCTION TO ENTOMOLOGY The family LAGRIIDy^, or the lagriid bark-beetles, includes elongate beetles, with a narrow, subcylindrical prothorax, and a more or less brassy color. They are closely allied to the preceding family, but differ in having the next to the last segment of the tarsi spongy beneath. They are found under bark and on leaves. The larva feed freely on foliage and are much less retiring in habits than those of the darkling beetles. Seventeen species are listed from the United States ; most of these are found in the South and Far West. Our most common species in the East is Arthromdcra cenea (Fig. 6i8) ; this species measures from 9.5 mm. to 13.5 mm. in length. Fig. 618. The family MONOMMID^ is represented in this country by only six species, found chiefly in the Far West and in Florida. They are small, black, oval beetles, in which the anterior coxal cavities are open behind, the hind tarsi four-jointed, and the other tarsi five-jointed; and in which the antennae are received in grooves on the under side of the prothorax. Except one species found in Florida, our species belong to the genus Hyporhdgus. The family MELANDRYID^ includes about eighty North American species. These are found under bark and in fungi. They are usually of elongate form, although some, like the one figured here, are not so. The maxillary palpi are fre- quently very long and much dilated ; and the first seg- ment of the hind tarsi is always much elongated . Among our more common species are two belonging to the genus Penthe. These are rather large, oval, depressed beetles, upwards of 12 mm. in length, and of a deep Fig. 619. black color. Penthe obliqudta is distingmshedhy having the scutellimi clothed with rust-red hairs (Fig. 619). Penthe pimelia closely resembles this species, except that the scutelltun is black. The family PTINIDyE has been restricted recently to one of the subfamilies of the old family Ptinidse, which included, in addition to the insects now retained in it, those classed in the three following families. In the Ptinidae, as now restricted, the antennae are inserted upon the front of the head and rather close together, and the thorax is not margined at the sides. Only thirty-seven of our listed species are retained in this famih'. They are all small beetles and some of them are household pests, infesting stored provisions, clothing, and books. The best -known species is P^zwM^/wr. This is a reddish brown beetle; in the female the elytra are marked with two patches of white hairs. It measures from 2.8 mm. to 3.5 mm. The family ANOBIIDyE, or the death-watch family, includes a large part of the old family Ptinidae, there being more than two hundred species in our fauna. In this family the antennas are inserted on the sides of the head in front of the eyes; the thorax is usually margined at the sides; and the tibiae are without spurs. These beetles are small, and are generally of a cylindrical form, though some are broadly oval or nearly globular. They live chiefly on dry H COLEOPTERA 515 vegetable matter and are often found boring in the woodwork of buildings. Some are pests in drug-stores and groceries, where they infest a great variety of substances both vegetable and animal. Among the better -known species are the drug-store beetle, Sitodrepa pamcea, which not only infests many kinds of drugs but is also some- times a pest in groceries where it infests cereals; and the cigarette- beetle, Lasioderma serricorne ^vhich. infests dried tobacco and destroys cigarettes and cigars by boring holes through them. To this family belongs the death-watch, Xestohimn rufovillosum, which bores in the timbers of buildings and makes a ticking sound by striking its head or jaws against the walls of its burrows. This sound heard in the night h\ superstitious watchers by sick-beds has been supposed to portend death. The family BOSTRICHID^, or the powder-post beetles, includes beetles which are elongate in form; the head is usually deflexed, and protected by the thorax, which is then hood-like in form; and the first ventral segment of the abdomen is scarcely longer than the second. These beetles live almost exclusively in dry wood either in c>-lindrical burrows or beneath the bark. Sometimes they infest timbers to such an extent that the wood is largely reduced to pow^der, hence the common name, powder-post beetles. The adult of one species, Amphicerus bicauddtus, bores into the living twigs of fruit- trees and grape-vines for food, but it breeds in dying wood, such as prunings and dying branches. This species is known as the apple-twig borer and also as the grape-cane borer. The family LYCTID^ is composed of a small number of beetles which resemble the powder-post beetles in habits. In this family the head is prominent and not covered by the prothorax; and the first ventral segment of the abdomen is much longer than the second. Most of our species belong to the genus Lyctus. The family SPHINDID^ is represented in North America only by six small species, which are found in dry fungi which grow on the trunks of trees and on logs. The family CISID^ includes very small beetles, rarely exceeding 3 mm. in length, found under the bark of trees and in the dry and woody species of fungi. The body is cylindrical; the prothorax is prolonged over the head; the abdomen has five ventral segments, of which the first is longer than the others; and the tarsi are all four- jointed. There are nearly one hundred species in our fauna. Family SCARAByEID^ The ScarahcBids or Lamellicorn Beetles This very large family is represented in our fauna by nearly one thousand species, and includes beetles that exhibit a wide range of variation in size, form, and habits. They are mostly short, stout-bodied beetles, of which the well-known June-bugs or May-beetles represent the most familiar type. The most useful character for distinguishing 516 AN INTRODUCTION TO ENTOMOLOGY these insects is the lamellate form of the club of the antennas, the segments constituting it being greatly flattened, and capable of being brought close together. It is this character that suggests the name lamellicorn beetles. In the next family, the Trogidae, which has recently been separated from this family, the antennas are lamellate. The two families can be separated by the fact that in the Scarabaeidas the epimera of the mesothorax extend to the coxae, while in the Trogidee they do not. According to their habits, the members of this family can be separated into two well-marked groups — the scavengers and the leaf- chafers. THE LAMELLICORN SCAVENGERS The lamellicorn scavengers in both the larval and adult states feed upon decaying vegetable matter. Nearly all the species live in dung, chiefly that of horses and cows; but a few species feed upon fungi. The following are the more common representatives of this division. I. The tumble-bugs. — These are the most familiar of all dung- beetles, for their peculiar habits have attracted much attention from the earliest times. They are of rounded form, and the wing-covers are shortened so as to expose the tip of the abdomen. They are generally black, but some are colored with rich metallic hues. They vary greatly in size. The name tumble-bug refers to the habit which many species exhibit of forming round balls of dung, which they roll long distances and then bury. They often work in pairs and it was formerly be- lieved that such a pair was a male and a female working together to make provision for their progeny ; but Fabre found by dissecting the beetles that the two members of a pair often proved to belong to the same sex; and concluded that the eager fellow-worker, under the deceitful pretense of lending a helping hand, nurses the scheme of purloining the ball at the first opportunity. According to the observations of Fabre ('79 and '11), the balls made early in the year are devoured by the beetles, which bury them- selves with them and feed upon them. Later other balls are made and buried, upon each of which an egg is laid. The larva hatching from this egg feeds upon the ball of dung, and when full-grown transforms within the cavity in which the ball was placed. This strange habit of rolling these balls has occasioned much speculation as to its object, and has been the source of many super- stitions, especially in ancient times. The only reasonable theory that we have met is that, as many predacious insects frequent the masses of dung from which the balls are obtained, in order to prey upon the larvae which live there, the more intelligent timible-bugs remove the food for their larvae to a safe distance. The most noted member of this group of genera is the sacred beetle of the Egyptians, Ateuchus sdcer. This insect was held in on Liitj iiiiuuit COLEOPTERA 517 high veneration by this ancient people. It was placed by them in the tombs with their dead; its picture was painted on sarcophagi, and its image was carved in stone and precious gems. These sculp- tured beetles can be found in almost any collection of Egyptian an- tiquities. From the habits and structure of this scarabaeid the Egyptians evolved a remarkable symbolism. The ball, which the beetles were supposed to roll from sunrise to sunset, represented the earth; the beetle itself personified the sun, because of the sharp projections on its head, which extend out like rays of light ; while the thirty segments of its six tarsi represented the days of the month. All individuals of this species were thought to be males, and a race of males symbolized a race of warriors. This latter superstition was carried over to Rome and the Roman soldiers wore images of the sacred beetle set in rings. Our common tiimble-bugs are distributed among three genera: Cdnthon, Copris, and Phanceus. In the genus Canthon the middle and posterior tibiae are slender, and scarcely enlarged at the extremity. Canthon Icevis is our most common species (Fig. 620). In Copris and Phanceus the middle and posterior tibi® are dilated at the ex- tremity. In PhancBus the fore tarsi are wanting, and the others are not furnished with claws; the species are brilliantly colored. PhancBus carnifex, with its rough copper-colored thorax and green elytra, is one pjg 520 of our most beautiful beetles, and is our best -known species. It is about 16 mm. in length, and the head of the male is furnished with a prominent horn. In Copris all the tarsi are present and furnished with claws. Copris Carolina is a large, well-known species, which measures more than 25 mm. in length. II. The aphodian dung-beetles . — These are small insects, our com- mon species measuring from 4 mm. to 8 mm. in length. The body is oblong, convex, or cylindrical in form, and, except in one small genus, the clypeus is expanded so as to cover the mouth-parts entirely. These insects are very abundant in pastures in the dung of horses and cattle, and immense nvunbers of them are often seen flying through the air during warm autumn afternoons. More than one hundred and fifty North American species have been described; of these, one hundred belong to the genus Aphodius. One of the more common species is Aphodius fimetdrius, which is about 8 mm. in \ ^^^ / length, and is easily recognized by its red wing-covers. ^^Ukr III. The earth-boring dung-beetles. — -These beetles >2j^^bw are of a rounded convex form (Fig. 621). They differ JQU^^^L from all other dung-beetles in having the antennae W^BHf eleven-jointed, and in the lab rum and mandibles r^^'^A being visible from above. This is a small group, only p- ^ twenty-two North American species having been de- scribed. The popular name is deiived from that of the typical genus, Geotriipes, which signifies earth-boring. Those species the habits of which are known, live in excrement. The females bore 518 AN INTRODUCTION TO ENTOMOLOGY holes into the earth either beneath the dung or near it; into these holes they convey a quantity of the dung ; this is to serve as food for the larvae, an egg being laid in each hole. This is an approach to the peculiar habits of the tvimble-bugs. THE LAMELLICORN LEAF-CHAFERS The leaf-chafers are herbivorous insects which in the adult state usually feed upon the leaves of trees, but many of the species devour the pollen and petals of flowers. In the larval state some of these insects are found in rotten wood; others live in the ground, where they feed upon the roots of grass and other plants. These larvae are thick, fleshy grubs, with well-developed legs (Fig. 622). The caudal segments of the abdomen are very large, and appear black on ac- count of the large amount of dirt in the intestine. The body is strongly curved, so that the larvae can crawl only with Pig 522. great difficulty; when in the ground they usually lie on their backs. The following groups include the more important representatives of this division. I. The May-beetles or June-hugs. — During the warm evenings of May and June we throw open our windows so that we may feel the refreshing coolness of the night air and the inspiration of the new simimer. Suddenly, as we sit working or reading, our peace is dis- turbed by a buzzing object which whirls above us. Then comes a sharp thud and silence. A little later the scratching of six pairs of tiny claws tells us the whereabouts of the intruder. But so familiar are we with his kind that we need not look to know how he appears, the mahogany-brown blunderer, with yellowish wings sticking out untidily from under his pohshed wing-covers. Although these insects are beetles, and attract our attention each year in May, they have received the infelicitous title of June-bugs. They are more properly termed May-beetles. The May-beetles belong to the genus Phylloph- aga, of which we have nearly one hundred species. The adults frequently do much injur}'' by eating the foliage of trees. In the case of large trees this injury usually passes unnoticed; but small trees are often completely defoliated by them. When troublesome, they can be easily gathered by shaking them from trees upon sheets. Figure 623 represents a common ^'§- ^-^■ species. The larvae of the different species of May-beetles are commonly classed together imder the name "white-grubs." They are often great COLEOPTERA 519 pests in meadows and in cultivated fields. We have known large strawberry plantations to be destroyed by them, and have seen large patches of ground in pastures from which the dead sod could be rolled as one would roll a carpet from a floor, the roots having been all destroyed and the ground just beneath the surface finely pulver- ized by these larvae. No satisfactory method of fighting this pest has been discovered as yet. If swine be turned into fields infested by white- grubs they will root them up and feed upon them. We have destroyed great numbers of the beetles by the use of trap-lanterns, but many beneficial insects were destroyed at the same time. II. The rose-bugs. — The common rose-bug, Macroddctylus suh- spinosus, is a well-known pest. It is a slender beetle, tapering before and behind, and measuring 9 mm. in length (Fig. 624). It is thickly clothed with fine, yellow, scale-hke hairs, which give it a yellow color; the legs are long, slender, and of a ^JtJ pale red color. These beetles appear in early summer, (wk and often do great injury to roses and other flowers, /W^VS and to the foliage of various fruit-trees and shrubs. This / \ is a very difficult pest to control. The best method now known is to use Paris green when safe to do so; in other ^^' ""*■ cases the beetles should be collected by jarring them into a large funnel which is fitted into a can. The larvae of rose-bugs feed on the roots of plants. III. The shining leaf -chafers . — These insects resemble the May- beetles in form, but can be distinguished from them by the position of the hind pair of spiracles, which are visible on the sides below the edges of the wing-covers ; and they differ from the other leaf-chafers in which the spiracles are in this position in that the tarsal claws are of unequal size, one claw of each pair being larger than the other. These beetles are usually polished, and many of them are of brilliant colors. To this family belong the most beautiful beetles known, many appearing as if made of burnished gold or silver, or other metal. The goldsmith-beetle, Cotalpa lanigera. — This is one of our most beautiful species. It measures from 20 mm. to 26 mm. in length, and is a broad oval in shape. It is of a lemon-yellow color above, glittering like burnished gold on the top of the head and thorax ; the under side of the body is copper-colored and thickly covered with whitish wool. The spotted pelidnota, Pelidnota punctata. — -This beetle is reddish brown above, with three black spots on each wing-cover and one on each side of the pro- Fig. 625. thorax (Fig. 625). The scutellum, base of the head, and entire body beneath, are of a deep, bronzed- green color. The adult is commonly found feeding on the leaves of grape. The larva feeds upon decaying roots and stumps of various trees. The Japanese beetle, Popillia japonica. — This is a very serious pest which feeds in the adult state on the foliage of many cultivated 520 AN INTRODUCTION TO ENTOMOLOGY and wild plants, being practically omnivorous, and in the larval state feeds on the roots of grasses. It was first observed in this country in a limited area in Burlington County, New Jersey, in 191 6, and has since spread over other counties of this state and into Pennsylvania. The adult insect is about the size of the Colorado potato-beetle, but slightly longer. The head and thorax are shining bronze-green in color, with the wing-covers tan or brownish, tinged with green on the edges. Along the sides of the abdomen are white spots, and two very distinct white spots at the tip of the abdomen below the wing-covers. The larva resembles the larvse of May beetles. This pest is regarded as of so great importance that a special laboratory, "The Japanese Beetle Laboratory," has been established for investigations regarding it at Riverton, N. J. IV. The rhinoceros-beetles.- — -The name rhinoceros-beetles was suggested for this group by the fact that in many species the male bears a horn on the middle of the head. In addition to this horn there may be one or more horns on the thorax. These beetles are of medium or large size ; in fact, the largest beetles known belong to this group. As with the flower-beetles, the claws of the tarsi are of equal size, but the fore coxae are transverse, and not prominent. One of the largest of our rhinoceros-beetles is Dynds- Fig- 626. ^^^ tUyrus. This is of a greenish gray color, with scattered black spots on the wing-covers, or, if only recently trans- formed, of a uniform dark brown. The male (Fig. 626) bears a prominent horn on the top of the head, and a large one and two small ones on the prothorax. The female has only a tubercle on the head. This insect is found in the Southern States; the larva lives in rotten wood. In the Far West there is a closely allied species, Dynastes grantii, in which the large horn on the thorax is twice as long as in JD. tityrus. In the West Indies there occurs a species, Dynastes ..hercules, which measures 150 mm. in length. Several other genera occur in this coimtry, in some of which the ■males have prominent horns; in others the horns are represented ^,by tubercles, or are wanting. The following species represents the Jatter type. The sugar-cane beetle, Euctheola riigiceps . — This beetle is a serious -pest in the cane-fields of Louisiana, and it sometimes injures corn. Figure 627 represents the adult, and its method of attacking a plant. V. The flower-beetles . — The flower-beetles are so called because many of them are often seen feeding upon pollen and flying from flower to flower. These beetles are somewhat flattened, or nearly level on the back; the claws of the tarsi are of equal size and the COLEOPTERA 521 fore coxae are conical and prominent occur in this country. The hermit flower-beetle, Os- moderma eremicola.- — This is one of the larger of our flower-beetles (Fig. 628). It is of a deep mahog- any-brown color, nearly smooth, and highly polished. It is supposed that the larva lives on decaying wood in forest-trees. The rough flower-beetle, Os- moderma scdbra, is closely allied to the preceding. It is not quite as large, measuring about 25 mm. in length. It is purplish black, and the wing-covers are rough- ened with irregular, coarsely punctured strice. It is nocturnal, concealing itself during the day in the crevices and hollows of trees. The larva lives in the decaying wood of apple and cherry, con- siuning the wood and inducing more rapid decay. The genus Euphoria repre- sents well the form of the more typical flower-beetles, which are distinguished by the margin of each wing-cover having a large, wavy indentation near its base, which renders the side pieces of the meso- thorax visible from above. This indenta- tion makes it unnecessarv More than one hundred species V\.H.UVCiHO\_S» Fig. 627. — The sugar-cane beetle. for these insects to raise or expand their wing- covers when flying, as most beetles do, as they are able to pass the wings out from the sides. The bumble flower-beetle. Euphoria tnda. — The most common of our flower-beetles, at least in the North, is a yellowish brown one, with the wing-covers sprinkled all over with small, irregular. Fig. 628. black spots (Fig. 629) . It is one of the first insects to appear in the spring. It flies near the surface of the ground with a loud humming sound, like that of a bumble-bee, for which It is often mistaken. During the summer months it is not seen ; 522 AN INTRODUCTION TO ENTOMOLOGY but a new brood appears about the middle of September. The adult is a general feeder occurring upon flowers, eating the pollen, upon corn-stalks and green com in the milk, sucking the juices, and upon peaches, grapes, and apples. Oc- casionally the ravages are very serious. The green June-beetle or fig-eater, Cotinus mtida. — This species extends over the Atlantic slope, and is very common in the South. It is a green, velvety insect, measuring from i6 mm. to 25 mm. in length. It is somewhat pointed in front, and usually has the sides of the thorax and elytra brownish yellow. These beetles often fly in great numbers at night, making a loud buzzing noise similar to that of the May-beetles. In fact, in the South the term June-bug is often applied to this insect. The larvae feed upon the vegetable mold of rich soils; sometimes they injure growing vegetables by severing the roots and growing stalks ; but the chief injury is due to the upheaval of the soil around the plants, which disturbs the roots; the larvse are also often troublesom.e on lawns and golf greens by making little mounds of earth on the surface. Sometimes they leave the ground and crawl from one place to another. When they do so, they, strangely enough, crawl upon their backs, making no use of their short legs. On one occasion we saw them crawl- ing over the pavements on the Capitol grounds at Washington in such numbers that bushels of them were swept up and carted away. The adults frequently attack fruit, especially figs, grapes, and peaches. Family TROGID^ The Skin-Beetles This is a small family, which is represented in this country by twenty-five species. Until recently these insects were included in the preceding family; they can be distinguished from scarabasids by the fact that the epimera of the mesothorax do not extend to the coxae as they do in the Scarabasidas. The members of this family are oblong, convex species, in which the surface of the body and wing- covers is usually very rough, and covered with a crust of dirt, which is removed with great difficulty. They are small or of medium size; our most common species measure from 8 mm. to 12 mm. in length. The abdomen is covered by the elytra ; the feet are hardly fitted for digging, but the femora of the front legs are greatly dilated. These beetles feed upon dried, decomposing animal matter; many species are found about the refuse of tanneries, and upon the hoofs and hair of decaying ^^^- ^•5°- animals. Except a few species found in the Far West, all of our species belong to the genus Trox (Fig. 630). ^ COLEOPTERA 523 Family LUCANID^ The Stag-Beetles The stag-beetles are so called on account of their large mandibles which in the males of some species are branched like the antlers of a stag. They and the members of the following family are dis- tinguished by the form of the club of the antenna?, which is composed of flattened plates ; but these plates are not capable of close appo- sition, as in the antennae of the lamellicorn beetles. In the stag-beetles the mentum is not emarginate and the ligula is covered by the mentum or is at its apex. The adult beetles are found in or beneath decaying logs and stumps. Some of them are attracted, at night, to lights. They are said to live on honeydew and the exudations of the leaves and bark of trees, for procur- ing which the brushes of their jaws and lips seem to be designed; but it seems probable that some species, at least, feed upon de- composing wood. They lay their eggs in crevices of the bark of trees, especially near the roots. The larv« feed upon juices of wood in various stages of decay. They re- semble the well-known larvae of May -beetles. The family is a small one; only thirty North American species are now known. The common stag-beetle, Lucdnus dama. — The most common of our stag-beetles is this species (Fig. 631). It flies by night with a loud buzzing sound, and is often -^^S- 631. attracted to lights in houses. The larva is a large, whitish grub re- sembling the larvae of the lamellicorn beetles. It is found in the trunks and roots of old, partially decayed trees, especially apple, cherry, willow, and oak. The specimen flgured here is a male; in the female the mandibles afe shorter. The giant stag-beetle, Lucdnus elaphus, is a large species found in the South. It measures from 35 mm. to 50 mm. in length, not including the mandibles, which in the case of the male are more than half as long as the body, and branched like the antlers of a stag. The antelope-beetle, Dorcus parallelus. — This beetle is somewhat smaller than the species of Lucanus, and differs in having the wing-covers marked with longi- Fig- 632. tudinal striae and the teeth on the outside of the fore tibiae much smaller (Fig. 632). Several species of stag-beetles that are much smaller than Dorcus are found in this country. 524 AN INTRODUCTION TO ENTOMOLOGY Family PASvSALID^ The members of this family resemble the stag-beetles in the form of the antennas, but differ in that the mentum is deeply emarginate, with the ligula filling the emargination. A single, widely distributed species is found in the United States; this is the homed passalus, Pdssalus cornutus (Fig. 633). It is a large, shining, black beetle, with a short horn, bent forwards, on the top of the head. This beetle and its larva are found in decaying wood. The larva appears to have only four legs, the hind legs being shortened and modified so as to form part of a stridulating organ. See Figure loi, page 89. The beetles of this genus are common through- out the tropics of both hemispheres. According to the observations of Ohaus, which have been Fig- 633. confirmed by Professor Wheeler ('23), these beetles are social. They form colonies, consisting of a male and female and their progeny, and make large, rough galleries in rather damp, rotten logs. The parent beetles triturate the rotten wood and apparently treat it with some digestive secretion which makes it a proper food for the larvse, since their mouth-parts are too feebly developed to enable them to attack the wood directly. All members of the colony are kept together by stridulatory signals. The stridulatory organ of the adult consists of patches of minute denticles on the dorsal surface of the abdomen, which may be rubbed against similar structures on the lower surface of the wings. Family CERAMBYCID^ The Long-horned Beetles or Cerambycids This is a very large family, there being more than eleven hundred de- scribed species in North America alone. As a rule the beetles are of medium or large size, and graceful in form ; many species are beautiful in color. The body is oblong, often cylindrical. The antennas are long, often ABC Fig. 634. — Tarsi of Phytophaga: A, typical; Spondylis; C, Parandra. B, COLEOPTERA 525 longer than the whole body; but except in one genus, Prionus, they are only eleven-jointed, as with most beetles. The legs are also long, and the tarsi are apparently four-jointed, the fourth segment being very small and hidden; the third segment of the tarsi is strongly bilobed (Fig. 634.). They are strong flyers and swift runners; but many of them have the habit of remaining motionless on the limbs of trees for long intervals, and when in this apparent trance they suffer themselves to be picked up. But, when once caught, many species make an indignant squeaking by rubbing the prothorax and meso- thorax together. The larva? are borers, living within the solid parts of trees or shrubs, or beneath bark. They are white or yel- lowish grubs. The body is soft, and tapers slightly from head to tail (Fig. 635); the jaws are powerful, enabling these insects to bore into the hardest wood. The larval state usually lasts two or three years. The pupa state is passed within the burrow made by the larva; frequently a chamber is made by partitioning off a section of the ^^' ^^' burrow with a plug of chips; but sometimes the larva builds a ring of chips around itself just beneath the bark before changing to a pupa. The pupal state is comparatively short, lasting only a few days or weeks. This family comprises three subfamilies, which are separated by LeConte and Horn as follows: A. Sides of the prothorax with a sharp margin, p. 525 PRiONiNiE AA. Prothorax not margined. B. Front tibiae not grooved ; palpi never acute at tip. p. 526 . CERAMBYCiNyE BB. Front tibiae obliquely grooved on the inner side; palpi with the last segment cylindrical and pointed, p. 528 Lamiin^e Subfamily PRIONIN^ The Prionids The larger of the long-homed beetles constitute this subfamily. They are distinguished from other cerambycids by having the sides of the prothorax prolonged outwards into a thin margin, which is more or less toothed. The wing-covers are usually leathery in ap- pearance, and of a brownish or black color. The following are our best-known species. The aberrant long-horned beetles. — The beetles of the genus Pa- randra exhibit some strikingdifferences from the more typical ceramby- cids, and were formerly placed in a separate family, the Spondylidcs; but they are now included in the Cerambycidae. There are only four North American species of this genus. These live under bark of pine trees. The fourth segment of the tarsus, although much reduced in size, is distinctly visible ; the first three segments are but slightly di- 526 AN INTRODUCTION TO ENTOMOLOGY Fig. 636. Fig. 637 lated, and the third is either bilobed or not (Fig. 634, C). The seg- ments of the antennae have deep impressions, in which are situated the organs of special sense (Fig. 636). The most common species is Parandra brunnea (Fig. 637); this insect is of a mahogany-brown color, and measures from 9 mm. to 18 mm. in length. The broad-necked prionus, Prionus laticdllis. — This is the largest of our common species; but the individuals vary from 22 mm. to 50 mm. in length. It is of a pitchy-black color, and of the form shown in Figure 638. The antennae are twelve-jointed in both sexes. The larva is a large, fleshy grub, and infests the roots of grape, apple, poplar, and other trees. The tile-homed prionus, Prionus imbricdrms, is very similar to the preceding species but can be distinguished at a glance by the form of the antennae. In the antennse of the male the nimiber of segments varies from eighteen to twenty, while in the female the number varies from sixteen to seventeen. The popular name refers to the fact that the segments of the an- tennae of the male overlap one another like the tiles on a roof. The larva infests the roots of grape and pear, and also feeds upon the roots of herbaceous plants. The straight-bodied prionid, Dero- brachus brunneus, is also a common spe- cies. The body is long, narrow, and some- what flattened; it measures from 25 mrii. to 35 mm. in length, and is of a light brown color. The prothorax is short, and is armed on each side with three sharp spines. The sides of the wing-covers are very nearly parallel ; this suggests the common name. The adult flies by night, and is often attracted to lights; the larva is supposed to infest pine. Fig. 63 8. Subfamily CERAMBYCINyE The Typical Cerambycids In this subfamily the prothorax is rounded on the sides, the tibiae of the fore legs are not grooved, and the palpi are never acute at the tip. There are nearly four hundred American species, representing more than one hundred genera. The few species mentioned below are those that the beginning student is most likely to meet. The ribbed pine-borer, Rhdgium linedtum. — This is a gray beetle mottled with black, and has a narrow thorax, with a spine on each COLEOPTERA 527 Fig. 639. side (Fig. 639). It received its name because of the three ridges extending lengthwise on each wing-cover. Its larva bores in the wood of pine-trees. On one occasion the writer found many of them in a pine-tree eight inches in diameter, which they had bored through and through. When the larva is full-grown it makes a hole nearly through the thick bark of the tree, so that it may easily push its way out after its transformations; it then retreats a short distance and makes a little ring of chips around itself, between the bark and the wood, and changes to a pupa within this rude cocoon. The adult beetle re- mains in this pupal cell through the winter. The cloaked knotty-horn, Desmocerus pallidtus. — This beautiful insect is of a dark blue color, with greenish reflections. The basal part of the wing-covers is orange-yellow, giving the insect the appearance of having a yellow cape thrown over its shoulders (Fig. 640). The segments in the middle of the antennae are thickened at the outer end, so that they look like a series of knots. The adult is quite common in June and July on elder, in the pith of which the larva bores. The beautiful maple-borer, Glycohius speciosus. — This is a handsome insect, marked with black and yellow, as indicated in Figure 641. It lays its eggs in midsum- mer on the trunks of sugar-maples, in the wood of which the larvae bore. If an infested tree be examined in the spring the presence of these borers can be detected by the dust that falls from the bur- rows. The larvae can be de- stroyed at this time by the use of a knife and a stiff wire. The locust-borer, Cyllene ro- hincB. — To the enthusiastic ento- mologist the goldenrod is a rich mine, yielding to the collector more treasures than any other flower. It gives up its gold-dust pollen to every insect-seeker; and because of this generous attitude to all comers it is truly emblematic of the country that has chosen it as its national flower. Among the insects that revel in this golden mine in the autumn is a black beetle with numerous transverse or wavy yellow bands (Fig. 642). This beetle is also found on locust- trees, where it lays its eggs. The larvse bore under the bark and into the hard wood; they attain their growth in a little less than a year. The locust-trees have been completely destroyed in some localities by the depredations of these larvae. Fig. 640. Fig. 642. Fig. 641 528 AN INTRODUCTION TO ENTOMOLOGY The painted hickor>^-borer, Cyllene cdryce. — This beetle resembles the preceding so closely that the same figure will represent either. But the hickory-borer not only infests a different kind of tree, but appears in the spring instead of the autiunn. In this species the second segment of the hind tarsus is densely pubescent beneath, while it is glabrous in the locust-borer. The oak-pruner, Hypermallus villosus. — The work of this insect is much more likely to attract attention than the insect itself. Fre- quently, in the autumn, the ground beneath oak-trees, and sometimes beneath apple-trees also, is strewn with small branches that have been neatly severed from the trees as if with a saw. These branches are sometimes nearly 25 mm. in diameter, and have been cut off by the larva of a beetle, which on account of this habit is called the oak- pruner. The beetle lays each of its eggs in a small twig. The larva eats out the inside of this twig, and works down into a larger branch, following the center of it towards the trunk of the tree. When full- grown the larva enlarges the burrow suddenly, so as nearly to sever the branch from the tree, leaving only the bark and a few fibers of wood. It then retreats up its burrow a short distance, and builds a plug of chips below it. The autimm winds break the branch from the tree. The larva remains in its burrow through the winter, and undergoes its transformations in the spring. No one has explained its object in severing the branch. The adult is a plain, brownish gray beetle. Whenever it becomes abundant its increase can be checked by gathering the fallen branches in the autiimn and burning them before the beetles have escaped. Subfamily LAMIIN^ The Lamiids As in the preceding subfamily, the prothorax is rounded with these beetles; but the lamiids are distinguished by hav- ing the fore tibiae oblique- ly grooved on the inner side, and the last segment of the palpi cylindrical and pointed. The follow- ing are some of the more important species. The sawyer, Mono- chamus notdtus. — This beautiful brown and ray. beetle is about 30gmm long,with antenna aslong as the body in the case of the female and twice as p. , long in the case of the ^^- ^^- male (Fig. 643). The larva bores in the sound wood of pine and of fir, making, when full- COLEOPTERA 529 grown, a hole 12 mm. in diameter. The pupa state is passed within the burrow. It sometimes occurs in such numbers as to kill the infested trees. The rounded-headed apple-tree borer, Saperda Candida. — Except- ing the codlin-moth, which infests the fruit, this is the worst enemy of the apple that we have. Its common name is used to distinguish it from the fiat-headed apple-tree borer, already described, the larva of this species being nearly cylindrical in form "(Fig. 635). The eggs are laid on the bark at the base of the tree late in June or July. The larva at first bores in the soft sap-wood, making a disk-shaped mine; after this it works in an upward direction in the harder wood, and at the close of its larval existence comes to the surface sev- eral inches above the place it entered. Itrequires nearly three years for this larva to attain its growth ; it changes to a pupa, near the upper end of its burrow, about the middle of May, and emerges as a beetle in June. The beetle (Fig. 644) is of a pale brown color above, with two broad white stripes extending the whole length of the body. Although the larva is found chiefly in apple, it infests many other trees. The presence of the borers can be detected by the saw- dust-like castings which the larvae throw out at the entrances of their burrows. The two-spotted oberea, Oberea himacidata, is sometimes a serious pest, boring in the canes of blackberry and raspberry. The larva resembles that of the preceding species. The adult (Fig. 645) is T_ _^ about 12 mm. in length and of a \^^^^ deep black color, except the protho- jpll rax, which is yellow. There are usu- vBI^ ally two or three black spots on the /l!^'^ pronotum, but frequently these are wanting. By cutting and burning all the picked, the borers in them can be Fig. 644. Fig. 645. Fig. 646. canes after the crop has been destroyed. The red milkweed-beetles, Tetraopes. — There are several species of bright red beetles that are common on milkweeds {Asclepias). These belong to the genus Tetraopes. Our most common species (Fig. 646) is T. tetraophthdlmus. In this species there are four black spots on each wing-cover, and the antenncC are black and not ringed with a lighter color. The larva bores in the roots and the lower parts of the stems of milkweeds. 530 AN INTRODUCTION TO ENTOMOLOGY Family CHRYSOMELID^ The Leaf -Beetles or Chrysomelids The leaf -beetles are so called because they feed upon the leaves of plants both as larvee and adults. They are usually short -bodied, and more or less oval in outline; the antennae are usually of moderate length ; and the front is not prolonged into a beak. The legs are usu- ally short, and are furnished with tarsi of the same type as those of the preceding family (see Fig. 634, p. 524). Although we are unable to cite any characteristic that will in- variably distinguish these beetles from the preceding family, the student will rarely have any difficulty in making the distinction. The beetles of the genus Dondcta, described below, are the only common ones that are liable to be misplaced. In other cases the more or less oval form of the body, and the comparatively short antennse, and the leaf -feeding habits, will serve to distinguish the chrysomelids. The leaf-beetles are nearly all comparatively small, the Colorado potato-beetle being one of our larger species. The eggs are usually elongated and yellowish, and are laid upon the leaves or stems of the plants upon which the larvae feed. Many of the larvae live exposed on the leaves of plants; others that live in similar situations cover themselves with their excrement; some are leaf -miners; and a few, as the striped squash -beetle, bore in the roots or stems of plants. This is a large family, of which nearly one thousand North Ameri- can species are known. The following illustrations will serve to show the variations in form and habits. The long-horned leaf-beetles, Dondcia. — These are the common leaf -beetles that are liable to be mistaken for cerambycids. They are of elongated form, with slender antennae (Fig. 647). They measure- from 6 mm. to 1 2 mm. in length, and are of a metallic color f- — either greenish, bronze, or purplish. The lower side of the body is paler and is clothed with very fine hair which serves as a water-proof coat when the insect is submerged. The larvffi feed upon the roots or in the stems of aquatic plants ; and the adults are found on the leaves of the same Fig- 647- plants. We have many species, but they resemble one another so closely that it is difficult to separate them. The three-lined lema, Lema trilinedta. — This insect is common, feeding on the leaves of potato. The beetle is 6 mm. long, yellow, with three black stripes on the wing-covers. The eggs are usually laid in rows along the midrib on the lower side of the leaves. The larvae feed on the leaves, and can be easily recognized by a habit they have of covering their backs with their own excrement. They transform in the ground in earthen cells. There are two broods each year; the second hibernates in the ground as pupae. The asparagus-beetle, Crioceris aspdragi. — This is a small red, yellow, and black beetle, that gnaws holes into the heads of young COLEOPTERA 531 asparagus, and lays oval, black eggs upon them. The larvas, which are small, brown, slug-like grubs, also feed upon the young heads in the spring, and later in the season a second brood feed upon the full-grown plant. Figure 648 represents a head of asparagus bearing the eggs of this beetle, also a beetle and a larva enlarged. The beetle measures about 6 mm. in length. When this pest occurs, care should be taken to destroy all wild asparagus. This will force the beetles to lay their eggs upon the shoots that are cut for market. The larvas hatching from such eggs will not have a chance to mature. The grape root-worm, Fldia longipes. — This insect is the most destructive enemy of the grape occurring east of the Rocky Mountains. The adult is a small, grayish brown beetle, measuring about 6 mm. in length. It feeds on the leaves in July, eating out characteristic chain-like holes. The eggs are laid beneath the loose bark of the vines. On hatching, the larvee drop to the ground and burrow down to the roots, which they destroy, causing the death of the vine. Most of the larvce do not transform till the following spring. The best means of fighting this pest is to poison the beetles while they are feeding on the leaves, and before they lay their eggs, by the use of a spray made by dissolving six pounds of arsenate of lead in 100 gallons of water. The Colorado potato-beetle, Leptinotarsa decemlinedta. — -A good many insect tramps have come to us from Europe and from Australia, and appropriated whatever pleased them of our grow- ing crops or stored grain. But two of our worst insect pests have swarmed out on us in hordes from their strongholds in the region of the Rocky Mountains. These are the Rocky Mountain locust and the Colorado potato-beetle (Fig. 649). The latter insect dwelt near the base of the Rocky Mountains, feeding upon the sand-burr {Solanuni rostratum), until about the year 1859. At that time it began to be a pest in the potato-fields of the settlers in that region. Having acquired the habit of feeding upon the cultivated potato, it began its eastward march across the conti- nent, spreading from potato patch to potato patch. At first the migration took place at about the rate of fifty miles a year, but later it was more rapid; and in 1874 the insect reached the Atlantic Coast. The adult beetles hibernate in the groimd; they emerge early in April or May, and lay their eggs on the young potato plants as soon as they appear; both larvae and adult beetles feed on the foliage of the potato. The larvae enter the ground to transform. This pest is usually controlled by the use of Paris green. Labidomera clivicollis. — This species is closely allied to the Colorado potato-beetle and resembles it in size and form. It is of a deep blue Fig. 649. 532 AN INTRODUCTION TO ENTOMOLOGY M color, except the wing-covers, which are orange, with three dark -blue spots on each (Fig. 650). There is considerable variation in the size and shape of these spots; frequently the two near the base of the wing-covers are joined so as to make a continuous band extending across both wing-covers. The larva feeds on milkweed {Asclepias) . Fig. 650. The diabroticas. — Several very important pests belong to the genus Diabrotica. In the East they are known as cucumber-beetles; but on the Pacific Coast, where they are more feared on account of their injuries to fruit and fruit-trees, they are commonly called the diabroticas. They are chiefly greenish yellow beetles, marked with black stripes or spots. The striped diabrotica, D. vttdta, has two black stripes on each wing-cover. The adult feeds on the leaves of cucumber, squash, and melon; and the lar\'a, which is a slender, worm -like creature, bores in the stems and roots of the same plants. The twelve-spotted diabrotica, D. duodecimpttnctdta, and Diabrotica soror, agree in having six black spots on each wing- cover. The former is verv' common in the East ; the latter occurs on the Pacific Coast, and is the most destructive of all of the diabroticas. Diabrotica longicornis is a green species, which feeds on the pollen and silk of corn and on the pollen of other plants. Its larva is known as the com root -worm ; it is very destructive to com in the Mississippi Valley. Its injuries are greatest where corn is grown on the same land year after year; hence a rotation of crops should be practised where this pest is troublesome. The other species of Diabrotica mentioned above are difficult to combat, as the leaves of cucumber, melon, and squash are very apt to be injured by the use of arsenical poisons. The most practicable way of protecting these vines is to cover them while young with frames covered with netting. Where they infest fruit-trees they can be fought with Paris green; but this poison must be used with great care on such trees as pnme and apricot. Squashes should not be grown in orchards, as is sometimes done in California. ' The flea-beetles. — There is a group of leaf-beetles, of which we have many species, in which the hind legs are fitted for leaping, the thighs being very large. These are commonly called the fiea-beetles. The striped flea-beetle, Phyllotreta vittdta, is exceed- ingly common on cabbage, turnip, radish, mustard, and allied plants. It is a small, black, shining beetle, with a broad, wavy, pale, dull yellow stripe upon each wing- cover (Fig. 651); it measures about 2.5 mm. in length. These beetles eat numerous little pits in the thicker ^^^- ^^^' leaves that they infest, and minute perforations in the thinner-leaved plants. The larva is a slender, white worm, about 8 mm. in length ; it feeds on the roots of the plants infested by the adult. The adult beetles can be destroved with kerosene emulsion. COLEOPTERA 533 The cucumber flea-beetle, Epitrix cucwneris, is a common pest of melon and cucumber vines; it also attacks the leaves of potatoes, raspberry, t u r n i ]j , cabbage, and other I? 1 a n t s . This is a minute black spe- cies, meas- in length. The body is finely punctured and clothed with a whitish pubescence ; there is a deep transverse furrow across the hind part of the prothorax; the antennas are dull yellow, and the legs are of the same hue, except the posterior femora, which are brown. The adult beetles feed on the leaves of plants in the same manner as the preced- ing species; and the larvse on the roots of the infested plants. The grape flea-beetle, Hdltica chalybea. ■ — This is a larger species than the two pre- ceding, measuring from 4 mm. to 5 mm. in length, and is of a dark, steel-blue color. It is a great pest in vineyards, eating into the buds of grape in early spring, and later gnawing holes in the leaves (Fig. 652). In May and June the brown, sluggish larvae may also be found feeding upon the surface of the leaves. The full-grown larva is chestnut brown marked with black spots (Fig. 653). It drops to the ground and makes a cell in the earth in which it transforms. The most important injury caused by this pest is the destruction of buds in early spring, which causes a great loss of foliage and fruit. This pest is most easily controlled by spraying the vines with an arsenical poison between the middle of June and the middle of July, while the larvae are feeding on the leaves. The wedge-shaped leaf -beetles . — These insects are characterized by the peculiar form of the body, which is narrow in front and broad behind. In most of the species the body is much roughened by deep pits, and usually the pits on the wing-covers are in regular rows. These insects and the tortoise-beetles differ from other leaf -beetles in having the fore part of the head prominent, so that the mouth is confined to the under surface. Some of the larvae feed externally upon the leaves and bear a parasol composed of their excrement; Fig. 652. 534 AN INTRODUCTION TO ENTOMOLOGY other species are leaf -miners. Baliosus rubra is a good representative of this group3(Fig. 654). It varies in length from 3 mm. to 5 mm. It is of a reddish color, with the elevated portions of •\^\ I ^ the elytra more or less spotted with black. The larva IV J mines in the leaves of apple, forming a blotch-mine; ^mC. the transformations are undergone within the mine. JfwBSa\, *^ We have also found this species mining the leaves of jflf&y JjSk basswood in great numbers. IJPiP The tortoise-beetles. — Among the more beautiful Fig. 654. Coleoptera are certain bright golden, green, or irides- cent beetles found on the leaves of sweet potato, moming-glor_y, nettle, and other plants. In these beetles the body is flattened below and convex above ; the head is nearly or quite con- cealed beneath the prothorax; and the margins of the prothorax and elytra are broadly expanded, forming an approximate- ly circular or oval outline, and suggesting a resem- blance to the shell of a tortoise (Fig. 655). Not all of the species are iridescent ; and in the case of those that are, the brightness of the colors is said to de- pend on the emotions of the insect. What a beautiful way to express one's feelings — to be able to glow like pjg 5^^ melted gold when one is happy ! Unfortimately for the beauty of our collections, these bright colors disappear after the death of the insect. The larvae of the tortoise-beetles are flattened, and have the margin of the body fringed with spines. At the caudal end of the body there is a forked appendage which serves a vers^ strange purpose. This fork is bent forward over the back, and to it are attached the cast-off skins of the larva and its excrement; these constitute a parasol. When about to change to the pupa state these larvae fasten the caudal end of the body to the under side of a leaf; the skin then splits open, and is forced back to this end of the body, where it remains. The one-dotted or five-dotted tortoise, Physonota unipunctata. — The largest of our bright-colored tortoise-beetles is common in mid- summer, feeding on the leaves of wild sunflower. It measures from 9 to 12 mm. in length, and is yellow, with the margins whitish. On the prothorax there are flve black dots — two close together in front, and three more widely separated behind. Sometimes all but one of these dots are wanting. It was this form that was first de- scribed, hence the name unipunctata. We have found the larv^ae abun- dant in July on the same plant with the adults. The milkweed-tortoise, Chelymorpha cassldea, is a large, brick red species, which measures from 9 mm. to 12 mm. in length, and has the prothorax and wing-covers marked with many black spots. This species feeds on milkweed (Asdepias) and various other plants. * COLEOPTERA 535 Family MYLABRID^ The Pea-Weevil Family These are small beetles, the larva; of which live in the seeds of legttminous plants. The head of the adult is prolonged into a broad beak; and the wing-covers are rather short, so that the tip of the abdomen is always exposed (Fig. 656). This is a compara- tively small family; ninety-three species are listed in our fauna, of which eightv-one belong to the genus Mylabris. The pea-weevil, Mylabris pisorum. — "Buggy peas" are /M^^ T well known in most sections of our country; but just how /^Hl\l the "bugs" find their way into the peas is not so generally understood. The eggs of the pea-weevil are laid upon the pod while the peas are quite small; when the larv^ hatch p^„ g^g^ they bore through the pod into the young peas. Here they feed upon the substance of the seed, which ripens, however, and in some cases will germinate when planted. The larva before transforming eats a circular hole on one side of the seed, leaving only a thin scale, which is easily pushed away by the mature beetle. The adult is about 5 mm. in length; it is dark brown, with a few white spots on the wing-covers, and one on the prothorax near the middle. Sometimes the beetles leave the peas during the autumn or winter; but as a rule they remain in the seed till spring, and are often planted with it. Seed peas should be placed in water, and the infested ones, which will float, should be picked out and destroyed. This species is not known to oviposit on dry peas. This and other grain-infesting insects can be destroyed by placing the grain in a closed receptacle with a small quantity of bisulphide of carbon. The bean-weevil, Mylabris obtectiis. — This species resembles the preceding quite closely; but it is a little smaller (Fig. 656), and lacks the white markings characteristic of M. pisorum. It infests beans, and often several individuals inhabit a single bean. The eggs are laid within the pod, being pushed through a slit which the female gnaws through the pod. This species will oviposit on dry beans, peas, and other grain, and will continue to breed for many generations in stored beans and peas. SERIES VII.— THE RHYNCHOPHORA* The six families included in this series constitute a well-marked division of the order, which has long been known as the Rhynchophora or snout-beetles. These names were suggested by the fact that in many of these insects the head is prolonged so as to form a snout or beak; but it should be remembered that, while these names are very appropriate for a large part of this series, in some members of it the head is not thus prolonged. This is especially true of the last twa *Rhynch6phora: rhynchos (New Latin), snout; phoros {i:ra do not entirely cover the abdomen, and each is separately rounded at the tip. Only five species are known from this country; all of these belong to \he germs Attelabus . The females pro- vide for their young in a very remarkable way. They make compact thimble-shaped rolls from the leaves of trees (Fig. 660), and lay a single egg in each. The larvae feed on the inner parts of these rolls, and when full-grown enter the ground to transform. Sometimes these rolls are found hanging by a narrow piece to the leaf from which they were made, and sometimes they are found lying on the Fig. 660. ground separated from the leaf. The subfamily Cyladin^ is represented in Florida, Louisiana, and Texas by a single species, the sweet-potato root-borer, Cylas formicd- rius. This beetle is somewhat ant-like in form; this fact suggested the specific name. It is about 6 mm. long; the color of the eltyra, head, and snout is bluish black, that of the prothorax reddish brown. Both larvae and adults bore into the stems and tubers of the sweet potato, and sometimes do very serious damage. This species was formerly included in the Brentidee. The subfamily Otiorhynchin^, or scarred snout-beetles, is one of the larger of the subfamilies of the Curculionidae ; it is repre- sented in our fauna by more than two hundred species. The most distinctive characteristic of these insects is the presence in the pupa state, and sometimes also in recently matured adults, of an ap- pendage on each mandible, and in the adult state of a scar indicating the place from which the appendage has fallen. This scar is on the anterior face of the mandible, and frequently at the tip of a slight process. Many species of this family are beautifully ornamented with scales which resemble in a striking manner the scales on the wings of butterflies. Among \ f the more important species are the following. ^TA^ The imbricated snout -beetle, Epiccerus imhri- ^fiT^ cdtMS, is usually a dull, silvery white beetle with /^^^\ brown markings; but the species is quite variable . /^HH^\ in color. It is represented, somewhat enlarged, in ^^^pnV Figure 661. It is omnivorous, gnawing holes in va- /^^A rious garden vegetables, strawberry plants, and other . fruits. The greater part of the insect is clothed with ^^' ^' imbricated scales, which suggested the specific name. COLEOPTERA 539 Fuller's rose-beetle, Pantomorus fulleri.- — This is an oval, black snout-beetle, lightly covered with dark brown scales, and about 6mm. in length. It attacks roses and many other greenhouse plants. The adults feed on the foliage, flowers, and buds, the larvae on the roots, of its food plants. The strawberry crown-girdler, Brachyrhlrms ovdtus. — This is a dark brown, almost black, snout-beetle, about 5 mm. in length, which often invades dwellings in search of shelter, in the Northern States and Canada. The larva? feed on the roots of the strawberry, cutting them off near the crown. The adults feed on the foliage. In the adult, the hind wings are wanting and the elytra are grown together. The black vine-weevil, Brachyrhinus sulcdtus.- — This beetle is larger than the preceding species, measuring 9 mm. in length; it is black, with small patches of yellowish hairs on the elytra. The larvae destroy the roots of strawberries; and both larvffi and adults infest various greenhouse plants. The subfamily Curculionin^, is represented in our fauna by more than one thousand species, among which are some very destruc- tive pests. In this family there is on the lower side of each wing-cover a strong fold near the outer margin, which limits a deep groove in which the upper edge of the abdomen fits; the mandibles have no scar; the antenna? are usually elbowed, and have a ringed or solid club; the tarsi are usually dilated, with the third segment bilobed and spongy beneath ; in a few cases the tarsi are narrow, but not spinose beneath. The larvcB are soft, white, maggot-like grubs destitute of feet. They feed chiefly on fruits, seeds, and nuts, but all parts of plants are subject to their attacks. In laying her eggs, the female first bores a hole with her snout, then drops an egg into this hole, and finally pushes the egg to the bottom of the hole with her snout. In many species the snout is highly developed for this purpose; sometimes it is twice as long as the remainder of the body. This is well shown in the acorn-weevils and the nut-weevils, which belong to the genus Balaninus. Figure 662 represents Balaninus rectus resting on an acorn; the specimen figured, when found, had her snout inserted in the acorn up to the antennae. Of the closely allied species Balaninus nasicus breeds in hickory-nuts, and Balaninus prohoscldeus in chestnuts. The following are some of the more important Fig- 662. pests belonging to this subfamily: The plum-curculio, Conotrachelus nenuphar. — ^This is the insect that stings plums, often destroying a large portion of the fruit; the larva is also the well-known "worm" of "wormy" cherries. This species is the most destructive insect that infests plums, cherries, and other stone fruits; it also breeds in apple. Its presence in an orchard can be determined early in the season by a peculiar mark it makes when laying its eggs in the young fruit. The female beetle makes an 540 ^A^ INTRODUCTION TO ENTOMOLOGY incision, with her snout, through the skin of the fruit. In this incision she lays a single egg, which she pushes with her snout to the bottom of the cavity that she has prepared. She then makes a crescent-shaped incision in front of the one containing the egg. This last cut under- mines the egg, leaving it in a little flap. The larvse feed within the fruit. In the case of the plums the infested fruit falls to the ground; but not so with cherries. When full-grown the larvae go into the ground to transform. This species infests nectarines, apricots, and peaches, as well as plums and cherries. This insect is fought in two ways: the beetles are jarred from the trees upon sheets in early spring, and destroyed before they have laid their eggs ; they are also poisoned by spraying the trees with arsenate of lead, either alone or combined with a fungicide before the fruit is large enough for them to oviposit in it. The adult beetle feeds upon the foliage, and can thus be poisoned. The apple-curculio, Anthonomus quadriglbhus, infests the fruit of apple, often in company w4th the pliim-curculio. The specific name was suggested by the fact that there are two wart-like projections near the hind end of each wing-cover. The strawberry-weevil, Anthonomus signdtus, infests strawberry, blackberr}', raspberry, and dewberry. The female beetle (Fig. 663) after laying an egg in the flower- p. ,, bud causes it to fall by cutting the pedicel; the larva de- ^^' ^' velops within the fallen bud. The cotton-boll weevil, Anthonomus grdndis, is one of the most serious insect pests known in the United States. • It infests only cotton. The egg is deposited in a young boll, which the larva destroys. The adults also feed upon the young bolls and upon the leaves, doing as much or more damage than that done by the larvae. This species is a native of Central America. It spread through Mexico, and entered Texas about 1890. Since that time it has spread over a large part of the cotton-belt. Ver\^ extensive investigations of this pest have been made by the Federal Government and by several state govern- ments ; and much literature regarding it is available to those interested. The subfamily Calendrin.^. includes the bill-bugs and the grain- weevils, some of which are among our more common snout-beetles. The larvae of the larger species feed upon the roots and bore in the stems of plants, especially grass and corn, while those of the smaller species infest grains and seeds. Most of our larger species belong to the genus Sphenoph- orus; one of these is represented in Figure 664. These are of medium or rather large size, and are often marked in a very characteristic manner by longitudinal elevated bands of darker color; frequently, when collected, they arecoveredwithacoat of clay. Tliey are commonly known as the bill-bugs. One species, Sphenophorus maidis, is an ^^S- 664. important pest of com in the South ; it bores in the tap- root and lower part of the stalk. Most of the beetles hibernate in the corn-stubble, and can be destroyed by pulling out and burning the stubble. I COLEOPTERA 541 Among the smaller members of this subfamily are two exceedingly important pests of stored grains; these are the granar>'-weevil, Calandra grandria, and the rice-weevil, Calandra oryzcB. The rice- weevil is so called because it was first found in rice in India; but it infests various kinds of stored grain; and in the South it is fully as important a granary-pest as is the granary -weevil. The two species are quite similar in appearance; but the granary- weevil is the larger, measuring from 3 mm. to 4 mm. in length; while the rice-weevil measures less than 3 mm. in length, and differs from the granary-weevil in having the elytra marked with four reddish spots. The thorax of the rice-weevil is closely pitted with round punctures; that of the granary -weevil, with sparse elongate punc- tures. The adult female of both of these species gnaws a tiny hole in a kernel of grain and then deposits an egg in it. The larva feeds on the grain, becomes full-grown, and transforms within the kernel. The adult continues the injury begun by the larva, eating out the inside of the kernel. The most effective method of destroying grain-weevils is by the use of carbon bisulphide. The grain is placed in a tight bin or other receptacle, and the carbon bisulphide is poured into a shallow tin pan placed on top of the grain, and then covered with blankets to keep in the fumes. Two or three pounds of carbon bisulphide should be used for each 1000 cubic feet of space. Care should be taken not to go near the bin with a lighted lantern or fire of any kind until after the blankets have been removed and the gas has been dissipated. Family PLATYPODID^ This is a small family, which is represented in our fauna by a single genus. Platypus, of which only five species have been found in America north of Mexico; these are found chiefly in the vSouth and the Far West. Formerly this group was classed as a subfamily of the Scolytidse. It is distinguished from the Scolytidae by the fact that the first segment of the anterior tarsi is longer than the second, third, and fourth together. The form of the body is cylindri- cal (Fig. 665) ; and the head is large, wider than the prothorax. The species of this genus attack many kinds of conifers and deciduous trees. They bore deeply into the heart -wood, making "pin-holes" that often render limiber useless. The eggs are de- posited in the galleries; and the larvae feed on a fungus, which is cultivated by the beetles and is known as ambrosia. In this respect Platypus resembles several genera of the Scolytidae, which also bore in solid wood and feed on ambrosia; Fi?. 665. — Platypus wilsoni, female. (After Swaine.) 542 AN INTRODUCTION TO ENTOMOLOGY all of these are known as ambrosia-beetles. The galleries of ambrosia- beetles are usually blackened by the fungus. See further account of the ambrosia-beetles in the discussion of the next family. Family SCOLYTID^ Fig. 666.— Phthoro- phlceus liminaris. The Engraver-Beetles and the Ambrosia-Beetles The members of the family Scolytidas are mostly of cylindrical form (Fig. 666) and of small or moderate size; some species measure only I mm. in length, but others are much larger, at- taining a length of 6 mm. or more. They are usually brown, sometimes black.and with many the hind end of the body is very blunt, as if cut off. The antennas are elbowed or bent in the mid- dle, and are clubbed at the tip; the tibise are usually serrate; and the first seg- ment of the anterior tarsi is shorter than the second, third, and fourth together. A few members of this family infest herba- ceous plants ; our most important one of these is the following. The clover-root borer, Hyldstinus ohscurus. — This pest was introduced from Europe and has become the most serious enemy of clover, especially red clover and mammoth clover, in New York State and in other sections of the North. It bores in the roots of plants beginning their second year of growth and destroys them (Fig. 667) . Where it is common it is practically impossible to keep fields in clover longer than the second simimer after seeding. In these regions it is the common practice to seed with i^ ''/^ll^li^H' clover and timothy mixed; after the clover iV B Al^H disappears the field becomes a timothy meadow. /^ 'J fl W No practical method of control of this pest has been found. Fig. 667. — Work of do- Most scolytid beetles infest woody plants; ver-root borer. (After among them are some of the most destructive Webster.) enemies of forest -trees, and a few attack fruit- trees. As a rule they are more liable to attack sickly trees, but their injuries are not confined to these. COLEOPTERA 543 The scolytid beetles exhibit two radically different types of habits; and from this point of view they can be grouped into two groups: first, the engraver-beetles or bark-beetles; and second, the ambrosia-beetles or timber-beetles. These two groups, however, do not represent a natural division of the family based on structural characters. The peculiar habits of the ambrosia-beetles are believed to have arisen independently in different parts of the series of scolytid beetles, and in the family Platypodidae as well. The Engraver-Beetles or Bark-Beetles If the bark be pulled from dead branches or trunks of trees, the inner layer and the sap-wood will be found, in many cases, to be ornamented with burrows of more or less regular form. The smoothly cut figures are the mines of engraver-beetles, which are also known as bark -beetles. Many kinds of these engravings can be found, each characteristic of a particular species of engraver beetles. A common pattern is shown in Figure 668. Many figures and detailed descriptions of the burrows of engraver- beetles have been published by writers on forest-insects; among the more important papers on this subject published in America are those by Hopkins ('09) and Swaine ('18), in which can be found references to many other papers. The different species of engraver-beetles vary so greatly in the details of their habits that it is difficult to make generalizations re- Fig. 668. garding them in the space available here. In a common type, the adult beetle, after penetrating the bark, makes a tunnel in the inner layer of the bark or in the sap-wood or in both ; this is known as the egg-tunnel, and may be either simple or branched. In the sides of the tunnel, most species make niches, the egg-niches, in which the eggs are laid. The larva when hatched feeds on the bark or sap-wood or both and thus makes a lateral tunnel. These lateral tunnels made by the larvas often extend parallel in a more or less regular manner, as shown in Figure 668. While most of the engraver-beetles infest forest-trees, the two following species are well-known pests of fruit-trees. 544 AN INTRODUCTION TO ENTOMOLOGY The fruit-tree bark -beetle, Scolytus rugtddsus. — This species in- fests apple, quince, plum, peach, and other stone-fruits. It is some- times called the shot-hole borer by fruit-growers on account of the small entrance holes of its burrows. The adult beetle measures from 2 mm. to 2.5 mm. in length, and is dark brown or nearly black. It infests chiefly sickly trees. The peach-tree bark-beetle, Phthorophlceus limindris. — This spe- cies resembles the preceding in size and habits, except that its injuries are confined chiefly to peach and cherr^^ It can be distinguished from the fruit-tree bark -beetle by the fact that the club of the antennae is lamellate, an unusual feature in this family (Fig. 666). The Ambrosia-Beetles or Timber-Beetles Certain members of the family Scolytidse differ in habits from the engraver-beetles or bark-beetles in a remarkable manner; these are those known as ambrosia-beetles or timber-beetles. Thev are termed Fig. 669. — Gallery of Monarthrum mail in maple. (From Hubbard.) ambrosia-beetles because they cultivate fungi, commonly called am- brosia, upon which they feed; and timber-beetles, because they burrow in the solid wood. The galleries of the ambrosia-beetles can be distinguished from those of other wood-boring insects by the fact that in all of their ramifications they are of uniform size and free from wood-dust and other refuse, and their walls are stained black or brown by the fungus that is grown upon them. The galleries of different species differ in form ; but usually there is a main gallery, which extends deeply into the solid wood and is often branched ; and extending from the sides of the main gallery there are short chambers, termed cradles, in each of which an egg is laid and a larva reared (Fig. 669). In some species, the female de- posits her eggs loosely in the galleries, and the young and old live together in the same quarters. COLEOPTERA 545 The galleries are excavated by the adult beetles. In some species the gallery is started by a single female, in others the males assist the females in this work. The entrances through the bark to the galleries are similar to those made by the bark-beetles and like them are known as "shot-holes." Under favorable conditions colonies may continue their excavations during two or three generations. The fungi upon which these beetles feed are carefully cultivated by them. So far as is known, each species of ambrosia-beetle culti- vates only a single species of fungus, and only the most closely allied species have the same food-fungus. The fungus is started by the moth- er-beetle upon a carefully packed bed or layer of chips. It is probable that some conidia are brought for this purpose from the gallery in which the female w^as developed. The excrement of the larvae is used in some and probably in all the species to form new beds for the propagation of the fungus. In those species in which the larvae are reared in separate cradles, "the mother-beetle is constantly in attendance upon her young during the period of their development, and guards them with jealous care. The mouth of each cradle is closed with a plug of the food-fungus, and as fast as this is consumed it is renewed with fresh material. The larvce from time to time perforate this plug and clean out their cells, pushing out the pellets of excrement through the opening. This debris is promptly removed by the mother and the opening again sealed with ambrosia. The young transform to perfect beetles before leaving their cradles and emerging into the galleries." A detailed account of the ambrosia-beetles of the United States was published by Hubbard ('97), from which I have drawn largely in the preparation of the account given here. While the ambrosia-beetles are chiefly injurious to forest-trees, there are certain species that injure wine and beer casks; and one species, the pear-blight beetle, Anisandrus pyri, sometimes infests the tips of pear and apple branches, causing an injury that is often mistaken for the bacterial disease known as pear-blight. Nearly four hundred species of scolytid beetles, representing many genera, have been described from America north of Mexico. CHAPTER XXIV ORDER STREPSIPTERA* The Stylopids or Twisted-winged Insects The members of this order are small, endoparasitic insects, which prey on other insects. Only the males are winged; in this sex, the fore wings are reduced to club-shaped appendages ; the hind wings are large com- pared with the size of the tiny body , fan-shaped, furnished with radiating wing-veins, and folded longitudinally when at rest. The adult female is larviform and legless. The mouth-parts are vestigial or wanting; the alimentation is probably by osmosis. Both sexes undergo a hyper- metamorphosis. The order Strepsiptera comprises insects that were formerly classed as a family of the Coleoptera, the Stylopidse; for this reason, these insects have been known as the stylopids. Recently since the establishment of the order Strepsiptera, the name the twisted-winged insects, derived from the technical name of the order, has been pro- posed for them; but the old name is less cumbersome, and will prob- ably continue to be used. The stylopids are small insects which live parasitically within the bodies of other insects, chiefly bees, wasps, digger wasps, and certain Homoptera. Their small size and the fact that nearly their entire existence is passed within the bodies of their hosts result in their being rarely seen except by those who are searching for them. During the first stadium the young larvse of both sexes are free, and the adult winged male leads a free existence for a brief period; but only the most skilled collectors are likely to observe these minute creatures during these periods, the only free stages of their existence. The stvlopids are most easily found by examin- ing adult individuals of the species of insects that they infest, in which may be found adult females and male pupae of the parasites. The presence of a stylopid is indicated by the projecting of the head end of the body from between two of the abdominal segments of the host (Fig. 670). Frequently a single host will contain several parasites. A female Polistes with eleven male stylopids has been recorded. If this projecting part of the parasite is a flat disk-like plate, it is the head end of a female ; but if it is the rounded and tuberculate end of a cdindrical body. Fig. 670.— Abdo- it is the head end of the puparium of a male. Adult men of stylo- male stvlopids can be bred bv keeping alive stvlo- pized insect: s, J ■ " \ , • • 1 - i o - 5 stylopids. pized msects contammg male pupae. *Strepsiptera: strepsis {ffTpi^Ls), a turning; pteron {TTTtpdv), a wing. (546) STREPSIPTERA 547 Fig. 671. — Opthalmochliis duryi. (After Pierce. Figure 671 will serve to illustrate the appearance of an adult male stylopid. The more striking features are the flabellate antenna; the large, stalked, com- pound eyes ; the shortness of the pro- thorax and the mesotho- rax, and the great length of the meta- thorax; the re- duction of the fore-wings to club-shaped appendages ; and the large size of the hind wings. The an- tennae of adult males differ greatly in form in the different families of this order. The number of antennal segments varies from four to seven; the third segment is always furnished with a lateral pro- longation, a fiabel- lum, and one or more of the follow- ing segments may or may not be fla- bellate. The compound eyes of adult males are large and more or less stalked. The facets are separated by densely ciliate walls. The mouth-parts are greatly reduced; those of two adult males are represented in Figure 672. The mouth opening is small. The labrum and labium are wanting as distinct parts. In Acroschlsmus bruesi (Fig. 672,0) the mandibles are slender, curved, and scimitar- like; beneath the mandibles are the maxillae; these are two-jointed; the second segment is believed to be the reduced palpus. In Pento- zocera austrdlensis (Fig. 672, b) the mandibles are greatly reduced, but the maxilllary palpi are quite large. The three pairs of legs are similar in form. The tarsi are five- jointed in one family (Mengeidce), and furnished with two claws; Fig. 672. — Mouth-parts of male stylopids: a, Acros- chismus bruesi. (After Pierce.) b, Pentozocera aiistral- ensis. (After Perkins.) 548 AN INTRODUCTION TO ENTOMOLOGY 2d A Fig- 673. — Wing of Paraxenos eberi. (From Pierce, after Saunders.) in the other families they are two- to four-jointed and without claws. The venation of the hind wings is degenerate. There is a variable nirmber of radiating veins, which in the most generalized wings are eight in number. These are sup- posed, by Pierce ('09), to be the eight principal veins of the typi- cal wing, the costa, subcosta, ra- dius, media, cubitus, and the three anal veins, respectively (Fig. 673). The abdomen is composed of ten segments. The adult female is very de- generate in form. That part of the body which projects from the body of the host is the cephalo- thorax, the head and thorax being consolidated into a single disk- like region. The abdomen, which is within the body of the host, is a great sac filled with eggs. The body of the adult female is in- closed in the skin of the last larval instar, which is termed the puparium; but there is no pupal stage in this sex. The postembryonic development of the stylopids is very peculiar. In the adult female the eggs are free in the body cavity, where they hatch. The young larvce are campodeiform and active. As they bear some resemblance to the triungulins of the parasitic blister-beetles, they are termed triungulins by some writers ; but as they do not possess three tarsal claws, this term is inappropriate when applied to them. For this reason the first instar of a stylopid larva is termed a triun- gulinid. The stylopids are very prolific; more than 2000 triungulinids pro- duced by a single female have been counted. This fecundity is doubtless correlated with the uncertainty of any individual triun- gulinid being able to find its proper host. The triungulinids escape from the body of the female through unpaired median genital apertures on the second to fifth abdominal segments. These apertures open into the space between the venter of the female and the puparium, which is termed the brood chamber. The triungulinids escape from this space through a slit in the cephalo- thorax of the puparium, between the head and the prothorax, and then crawl over the body of the host. This is the beginning of the most critical period in the life of the stylopids. For the continued existence of any individual of the brood it must find a larva or a nymph of the particular species that is its proper host. This is doubtless accom- plished in different ways in the different species. Those that infest Homoptera and other insects that do not build nests must wander STREPSIPTERA 549 over the plants on which these insects Hve till they find a nymph of their host species. In the case of stylopids that infest social insects the problem is obviously not so difficult, especially if the triunj^linids leave their host while it is in or near the nest. But those stylopids that infest solitary nest-building species are beset with more serious difficulties. It is believed that parasitized female bees and wasps are so weakened that they do not build nests; hence the triungulinids issuing from them, and from males as well, must attach themselves to other females of the same species in order to be carried to a nest where they can find their appropriate victims. This transfer is probably made in the flowers visited by these insects. When a triungulinid finds a larva or a nyonph of its host species it quickly bores into it, and begins its parasitic life. The most com- plete account of the metamorphosis of a stylopid yet published is that of Xenos vespdrum by Nassonow ('92). An abstract of this author's results is given by Pierce ('09, pp. 47-48) ; the more important features of them are the following. The campodeiform triungulinid grows rapidly after entering the body of its host ; at the first molt it loses its legs and becomes scarabsi- form ; later the body becomes cylindrical. From this point the develop- ment of the two sexes is different. In the case of the females, there are seven larval instars ; in the fifth instar the head and thorax are fused, forming a cephalothorax ; the seventh instar pushes its cephalo- thorax out between two of the abdominal segments of the host ; the skin of this instar becomes the "puparium," in which the adult female is inclosed, and which she never leaves; the adult female is larviform; there is no pupal stage in this sex. In the case of males, the head and thorax of the fifth instar are fused, forming a cephalothorax; the seventh instar is inclosed in the skin of the sixth, and has strongly de- veloped appendages; for this reason it may be termed a prepupa; during the seventh stadium the cephalothorax is exserted between two abdominal segments of the host ; the true pupa is formed within the skin of the seventh instar; the adult male thrusts off the cap of the puparium and emerges as a winged individual. The manner in which the female is fertilized, inclosed as she is in a puparium, has not been determined; it has been suggested that the seminal fluid is discharged into the space between the venter of the female and the puparium, the brood chamber. If this is true, the mobile spermatozoa probably pass from the brood chamber through the genital apertures into the abdominal cavity, where the eggs are massed free. The slit in the cephalothorax of the puparium, through which the triungulinids escape, may serve for the introduction of the seminal fluid into the brood chamber. The order Strepsiptera is well represented in this country. Leng ('20) listsninety-seven American species, and doubtless there are many undiscovered species here. The described American species represent five families and eighteen genera. Students wishing to study the classification of these insects should consult the very complete monographs of the order by W. Dwight Pierce ('09, '11, and '18), and other papers listed in these works. CHAPTER XXV ORDER MECOPTERA* The Scorpion-Flies and Their Allies The winged members of this order have four wings; these are usually long, narrow, membranous, and furnished with a considerable number of cross-veins; the wings are wanting or vestigial in two genera. The head is prolonged into a deflexed beak, at the end of which chewing month-parts are situated. The metamorphosis is complete. This is a small order composed of very remarkable insects. The most striking character common to all is the shape of the head, which is prolonged into a deflexed beak (Fig. 674). The dorsal wall of this beak is composed largely of the greatly elongated clypeus (Fig. 675, A, c); the central portion of the ventral wall is the greatly elongated submentum (Fig. 675, 5, sm) ; and on each side of the submentimi there Fig. 674. — Head and tail of Panorpa. Fig. 675. — Head of Panorpa: A, dorsal aspect; B, ventral aspect; af, antennal foramen; ca, cardo; e, eye; g, gena; /, labrum; Ip, labial palpi; m, mentum; mp, maxillary palpi; mx, maxillae; 0, ocelli; sm, submentum; st, stipes. (After Miyake.) is a greatly elongated stipes of the maxilla, at the distal end of which is borne the maxillary palpus. The mentum and labium are com- paratively short; and from each side of the labitmi there extends a labial palpus. The mandibles are rather small and slender and are articulated to the apex of the beak, and can cross freely. The antennas are long, very slender, and many-jointed. The compound eyes are moderately large. There are usually three promi- nent ocelli, but these are wanting in Merope and in Boreus. *Mecoptera: mecos {fifjKoi), length; pteron (nTepdv), a wing. (550) MECOPTERA 551 The prothorax is small ; the mesothorax and metathorax are large. The legs are long and slender; the tarsi are five-jointed; in some genera there are two tarsal claws, in others only one. The wings are membranous, and are usually long and narrow, but in two genera, Notiothauma and Merope, the representatives of which are ver\' rare insects, the wings are comparatively broad. In the genus Boreus the wings are vestigial or wanting. The type of the venation of the wings in this order is well shown by the wings of Panorpa (Fig. 676). In the species figured here, the Fig. 676. — Wings of Panorpa. number and arrangement of the wing-veins in the fore wings is that of the hypothetical primitive type, with the addition of a considerable number of cross- veins, and an ac- cessory vein on vein R2. The same is true of the hind wings except that each of the branches of cubitus anasto- moses with the ad- jacent vein; that is, vein Cui anasto- moses with vein M, and vein Cu2 with the first anal vein Fig. 677. — Base of hind wing of Panorpa. 552 AN INTRODUCTION TO ENTOMOLOGY (Fig. 677). For further details regarding the venation of the wings in this order, see "The "Wings of Insects" (Comstock '18 a). The metamorphosis is complete. The larvae are caterpillar-like, with three pairs of thoracic legs and with or without abdominal pro- legs. The pupae are exarate, that is, the wings and legs are free, as in the Coleoptera and Hymenoptera. This order is represented in our fauna bv six genera; these can be separated by the following table : A. With well-developed wings. B. Wings long and narrow; ocelli present. C. Tarsi with a single claw, and fitted for grasping Bittacus CC. Tarsi with two claws, and not fitted for grasping. D. Tarsal claws toothed Panorpa DD. Tarsal claws simple Panorpodes BB. Wings comparatively wide, with many cross-veins extending from the subcosta to the costa; ocelli wanting Merope AA. Wings wanting or imperfectly developed. B. Without ocelli; small insects, less than 6 mm., in length BoREUs BB. Ocelli present; body about 20 mm., in length Apterobittacus Panorpa or the scorpion -flies. — The most common members of this order belong to the genus Panorpa, of which there are nearly twenty described North American species. Figure 678 represents a female of this genus. In our more common species the wings are yellowish, spot- ted with black. The males of this genus are remarkable for the peculiar form of the caudal part of the abdomen (Fig. 679). This at first sight reminds one of the corresponding part of a scorpion, and suggested the common name^cor- pion-flies for these insects. But in reality the two are very different; the last segment of the male Panorpa, instead of ending in a sting, like that of a scorpion, is greatly enlarged and bears a pair of clasping organs. The tarsal claws are toothed (Fig. 680, a) . The adults are found resting on the surface of foliage of rank herbage growing on the banks of shaded streams and in damp woods where there is a luxuriant undergrowth of herbaceous plants. They feed on dead or injured insects and upon fruits ; it appears that they rarely if ever capture living prey. Fig. 678.— Paw - orpa, female. Fig. 679. — Abdomen of Panorpa rufescens. Fig. 680. — a, fore leg of Pan- orpa; b, last two segments of tarsus of Bittacus, ap- posed; c, last three seg- ments of tarsus of Bittacus. MECOPTERA 553 The females lay their eggs in crevices in the earth. The larvae are caterpillar-like in form; they have three pairs of true legs and eight pairs of abdominal prolegs; and the body is armed with promi- nent spines (Fig. 68i) ; the larvae are carnivorous. The transformation takes place in a cell in the ground. Panorpodes. — The members of this genus resemble Panorpa in general appearance, and as in that genus the abdomen of the male is furnished with a pair of clasping organs; but in Panorpodes the tarsal claws are simple. Only two species have been described from North America. These are not common; and but little is known regarding their habits. Merope. — This genus includes only a single known species, Merope tuber. This is an exceedingly rare insect. In this genus the wings are comparatively wide (Fig. 682); and there are many cross-veins ex- tending from the subcosta to the costa. I have figured the venation of the wings in "The Wings of Insects" (Comstock '18 a). The ocelli are wanting. The abdomen of the male is terminated by a pair of long, stout forceps. This is prob- ably a nocturnal insect as it is attracted to lights at night. Its life-history is un- known. Boreus. — This ge- nus includes small Me- coptera, our species Fig. 681. -Larva of Fig. 682.-Merope tuber, slightly measunng from 2.5 enlarged. (Photographed by mm. to 5 mm. m J. G. Needham.) length, which are of- ten found on snow in winter. The wings of the female are vestigial or wanting; those of the male, imperfectly developed. The ocelli are wanting. The female has a long, protruding ovipositor, which in some species is nearly as long as the abdomen. The larva differs from that of Panorpa in lacking the abdominal prolegs. The pupa state is passed in an earthen cell in the ground. Four American species have been described, two from the East and two from the West. BUtacus.— Insects belonging to this genus have long, narrow wings, long legs, and a slender abdomen. They resemble crane-flies very closely when on the wing, but can be distinguished by the presence of two pairs of wings. They are almost as common as Panorpa rufes- cens, first instar. (After Felt.) 554 .47V INTRODUCTION TO ENTOMOLOGY Panorpa; and, like the scorpion -flies, are found among rank herbage growing on the banks of shaded streams and in damp woods where there is a luxuriant undergrowth of herbaceous plants. When at rest, they do not sit on the surface of foliage as does Panorpa, but hang suspended, by their front legs, from some support (Fig. 683). The members of this genus capture and feed upon living insects. They are enabled to capture their prey by means of their curiously modified tarsi, the last two segments of which are armed with teeth, and the last segment can be folded back against the next to the last segment. In this way there is formed an efficient grasping organ (Fig. 680, b, c). It is an interesting fact that, while in other predacious insects the fore legs are the chief organs of prehension, in Bittacus the hind legs are used for this purpose fully as often as the others, especially when the Bittacus is hanging suspended by its fore legs and captures an insect that comes within reach of it. Nine North American species of Bittacus have been described. ApterobUtacus. — This genus includes a single known species, ApterobUtacus apterus, found in California. It re- sembles Bittacus except that the wings are completely wanting. A review of the species of the Mecoptera of America north of Mexico was published by James S. Hine (Hine '01). Fig. 683.— Natural position of Bitta cus. (From Felt.^ CHAPTER XXVI ORDER TRICHOPTERA* The Caddice-Flics The members of this order have four wings; these are membranous and usually more or less densely clothed with long, silky hairs. In the more generalized members of the order, the venation of the wings corre- sponds closely to that oj the hypothetical primitive type with but few or no accessory veins; in some of the more specialized members of the order, the venation of the wings is reduced. The mouth-parts of adults, except the palpi, are vestigial. The metamorphosis is complete. The caddice-flies are moth-like insects, which are common in the vicinity of streams, ponds, and lakes, and are frequently attracted to lights at night (Fig. 684). The larvae of these insects are the well-known caddice- worms ; these live in the water, and most of them build cases about their bodies. In the adult insect, the body-wall is soft, being membranous or at the most parch- ment-like, and is thickly clothed with hairs. Fig- 684.^A caddice-fly. The two pairs of wings are membranous and usually more or less clothed with long, silky hair. The fore wings are denser than the hind wings and are often slightly coriaceous; in a few forms the wings are naked. The hind wings are shorter than the fore wings; but they are usually broader; this is due to an ex- pansion of the anal area of the hind wings. In a few species the hind wings are reduced so that they are smaller than the fore wings; in one species the female is apterous, and in another the wings of the female are vestigial. When not in use the wings are folded roof-like over the abdomen. The posterior lobe of the fore wings is speciahzed as a fibula, which is well developed in the more generalized forms, as Rhyacophila, but more or less reduced in the more specialized genera. The costal border of the hind wings is furnished with hamuli in some forms, as in the Leptoceridae and some Hy dropsy chidse. In the more generalized forms the venation of the wings cor- responds quite closely with the hypothetical primitive type; this is well shown by the wings of Rhyacophila fuscula (Fig. 685). The more important modifications of this type shown by the wings of Rhyacophila are the following : in the fore wing the tips of the second anal vein and two of the branches of the third anal vein coalesce; the subcosta bears an accessory vein; this, however, is unimportant; accessory veins borne by the subcosta exist in only a few genera of this order; the coalescence of veins Cu and ist A at the base of the *Trich6ptera: trichos (Opli, rptx^s), the hair; pteron {irTepdv), awing. (555) 556 AN INTRODUCTION TO ENTOMOLOGY wing; and the formation of a serial vein consisting of the base of media, the posterior arculus (pa), and the distal part of vein Cu. In the hind wings, media has been reduced to a three-branched condition by the coalescence of veins M3 and M4. In the more specialized members of this order the specialization of the preanal area of the wings is always by reduction. In the anal area of the hind wings the specialization is in some cases by addition, resulting in a broadly expanded anal area; in others it is by reduction. The head is small ; the antennse are setaceous, and frequently several times as long as the bod}'; the compound eyes are usually ?d A ,st A C112 ^"^ Fig. 685. — Wings of Rhyacophila fuscula. small and with small facets; the ocelli are either present or absent; when present they are three in nimiber; the mandibles are mere tubercles at the base of the labrum ; the maxillae are small, and ordi- narily furnished with an obtuse maxillary lobe; the maxillary palpi are well-developed, and furnish characters which are much used in classification; the labium is usually well-developed, and bears three- jointed palpi. The legs are long and usually slender; the coxse are very large; the femora are long and slender, and generally without spines; the tibiae are also long and slender; the tarsi are always five-jointed. The tibiae and tarsi are often furnished with black or brown, some- times yellow, spine-like setae. In addition to the spine-like setae, the tibiae bear movable spurs either at the apex only, or also at some TRICHOPTERA 557 Fig. 686. — Two egg-masses of caddice-fliesro, Phryganea interrupta; h, Tricenodes sp. (From Lloyd.) distance before the apex ; these are larger than the spine-hke setae and are usually differently colored. The number of these spurs is much used in classification. The eggs of caddice-flies are round or slightly oval in form. They are laid either in water or upon objects above water from which the larvae when hatched can find their way into the water. Some species that lay their eggs in water descend below the surface in order to glue their eggs to some submerged support. So far as is known, all species of caddice-flies, except some of the RhyacophilidcC, lay their eggs in a mass enveloped either in a cement, by which the mass is glued to some support, or in a gelatinous covering. In the latter case, the covering absorbs water and thus increases greatly in size. The form of the gelatinous mass and the arrangement of the eggs within it are often characteristic of the species (Fig. 686). The larv£E of most caddice-flies, the caddice-worms, are somewhat caterpillar-like (eruciform) in shape (Fig. 687) ; but some are more nearly campodei- form. Those that are eruciform build a portable case in which they live; most of the campodeiform larva; do not build port- able cases. In the eruciform larvs the head is bent down, as in a caterpillar; in the campodeiform larvae the head is hori- zontal, the mouth-parts projecting for- ward. Both types differ from the cater- pillars in having only one pair of prolegs, the anal prolegs. These are each furnished with a chitinous hook. The mouth-parts are fitted for chewing. The thoracic legs are well developed. In the case-building forms, the first abdominal segment often bears three tubercles, one dorsal and one on each side; these are the "spacing- humps," and serve to keep a space between the insect and its case for the free circu- lation of water for respiration. In several families the larvae possess abdominal tra- cheal gills; these are filamentous and are sometimes branched; they arise singly or in tufts. With the exception of a single European genus, Enoicyla, all caddice- worms are aquatic. Most caddice-worms build portable cases in which they live and which they drag about whenever they go, projecting only the front Fig. 687. — A caddice-worm, Anabolia nervosa: A, larva extracted from its case; B, one of the dorsal spaces of the abdominal seg- ments more strongly mag- nified. (From Sharp.) 558 AN INTRODUCTION TO ENTOMOLOGY end of the body and the legs from the case when they travel. The cases of different species differ greatly in form and in materials used in their construction; but silk is used in building all of them. This silk, like that of caterpillars, is secreted by modified salivary glands and is emitted through an opening in the labium; but in most cases it is not spun into a thread, but is poured forth in a glue-like sheet upon the objects to be cemented together; sorae species, however, build nets of silken strands. Some caddice-worms build their cases entirely of silk; but most of the case-building species use other materials also; these may be grains of sand, small stones, bits of wood, moss, or pieces of leaves; and some species fasten shells of small mollusks to their cases. The materials used are glued together with silk; and the case is lined with silk, so as to form a suitable protection for the soft abdomen. Ex- amples of different types of cases are figured later. When the caddice-worms are full-grown they do not leave the water to transform, as do nearly all other aquatic larvee, the pupae being as truly aquatic as the larvae. Some of the case-building species change the form and material of their cases at this time; and nearly all of them partly close their cases so as to keep out intruders and silt ; but usually provision is made for the ingress of water for respiration. Some species merelv cement a stone or grains of sand over each open- ing of the case; others build a silken lid with a slit in it; and still others build a silken grating in each end of the case. Frequently caddice-worms leave the open water in which the larval life has been spent and seek some more secluded place in which to transform, such as crevices in bark or among roots, or they may burrow into wood or into the soil. The pupas are of the exarate type, that is, the wings and legs are free (Fig. 688). Some pupae have tracheal gills, others do not; this, however, is not correlated with the presence or absence of tracheal gills in the larva; tracheal gills may be present in either of these stages and absent in the other. In the case of those caddice-flies that emerge from rapidly flowing water, as the net-building species, the wings expand instantly when the in- sect reaches the surface of the water and are then fitted for flight; it is evident that if much time were required for the wings to become fit for use, as is the case with most other insects, the wave succeeding that which swept the insect from the water would sweep it back again and destroy it. The Trichoptera can be regarded as beneficial insects, as the larva? form an important element in the food of fishes, and especially of the brook trout. Sometimes in cities near rivers, the adults are annoying on account of the great numbers of them that are attracted to lights. Fig. 688.— A, pupa of Phryganea pi- losa. (After Pic- tet.) B, mandi- bles of pupa of Molanna angusta- ta. (From Sharp.) TRICHOPTERA 559 This order includes thirteen families, all of which are represented in North America. Nearly four hundred species have been described from this region. Among the more important works on the classification of these insects are McLachlan ('74-80), Ulmer ('07), andUlmer ('09). This last -mentioned work is especially important for its accounts of the early stages of these insects. The latest and most extended work on the life-histories of North American caddice-worms is that by Lloyd ('21). In this work there is a list of the more important papers on this subject, which, for this reason, need not be enumerated here. This monograph by Mr. Lloyd has been of great assistance to me in the preparation of the following account of the habits of representatives of the different families. A monograph treating of all stages of North American Trichoptera has been prepared by Dr. Cornelius Betten and is to appear as a bulletin of the New York State Museum. The following table of families is copied from Needham ('18). TABLE OF FAMILIES OF THE TRICHOPTERA For the Classification of Adults A. Micro-caddice-flies; very small, moth-like, hairy, the fore wings bearing numerous erect clavate hairs; the marginal fringe of the wings longer than their greatest breadth; form of wings narrowly lanceolate; antenna; rather stout and not longer than the fore wings, p. 561 Hydroptilid^ AA. Larger caddice-flies, with broader wings; marginal fringes never as long as the wings are broad; antennae usually longer than the fore wings. B. Maxillary palpi five-jointed. C. Last joint of the maxillary palpi simple, and not longer than the other joints. D. Ocelli present. E. Front tibiae with two or three spurs, middle tibiae with four spurs. F. The first two joints of the maxillary palpi short and thick, the third joint much longer and thinner, p. 560 . . . .Rhyacophilid^ FF. The second joint of the maxillary palpi much longer than the first. Females, p. 564 Phryganeid^ EE. Front tibiffi with a single spur, or with none; middle tibiae with only two or three spurs. Females, p. 568 Limnophilid^ DD. Ocelli wanting. E. A closed cell in the principal fork of the median vein in the fore wings, p. 567 Calamoceratid.^ EE. No closed cell in the median fork. F. A closed cell in the first fork of the radial sector. G. Both branches of the radial sector forked. H. Veins R, and R2 confluent apicallyor connected by an apical cross-vein in the fore wing. Females, p. 567..0dontocerid^ HH. Veins Ri and R^ not connected apically. p. 569 Sekicostomatid^ GG. Only the anterior branch of the radial sector forked, p. 566. Leptocerid^ FF. No closed cell in the first fork of the radial sector, p. 566. . Molannid^ CC. Last joint of the maxillary palpi usually much longer than the others, twisted, and divided imperfectly into subsegments. D. Ocelli present, p. 563 Philopotamid/E DD. Ocelli wanting. E. Front tibiae with three spurs, p. 563 PoLYCENTROPiDiE EE. Spurs of front tibiae fewer than three. 560 AN INTRODUCTION TO ENTOMOLOGY F. Anterior branch of the radial sector in the fore wings forked. p. 562 Hydropsychid^ FF. Anterior branch of the radial sector simple, p. 564 PSYCHOMYID^ BB. Maxillary palpi with fewer than five joints. C. Maxillary palpi with four joints; ocelh present. Males, p. 564... Phryganeid.^ CC. Maxillary palpi with two or three joints. D. Maxillary palpi filiform, with cylindric smooth joints; fore tibiae with a single spur. Males, p. 568 Limnophilid^ DD. Maxillary palpi hairy or scaly, appressed against and often covering the face; fore tibias with two spurs. Males, p. 569. .Sericostomatid^ TABLE OF TRICHOPTEROUS LARV^ The following table will aid in the classification of caddice-worms. It is based on a more detailed table of the family characters of trichopterous larvae given by Lloyd ('21). A. Anal prolegs not fused in median line to form an apparent tenth abdominal segment. B. Abdomen much wider than the thorax, p. 561 Hydroptilid^ BB. Abdomen not much wider than the thorax. C. Dorsal surface of the ninth abdominal segment with a chitinous shield. p. 560 Rhyacophilid^ CC. Dorsal surface of the ninth abdominal segment without a chitinous shield. D. Tracheal gills present, branched, p. 562 Hydropsychid^ DD. Tracheal gills absent. E. Labrum entirely membranous, white, p. 563. .Philopotamid.^ EE. Labrum entirely chitinized. F. Frons long, extending back to the caudal margin of the head. p. 563 Polycentropid^ FF. Frons normal, p. 564 Psychomyid^e AA. Anal prolegs fused in median line so as to form an apparent tenth segment. B. Dorsal surface of the labrum with a row of twenty or more heavy bristles. p. 567 CALAMOCERATID.E BB. Dorsal surface of labrum normal. C. Labrum much longer than broad, p. 567 Odontocerid^ CC. Labrum broader than long. D. Metanotum with three pairs of plates, p. 568 Limnophilid^ DD. Metanotum soft. E. Mesonotum soft or with one pair of minute plates, p. 564 Phryganeid^ EE. Mesonotum chitinized. F. Femur of hind legs divided into two segments or apparently so. p. 566 Leptocerid^ FF. Femur of hind legs not divided. G. p. 569 Sericostom.\tid je. GG. p. 566..: MOLANID^ Family RHYACOPHILID^ The larvse are campodeiform ; they Hve in rapidly flowing streams with stony bottoms. The American species of this family represent two subfamilies. The members of one subfamily, the Rhyacophilinas, TRICHOPTERA 561 do not build cases, but crawl about naked beneath stones seeking their food; they feed on small larva.^ and filamentous alga?. The larva of our most common species, Rhyacophila fiiscula, when full-grown enters a crev- ice between two large stones and builds a wall of pebbles about itself; this wall is ce- mented in place with silk; and the chamber thus inclosed is much larger than the insect (Fig. 689); it then spins a parchment -like cocoon about its body, within which it trans- forms. The making of a co- coon is a family characteris- „. , , , , ^ „, .,•,,■,,• tic of the RhyacophiHd.;only ^■^''S.^-'ch'^Se^expS^bfli^t^i'ol afewothercaddice-wormsspm the stone beneath which is was. (From cocoons. Needham and Lloyd.) The members of the subfamily Glossosmatiuce build cases out of sand or small stones. Our best- known species is Glossosoma ameri- cdna, the habits of which are de- scribed by Lloyd. Figure 690 repre- sents a dorsal and a ventral view of the case. The larvse live singly on the stones of the stream's bottom; but before pupating they congre- gate in dense colonies on the sides and bottoms of stones, with their cases placed edge to edge, sometimes one on top of another. At this time the floor of the case is cut away and the rim of the cup-like roof is glued to the supporting rock. Fig. 690. — Case of Glossosoma ameri- cana: a, dorsal view; h, ventral view. (After Lloyd.) Family HYDROPTILID.^ The Micro-Caddice-Flies This family is composed of minute caddice-flies, which resemble tineid moths in appearance. The larvee are found in both quiet water and rapid streams, and often occur in very great numbers. They build cases which differ in form in the different species, but are usually fiat; some are elliptical, some flask -like, and others kidney-shaped; all are open at both ends; they are much larger than the larvae. They are usually composed entirely of silk ; but in some species grains of sand or minute bits of vegetable matter are used. ''Agraylea 562 AN INTRODUCTION TO ENTOMOLOGY decorates the parchment with filaments of Spirogyra, arranged concentrically over the sides in a single ex- ternal layer." (Needham and Lloyd.) When moving about, the larva usually drags its case on one edge. There is one species, Ithytrichia ccnfusa, which cements its case firmly to rocks in flowing water. These cases are common ; they are parch- ment-like, elliptical, with a small opening at each end (Fig. 691, 2), and measure from 5 mm. to 6 mm. in length. They are incomplete, being ce- mented along the edges to the rock, with no floor below the larva. The larva is very remarkable in form (Fig. 691, i). When feeding, it protrudes the narrower part of its body from its case and gathers food from the surface of the rock; the expanded abdominal segments are much wider than the openings in the case. Family HYDROPSYCHID^ The famil v H vdropsvchidas of the older authors Fig. egi^-^mytrickmi^^^ ^^gg^ divided into four families by Ulmer,— 2'' case. '' (After Hydropsychidae, Philopotamidas, Polycentropidae, Lloyd.) and Psychomyidae. It is to this group of families that the net-spinning caddice-worms belong. The best -known of these are species of the genus Hydropsyche, the nets of which have been described by many writers. The larvae of Hydropsyche live only in rapid streams and on the wave-beaten shores of lakes. They are campodeiform, and do not build portable cases, but live in tubes composed of silk and debris, and fastened permanently in place; sometimes they establish them- selves in old worm-holes in submerged wood. The most striking feature in their habits, however, is the fact that each one builds a net for the capture of its food. This net is built adjacent to the tube in which the larva lives; it is funnel-shaped and has at its down- stream end an opening in which is built a strainer. This is a beautiful object, consisting of two sets of regularly spaced strands of silk extending across the opening at right angles to each other (Fig. 692). These nets are often built in crevices between stones; but fully as often they are built up from a flat surface, as on the brink of a waterfall. In this case they are in the form of semi- elliptical cups, which are kept distended by the current. Much of the coating of dirt with which rocks in such places are clothed in summer is due to its being caught in these nets. Sometimes when Fig. 692. — Net of Hydropsyche. TRICHOPTERA 563 the net is built up from a horizontal surface its sides are supported by bits of wood. Algae, larvae, and other small animals in the water that passes through the net are held by the strainer and thus made avail- able to the caddice-worm for food. When the larva is full-grown it surrounds itself with a case composed of fine sand or gravel in which to transform; this case is firmly cemented in place, and, in some species at least, is closed at each end with a silken grating. The instantaneous flight of the newly emerged adult when it reaches the surface of the water has been referred to on an earlier page. Family PHILOPOTAMID^ The larvae of members of this family are campodeiform and live in rapid streams. Several of them were studied by Miss Alice A. Noyes, but as yet an account of only one of them, Chimarrha aterrima, has been pubHshed (Noyes '14). This larva spins a delicate silken net resem- bling in shape the finger of a glove. The average size of the net of a growing larva is about 25 mm. long and 3 mm. wide. The nets are rarely found singly, but are generally placed five or six in a row (Fig. 693) ; sometimes they occur in great num- bers, completely covering the stones with a thin, flocculent mass of dirty silk. There is a large opening at the end of the net facing the current, t^- ^ m . r /-, • 1 11 • . .1 1 • J i'lg- DQ.^- — Nets 01 Lhtmarrha aterrt- and a smaller openmg at the hmd %^a,natma\ size. (From Noyes.) end. The nets are fastened m place at the entrance; the rest of the sac floats freely, and is kept distended by the current. The net serves both as a hiding-place for the larva and as a sieve through which the flowing water is strained; the larva feeding on the organic particles that are entanded in it. The full-grown larva covers itself with an irregular dome of pebbles in which to transform, and spins about its body a delicate cocoon. Family POLYCENTROPID^ The larvae are campodeiform; they usually live in flowing water, but some are found in standing water. They do not build portable cases, but make fixed silken tubes or nets. The nets of several European genera have been described; for an abstract of these accounts, see Noyes ('14). The nets of American species have been described by Clark ('91), Vorhies (09), Noyes ('14), and Lloyd ('21). 564 AN INTRODUCTION TO ENTOMOLOGY "Several species of the genus Polycentropus live in still or slowly flowing water with sandy or muck bottoms. These larvas spin sub- terranean tubes of silk which sometimes reach lo centimeters in length. Often the tubes have one or more branches, and al- ways they contain a bulb- ous swelling near the middle in which the larva probably rests, and in which pupation takes place. In natural posi- tion the tubes are be- neath the ground, except about half an inch which projects upward into the water." (Lloyd.) Two quite different larval tubes of members of this family are described and figured by Miss Noyes. One of these is represented in Figure 694. This tube is found on the under side of stones, and is fastened along its entire length. "It is 21 mm. long and 5.5 mm. wide, with an expanded opening at either end. Connected with each opening and along either side is a mass of tangled, silken threads, about 20 mm. square and loosely attached to the stone. This tangled mass may float partially over the tube and so obscure it." "I have never observed the larvfe feeding, but do not doubt that Mayfly nymphs and chironomid larvae become entangled in the meshes as they crawl about over the stones, for remains of these forms are abundant in the stomach contents." (Noyes.) Fig. 694. — Dwelling of Polycentropus sp. (From Noyes.) Family PSYCHOMYID.^ The larvffi are campodeiform. There is no account of the life- history of any American species published. The European species do not make portable cases; but the larvae live on stones in long, loosely-spun galleries of silk and sand grains. They are found mostly in swift water, but also inhabit ponds and lakes. Family PHRYGANEID^ The larvce are caterpillar-like, and usually live in standing water in which plants are growing, or in slowly moving streams of spring water. They make portable cases which are very regular in form. As these larva? live in quiet water, they can be fed and reared in aquaria where their habits can be easily observed. The most extended account of the immature stages of these insects is that of Lloyd ('21), from TRICHOPTERA 565 Fig, which the following brief notes are compiled. This author discusses three species of Neuronia-a.nd three species of Phryganea. Neiirdnia.- — The larvae are found in slowly moving streams of spring water; rarely the\' are found along the edge of the large, warm streams where cool seepage enters. One species was found in a pond. The cases are cylindrical tubes of thin, rectangular bits of leaves arranged in a series of rings (Fig. 695, a). In the cases of old larva: the rings are neatly fitted without overlapping; young larvae sometimes leave the hind ends of the leaf-fragments pro- truding in long strips. Unlike other caddice-worms, these larvae often abandon their cases and wander naked through the water. The form of the case indicates that they are not long retained ; their uniform di- ameter proves that they are con- structed more rapidly than the di- ameter of the larva increases. When the season for pupation draws near, the larva? of Neuronia burrow into wood, or wedge themselves beneath bark, or in crevices, or, if the stream bottom be of clay, they may burrow into the soil. When entering the soil the larva stands on its head, with its case perpendicular to the bottom, and slowly enters, dragging its case with it. Phryganea. — The larvae live in ponds; they dwell, for the most part, among submerged plants above the bottom of the pond; hence they can be taken with a water net. They never abandon their cases as do the larvas of Neuronia. The case is a straight tube com- posed of narrow strips of leaf arranged in spiral form around the circumference of the case (Fig. 695, b). Young larvas often fail to cut the leaf-fragments used in the construction of the case into the rectangular form seen in the cases of old larvse ; but the bases of the untrimmed fragments are arranged in a spiral (Fig. 695, c). In pre- paring to pupate, the larvas leave their abode among living plants and travel to some submerged log or chunk of wood and burrow into it until the last bit of the case is concealed. This operation sometimes requires several days of labor. When sufficient depth is reached, the larva spins a silken mesh across each end of the case. The larva of a species of Tricenodes of the family Leptoceridae makes a case somewhat similar to that of Phryganea; this is described in the account of that family. 695. — Cases of phryganeids: case of Neuronia postica; b, case of old larva of Phryganea vestita; c, case of young larva of Phryganea vestita. (After Lloyd.) 566 AN INTRODUCTION TO ENTOMOLOGY Family MOLANNID^ Fig. 696. — Case of Mo- lanna. (After Lloyd.) The only members of this family the larvae and cases of which have been described in this country belong to the genus Molanna. The larvce are found on sandy bottoms of streams and of lakes. The cases have been figured by several writers, and are very char- acteristic in form (Fig. 696). The case is made of grains of sand, and, has .on each side an ex- tension, and at the head end a dorsal hood, which completely protects the larva when crawling or feeding. Family LEPTOCERID^ The larvs are caterpillar-like, and make portable cases. Most species live in standing water, as in lakes, ponds, and the bays of streams; but some are found in flowing water and on wave-beaten shores of lakes. The cases made by the different species differ greatly in form and in the materials used in their con- struction. Among the better-known species are the following. Setodes grandis. — The larva of this species lives among aquatic vegeta- tion in ponds and lakes. Its case is composed en- tirely of silk, and is translucent, so that the body of the larva can be seen through it. It is cylindrical, tapering, and slightly curved (Fig. 697, a). When ready to pu- pate, the larva fastens its case to th e stem of a plant with a band of silk, and closes the anterior end of the case with a silken membrane, in which there is a central slit for the ingress of water. Leptocerus dncylus. — The larva is found on stones in the riffles of streams and on the stones of wave-beaten lake shores. Itmakesacaseof grains of sand. The larvas studied by Lloyd Fig. 697. — Cases of leptocerids : a, case of Setodes grandis; b, case of Leptocerus ancylus; c, case of Mystacides sepulchralis; d, case of Tricenodes. (After Lloyd.) TRICHOPTERA 567 at Ithaca, N. Y., made cases in the form of curved cornucopias (Fig. 697, h); those found in Wisconsin by Vorhies, who first described the species, make a case with decided lateral flanges and a hood that completely covers the head of the larva. Mystdcides sepulchrdlis .■ — The larva of this species and its case were described by Lloyd. It was found in ponds and in slow deep pools of creeks; it lives among the rubbish on the bottom. The case (Fig. 697, c) consists of a slightly tapering tube of sand or of minute fragments of bark, lined with silk; it measures about 12 mm. in length. On opposite sides are fastened pine needles, or grass stems, or slender sticks, which extend beyond both ends of the case. Before pupation a sheet of silk with a minute perforation in the center is spun across each end of the case. Triccnodes. — The larvse of species of this genus live in ponds and bays of creeks among branches of submerged plants. They are able to swim rapidly from place to place through the open water. The case (Fig. 697, d) is made of thread-like fragments of leaves arranged in a spiral. It resembles in form the case of Phryganea (Fig. 695, 6), but is much smaller and more flexible, and the leaf-fragments are much narrower. Family ODONTOCERID^ The immature stages of only a single species belonging to this small family have been described in this country; the following notes re- garding this species are from Lloyd ('21). Psilotreta frontalis. — The larvse were found in up- land streams and were confined to the riffles and the portions of the streams with stony bottoms. The case of the mature larva (Fig. 698) is a slightly curved cylinder made of sand ; cases of immature larvas differ only in being tapered toward the caudal end. The case of the pupa has a fiat pebble set neatly within the aperture at each end. All spaces around these "stones are tightly closed with heavy silk, leaving no apertures for the circulation of water; this is an unusual feature in the case-building Trichoptera. During their early life the larvae are free-moving, crawling separately over the bottom of the stream. But in the early spring, just before pupation, the larvae develop a remarkable gregarious habit. Almost all of the larvae within certain areas of the stream congregate on the sides of a few selected stones in such numbers that their cases are sometimes piled one on top of another to the depth of an inch or more, while other stones in the region are entirely uninhabited. The cases are always placed parallel to each other, with their cephalic ends directed toward the surface of the water. Family CALAMOCERATID^ This is a small family of which only one American larva is known. The habits of this species have been described by Lloyd, from whose accounts I quote. 568 AN INTRODUCTION TO ENTOMOLOGY Ganonema americdna. — The larvae were found abundant in alder- bordered streams. The cases made by this species differ greatly from those of other described American caddice- worms. The case is made of a single piece of wood or bark or a twig; this is hollowed from end to end, and lined with silk. Although common, they are most inconspicuous among the debris on the bottom of the stream. Figure 699 represents a case with the silk tube cut away, except around the larva. Family LIAINOPHILID^ The larvae of members of this family are cater- pillar-like, and are found in a great variety of aquatic situations, but especially in ponds and slow- moving streams, even in those that become dry during the droughts of summer; a few, Neophylax, are found in rapids. Many of the larvae that live in quiet water can be kept in aquaria. The cases made by different members of this family differ greatly in form and in the materials used in their construction; in some species the case made by an old larva differs greatly from that made by it when young. In several genera of this family the larvae make cylindrical cases of sticks and fragments of bark, which are very irregular in form; one of these is represented by Figure 700. To this family belong the larvae that build cases of the "log-cabin type"; these are composed of sticks or of pieces of grass placed cross- wise of the case (Fig. 701) . A case closely resembling this in plan but differing in appearance is made of bits of moss. Among the larvae that change the form of their case when full- grown is Limnophilus combindtus, which is described by Lloyd. Dur- Fig. 699.-Caseof Ganonema a me r icana. (After Lloyd.) Fig. 700. — Case of limnophilid larva. Fig. 701.— Log- cabin type of ing early life this larva frequents the grass and sedges that fringe the edges of streams, and makes a case of the cross-stick or log-cabin type. When the time for pupation draws near, it migrates away from the grassy area and makes a case differing entirely in appearance from TRICIIOPTERA 569 the lo^f -cabin type. Some individuals make a case composed of small chunks of bark (Fig. 702, a); others make cases composed almost entirely of shells of water snails (Fig. 702, b). Different combinations of these types are frequently found. Some larvffi of this family make cases of leaves; these are either fastened so as to form a flat case, or arranged in three planes so as to form a tube, a cross- section of which is a triangle. Larvce of the genus Neophylax make cases of sand with large ballast stones at the sides; these are similar in form to those made by Goera calcarata of the next family, but are more slender, smaller, and made of lighter material. Family vSERICOSTOMATID^ Fig. 702. — Case oiLimnophilus combinatus. (After Lloyd.) Fig. 703. — Case of Helicopsyche. (From Lloyd.) The larvae are caterpillar-like, and are found in streams and lakes. The cases made by members of the different genera differ greatly in form; the three following are our best -known examples. Helicopsyche horedlis. — The larvse of this species are found in stony streams and along the rocky shores of lakes. They make a spiral case of grains of sand (Fig. 703). This case so closely resembles that of a snail in form that it has been described as the shell of a mollusk. When about to pupate, the larvae fasten their cases to a submerged rock; at this time they display a gregarious instinct, large numbers of them congregating within a very small area. They are more easily found at this time than in their earlier stages when they are living free among the sand and gravel of the bot- tom of the stream. Goera calcarata. — The larvae of this species are found in the riffles of streams and on stones in wave-beaten areas of lake shores, where they crawl over the surface of bare, current-swept rocks. The -Case of Goera larval case (Fig. 704) is a at a. (Aft er ^y|-,g made of fine grains of sand on each side of which Fig. 704.- c alcar Lloyd.) 705. — Case of Brachycentrus nigrisoma. (From Lloyd.) 570 AN INTRODUCTION TO ENTOMOLOGY are fastened heavy ballast stones, usually two on each side. Brachycentrus nigrisoma. — The larva of this species builds a case of the remarkable form shown in Figure 705. "It is constructed of minute twigs, root-fibers, and fragments of wood cut to the proper length to give even and straight edges, gradually diverging toward the anterior end. In cross-section the outer surface of the case is square; the interior is lined with a cylindrical tube of tough silk." "During the first six weeks of their lives the larvae are active, crawling about in quiet eddies along the banks of streams in search of food. After this period they move to the center of the stream and live sedentary lives, with one edge of the larger end of their cases firmly cemented to submerged rocks or sticks. Always they inhabit positions on the exposed surface of their support and always they assume the position shown in Figure 705, protruding their heads slightly and extending their prothoracic legs straight forward. The mesothoracic legs are held upward while the metathoracic legs are extended to the sides. From this position they eagerly seize and quickly devour small larvae or bits of vegetation that float within their grasp." (Lloyd.) CHAPTER XXVII ORDER LEPIDOPTERA^ The Moths, the Skippers, and the Butterflies The winged members of this order have four wings; these are mem- branous, and covered with overlapping scales. The mouth-parts are formed for sucking. The metamorphosis is complete. The members of this order, the moths, the skippers, and the butterflies, are well known to every ob- server of nature. Their most easily ob- served distinguishing characteristic is that which suggested the name of the order, the scaly covering of the wings and body. Every lad that lives in the country knows that the wings of moths and butterflies are covered with dust, which comes off upon one's fingers when these insects are handled. This dust when examined with a microscope is found to be composed of very minute scales of regular form; and when a wing is looked at in the same way, the scales are seen arranged with more or less regularity upon it (Fig. 706). The body, the legs, and other appendages are also covered with scales. Fig. 706. -Part butterfly, greatly L wing of magnified. Fig. 707. — Scales of Eiiclea delphini. (After Kellogg.) "Lepidoptera : lepido (kfircs, Xeiridos), scale; pteron {irrepdv), a wing. (571) 572 AN INTRODUCTION TO ENTOMOLOGY It is well known that these scales are merely modified setae. That is, they are setas which, instead of growing long and slender as setae usually do, grow ver>' wide as compared with their length. Even,' gradation in form can be found, from that of the ordinary seta, which occurs most abundantly upon the body, to the short and broad scale, which is best seen upon the wings (Fig. 707). This fact was pointed out by Reaumur nearh^ two hundred 3'ears ago; and in recent times the morphological iden- tity of setas and scales has been established by studies of their development. Mayer ('96) gave a complete account of the de- velopment of scales and illustrated his paper by most excellent figures of all stages of this development. The structure of scales is what would be expected from the fact that they are modified sets, the scales, like setse, being hollow; and the manner of their attachment to the cuticula of the body and its appendages is the same as that of the setae, each scale being provided with a pedicel which fits into a cup-like socket in the cuticula. A striking feature of the scales of Lepidoptera is the mark- ings that exist on their exposed surface. These may consist merely c c 1 °^ many very fine longitudinal ridges (Fig. 707); or they may Fig. 708 .-Scale \^Q series of transverse ridges between the longitudinal ones (Fig. oi Seryda 708). c onstans . (After Kel- A cross-section of certain scales indicates that the logg.) ridges are produced by foldings of the outer wall (?. e., the w^all of the scale that is exposed when the scale is in place on the ^ wing). Figure 709 represents <5C3:x:;:«s5^^;^^^Ht;;5jJ^^^^ cross-sections of a scale illustrating ^j;;?*?^^'^^'^"-^;^ this condition. In some scales, however, the lumen of the scale has been filled to a considerable Fig. 709. — Cross-section of scales of Par- extent by chitin, and the origin of nassus sminthens. (After Kellogg.) the ridges is not so obvious. The scales of the Lepidoptera were probably developed from that type of setas known as clothing hairs, and were primarily merely protective in function. This is doubtless their chief, if not only, function on most parts of the body, where they form a very perfect armor. The development of ridges on the surface of scales adds greatly to their stiflfness, and thus increases their efficiency as a protective covering, as the corrugations in the sheets of iron used for covering the sides of buildings add to the stiffness of the metal. Upon the wings a covering of rigid scales would serve not merely to protect the wings but would tend to stiffen them, and thus arose a secondary function of scales which has resulted in the perfecting of their arrangement upon the wings in the more specialized members of the order as already indicated. There are great differences among the insects of this order regarding the regu- larity of the arrangement of the scales upon the wings. With some of the more generalized moths the scales are scattered irregularly over the surface of the wings. But if a wing of one of the more specialized butterflies be examined with a microscope, the scales will be found arranged in regular overlapping rows; the arrangement being as regular as that of the scales on a fish or of the shingles on a roof. Figure 706 represents a small portion of a wing of one of the more special- ized butterflies, where the arrangement of the scales is most perfect. In the upper part of the figure the membrane is represented with the scales removed. Even in those insects in which a very perfect arrangement of the scales upon the wings has been attained, great differences in the degree of perfection of this arrangement exist in the two wings of the same side and in the different parts of the same wing. The arrangement is most perfect in those wings and in those LEPIDOPTERA 573 parts of each wing that are subjected to the greater strain during flight; and is more perfect in swift-flying species than in those of slow flight. The taxonomic vakxe of these differences in the arrangement of the scales of the wings of the Lepidoptera, and also of the different types of scales found in different divisions of the order, was investigated by Professor Kellogg ('94), to whose extended account the reader is referred for a discussion of this phase of the subject. A secondary use of the scales of the Lepidoptera is that of ornamentation; for the beautiful colors and markings of these insects are due entirely to the scales, and are destroyed when the scales are removed. The various colors of insects and of other animals are produced in quite different ways ; and classifications of these colors have been proposed based on the methods of their production. The literature of this subject is too extensive to be referred to in detail here. A most enjoyable popular account is given by Pro- fessor Kellogg in his "/American Insects" (Kellogg '08, pp. 583-614) and a de- tailed analysis of the methods of the production of color is given by Professor Tower in his "Colors and Color-Patterns of Coleoptera" (Tower '03). Following the classification of Tower, the colors of the scales of the Lepi- doptera may be either chemical, physical, or chemico-physical. The chemical colors are produced by pigments in the scales; the physical colors are produced either by reflection, refraction, or diffraction of light; and the chemico-physical colors are produced by either a reflecting, refracting, or diffracting structure overlying a layer of pigment. There are also what Tower calls combination colors due to a combination of the causes just mentioned. As the production of colors by pigments is the most obvious method in nature, it is the one to which the colors of the Lepidoptera are commonly attributed. But it is now well known that a large proportion of the most beautiful colors of these insects are either physical or chemico-physical; this is true of the various metallic and iridescent colors so commonly found in butterflies and many moths. Explanations of the methods of production of physical colors are given in text- books on physics; it is, therefore, only necessary here to point out a feature in the structure of the scales of Lepidoptera that results in the production of these colors. This feature is the presence of the fine longitudinal striae described above. When the striae are very fine and close together they act in the same way as does a diffraction grating, producing the beautiful iridescent colors. Kellogg ('94) found that on certain scales from a species of Morpho the striae were from ,0007 mm. to .00072 mm. apart, or at the rate of about 35,000 to an inch. The fact that certain colors are due to the way in which light is reflected from the scales can be shown by the following experiment. Place on the stage of a microscope the wing of a bright blue butterfly, and shade the specimen so that it is viewed only by transmitted light from the mirror of the microscope; when examined in this way the blue color wall be absent. This is due to the fact that the light passing directly through the scales is not broken up, and only the colors produced by pigment are visible. There is still another function of the scales of Lepidoptera; they may serve as the outlets of scent glands. As the scales that serve this pvupose are found chiefly on the wings of males, they have received the special name of androconia, signifying male dust. See page 100. In the suborder Jugatee and in "1^-^ ITca^^i- ^--Zj^Zr^Iir' Zr-^ some of the more generalized -^ "^C~"~^^^S= ^ni~5^'~ families of the suborder Frenatas, ^—z:: ~,^j^^^^^^^^^^f^ there are, in addition to the more — ^~^^jr~ ~-^^~^^^^^^^^^^ obvious setae and scales, many '^ ~Z^^= _J^^r~l,-^ ~3z ~~ very small, hair-like structures, "^j^^^^^^^^^^-'^— _r^ which differ from setse in being di- — ^^:^^^^^^^^^_^g^^_r~' ,zr'^_ rectly continuous with the cu- lif-^C^^^^^^^^E*--'^' "^ — ~~ ticula, and not connected with it j^. t^ ^ * • c 1 .. 1 ■ ■ . ,^- \ j.\. Fig- yio- — Part of a wmg of an aculeate by a jomt (Fig. 710); these are ^J^h, with most of the scales re- termed the fixed hairs or aculecB. moved so as to expose the aculeae. 574 AN INTRODUCTION TO ENTOMOLOGY They are so small that they can be seen only by the aid of a micro- scope, and being covered by the scales they can be seen only in bleached and stained or denuded wings. In the more generalized members of this order, the venation of the wings corresponds quite closely to the hypothetical primitive type. The most striking divergence from this type is the fact that vein M is only three-branched. This is probably due to a coalescence of veins M4 and Cuj. If this is true, the vein that is commonly desig- nated as vein Cui is really yein M4 plus Cui; but for the sake of simplicity it seems best to designate it ordinarily as vein Cui. For a detailed discussion of this problem, see "The Wing's of Insects," pp. 334-337- Although the wings of Lepidoptera, except in certain specialized forms, are broadly expanded, there are but few cross-veins, and nor- mally no accessory veins. In the more specialized members of this order the number of the wing- veins is reduced. This reduction is due in some cases to the atrophy of a vein or veins, as, for example, the loss of the main stem of vein M in many families; in other cases, it is due to the coalescence of adjacent veins, as, for example, the reduction of the number of branches of radius or of media which has taken place in many members of the order. In many genera of this order the branches of radius of the fore wings anastomose so as to form one or more closed cells; these have been termed accessory cells. There are several methods by which the fore and hind wings of Lepidoptera are held together in flight, in order to insure their synchronous action. In the suborder Jugatae the posterior lobe of the fore wing functions either as a jugum (see p. 61) or as a fibula (see p. 62). In most moths the wings of each side are imited by a frenulum (see p. 61). In some moths and in the skippers and butterflies, the humeral angle of the hind wing is greatly ex- panded and projects be- neath the fore wing; this insures the synchronous action of the two wings and renders a frenulum unnecessary ; in these forms, which doubtless descended from frenate Fig. 711.— Wings of Obrussa ochrefasciella, male, ancestors, the frenulum (After Braun.) has been lost. The frenulum when well developed consists of a bunch of bristles situated at the base of the costa of the hind wings, on the costal sclerite. As a rule these bristles are separate in females, and consolidated into a single strong, spine-like organ in males. LEPIDOPTERA 575 Fig. 7 1 2 . — Diagram of a fore wing of a noctuid moth . The lettering is explained in the text. (After Crosby and Leonard.) Six transverse lines or bands and three -This is a band extending halfway In some of the more generalized Lepidoptera there is a series of shghtly curved, spine-hke setas on the costa of the hind wing near the base, which aid in holding the wings together. These setse lie beyond the costal sclerite, not on it as does the frenulum; they are termed by Braun ('19) the costal spines. The frenulum and costal spines are both present in some moths (Fig. 711). In many moths, and ^ tp st especially in the Noc- tuidae, the fore wings are marked by transverse lines or bands, and by spots that are so uniform in position in different species that they have been given names, which are used to designate them in the descriptions of those species in which they occur. Figure 712 is a diagram of a fore wing of a noctuid moth indicating the positions of the named lines or bands and spots, spots have been named, as follows: The basal or siibbasal band (Fig. 712, b).- across the wing near its base. The transverse anterior band (Fig. 712 t. a). — -This is often designated as the /. a. line; in some English books it is termed the first line. The median line (Fig. 712, m). The transverse posterior band (Fig. 712, /. p). — This is often designated as the /. p. line; it is the secottd line of English authors. The subterminal band (Fig. 712, 5. /). The terminal band (Fig. 712, /). The orbicular or round spot (Fig. 712, 0). — This is a round or oval spot situ- ated in the discal cell. The reniform spot (Fig. 712, r). — This is a somewhat kidney-shaped spot at the end of the discal cell. The claviform spot (Fig. 712, c). — An elongate spot extending from the /. a. line toward the /. p. line in cell Cu. The typical mouth-parts of adult Lepidoptera are fitted for suck- ing. In some families, the members of which do not take food during the adult stadivmi, the mouth-parts are vestigi- al; and in one family, the A-Iicropterygidae, which is doubtfully in- cluded in this order, the mouth-parts are of the mandibular type. ^^ ,„„ ^saaaw^ ^^ those families in ^^ ? "^^^ which the typical form of the mouth-parts is well shown, the only parts of these organs that are well developed are the maxillae and the palpi, the other parts being either absent or Fig. 713. — Maxillae of the cotton-moth, and the tip of the same enlarged. 576 AN INTRODUCTION TO ENTOMOLOGY reduced to mere vesti«jes. When only one pair of palpi are developed the}' are the labial palpi ; when maxillary palpi are present they can be dis- tinguished by their at- tachment to the maxillae. If the head of a but- terfly or of a moth in which the mouth-parts are not vestigial be ex- Tj- ^^ . ^ , . r -,1 amined, there will be t\g. 714. — Cross-section 01 maxillae. . ^ . - . found a long suckmg- tube which when not in use is coiled on the lower side of the head be- tween two forward -projecting appendages. This long sucking-tube is composed of the two maxillce, greatly elongated, and fastened to- gether side by side. In Figure 713 there is represented a side view of the maxillae of a moth; and in Figure 714 a cross-section of these organs. Each maxilla is furnished with a groove, and the two maxillae are so fastened together that the two grooves form a tube through which the liquid food is sucked. As a rule the maxillae of insects of this order are merely fitted for extracting the nectar from flowers, but sometimes the tips of the maxillae are armed with spines, as shown in Figure 713. This enables the insect to lacerate the tissue of ripe fruits and thus set the juice free, which is then sucked up. Many moths do not eat in the adult state; with these the maxillae are wanting. The two forward-projecting organs between which the maxillae are coiled when present are the labial palpi. In some moths the maxillary palpi are also developed. The compound eyes are large and are composed of many small ommatidia. The ocelli, when present, are two in number; they are situated one on each side, above the compound eye and near its mar- gin; the median ocellus is lacking throughout the order; and in the butterflies, the skippers, and some families of moths, all of the ocelli are wanting. The antennae are alwa^'s conspicuous ; they differ greatly in form in dififerent divisions of the order, and, therefore, furnish characters that are much used in the classification of these insects. In some families the basal segment of the antennae is greatly enlarged and forms what has been termed the eye-cap. Theprothorax is small, being reduced to a collar between the head and the wing-bearing segments. In many of the more specialized Lepidoptera the pronotum is produced on each side into a flat lobe which in some cases is even constricted at the base so as to become a stalked plate; these lobes are the patagia. The legs are long and slender. In some families the front tibiae bear on their inner aspect a mobile pad ; this is termed the epiphysis; in some cases, at least, it is a combing organ used for cleaning the antennae. A special feature of the abdomen is the presence in the female LEPIDOPTERA 57^ of a bursa copulatrix; that of the female of the milk-weed butterfly is figured on page i6o. Close to the junction of the thorax and abdomen there is, in the majority of Lepidoptera, a pair of organs, which are known as the tympana. These are situ- ated on each side near the first abdominal spiracle. Several types of these organs have been described by Forbes ('i6) and by Eggers ('19), which are characteristic of certain families and groups of families. The first ty])e is that of the Geometridae; it appears superficially as a hollow bulla located immediately below the spiracle, oi)ening forward against the coxa of the hind leg. The Pyralidas have rudimentary tympana in the same position. The second type is likewise wholly on the abdomen, but it is higher on the body, and its opening faces backward towards the second abdominal segment. It characterizes the Thatiridae and Drepanids. The third type presents a variety of appearances. Its essential part is a membranous disk, the tympanum proper, on the metathorax just below the root of the wing. In the Dioptidas, Notodontidae, Agaristida?, and a few noctuids and lithosians, the disk lies exposed or is merely sunk in a pit at the junction of the thorax and abdomen. In other moths having this type of tympana the disk is covered by a hood formed by the side of the first segment of the abdomen; in the Arctiida;, Pericopidae, Liparidae, and the subfamily Herminiinae of the Noc- tuidas, this hood lies subdorsally, wholly above the spiracle; while in the majority of the Noctuidae it is lower and incloses the spiracle, in some cases (Euteliinae, etc.) being supplemented by a second hood formed by the alula of the hind wing. The function of the tympana is probably auditory, as Eggers has described chordotonal organs in connection with them in several families. In the Lepidoptera the metamorphosis is complete. The larvae are known as caterpillars; they van,^ greatly in form and appearance, but are usually cy- lindrical, and pro- vided with from ten to sixteen legs, — ■ six thoracic legs and from four to ten abdominal legs. The thoracic legs have a hard exter- nal skeleton ; and are jointed, taper- ing, and armed at the end with a little claw. The abdom- inal legs, which are shed with the last larval skin; are thick, fleshy, with- out joints, elastic or contractile, and armed at the ex- tremity with numer- ous minute hooks (Fig. 715); they are termed prolegs. When all five pairs are present they are borne by the third, fourth, fifth, sixth, and tenth abdominal segments. Larva of a hawk-moth. 578 AN INTRODUCTION TO ENTOMOLOGY (a and b from The hooks or crochets with which the prolegs of caterpillars are armed vary in their arrangement in different families and thus afford useful characters for the classification of these larvae. These hooks are usually arranged in a circle or in rows on the tip of the proleg. When they are in a single row or series, they are said to heuniserial; when in two concentric rows, hiserial; when in several rows, multi- serial. When the hooks of a row are uniform in length throughout or shorter towards the ends of the row, they are said toheuniordinal; when they are of two alternating lengths, hiordinal; when of several lengths, multiordinal. The tip of a proleg on which the hooks or crochets are borne is termed the planta. In most lepidopterous larvce the clothing of setae is comparatively inconspicuous; such larvae are commonly termed naked in contra- distinction to the hairy caterpil- lars. But in the so-called naked larvae, each seg- ment of the body, when not too highly special- ized, is armed with a definite number of setae which occupy definite posi- tions. Each seta is borne on a small chitinous tubercle; the number of these setijerous tubercles and the positions they occupy differ in the different families, and, therefore, afford characters which are much used in the classification of Lepidoptera. The small tubercle bearing a single seta (Fig. 716, a) is evidently the primitive form of setiferous tubercle ; for it is the only form found in the more generalized families. In some of the more specialized families the tubercles are larger and many-haired (Fig. 716, h)\ this type of tubercles is termed a verruca; it is characteristic of the so- called hairy caterpillars, as, for example, the larvae of most of the Arctiidae. In the larvae of the Saturnioidea and of certain butterflies, some of the tubercles are spinose projections of the body-wall (Fig. 716, c); such a projection is termed a scolus. Some caterpillars are clothed with more or less nimierous setae which are scattered and which have no constant position; such setae are termed secondary setce, in contradistinction to those borne on setiferous tubercles which are of a definite number and occupy definite positions; these are termed primary setce. Among the setiferous tubercles that are constant in position, there are a few that are not present in the first instar of generalized groups; although the setae borne by these tubercles are regarded as primary setae when con- trasted with secondary setae, they are distinguished from those found in the first instar as suhprimary setce. Fig. 716. — Types of setiferous tubercles. Dyar.) LEPIDOPTERA 579 In order to make use of the primary and subprimary seta in classification, it is necessary that each of these setse should be desig- nated by a distinctive term. The terminology most generally used is that proposed by Dyar ('94), who was the first author to base a classification of lepidopterous larvas on the variations in the arrange- ment of the setiferous tubercles. The terminology of Dyar was based on a study of the tubercles of the abdominal segments. He recognized on each side of each ab- dominal segment, except the last two, eight tubercles, which he numbered with Roman numerals beginning with the one nearest the middle line of the back; the ntmiber VII was applied to a group of three tubercles on the outside of the proleg, or in a corres- ponding position in the legless abdominal segments. Subsequent studies, and especially those by Forbes ('io)and Fracker ('15), have revealed the presence of setiferous tubercles not num- bered by Dyar. Figure 717,6, represents the arrangement of the tubercles of a middle ab- dominal segment of a noctuid larva as figured by Forbes. The tubercles are numbered ac- cording to the terminology of D}'ar, with the addition of tubercles X, Ilia, and IX, not figured by Dyar.* The arrangement of the setiferous tubercles on the thoracic segments of any cater- pillar differs to a considerable extent from that on the ab- Fig- 7i7-^Arrangement of setiferous tu- 1 • 1 j_ c j^i bercles m a noctuid larva: a, tubercles dommal segments of the same ^f ^ metathorax; 6, tubercles of a msect. In Figure 717, arepre- middle abdominal segment. (After sents the arrangement of the Forbes.) tubercles on the metathorax and h that of the tubercles of a middle abdominal segment of a noctuid larva as figured by Forbes ('10). This writer also figures and numbers the setae on the head of a caterpillar. Fracker ('15) made an extended study of the classification of lepidopterous larvas, which was based quite largely on the variations in the number and positions of the setiferous tubercles; and his paper is illustrated by a large number of setal maps. This writer proposes a new terminology for the setae, using Greek letters instead of Roman numerals. *In diagrams indicating the arrangement of setiferous tubercles, one side of a single segment is represented as if cut on the mid-dorsal and mid-ventral lines, and laid flat. The anterior edge is to the left, and the mid-dorsal line at the up- per edge. In Figure 717 the positions of the .spiracle and of the proleg are also indicated. 580 AN INTRODUCTION TO ENTOMOLOGY Schierbeek ('i6 and '17) proposes still another terminology for the setae, applying a Latin name to each. A-Iost caterpillars, except, as a rule, the larvae of butterflies, spin a cocoon. In some instances, as in the case of silk-worms, a great amount of silk is used in the construction of the cocoon; in others the cocoon is composed principally of the hairs of the larva, which are fastened together with a fine web of silk. The pupas of the Lepidoptera are typically of the obtected type; that is, the developing wings, legs, mandibles, maxillae, and antennae are glued to the surface of the body (Fig. 718); but in some of the more generalized forms these appendages are free. In the Micro- jugatae, which are provisionally in- cluded in this order, these append- ages are free, the pupae resembling those of the Trichoptera; but in the Hepialidae the appendages are glued to the surface of the body as in the specialized Frenatae. In some of the more generalized Frenatae, as the -Pupa of a moth. Nepticulidae, and in the Heliozelidae, the appendages are all free ; between this condition and that of the truly obtected pupa of the more specialized Frenatae, various intergrades exist. The pupae of this order vary also in the number of segments of the body that are movable. The eighth, ninth, and tenth abdominal seg- ments are always fixed. All of the. other segments are movable in the most generalized forms, and all are fixed in the most specialized forms; there are various intergrades between these two extremes. Different pupae of this order differ also in various other ways, thus affording characters that are of taxonomic importance. It is only recently that these characters have been used in an extended manner. A pioneer paper in this field is that of Miss Edna Mosher ('16). More than nine thousand species of Lepidoptera are known to occur in America north of Mexico. These represent two suborders and seventy families. In popular language the Lepidoptera includes two quite distinct groups of insects, the moths and the butterflies. Under the term moths are included all of the members of the first suborder, the Jugatae, and the larger number of the families of the second suborder, the Frenatcc; under the term butterflies are included the remaining families of the suborder Frenatae. These two groups are distinguished as follows. The moths. — These are the insects that are commonly called millers. Most of the species fly by night and are frequently attracted to lights. When at rest the wings are either wrapped around the body, or spread horizontally, or folded roof -like on the abdomen; except in a few cases they are not held in a vertical position above the body. The antennas of moths are of various forms; they are usually thread- LEPIDOPTERA 581 like or feather-like; only in rare cases are they enlarged towards the tip. The moths have been termed the Heterocera* by many ento- mological writers, in contradistinction to Rhopalocera,* a term ap- plied to the butterflies. The butterflies. — All of our species of butterflies fly in the daytime; and, with few exceptions, they fold the wings together above the back in a vertical position when at rest. The antenna; are thread-like, and usually with a club at the tip. It was this feature that suggested the term Rhopalocera, which is applied to them. The group butterflies as defined here includes the representatives of two quite distinct superfamilies, the Hesperioidea or skippers, and the Papilionoidea or true butterflies. The distinctive characters of these two superfamilies are discussed later. The division of the Lepidoptera into moths and butterflies is an artificial one, the group moths including representatives of both of the two suborders into which the order is divided, as indicated above. In the natural classification, the primary division of the order is based on differences in the method of uniting the two wings of each side, and on differences in the venation of the hind wings. In one suborder, the Jugate, the posterior lobe of the fore wing is specialized so as to form an organ, a jugum or a fibula, which unites the fore and hind wings ; and the venation of the hind wings is similar to that of the fore wings. In the other suborder, the Frenatas, the two wings of each side are united by a frenulum in the more generalized forms and by a substitute for a frenultmi in certain specialized forms ; and the venation of the hind wings is quite different from that of the fore wings. Hilbner's Tentamen. — At some undetermined date, but previous to 1810 and probably in 1806, Jacob Hiibner distributed a two-page work, giving a classifica- tion of the Lepidoptera. This work is commonly known as "Hiibner's Tenta- men," tentamen being the first word in its long Latin title. Entomologists differ regarding the standing of this work; some believe that it was merely privately printed, while others regard it as a published work and adopt the generic names that were used in it. This difference of opinion is the cause of serious confusion in the names of certain genera and families. It seems to the writer that the evi- dence supporting the view that the "Tentamen" was published is conclusive. See "Entomologists Record and Journal of Variation," Vol. 31 (1919), vSupple- ment. SYNOPSIS OF THE LEPIDOPTERA The families comprising this order are grouped in various ways by different writers; none of these groupings can be regarded as final in the present state of our knowledge. The following provisional arrangement has been adopted for use in this book. A. The Jugate Lepidoptera. — -Moths in which the two wings of each side are united by a jugum or by a fibula, p. 592 Suborder Jugate B. The Microjugat^. C. The Mandibulate Jugates. p. 592 Family Micropterygid^ CC. The Haustellate Jugates. p. 593 Family Eriocraniid^ BB. The Macrojugat^. The Swifts, p. 594 Family Hepialid.-e *Heter6cera: hetero (eVepos), other, different; ceras (K^pas), a horn. *Rhopal6cera : rhopalon {pdwaLof), a club; ceras (Ke'pas), a horn. 582 AN INTRODUCTION TO ENTOMOLOGY AA. The Frenate Lepidoptera. — Moths, skippers, and butterflies in which the two wings of each side are united by a frenulum or by its substitute, a large humeral area of the hind wings, p. 596 Suborder Frenate B. The Generalized Frenate. — Moths that are supposed to retain more nearly than other Frenatas the form of the primitive Frenatse, those that were the first to appear on earth. C. The Aculeate Frenat/e. — Moths in which the aculeas are distributed over the general surface of the wings. The Incurvariids. p. 598 Family Incurvariid^ The Nepticulids. p. 600 Family Nepticulid^ CC. The Non-aculeate Generalized Frenatae. — Moths in which the aculeae are confined to small areas of the wings or are absent. The Carpenter Moths, p. 601 Family Cossid.e The Smoky Moths, p. 604 Family Pyromorphid.e The Dalcerids. p. 605 Family Dalcerid^ The Flannel-moths, p. 606 Family Megalofygid.-e The Slug-caterpillar-moths, p. 608 Family Eucleid.e The Epipyropids. p. 610 Family Epipyropid^ BB. The Specialized Frenate. — Moths, skippers, and butterflies that de- part more widely than do the Generalized Frenatae from the primitive type of Lepidoptera, being more highly modified for special conditions of existence. An indication of the specialized condition of these insects is the modified form of the wings. In nearly all the base of vein M has been lost and the branches of this vein joined to veins R and Cu. C. The vSpecialized MiCROFRENATi*;. — Frenulum-bearing moths which are usually of small, often of minute, size. In many of these moths the anal area of the hind wings is not reduced, having three anal veins; in some others the hind wings are very narrow and a broad fringe acts as a sub- stitute for the membrane of the anal area. The Acrolophids. p. 611 Family Acrolophid.e The Tineids. p. 611 Family Tineid.-e The Bag- worm Moths, p. 613 Family Psychid.e The Tischeriids. p. 615 Family Tischeriid.e The Lj'Onetiids. p. 616 Family Lyonetiid.^ The Opostegids. p. 617 Family Opostegid.^ The Oinophilids. p. 617 Family Oinophilid.e The Gracilariids. p. 617 Family Gracilariid^ The Coleophorids. p. 620 Family Coleophorid.'E The Elachistids. p. 621 Family Elachistid-E The Heliozelids. p. 622 Family Heliozelid.e; The Douglasiids. p. 623 Family Dougl.\siid.« The CEcophorids. p. 624 Family O^cophorid.e The Ethmiids. p. 625 Family Ethmiid.^ The Stenomids. p. 625 Family Stenomid.e The Gelechiids. p. 625 Family Gelechiid.e The Blastobasids. p. 628 Family Blastobasid.-e . The Cosmopterygids. p. 629 Family Cosmopterygid.e The Scythridids. p. 631 Family Scythridid.e The Yponomeutids. p. 631 Family Yponomeutid.e The Plutellids. p. 632 Family Plutellid.e . The Glyphipterygids. p. 633 Family Glyphipterygid.e The Heliodinids. p. 634 Family Heliodinid.'E The Clear-winged Moths, p. 634 Family ^geriid^ Superfamily Tortricoidea The Olethreutids. p. 639 Family Olethreutid^ The Typical Tortricids. p. 642 Family Tortricid^ The Phaloniids. p. 643 Family Phaloniid.-e The Carposinids. p. 644 Family Carposinid.-e CC. The Pyralids and Their Allies Superfamily Pyr.\lidoidea The Pyralids. p. 644 Family Pyralidid.-e The Plume-moths, p. 652 Family Pterophorid^ LEPIDOPTERA 583 The Many-plume Moths, p. 653 Family OrneodidvE The Window- winged Moths, p. 653 Family Thyridid/E The Hyblaeids. p. 655 Family Hybl/Eid^ CCC. The Specialized Macrofrenat^e. — Specialized Frenats which arc usually of medium or large size. This division includes certain moths and all skippers and butterflies. In these insects the anal area of the hind wings is reduced, containing only one or two anal veins. D. The Frenidum-conservers. — Specialized Macrofrenatae in which the two wings of each side are typically united by a frenulum; but in some highly specialized genera of some families (Sphingidae, Geometrids, and Dre- panida;) the supplanting of the frenulum by an expanded humeral angle of the hind wing is either far advanced or complete. This group of families includes only moths. The hawk-moths or sphinxes, p. 655 Family Sphingid^ Superfamily Geometroidea The Geometrids. p. 663 Family Geometrid^ The Manidiids. p. 673 Family Manidiid^ The Noctuids and Their Allies The Dioptids. p. 673 Family Dioptid^ The Prominents. p. 674 Family Notodontid^ The Tussock-moths, p. 679 Family Lymantriid^ The Noctuids. p. 683 Family NoCTUiDyE The Foresters, p. 697 Family Agaristid^ The Pericopids. p. 698 Family Pericopid^ The Arctiids. p. 699 Family Arctiid/E The Euchromiids. p. 706 Family Euchromiid^ The Eupterotids. p. 707 Family Eupterotid^ The Epiplemids. p. 708 Family Epiplemid^e The Thyatirids. p. 709 Family Thyatirid/E The Drepanids. p. 710 Family Drepanid^ DD. The Frenulum-losers. — SpeciaHzed Macrofrenatae, in which the frenulum has been supplanted by a greatly extended humeral area of the hind wings. In some of the more generalized forms a vestigial frenulum persists (Bombycidae and Lacosomidae). This division in- cludes three groups of families: the Frenulum-] osing moths, the skip- pers, and the butterflies. The grouping together of the families in- cluded in this division is merely provisional, as doubtless the loss of the frenulum has arisen independently several times. E. The Frenulum-losing Moihs. — In these moths the antennae are usually pectinate; they are never enlarged into a club at the tip. The Lacosomids. p. 712 Family Lacosomid^ Superfamily Saturnioidea The Royal-moths, p. 715 Family Citheroniid^ The Giant Silk-worms, p. 719 Family Saturniid^ The Silk-worms, p. 727 Family Bombycid.e The Lasiocampids. p. 728 Family Lasiocampid^ EE. The Skippers. — These are day-flying Lepidoptera which resemble butterflies in usually holding their wings erect when at rest, but are distinguished by the peculiar venation of the fore wings, vein R being five-branched, and all of the branches arising from the discal cell. The antennee are enlarged into a club towards the tip. vSuperfamily Hesperioidea The Giant Skippers, p. 733 Family Megathymid^ The Common Skippers, p. 734 Family Hesperiid^ EEE. The Butterflies. — Day-flying Lepidoptera that hold their wings erect when at rest, that have clubbed antennae, and that diff'er froin the skippers in the venation of the fore wings, some of the branches of vein R coalescing beyond the discal cell. Superfamily Papilionoidea The Swallow-tails and the Parnassians, p. 740 Family Papilionid^e 584 AN INTRODUCTION TO ENTOMOLOGY The Pierids. p. 744 Family Pierid^ The Four-footed Butterflies, p. 750 Family Xymphalid^ The Metal-marks, p. 767 Family Riodinid^ The Gossamer-winged Butterflies, p. 768 Family LyC'EMD^ TABLES FOR DETERMINING THE FAMILIES OF LEPIDOPTERA TABLE A A.'^ Wingless or with vestigial wings. This division includes only females. All males of Lepidoptera are winged. B. The larvae case-bearers; the adult female either remains within the case to lay her eggs, or leaves the case and sits on the outside of it. p. 6i3.Psychid^ BB. The larvae not case-bearers; the wingless adult not in a case. C. The adult female remains upon her cocoon to lay her eggs; the body of the adult is clothed with fine hairs, p. 679 Lymantriid/E CC. The adult female is active and lays her eggs remote from her cocoon; the body of the adult is closely scaled, or spined, or with bristling dark gray hair. p. 663 GeometriD/E CCC. In addition to the above there are some arctic species of the Noc- tuidae and of the Arctiidas in which the wings of the females are vestigial. AA. With well-developed wings. B. Fore and hind wings similar in form and venation, the radius of the hind wings being, like that of the fore wings, five-branched (Suborder Jug.\t^). C. Minute moths resembling tineids in appearance. D. Adult moths with well-developed functional mandibles; subcosta of the fore wings forked near its middle, p. 592 Micropterygid^ DD. Mandibles of the adult vestigial; maxillag formed for sucking; subcosta of fore wings forked near its apex. p. 593 EriocraniidvE CC. Moths of medium or large size, without functional mouth-parts, p. 594 HEPIALIDyE BB. Fore and hind wings differing in form and venation; the radial sector of the hind wings being unbranched, and vein Ri of the hind wings usually coalesced with vein Sc (Suborder Frenat^). C. Antennae of various forms, but rarely clubbed as in the skippers and butterflies; if the antennae are clubbed the hind wings bear a frenulum. D. The fringe on the inner angle of the hind wings as long as, or longer than, the width of the wing; the hind wings often lanceolate, but never fissured. (Microfrenatas.) Pass to Table B. DD. Hind wings much broader than their frijige, and not lanceolate. E. Wings fissured deeply. F. Each wing divided into six lobes, p. 653 Orneodid.« FF. Wings never more than four-lobed; usually the fore wings. bilobed and the hind wings trilobed. p. 652 Pterophorid^ EE. Wings not fissured or the front wings slightly fissured. F. Fore wings very narrow, the width at the middle less than one- fourth the length of the wing; a considerable part of the hind wings, and in many cases of the fore wings also, free from scales; inner margin of fore wings and costal margin of hind wings with a series of recurved and interlocking spines, p. 634 ^geriid^ FF. Wings scaled throughout, or if clear with the fore wings trian- gular in outline; wings not interlocking at middle with series of re- curved spines. G. With a double series of enlarged and divergent scales along vein Cu of the hind wings below; wings, body, and legs very long. {Agdistis.) p. 652 Pterophorid^. GG. Without such scales on vein Cu of the hind wings. H. Hind wings with three anal veins. Care must be taken not to mistake a mere fold in the wing for a vein. When there is no thickening of the membrane of the wing along a fold, it is not counted as a vein. LEPIDOPTERA 585 I. \' cins Sc -L Ri and Rs of the hind wings grown together for a greater or less distance between the apex of the discal cell and the apex of the wing, or in some cases separate but very closely parallel, p. 644 Pyralidid^ II. Veins Sc + Ri and R<; of the hind wings widely separate beyond the apex of the discal cell. J. The fringe on the anal angle of the hind wings con- siderably longer than elsewhere (sometimes not obviously so in rubbed specimens) ; the spurs of the tibiae more than twice as long as the width of the tibiae. (Microfrenatae.) Pass to Table B.* J J. The fringe on the anal angle of the hind wings not longer than elsewhere or but slightly so; the spurs of the tibiae about as long as the width of the tibiae. K. Veins Sc + Ri and Rs of the hind wings grown together to near the end of the discal cell (Fig. 734), or anastomosing beyond the middle of the cell (Fig. 730). L. Small moths, chiefly of a smoky black color, with thinly scaled wings, p. 604 Pvromorphid^ LL. Moths of medium size, and densely clothed with long, woolly hairs, which are light-colored or brown. p. 606 MEGALOPYGID.E KK. Veins Sc + R, and Rs of the hind wings separate or grown together for only a short distance. L. 1st and 2d anal veins of the fore wings united by a cross-vein. M. Accessory cell present (Hypoptinae). p. 603. CossiD^ MM. Accessory cell absent, p. 613 . .. .Psychid.^ LL. 1st and 2d anal veins not united by a cross-vein. M. Vein M2 of the fore wings arising from the discal cell nearly midway between veins Mi and M3. N. Vein M3 of both fore and hind wings coalesced with vein Cui for a considerable distance beyond • the end of the discal cell. p. 673. . ..Dioptid.« NN. Veins M3 and Cui not coalesced beyond the end of the discal cell. O. Veins R2 and Rj coalesced at base, but separate from veins R^ and Rj, which also coalesce at base. p. 712 L.\cosomid^ 00. Veins R,, Rj, R4, and R5 united at base. p. 727 BOMBYCID.E MM. Vein M, of the fore wings emerging from the discal cell nearer to cubitus than to radius, causing cubitus to appear four-branched. N. Fore wings with an accessory cell. O. Moths with heavy, spindle-shaped bodies, and narrow, strong wings, p. 601. Cossid/E 00. Moths in which the body is slender and the wings are ample. P. Wings ample (fore wings not half longer than wide); mouth-parts vestigial, p. 605. D.\LCERID.E PP. Wings more or less oblong, usually twice as long as wide; mouth-parts usually developed with scaled tongue. (Micro- frenatae.) Pass to Table B. NN. Fore wings without an accessory cell. *A few of the Eucleidae present these characters; but with these moths the wings are broad and the base of media extends through the middle of the discal cell. 586 AN INTRODUCTION TO ENTOMOLOGY O. With some of the branches of radius of the fore wings coalesced beyond the apex of the discal cell. p. 608 Eucleid^ 00. With each of the five branches of radius of the fore wings arising from the discal cell. p. 655 Hybl^id^ HH. Hind wings with less than three anal veins. I. Fore wings with two distinct anal veins or with the anal veins partly grown together so as to appear as a branched vein. J. Anal veins of fore wings partly grown together so as to appear as a branched vein. p. 613 Psychid^ JJ. Fore wings with two distinct anal veins (Harrisina). p. 605 Pyromorphid^ II. Fore wings with a single fully preserved anal vein, This is the second anal vein; the first anal vein is absent or represented merely by a fold; and the third anal vein is short, not reaching to the margin of the wing, or is wanting; usually when the third anal vein is present it is joined to the second anal vein, so that the latter appears to be forked towards the base. J. Frenulum present. In most cases, the humeral angle of the hind wings is not greatly expanded. K. The five branches of radius and the three branches of media of the fore wings all present, and each one arising separate from the discal cell. p. 653 Thyridid^ KK. With some of the branches of radius of the fore wings stalked, or else with some branches coalesced to the margin of the wing. L. The fringe on the anal angle of the hind wings con- siderably longer than elsewhere. M. Veins Sc and R of the hind wings seperate, but usually connected by a more or less distinct basal part of vein Ri. (Microfrenatae.) Pass toTableB. MM. Veins Sc and R'of the hind wings fused for a greater or less distance. N. OcelH present, p. 683 Noctuid^ NN. Ocelli absent, p. 704 Lithosiin.-e LL. The fringe on the anal angle of the hind wings not considerably longer than elsewhere. M. The basal part of vein Ri of the hind wings, the part extending from radius to the subcosta, ap- pearing like a cross-vein which is as stout as the other veins; veins Sc -+- Ri closely parallel to the end of the discal cell or beyond, p. 655. Sphingid^ MM. The basal part of vein Ri of the hind wings rarely appearing like a stout cross-vein; when it does appear like a cross-vein, veins Sc + Ri and Rs strongly divergent from the point of union of veins Ri and Sc. N. Vein M2 of the fore wings not more closely joined to cubitus than to radius, cubitus being apparently three-branched. O. The basal part of the subcosta of the hind wings extending from the base towards the apex of the wing in a regular curve. P. Vein M2 of the hind wings arising nearer to cubitus than to radius; vein Mi of the hind ^ wings joined to radius before the apex of the discal cell. p. 709 Thyatirid^ PP. Vein Mj of the hind wings either wanting LEPIDOPTERA 587 or present, but when present arising either midway between radius and cubitus, or nearer to radius than to cubitus; vein Mi of the hind wing joined to radius at or beyond the apex of the discal cell. Q. Veins Sc and R of the hind wings sepa- rate at the extreme base, then closely approximate or fused for a greater or less distance. R. Tongue (maxillae) wanting; fore wings with veins R2 + 3 and R4 + 5 stalked together, northern species with hyaline dots on fore wings, p. 707 . EuPTEROTIDyE RR. Tongue present, often weak; fore wings fully scaled; usually with acces- sory cell or with veins R3 and R4 stalked together, p. 674. Notodontid^ QQ. Veins Sc-t-Ri and Rs of the hind wings sharply divergent from close to base of the wing. p. 704 Epiplemid/E 00. The basal part of the subcosta of the hind wings joined to radius for a considerable distance and then making a prominent bend towards the costal margin (Fig. 909). Veins Rj and R4 of the fore wings separate from each other. (See also 000.) p. 712. Lacosomid^ 000. The basal part of the subcosta of the hind wings making a prominent bend into the humeral area of the wing, and usually con- nected to the humeral angle by a strong cross- vein (Fig. 817). P. Antennae clubbed, p. 673. .Manidiid^ PP. Antennae not clubbed, p. 663 Geometrid^ NN. Vein M2 of the fore wings more closely joined to cubitus than to radius ; cubitus being in most cases apparently four-branched. O. Small moths, with the apex of the fore wings sickle-shaped, p. 710 Drepanid^ 00. Apex of the fore wings not sickle-shaped. P. Vein Sc of the hind wings apparently ab- sent, being fused except at the extreme base with radius. Care should be taken not to mistake vein Mi for radius (see Fig. 897). p. 706 EUCHROMIID^ PP. Veins Sc and R of the hind wings dis- tinct and parallel to the point where vein R separates from the discal cell, and then approaching very close or fusing for a short distance. (See also PPP.) Q. Small moths with snow-white wings (Eudeilinia). p. 710 Drepanid^ QQ. Moths that are not white. R. Vein R5 of the fore wings stalked with veins R3 and R4 (Chrysauginae) . p. 644. Pyralidid^ RR. Vein Rs free {Meskea). p. 653. THYRIDID.E PPP. Veins Sc and R of the hind wings not as described under PP above. Q. Antennae more or less thickened towards the tip. p. 697 Agaristid^ AN INTRODUCTION TO ENTOMOLOGY QQ. Antenna^ not clubbed. R. Dorsal surface of the first abdominal segment with two prominent rounded bosses, the hoods of the tympana. These hoods are wholly above the spiracles, and separated by only about one-third of the width of the abdomen. Black moths with white or yellow bands or spots on the wings and often with metallic tints. Found only in the Far West or in the Gulf States, p. 698. Pericopid/e RR. Hoods of the tympana less con- spicuous dorsally and more widely separated. S. Veins Sc and R of the hind wings extending separate, or the two joined for a short distance near the base of the wing; ocelli present. T. White or yellow species, with palpi not reaching the middle of the smooth-scaled front; vein Cu apparently four-branched in both fore and hind wings {Haploa). p. 700 Arctiid.« TT. Species with longer palpi, and vein Cu of the hind wings ap- parently three-branched, or species of a gray ground color, p. 683. NoCTUIDiE SS. Veins Sc and R of the hind wings fused or closely parallel near the middle of the discal cell, or con- nected by a short cross-vein (the free part of vein Ri); ocelli absent. (See alsoSSS.) p. 679. Lymantriid.'E SSS. Veins Sc and R of the hind wings united for one-fifth or more of the length of the discal cell. T. Ocelli present (ArCtiinae). p. 700. Arctiid^ TT. OcelH absent. U. Fore wings with raised tufts of scales (Nolinae). p. 705.Arctiid^ UU. Fore wings smoothly scaled. V. Vein M^ of the hind wings well developed and aris- ing slightly nearer to vein M^ than to vein Mi {Menopsimus) . p.683 NOCTUID^ VV. Vein M^ of the hind wings arising much nearer to vein M3 than to vein Mi, or wanting (Lithosiinas). p. 704. Arctiid^ J J. Frenulum absent. K. Vein Cu of both fore and hind wings apparently four-branched. L. Small moths with slender bodies, and with the apex of the fore wings sickle-shaped ; humeral veins absent, p. 710 Drepanid^ LEPIDOPTERA 589 LL. Moths of various sizes, but with robust bodies, and with the apex of the fore wings not sickle-shaped; hind wings with humeral veins, p. 728.Lasiocampid^ KK. Vein Cu of both fore and hind wings apparently three-branched. L. Robust moths of medium or large size, with strong wings, p. 714 S.\TURNIOIDE.\ LL. Small moths with slender bodies and weak wings (Dyspteris). p. 667 Geometrid^ CC. Antennee thread-like with a knob at the extremity; hind wings without a frenulum; ocelli wanting. D. Radius of the fore wings five-branched, and with all the branches arising from the discal cell; club of antennae usually terminated by a re- curved hook. The skippers, p. 732 Hesperioide.\ DD. With some of the branches of radius of the fore wings coalesced be- yond the apex of the discal cell; club of antennte not terminated by a re- curved hook. The Butterflies, p. 739 Papilionoidea TABLE B THE FAMILIES OF THE MICROFRENAT^ Contributed by Dr. William T. M. Forbes A. Basal segment of the antennae enlarged and concave beneath, forming an eye-cap. B. Fore wings with radius, media, and cubitus unbranched. p. 6i7.0postegid^ BB. Fore wings with more complex venation. C. Discal cell of fore wings very short and trapezoidal, or absent, p. 600. Nepticulid^. CC. Discal cell more than half as long as the wing. D. Discal cell oblique, its lower outer corner nearly touching the inner margin. (A few species only.) p. 628 Blastobasid.e DD. Discal cell central in the wing. E. Labial palpi minute and drooping, or absent, p. 616.. .Lyonetiid^ EE. Labial palpi moderate, upcurved. {Phyllocnistis in part, and one or two Florida genera.) p. 617 Gracilariid^ AA. Basal segment of antennas not forming an eye-cap. B. Palpus with the first segment relatively very large, normally upcurved to the middle of the front; when the palpus is short the first segment is longer than the second, p. 611 Acrolophid^ BB. First segment of palpus small. C. Labial palpi bristled on the outer side of the second segment. D. Aculeae present over the general surface of the wings; female with piercing ovipositor; antennae typically smooth and velvety-looking, with fine bristles, or narrow, closely appressed scales, sometimes very long. p. 598 Incurvariid^ DD. Aculeas absent, or present only in a small area at the base of the discal cell; ovipositor membranous, retractile; antennae typically rough, with an outer whorl of erect scales on each segment, rarely as in D. p. 61 1 TlNEID.^ CC. Labial palpi scaled or loose-hairy only. D. Maxillary palpi well developed and of the folded type. E. Fore wings with all veins present and with vein R; running to the outer margin; hind wings narrow; vertex with a small, loose tuft only (Acrolepia). p. 632 Plutellid.-e EE. Fore wings with vein R5 extending to the costa or absent. F. Head smooth; hind wings narrow-lanceolate; fore wings down- curved at apex. p. 617 Oinophilid^ FF. Vertex rough or rarely smooth in forms with ample hind wings; fore wings flat. G. Aculeas present, etc., as in D under C above, p. 598 Incurvariid^ 590 AN INTRODUCTION TO ENTOMOLOGY GG. Aculese absent, etc., as in DD under C above, p. 6i i ..Tineid^ DD. Maxillary palpi porrect or vestigial. E. Vertex and upper face at least with dense bristly hairs; third seg- ment of labial palpi fusiform and equal to the second in length. F. Aculeae present, etc., as in D under C above, p. 598 . Incurvariid^ FF. Aculeae absent, etc., as in DD under C above, p. 6ii.Tineid/e EE. Face at least smoothly and shortly scaled; third segment of labial palpus long and pointed, or very short in forms with roughest vestiture. F. Hind wings ample, with well-marked anal angle, often wider than, their fringe. G. Hind wings with veins Mi and M^ both lost, only one vein being associated with the R-stem. p. 644 Carposinid^ GG. Hind wings with vein Mi preserved, associated with the R- stem. H. Vein Cu2 of the fore wings arising from a point before the outer fourth of the discal cell; palpus more or less triangular, with a short, blunt, third segment, roughly scaled (short and nearly smooth in Laspeyresia, in which there is a strong fringe on base of vein Cu of the hind wings, save in L. lautana). p. 639, 642 Olethreutid^ and Tortricid/e HH. Vein Cu2 of the fore wings arising from the outer fourth of the discal cell, save in a few Glyphipter\'gidas, which have short, smooth-scaled palpi, or second segment tufted and third long and slender, and no fringe on vein Cu. I. Vein 1st A of fore wings lost completely; hind wings with veins Rs and Mi connate, approximate, or stalked. J. Palpi with third segment long, slender, and tapering, often exceeding vertex, normally close-scaled, save in male Anarsia where veins R4 and R; are stalked and both run to the costa. p. 625 Gelechiid^ JJ. Palpi with third segment short and blunt, roughly scaled; vein Rj normally running to outer margin, and often free from vein R4. p. 643 Phaloniid^ II. Vein 1st A preserved, at least at the margin of the wing. J. Hind wings with veins Rs and Mi widely separate at origin, more or less parallel. K. Palpi long, often exceeding vertex; tongue distinct. L. Veins R4 and R5 stalked and both running to costa, or united. M. Vein M2 of the hind wings arising- nearer to vein Mi than to M3. p. 625 Ethmiid^ MM. Vein M2 of the hind wings arising nearer to vein Mj than to M,. p. 624 CEcophorid/E LL. Veins P.4 and R5 long stalked ; vein R^ running to outer margin. (See also LLL.) M. Ocelli very large and conspicuous {Allononyma) . p. 633 Glyphipterygid^ MM. Ocelli small or absent. N. Vein M2 of the hind wings arising nearer to vein Mi than to M3. p. 625 Ethmiid.« NN. Vein M2 of the hind wings arising nearer to vein M3 than to Mi. p. 624. . .CEcophorid^ LLL. Veins R4 and R5 separate, vein R5 running to outer margin, p. 631 Yponomeutid^ KK. Palpi small, hardly exceeding the front, or obsolete; tongue obsolete; female with a brush-like tuft at end of abdomen {Kearfottia, Solenobia). p. 614. . . .Psychid/E JJ. Hind wings with veins Rs and Mi coalesced or stalked. K. Wings narrow; fore wings falcate; maxillary palpi well marked and porrect {Cerostoma, etc.). p. 631 Yponomeutid^ Hif; LEPIDOPTERA 591 KK. Wings broad, ample, not falcate; maxillary palpi of folded type, inconspicuous, invisible in Setiostoma. p. 625 Stenomid^ FF. Hind wings with pointed apex and excavated below, rarely bifid. (See also FFF.) p. 625 Gelechiid/e FFF. Hind wings narrow-lanceolate and ])ointed or linear, and much narrower than their fringe. G. Hind wings lanceolate, though sometimes very small, and with the principal vein running nearly through its center, widely separated from Sc. H. Hind wings with a discal cell. p. 621 Elachistid^ HH. Hind wings without a discal cell. I. Vein Rs of hind wings separating from media near the middle of the length of the wing. p. 623 Douglasiid. nor- mally long and parallel to the medial veins. K. Male antenna heavily ciliate; accessory cell of fore wings extending halfway to base of wing; head with a. large, loose, but often obscure, semierectile tuft. p. 615. TlSCHERIID.^ KK. Male antennae rarely ciliate; accessory cell small or absent. L. Palpi minute and drooping; vertex tufted; hind wings hnear [Bedellia). p. 616 Lyonetiid^e LL. Palpi moderate, with fusiform third segment; maxillary palpi often well developed and porrect. (See also LLL.) p. 617 Gbacilariid^ 592 AN INTRODUCTION TO ENTOMOLOGY LLL. Palpi upturned, with acuminate third segment, often exceeding the vertex; maxillary palpi of folded type but ver}^ minute or obsolete. M. Vein Ri of the fore wings more than twice as long as vein R2 and arising before the middle of the discal cell. p. 629 Cosmoptervgid.« MM. Vein Ri of the fore wings but little longer than vein R2, and arising beyond the middle of the discal cell. p. 631 SCYTHRIDID^ Suborder JUGATE This suborder includes those Lepidoptera in which the posterior lobe of the fore wing is specialized so as to form an organ which unites the fore and hind wings; and in which the venation of the hind wings is similar to that of the fore wings. The Jugatae includes the more generalized members of the order Lepidoptera now living, those which are believed to resemble most closely the primitive in- sects from which in ancient times the Lepidoptera were evolved. In fact the first two families here included in the Jugatae may be of even more ancient origin, repre- senting one or two lines of evolution distinct from the lepidopterous stem. Several writers have called attention to indications of trichopterous affinities of the two families in question; and a study of the wing- venation of these in- sects led me to believe that they are more closely allied to the Trichoptera than to the Lepidoptera. For this reason, in "The Wings of Insects" I classed them with the Trichoptera. Although these indications of trichopterous affinities are undoubted, it appears that the view now generally held is that, while they show a close community of descent of the Trichoptera and the Lepidoptera, they are not sufficient to warrant the removal of the families in question from the Lepidoptera. I, therefore, in- clude them, provisionsally, in this order in the following account. For a detailed discussion of this subject, see Braun ('19) and Crampton ('20 b). The suborder Jugatae, as now more commonly limited, in- cludes several families, representatives of three of which have been found in America; these are the Micropterygidas, the Eriocraniidas, and the Hepialidae. The members of the first two of these families differ greatly in appearance from those of the third family, being very small moths which resemble the small tineids in size and appearance ; our largest species has a wing expanse of from 12 to 14 mm. For this reason they may be known as the Microjugatae. They have also been termed the Jugo-frenata, because, in addition to having the posterior lobe of the fore wing specialized so as to form an organ which serves in uniting the fore and hind wings, there is also a bunch of bristles borne by the hind wing near the humeral angle, which resembles a frenulum ; these bristles, however, are not homologous with the frenulum, but are the costal spines described on page 575. On the other hand, the members of the third family are mostly large moths ; many of them are very large ; and the smaller species have a wing-expanse of 2 5 mm. The members of this family may be known as the Macrojugatae. Family MICROPTERYGID.^ The Mandihidate Jugates The members of this family are small insects which resemble tineid moths in general appearance. As with other members of the LEPIDOPTERA 593 suborder Jugatas, the venation of the hind wings closely resembles that of the fore wings (Fig. 719). But these insects differ from all Fig. 719.^ — Wings of Micropteryx. other Lepidoptera in having in the adult instar well-developed func- tional mandibles, and in that the females lack a bursa copulatrix. Chapman ('17) regards the presence of well-developed mandibles and the absence of a bursa copulatrix of sufficient importance to warrant the removal of these insects from the Lepidoptera and the establish- ment of a distinct order for them ; for this order he proposed the name Zeugloptera. Tillyard ('19) states that the wing-coupling apparatus in this family functions differently from that of the following family, in that in the Micropterygidae the jugal lobe is bent under the fore wing and acts as a retinaculum for the bunch of costal spines, borne by the hind wings. In this family, the subcosta of the fore wings is forked near its middle (Fig. 719); the abdomen of the adult female consists of ten distinct segments; and there is no ovipositor. There is no published account of the transformations of our American species. The larvae of certain exotic species have been de- scribed; they are very delicate, have long antennae, and feed upon wet moss. The pupa state is passed in the ground; the pupa has large, crossed mandibles. The adults feed on pollen. Two American species have been described; these are Epimar- tyria auricrinella, which is found in the East, and Epimartyria par- della, found in Oregon. Family ERIOCRANIID^ The Haustellate Jugates The members of this family, like those of the preceding one, are small insects which resemble tineid moths in general appearance. 594 ^iV INTRODUCTION TO ENTOMOLOGY In this family the mandibles of the adult are vestigial; the maxillae are formed for sucking, each maxilla forming half of a long sucking- tube, as in higher Lepidoptera ; and the females have a bursa copu- latrix and a piercing ovipositor. An easily observed recognition character is the fact that the subcosta of the fore wings is forked near its apex (Fig. 720). The jugal lobe of the fore wing extends back above the base of the hind wing and is clasped over an elevated part of the hind wing, thus being of the type described as a fibula (see page 62). Our best-known representative of this family is Mnemonica auricydnea. The structure and transformations of this species have Sc, Sc2 Ri 2d A Fig. 720. — Wings of Mnemonica. been described by Busck and Boving ('14). The adult has a wing- expanse of from 1 2 to 1 4 mm. The larva mines in the leaves of chestnut, oak, and chinquapin in early spring, making a large, bulgy blotch mine; it completes its growth within a week or ten days, and goes into the ground to transform, where it spins a tough cocoon; the change to pupa takes place in the following winter ; the adult emerges in April. The pupa has long, arm-like toothed mandibles, with which it cuts the tough cocoon and with which it digs its way up to the surface of the ground. This species is found in the East. Family HEPIALID^ The Swifts or the Macrojugatce The members of this family are of medium or large size. LEPIDOPTERA 595 Figure 721 represents in natural size one of the larger of the American species, but many exotic species are larger than this one. Our smaller species have a wing-expanse of at least 25 mm. Our best- known species are brown or ashy gray in color, with the wings marked with silvery white spots. It is said that these moths fly near the earth, and only in the eve- ning after sunset, hiding under some low plant, or clinging to the stalk of an herb during the dav. Some of them fly with extreme rapidity, with an irregular mazy flight, and have, therefore, been named swifts by collectors. So long as either or both of the two preceding families are retained in the suborder Jugatas, the Hepialidte may be dis- tinguished as the Macrojugatae. In the Hepialidffi the posterior lobe of the fore wing is a slender, finger-like organ, which is stiffened by a branch of the third anal vein, and which projects beneath the costal margin of the hind wing. As Fig. 721. — Sthenopis purpiirascens. the greater part of the inner margin of the fore wing overlaps the hind wing, the hind wing is held between the two. This is the type of posterior lobe of the fore wing to which the term jugum is ap- phed. (Figs. 74 and 75.) The larvas are cruciform and furnished with sixteen legs; they feed upon wood or bark, and are found at the roots or within the stems of plants. They transform either in their burrows, or, in the case of those that feed outside of roots, within loose cocoons. The pupae have transverse rows of teeth on the abdominal segments; these aid them in emerging from their burrows. This family is represented in our fauna by two genera, Hepialus and Sthenopis. Hepialus. — This genus includes our smaller species, which range in wing-expanse from 25 to 55 mm. In Hepialus the apices of the fore wings are more rounded than in Sthenopis. Ten North American species have been described. Sthenopis. — This genus includes our larger species. In these the apices of the fore wings are more pointed than in Hepialus, and in some species are subfalcate. Four species have been found in our 596 AN INTRODUCTION TO ENTOMOLOGY fauna; one of these, Sthenopis purpurdscens , is represented in Figure 721. The larva of Sthenopis argenteomaculdtus bores in the stems of the speckled or hoary alder (Alnus incana) ; that of Sthenopis thule, in willow. Suborder FRENAT^ The members of the Frenatae are most easily recognized by the fact that the venation of the hind wings differs markedly from that of the fore wings, being much more reduced. In this suborder, vein Ri of the hind wings coalesces with subcosta, the two appearing as a single vein, except that, in some cases, a short section of the base of Ri is distinct, presenting the appearance of a cross-vein between ja'yi 2d A Fig. 722.^ — Wings of Prionoxystus rohinia. radius and subcosta (Fig. 722, Ri). After the separation of vein Ri, the radial sector continues unbranched to the margin of the wing (Fig. 722, Rs). Rarely, as in some members of the Gracilariidce and of the Cosmopterygidae, vein Ri of the hind wings is free, not co- alesced with vein Sc. The essential characteristic of the Frenatse is that they are descendants of those primitive Lepidoptera in which the two wings of each side were united by a frenulimi. This fact should be clearly understood, for in many of the Frenatae the frenulum has been lost. The loss of the frenultim in these cases is due to its having been supplanted by a substitute for it, by an enlarged humeral area of the hind wings, which causes the two wings of each side to overlap to a LEPIDOPTERA 597 great extent. This overlapping of the two wings insures their syn- chronous action; and the frenulum, being no longer needed for this purpose, is lost. Illustra- tions of different stages in the reduction and loss of the frenulum are given in the discussions of family characters given later. As a rule the frenulum of the female, when present, consists of several bristles, while that of the male con- sists of a single strong, spine-like organ. If one of the bristles of the compound frenulum of a female be ex- amined, it will be found to be a typical seta, containing a single cavity. But if a frenulimi of a male be ex- amined, it will be found to contain several parallel cav- ities. Evidently the fren- uKmi of the male is com- posed of several setae, as is that of the female, but these setae are grown together. Fig. 723. hook. -Wings of a moth : / h, f renulum- This can be seen by examining a bleached wing that has been mounted in balsam ; usually the cavities in the setae contain air, which renders them visible. The frenulum -hook, which is present in the males of certain moths, is a membranous fold on the lower surface of the fore wing for receiv- ing the end of the frenulum, and thus more securely fastening the two wings together (Fig. 723, / /z). As a rule the frenulum-hook arises from the membrane of the wing near the base of cell C; but in some moths iCastnia) it seems to have been pulled back so that it arises from the subcostal vein. THE GENERALIZED FRENAT^ Under this heading are grouped those families of moths that are supposed to retain more nearly than any other Frenatffi the form of the primitive Frenatae, those that were the first to appear on earth. In most of the families included here, the wings approach the typical form, except in the reduction of the number of branches of radius of the hind wings, which is true of all Frenatse ; usually the base of media of one or both pairs of wings is preserved throughout a considerable part, at least, of the discal cell; and the anal veins are well preserved, there being two or three in the fore wing and three in the hind wing. The frenulum is usually well preserved. 598 .4 7V INTRODUCTION TO ENTOMOLOGY There are also included in this group of families those families in which the fixed hairs or aculese are retained over the general surface of the wings, even though in some cases, as in the Nepticulidas, the venation of the wings may be greatly reduced. The presence of aculeas distributed over the general surface of the wings is believed to indicate a generalized condition, as it is found elsewhere in the Lepidoptera only in the Jugatae. As this condition is also found in the Trichoptera, it was probably inherited from the stem form from which the Lepidoptera and the Trichoptera were evolved. In the more specialized Lepidoptera the aculese are confined to small areas of the wing surface or have been lost. Family INCURVARIID.E This family and the following one differ from all other Frenatae and agree with the Jugatae in having retained aculeae distributed over the general surface of the wing (Fig. 710). In this famity the venation of the wings is but little reduced; the antennae are without an eye- cap; and the females, so far as is known, are furnished with a piercing ovipositor. The moths are small or of moderate size. Many of the larvae are miners when young, and later are case bearers. The family Incurvariidae includes three subfamilies, which are not very distinct but which, however, are treated as families by some writers. Subfamily Adeline. — These tiny moths are characterized by the unusually long and fine antennae of the males, which may be twice or more than twice as long as the wings. Some of the species are also conspicuous on account of their striking colors and markings. The larv^ae are elongate, cylindrical, with thoracic legs and five pairs of prolegs. They are at first miners; later they live in portable cases. They feed on the leaves of various herbs and shrubs; but none of our species is known to be of economic importance. Nearly all of our species belong to the genus Adela. Subfamily Incurvariin^..^ — An interesting representative of this division of the family Incurvariids is the following well-known species. The maple-leaf cutter, Paraclemaisia acerifoliella.- — The larva in- fests the leaves of maple, and occasionally is so abundant that it does serious injurv. The larva is at first a leaf -miner, like other adelids; but later it is a case-bearer. The leaves of an infested tree present a strange appearance (Fig. 724). They are perforated with numerous elliptical holes, and marked by many, more or less perfect, ring-like patches in which the green substance of the leaf has been destroyed but each of which incloses an uninjured spot. These injuries are produced as follows: The larva, after living for a time as a leaf-miner, cuts an oval piece out of a leaf, places it over its back, and fastens it down with silk around the edges. This serves as a house beneath which it lives. As it grows, this house becomes too small for it. It then cuts out a larger piece which it fastens to the outer edges of the smaller one, the LEPIDOPTERA 599 Fig. 724. — Leaf infested by the maple-leaf cutter. larva being between the two. Then it crawls halfway out upon the leaf, and by a dexterous lifting of the rear end of its body turns the case over so that the larger piece is • over its back. When it wishes to change its location it thrusts out its head and fore legs from the case and walks off, looking like a tiny turtle. When it wishes to eat, it fastens the case to the leaf and, thrusting its head out, eats the fleshy part of the leaf as far as it can reach. This explains the circular form of the patches, the round spot in the center indicating the position of the case. The insect passes the winter in the pupa state within its case, which falls to the ground with the infested leaf. The moth is of a brilliant steel- blue or bluish green color, without spots but with an orange-colored head; it appears in early summer. Subfamily Prodoxin^..^ — This subfamily includes the remarkable insects that are known as the yucca- moths and the closely allied bogus yucca-moths. The yucca-moths, Tegettcula. — Four species of this genus are now recognized; the best-known of these is Tegettcula alba. The life- history of this species was first described by Mr. C. V. Riley ('73), under the name Pronuba yuccasella; and in most of the accounts of this insect this name is used. The moth, however, was first de- scribed as Tegeticula alba. The most complete account of this and the allied species is that of Riley ('92). This species infests Yticca filamentosa, a plant not fitted for self- pollination or for pollination by insects in the ordinary ways; in fact, it is pollinized only by moths of the genus Tegeticula, the larvae of which feed on its seeds. This is one of the few cases in which a particular plant and a particular insect are so specialized that each is dependent upon the other for the perpetuation of the species. In the female moth, the maxillse are each furnished with a long, curled, and spinose appendage, the maxillary tentacle (Fig. 725, b), fitted for the collection of pollen. After collecting a large load of pollen, often thrice as large as the head (Fig. 725,), the female moth places her eggs, by means of her long, extensile ovipositor, into an ovary, usually of another flower than that from which the pollen was collected. After oviposition, the moth runs up to the tip of the pistil and thrusts the pollen into the stigmatic opening. Thus is insured the develop- rhent of seeds, upon which the larvse hatched from the eggs placed in the ovary are to feed. As many more seeds are developed than are needed by the larvae, the perpetuation of the yuccas is assured. 600 AN INTRODUCTION TO ENTOMOLOGY The full-grown larva leaves the yucca pod and makes its way to the ground, where it spins a dense cocoon several inches belowthe surface. The adult moth has a wing-ex- panse of about 2 5 mm. The front wings are silvery white above ; the hind wings, semi- transparent. The bogus \aicca- moths, Prodoxus. — The moths of this ge- nus are closely allied to the yucca-moths, but differ in the im- portant particular that the females lack maxillary tentacles; they are consequently incapable of pollinat- ing the yuccas as do the true A^ucca -moths. The larvae of Prodoxus feed in the flower-stem or in the flesh of the fruit. But as, in Yucca filamentosa at least, the flowers drop and the flower-stem withers if the flowers are not pollinated, the bogus yucca-moths are dependent on the true yucca-moths for the conditions necessary for the develop- . ment of their larvae. The pupa state is passed in the burrow made by the larva. Eleven species of Prodoxus have been described. Fig. 725. — Tegeticula alba: a, side view of head and neck of female denuded ; i , load of pollen ; 2, maxil- lary tentacle; 3, maxilte; 4, maxillarj' palpi; 5, antennae; b, maxillar\^ tentacle and palpus; c, an enlarged spine; d, maxillary palpus of male; f, scale from front wing; /, front leg; g, labial pal- pus; /;•, i, venation of wings; j, last segment of abdomen of female, with ovipositor extruded. All enlarged. (From Riley.) Family NEPTICULID^ In this family, as in the preceding one, fixed hairs or aculeae are distributed over the general surface of the wings. In the Nepticulidae the venation of the wings is much reduced; the basal segment of the antennae is enlarged and concave beneath, so as to form an eye-cap ; the female is without an ovipositor; the labial palpi are short; the maxillary palpi are long; and the maxillse are vestigial. This family includes the smallest of the Lepidoptera, some of the -species having a wing-expanse of scarcely 3 mm. Although this family presents characteristics which indicate that it should be placed among the generalized Lepidoptera, the venation of the wings is greatly reduced. This indicates that it represents a distinct line of development which in some respects has become more highly specialized than are the other families included in this division of the Lepidoptera. The f renulimi of the female consists merely of a group of small , functionless bristles; but in the male the frenulum is a strong, spine- LEPIDOPTERA 601 like organ, which hooks into a well-developed frenulum hook (Fig. 726); in most cases the costal spines are well developed; this is shown in the accompany- ing figure; and the anal lobe of the fore wing is sometimes quite distinct. With the exception of several gall-making spe- cies of Ectoedcmia, the lar- vas of all species of which the life-history is known are miners within the tissues of leaves (rarely in fruits) or in bark. They show a preference for trees and shrubs, but some mine in the leaves of herbaceous plants. The larva at first makes a very narrow linear mine. This mine may continue as a linear mine, gradually broadening throughout its course, or it may at some period abruptly enlarge into a blotch. When full-grown, the larva, with few exceptions, leaves the mine and, drop- ping to the ground, spins a dense, flattened cocoon amongst rubbish or in the loose surface soil. (Braun '17.) More than seventy species have been described from our fauna, and doubtless many more are to be discovered. The Nepticulidas of North America was monographed by Braun ('17). Fig. 726. — Wings of Obrussa ochre fasciella, male. (After Braun.) Family COSSID^ The Carpenter-Moths This family includes moths with spindle-shaped bodies, and nar- row, strong wings, some of the species resembling hawk -moths quite closely in this respect. The larvae are borers; many of them live in the solid wood of the trunks of trees. The wood-boring habits of the larvae suggest the popular name carpenter-moths for the insects of this family. These moths fly by night and lay their eggs on the bark of trees, or within tunnels in trees from which adult carpenter-moths have emerged. The caterpillars are nearly naked, and, although furnished with pro-legs as well as true legs, are grub-like in form. The pupa state is passed within the burrow made by the larva. When ready to change to an adult, the pupa works its way partially out from its burrow. This is accomplished by means of backward-projecting saw- like teeth, there being one or two rows of these on each abdominal segment. After the moths have emerged, the empty pupa-skins can be found projecting from the deserted burrows. 602 AN INTRODUCTION TO ENTOMOLOGY The carpenter-moths are of mediiim or large size. The antennce of the males are mostly bipectinate; those of the females are either very slightly bipectinate or ciliate. In a few species the antennas are lamellate. The ocelli are wanting, and the maxillae are vestigial. The venation of the wings of our most common and most widely distributed species is shown in Figure 727. There are two well-preserved anal veins in the fore wing, and three in the hind wing. The base of media is preser^^ed, and is forked within the discal cell. In the fore 7^4 — TdA'^^^ Fig. 727. — Wings of Prionoxystus robinice. wing the veins R3 and R4+5 anastomose, forming an accessory cell. The frenulum is vestigial in this genus ; but in some other genera it is well developed. Authors differ greatly regarding the appropriate position of this family in the series of families. Certain characteristics of the larvae indicate that it belongs somewhere among the specialized Micro- frenatas; but I place it here at the beginning of the Non-aculeate Generalized Frenatae on account of the generalized structure of the wings. This family is represented in our fauna by thirty-four described species; it has been monographed by Barnes and McDunnough ('11). The family includes three subfamilies, which are separated as follows: LEPIDOPTERj 603 A. Anal veins of the fore wings united near the margin of the wing by a cross- vein HYPOPTIN^ AA. Anal veins of the fore wings not united near the margin of the wing, by a cross- vein. B. Veins Rs and Mi of the hind wings stalked or close together at the end of the discal cell; antennas of male pectinate throughout Cossin^ BB. Veins Rs and Mi of the hind wings widely separate; antennas of male pectinate on basal half only Zeuzerin^ Subfamily Hypoptin^.- — The members of this subfamily are dis- tinguished by the presence of the anal cross-vein near the margin of the front v^ings . Nearly one-half our species belong to this, subfamily. They have been described from Florida, Texas, Colorado, and west- ward to California. I have found no ac- count of the early stages of any of them. Subfamily Cos- sin^,. — This subfam- ily is represented in our fauna by six gen- era including fourteen species ; but most of these are confined to the Far West and are known only in the adult state. Our best -known species are the following. The locust-tree carpenter-moth, Prionoxystus rohlnicB.- — Figure 728 represents the female, natural size. The male is but little more than half as large as the female. It is much darker than the female, from which it differs also in having a large yellow spot, which nearly covers the outer half of the hind wings. The moths fly in June and July; the larvae bore in the trunks of locust, oak, poplar, willow, and other trees. It is supposed that the species requires three years to complete its transformations. It is found from the Atlantic Coast to California. The lesser oak cavpenter-worm, Prionoxystus macmurtrei. — This is a slightly smaller species than the preceding. The larva bores in the trunks of oak in the East. The moth has thin, slightly transparent wings, which are crossed by numerous black lines. The male is much smaller than that of P. rohinice, and lacks the yellow spot on the hind wings. Subfamily Zeuzerin^.. — Excepting three little-known species of Hamilcara, found in Texas and Arizona, the following species is the only representative of this subfamily in our fauna. The leopard -moth, Zeuzera pyrina.- — This species is white, spotted with ntimerous small, black spots, which suggested its common name. The adult has a wing-expanse of from^o to 60 mm. It is a European Fig. 728. — Prionoxystus rohinicE, female. 604 AN INTRODUCTION TO ENTOMOLOGY Species, which was first obsen^ed in the vicinity of New York Citv in 1882; since that time it has spread to other parts of the East. The lar\^a is a very injurious borer in many species of trees and shrubs. The young larvae bore in the small twigs ; later they migrate to larger limbs or to the trunk. Family PYROMORPHID^ Fig. 729.— .4c- oloithus fal- sarius. Fig. 730. — Wings of Acoloithus falsarius. The Smoky Moths There are but few insects in our countr}^ pertaining to this family ; only fifteen species are now recognized, but these represent sLx genera. These are small moths, ^^^v^^^ which are ^^Pft^^ chiefiy of a " smoky black color; some are marked with brighter colors; the wings are thinly scaled ; and the maxillae are well developed. The larvas are clothed with tufted hair; they have five pairs of proiegs, which are provided with normal hooks. A tiny representative of the family which seems to be not uncommon in the East is Acoloithus falsarius. This moth (Fig. 729) expands 16 mm. It is black, with the prothorax of an orange color. The venation of the wings (Fig. 730) is peculiar, in that subcosta and radius of the hind wings coalesce for onlv a short distance beyond the middle of the discal cell, and a stump of radius projects towards the base of the wing, from the point of union of the two veins. The larva feeds in early siunmer on the leaves of grape and of Virginia creeper. It is said that the pupa state lasts fourteen days and is passed within a parchment-like cocoon. The adults frequent flowers in the daytime. Another well-known species is Pyrcmorpha dimididta. This is found in the Atlantic and Western States. The entire insect is smoky black, except the basal half of the fore wings in front of the second anal vein, and the basal half of the costa of the hind wings, which are yellow. The wings are thinly scaled and expand 25 mm. or a little more. The male is larger than the female and is more active. Figure 731 represents the venation of the wings. Some spe- cies of the genus Pyromorpha are remarkable in that none of the branches of radius of the fore wings coalesce beyond the discal cell. LEPIDOPTERA 605 Figure 732 represents the venation of the wings of Pyromorpha marteni, a spe- cies found in the Rocky Mountains. The species of the genus Harrisina differ from the typical form of the family in that the anal area of the hind wings is greatly re- duced, there being only two short, strongly curved, anal veins. As in other mem- bers of the family, there are two well-developed anal veins preserved in the fore wings. The following is the best-known species of this genus. The grape-leaf skeleton- izer, Harnsma americdna. — The wings of this moth are Fig- 731- — -Wings of Pyromorpha dimidiata long and narrow (Fig. 733); the abdomen is long, and widened towards /?. J^ Fig. 732. — Wings of Pyromorpha marteni. Fig- 733- — Harrisina americana. the 'caudal end. It is green- ish black in color, with the prothorax reddish orange. The larva feeds on the leaves of grape and of the Virginia creeper. An entire brood of these larvae will feed side by side on a single leaf while young. This species rarely becomes of economic im- portance. Family DALCERID^ In this family the body is small; the antennae are short; and the wings are broad. In the fore wings there is a large acces- sory cell which is ist R3; and in the hind wings veins Sc and R are connected at a point. 606 AN INTRODUCTION TO ENTOMOLOGY The best -known species in our fauna is Dalcerides ingenita, found in Arizona. The expanse of the wings is about 25 mm. The wings are deep yellow, inclining to orange, without markings. The larva is unknown. Another species, Pinconia coa, which is not uncommon in Mexico has been reported from Arizona by Holland ('03). Family MEGALOPYGID^ The Flannel-Moths, In this family the wings are heavily and loosely scaled, and mixed with the scales are long, curly hairs ; these give the wings the appear- ance of bits of flannel. It is this that suggested the com- mon name of these moths. The body is stout and clothed with long hairs. The venation of the wings of our most common species, Lagda crispdta, is represented in Figure 734. There are three anal veins in both fore and hind wings; but in the fore wings the second and third anal veins are partially grown together. The basal part of media is more or less distinctly presented and divides the dis- cal cell into two nearly equal parts. The subcosta and ra- dius of the hind wings coalesce for nearly the entire length of the discal cell. In these moths the maxillae are vestigial. The larvse are remarkable for the possession of seven pairs of prolegs ; these are borne by ab- dominal segments 2 to 7 and 10; but those of segments 2 and 7 are without hooks. The setiferous tubercles are verrucse bearing large numbers of fine setse ; so that the body is densely hairy ; and inter- spersed among the fine setse are venomous setae. There are only ten North American species of this family; these represent four genera. Our most common species are the two follow- ing. The crinkled flannel-moth, Lagda crispdta. — This moth is cream- colored, with the fore wings marked with wavy lines of crinkled black and brownish hairs. The male is represented in Figure LEPIDOPTERA 607 Fig- 736. — Old LOLcjon Megalopyge open iilai is. 735; the female is larger expanding, 40 mm. In the female the an- tennse are very narrowly pectinate. The lar- vae feed on many trees and shrubs, including oak, elm, apple, and raspberry. They are short, thick, -Lagoa crispata, male, and fleshy, and are covered with a dense coat of long, silky, brown hairs, which project upward and meet to fonn a ridge or crest along the middle of the back ; interspersed among these fine hairs are venomous setce. The cocoons are of a firm, parchment-like texture, covered with a thin w^eb of rather coarse threads. Mixed, with the silk of the cocoon are hairs of the lar\'a. The cocoon is provided with a hinged lid. This species is found in the Atlantic States. Megalopyge operciddris. — This species is somewhat smaller than the preceding one; the male has a wing-expanse of about 25 mm., and the female of about 37 mm. The fore wings are umber brown at base, fading to pale yellow outwardly; they are marked with wavy lines of white and blackish hairs, and the fore margins are nearly black. The larvag are clothed with long, silky hairs, underneath which are venomous setae. The cocoons are firmly attached to a twig of the infested tree, and are each fur- nished with a trapdoor. The old cocoons that one sees in collec- tions present the appearance rep- resented in Figure 736. But I found in Mississippi a cocoon, which I believe to be of this species, that is of the form shown in Figure 737. From this it ap- pears that after the outer layer of the cocoon has been made, the larva constructs a hinged partition near one end of it, and adds no more silk to that part of the cocoon which is outside the partition. This part of the cocoon is quite delicate, and is destroyed when the moth emerges if not before. =^^W Complete cocoon of Megal- This species is found from North Carolina to Texas, is a very general feeder; it is often found on oak. The larva 608 AN INTRODUCTION TO ENTOMOLOG Y Family EUCLEID^* The Slug-Caterpillar Moths One often finds on the leaves of shrubs or trees, elHptical or oval larvae that resemble slugs in the form of the body and in their gliding motion. As these are the larvae of moths they have been # termed slug-caterpillars; but they present very little similarity in form to other caterpillars. The resemblance to slugs is greatly increased by the fact that the lower sur- face of the body is closely applied to the object upon which Fig. 738. the larva is creeping, the thoracic legs being small and the prolegs wanting. There is, however, on the ventral side of the abdomen a series of sucking-disks, which serve the purpose of prolegs. The head of the larva is small and retractile. In some species the body is naked; in others it is clothed with tufts of hairs; and in others there is an armature of branching spines. Several species bear venomous setae. The larvffi when full-grown spin very dense cocoons of brown silk; these are egg-shaped or nearly spherical, and are furnished at one end with a cap which can be pushed aside by the adult when it emerges (Fig. 738). The cocoons are usu- ally spun between leaves. The moths are of me- dium or small size ; the body is stout, and the wings are heavily and loosely scaled. The maxillae are vestigial. These moths vary greatly in appearance, and many of them are very prettily col- ored. Considerable variation exists in the venation of the wings in this family (Fig. 739 and Fig. 740). The base of media may be preserved or wanting; in some species it is forked within the discal cell, in others not. There is , also considerable variation '"^ in the coalescence of the ^^S- 739-— Wings of Adonda spmuloides. branches of radius, but veins R3 and R4 coalesce to a greater extent than any other branches of this vein. There is no accessory cell. In the hind wings veins So *This family is termed the Cochlidiidae by some writers, and by others the Lima codidae. LEPIDOPTERA 609 and R coalesce for a short distance at the point where vein Ri joins vein Sc. Only forty-three North American spe- cies of eucleids have been described ; but these represent twen- ty genera. The larva> are rarely abundant enough to be of eco- n o m i c importance ; they are chiefly inter- esting on account of their remarkable forms. The following are some of the bet- ter-known species: The saddle-back caterpillar, Sabine stimulea.- — This larva can be recognized by Figure 741. Its most characteristic feature is a large green patch on the back, resem- bling a saddle-cloth, while the saddle is represented by an oval purplish brown spot. The moth is dark, velvety, reddish brown, with two white dots near the apex of the fore wings. The larva feeds on oaks and oth- er forest trees. This is one of the species that are armed with ven- omous setas. The spiny oak-slug, Euclea delphmii. — This larva (Fig. 742) is one of the most common of our slug caterpil- lars and one of those that are armed with venomous setae. It feeds on the leaves of oak, pear, willow, and other trees. The moth (Fig. 743) is cinnamon-brown, with a variable number of bright green spots on the fore wings. The hag-moth, Phobetron pithecium. — The common name hag- m oth is applied to the larva of this species on account of its remarg- Fig. 740. "/ IS/- A -Wings of Packardia geminata. Euclea delphinii, 610 AN INTRODUCTION TO ENTOMOLOGY able appearance (Fig. 744). It bears nine pairs of fleshy appendages which are covered with brown hairs. In the full-grown larva the third, fifth, and seventh pairs of appendages are longest ; these are twist- ed up and back, and sug- gest the disheveled locks of a hag. This larva feeds on various low shrubs and the lower branches of trees. At the time of spinning, the larva sheds the fleshy processes, and they re- main on the outside of the cocoon. The skiff -caterpillar, Prolimacodes hddia. — This remarkable larva (Fig. 745) is not un- common on oak and other forest trees. It is pale apple-green, with a chestnut-brown patch on its back. The moth (Fig. 746) is light cinnamon-brown, with a tan- brown triangular spot on each fore wing. Fig. 744. — Phobetron pithe- cium, larva. (After Dyar.) Fig- 7 A5-— Prolima- codes badia, larva. Family EPIPYROPID^ Fig. 746. — Prolima- codes badia. This family is represented in our fauna by a single rare species which was found in New Mexico. Our species is Eptpyrops barheridna. Another species, Eptpyrops ancmala, has been described from China; and larvae that are believed to belong to this genus have been found in Central America. These insects are remarkable on account of the extraordinary habits of the larva?, which are found firmly attached to living insects of the family Fulgorida?. They are usually attached to the dorsal surface of the abdomen beneath the wings of their host. The body of the larva is covered with a cottony coat, causing it to resemble a Coccus. It is supposed that these larvse feed on waxy matter excreted by the fulgorids. For a detailed account of our species, see Dyar ('02). THE SPECIALIZED MICROFRENAT^ In the "Synopsis of the Lepidoptera" given on pages 581 to 584 I have grouped together under the heading "Specialized Microfren- atas" twenty-six families of moths, which are more highly specialized than are the preceding families, and which as a rule are composed of small insects. This group of families includes most of those families that were formerly classed together as the Microlepidoptera; but later studies have resulted in the removal from the old group Microlepidoptera o LEPIDOPTERA 611 several families of small moths, hence this name is no longer distinc- tive. Among the families of small moths removed from theMicro- lepidoptera are theMicropterygidas and theEriocraniidee.now placed in the suborder Jugate; the Incurvariidae and the Nepticulidaj, placed at the beginning of the Frenatae; and the group of families now known as the Pyralids, which are believed to be genetically quite distinct from the other families of small moths. On the other hand, in ad- dition to the families here placed in this series some authors include the Cossidse. The families of the Microfrenat£E are grouped into superfamilies in various ways by different writers ; but none of these groupings is sufficiently well established to be adopted here. Family ACROLOPHID^ These are large, stout, noctuid-like moths; some of the species have a wing-expanse of 30 mm. or more. The eyes are usually hairy, in which respect they differ from other "Micros." The antennas are without an eye-cap. The labial palpi are large, and usually upcurved to the middle of the front; in the males of some species they are thrown back on the dorsum of the thorax, which they equal in length. The first segment is relatively very large; when the palpus is short it is longer than the second segment ; the thorax is tufted. The vena- tion of the wings is quite generalized ; the base of media is more or less preserved, and all the branches of the branched veins are present ; there are three anal veins in both fore and hind wings; in the fore wings the tip of the third anal vein coalesces with the second anal vein. Forty-two species have been described from our fauna; these were formerly classed in several genera ; but recent writers refer them all to the genus Acrolophus. The burrowing web-worms, A. arcanellus, A. mortipennellus , and A. popeanellus. — The habits of these three species were described by Professor Forbes in his Twelfth Illinois Report (1905). The larvag normally live in the ground feeding on the roots of grass. Each larva makes "a tubular web opening at the surface and leading down into a vertical cylindrical burrow about the diameter of a lead-pencil, and six inches to two feet, or even more in depth." The larva measures about 25 mm in length. Sometimes the larvae injure young corn when planted on sod. They surround the base of each plant with a fine web mixed with earth and pellets, building this up in the lower blades, which they slowly eat away. As they get larger they eat the stripped plant to the ground. When disturbed they retreat into their web-lined burrows. Family TINEID^ The head is usually clothed with erect hair-like scales. The antennce are shorter than the front wings. The maxillag are usually small or vestigial. The maxillary palpi are usually large and folded. 612 AN INTRODUCTION TO ENTOMOLOGY Fig. 747. — Wings of Tinea parasitella. (After Spuler.) The labial palpi are short and clothed with bristles or with the first segment enlarged. In the typical genera the venation of the wings is quite generalized (Fig. 747), the base of me- dia being preserved in both fore and hind wings and all of the veins characteristic of theFrenatffibeingpres- ent ; but in other gen- era the venation is somewhat reduced. Many of the larvae are case-bearers ; many are scavengers or feed on fungi; some feed on fabrics, especially those that contain much wool ; few if any feed on leaves. This is a large family. More than one hundred twenty -five North American species are already known; fifty of these belong to the genus Tinea. To this family belong the well-known clothes-moths. The naked clothes-moth, Tineola hiselliella. — This is our most common clothes-moth. Although the larva spins some silk wherever it goes, it makes neither a case nor a gallerv^; it is, therefore, named the naked clothes-moth. But when the larva is full-grown it makes a cocoon, which is composed of fragments of its food-material fas- tened together with silk. The adult is a tiny moth with a wing- expanse of from 12 to 16 mm.; it is of a delicate straw-color, without dark spots on its wings. The case-bearing clothes-moth, Tinea pellionella. — The larva of this species is a true case-bearer, making a case out of bits of its food-material fastened together with silk. The case is a nearly cylin- drical tube open at both ends. The pupa state is passed within the case. The adult is a small, silky, brown moth, with three dark spots on each fore wing. It expands from 11 to 17 mm. The tube-building clothes-moth or the tapestry-moth, Trichoph- aga tapetiella. — The larva of this species makes a gallery composed of silk mixed with fragments of cloth. This gallery is long and wind- ing and can be easily distinguished from the case of the preceding species. The pupa state is passed within the gallery. The moth differs greatly in appearance from the other two species, the fore wings being black from the base to near the middle, and white beyond. It expands from 12 to 24 mm. LEPIDOPTERA 613 Family PSYCHID^ The Bag-Worm Moths The bag-worm moths are so called on account of tiie silken sacs made by the larv«, in which they live and in which they change to pupse. In our more conspicuous and best-known species the sac is covered either with little twigs (Fig. 748) or, in the case of a species that feeds on cedar or arbor-vitas, with bits of leaves of these plants. When the larva is full-grown it fastens its sac to a twig or other object and transforms within it. In the adult state the two sexes differ greatly. The female is wingless, and in some genera the eyes, an- tennae, mouth-parts, and legs are vestigial or wanting, the body being quite maggot-like. At the caudal end of the body there is a tuft of hair-like scales which are mixed with the eggs. In most species the female does not leave the sac before oviposition but deposits her eggs within it. The male moths are winged; they are small or of Fig. 748. — Bag moderate size. The wings are thinly scaled and in °^ Oiketicus some species nearly naked; when clothed with scales ^^^°^'^- they are usually of a smoky color without markings. The venation of the wings varies ^^Jil greatly within the ^'^"""^"^ " family. Figure 749 represents the vena- tion of our most com- mon species. Only about twenty species are known from our fauna, of which the following are most likely to be observed. Abbot's bag- worm, Oiketicus abhoti. — This species occurs in the more southern part of our country. The lar- va makes a bag with sticks attached to it crosswise (Fig. 748). The adult male is Fig.j^g.—Wingsoi Thyridopteryx ephemerce. sable brown, with a formis. vitreous bar at the ex- tremity of the discal cell of the fore wings ; the narrow external edging of the wings is pale ; the expanse of the wings is 33 mm. 614 AN INTRODUCTION TO ENTOMOLOGY The evergreen bag-worm or the bag-worm, Thyridopteryx ephe- mercBformis.- — This species prefers red cedar and arbor-vitae, and for this reason has been named the evergreen bag-worm; but it also feeds on many other kinds of trees, and as it is the species that is mosthkely to attract attention, and is sometimes a serious pest, it is often called the bag-worm. It is our best -known species, and its life-history will serve as an illustration of the habits of the members of the family Psychidae. The bag of this species is about the same size as that of Abbot's bag -worm (Fig. 748); but it differs in being covered with bits of leaves when it feeds on cedar or arbor-vits, or with twigs attached lengthwise when it feeds on other trees. When full-grown the larva fastens the bag to a twig with a band of silk, and then changes to a pupa. When the male is ready to emerge, the pupa works its way to the lower end of the bag and halfway out of the opening at the extremity. Then its skin bursts and the adult emerges. The male moth has a black, hairy body and nearly naked wings (Fig. 750). The adult female partly emerges from the pupa skin and pushes her way to the lower end of the bag, where she awaits the approach of 750. — Thyridop- the male. She is entirelv destitute of wings and ephemerce- ^^gg ^j^g genitalia "of the male can be greatly extended, making possible the pairing while the female is still in the bag. After pairing, the female works her way back into the pupa skin, where she deposits her eggs mixed with the hair-like scales from the end of her body. She then works her shrunken body out of the bag, drops to the ground, and perishes. The eggs remain in the pupa skin in the sac till the following spring. Where this insect is a pest, two methods of control are practiced, first, the bags are collected and destroyed in the winter, while they still contain the eggs; second, when impracticable to collect the bags: on account of the height of the infested trees, a spray of arsenate of lead is used in the spring as soon as possible after the larvae appear. Eurycyttarus confederdta. — This is a smaller species than the two preceding ones. Figure 751 represents the sac of a male with the empty pupa-skin projecting from the lower end, and Figure 752 the fully developed male. -^^S- 752. Solendbia walshella. — This is a small Fig. 751. tineid-like species; the male has a wing-expanse of about 13 mm. and the hind wings have a quite wide fringe. The fore wings are light gray speckled with brown. The bag of the larva is about 8 mm. long, made of silk, and covered with fine grains of sand or with particles of lichens and excrement of the larva. Cham- bers states that he has sometimes found small molluscan shells ad- hering to it. The larvae are found on the trunks of trees and feed iP|» LEPIDOPTERA 615 upon lichens. Figure 753 represents the venation of the wings of a European species of this genus. Fig. 753- ler.) -Wings of Solenohia. (After Spu- Family TISCHERIID^ The vertex of the head is clothed with erect, broad, and short scales. The an- tennee are long, with the first segment small. The maxillae are longer than the head and thorax. The max- illary palpi are small or ab- sent. The labial palpi are short, porrect, and without bristles on the outer side of the second segment. In the front wings (Fig. 754), the costal margin is strongly arched, the apex is pro- longed into a sharp point, the discal cell is long and narrow, the accessory cell is very long, and the "base of media is preserved. The hind wings are long and narrow and with greatly reduced venation. (Fig. 754). The hind tibiae are very hairy. Nearly all of our spe- cies belong to the genus Tischeria. The larvae lack thoracic legs; most of them make blotch mines in the leaves of oak; but the following one infests apple; and some other species infest blackberry and rasp- berry. The trumpet-leaf miner of apple, Tischeria malifoliella. — This spe- cies infests the leaves of apple over the Eastern half of the United States and Canada, and sometimes does serious injury. The larva makes a trumpet-shaped mine just beneath the epidermis on the upper side of the leaf; the first half of the mine is usually crossed by crescent-shaped stripes of white. There are two generations annually in the North, and several in the South. The larvae pupate in their mines. The larvae of the last generation line their mines with silk and pass the winter in them. They transform Fig- 754- — Wings of Tischeria marginea. Spuler.) (After ei6 AN INTRODUCTION TO ENTOMOLOGY to pupas in the spring and emerge as adults eight or ten days later. The adult moth expands about 6 mm. ; it has shining dark brown front wings, tinged with purplish and dusted with pale yellowish scales. To control this pest, plow the orchard after the leaves have fallen, or rake and bum the fallen leaves. Family LYONETIID^E Pig. 755. — Wings of Bedellia somnulentella. (After Clemens.) Moths with the head smooth, at least on the front. The scape of the antennae usually forms an eye-cap. The ocelli and the maxillary- palpi are wanting. The „ 5^ labial palpi are usually j^j___5^-- ^c:;;;;^ — :::rr::;-^ very small. The wings are ver\' narrow (Fig. 755); the hind wings are often linear, with the radial sector ex- tending through the axis of the wing. The apices of the wings are usually warped up or down. The larvae are leaf-miners or live in webs between leaves. The following species will serv^e as examples of this family. The morning-glory leaf-miner, Bedellia somnu- lentella.-— The young larva makes a serpentine mine with a central line of frass; later it leaves this mine and makes a blotch mine. The pupa is naked, and fixed by the caudal end to some cross- threads on the under side of the leaf. The adult is yellow and expands about 10 mm. The apple bucculatrix, Bucculdtrix pomifoU- ella. — The larv^a of this species infests the leaves of apple, and when full-grown it makes a small white cocoon which is attached to the lower sur- face of a twig. These cocoons sometimes occur in great nimibers, side by side, on the twigs of an infested tree (Fig. 756). They are easily recog- nized by their shape, being slender and ribbed lengthwise. It is these cocoons that usually first reveal the presence of the pest in an orchard. They are very conspicuous during the winter, when the leaves are off the trees. At this time each cocoon contains a pupa. The adult moth emerges in early spring. The eggs are laid on the lower sur- face of the leaves. Each larva when it hatches bores directly from the egg to the upper surface of the leaf, where it makes a brown serpentine mine. When these Fig. 756. — Cocoons of Bucculatrix pomifoliella. LEPIDOPTERA 617 mines are abundant in a leaf, it turns yellow and dies. When the larva has made a mine from 12 to 18 mm. in length, which it does in from four to five days, it eats its way out through the upper surface. Then somewhere on the upper surface of the leaf it weaves a circular silken covering about 2.5 mm. in diameter. Stretched out on this network, the larva, which is now about 2.5 mm. long, makes a small hole in it near the edge, then, as one would turn a somersault, it puts its head into this hole and disappears beneath the silken covering, where it undergoes a change of skin. It remains in the molting cocoon usually less than 24 hours. After leaving this cocoon it feeds upon the leaves without making a mine; and in a few days makes a second molting cocoon which differs from the first only in being about 3 mm. in diameter. After leaving this it again feeds for a few days, and then migrates to a twig where it makes the long ribbed cocoon within which the pupa state is passed. The adult is a tiny, light brown moth, with the fore wings whitish, tinged with pale yellowish, freely dusted with brown ; on the middle of the inner margin there is a dark brown oval patch. The genus Bucculatnx, to which the above species belongs, is placed by some writers in a separate family, the BucculatrigidcB. The family Opostegid^ has been established for the genus Opostega, of which only three species have been found in this country. These are moths with folded maxillary palpi, with the scape of the antennae forming a large eye-cap, andwith radius, media, and cubitus of the fore wings unbranched. The hind wings are linear. The combination of the eye-cap and the unbranched veins of the fore wings is a distinctive feature of this family. The larvae are very slender, cylindrical, without legs, and are bast- miners. Family OINOPHILID^ This family includes "strongly flattened moths, with flat coxae closely appressed to the body, usually with smooth heads, rising to a rounded ridge between the antennas, but often with a loose tuft on the vertex, and rather small maxillary palpi of the folded type. The labial palpi have a well-set-ofi^, fusiform, terminal joint as in the Tineidae, and are normally without bristles. The venation in the known genera is more or less reduced." (Forbes.) Only one species representing this family has been found in our fauna. This is Phceoses sabinella, described by Forbes ('22), from Louisiana and Mississippi. It is a shining gray-brown (mouse gray) moth, with a wing-expanse of 9 mm. The known larvae of this family feed on decaying vegetable matter and fungi. Family GRACILARIID^ The vestiture of the head varies greatly; the vertex is clothed with prominent scales in some forms, in others it is smooth. The 618 AN INTRODUCTION TO ENTOMOLOGY Fig- 757- — Wings of Cracilaria. (After Spuler.) antennae are long; the scape forms an eye-cap in some species and not in others. The fore wings are lanceolate, normal or with some- what reduced vena- tion (Fig. 757) ; usu- ally without an ac- cessory cell, but sometimes one is present in the genus Ornix. The hind wings are lanceolate or linear; in many members of the family they are ex- panded near the base, formingamore or less prominent hump in the costal margin, and in some species vein Ri is free, not coalesced with vein Sc. The adult moths when at rest elevate the front part of the body, the fore legs being held vertically so that the tips of the wings touch the surface on which the insect rests. The larvae are extraordinary; when young they are very much flattened and have thin, blade-like mandibles and vestigial maxillae and labium; they merely slash open the cells of the leaf and suck up the cell-sap; later they usually have normal mouth-parts and eat the parenchyma. The young larvcS always make a fiat blotch mine; later they make a blotch mine in which the epidermis of one side of the leaf is thrown into a fold by the growth of the leaf, i. e., a tenti- form mine, or they roll a leaf. The larvae have only fourteen legs or none, never any on the sixth segment of the abdomen. This is a large famly ; about two hundred North American species have been described, and doubtless many more are to be discovered. About one-half of our described species belong to the genus which is commonly known as Ltthocolletis , but which is termed Phyllonoryc- ter by those who recognize the names in the "Tentamen" of Hubner. The following species will ser^^e as an example of this genus. The white-blotch oak-leaf miner, Phyllonorycter hamadryadella. — This little miner infests the leaves of many different species of oaks, and is very common throughout the Atlantic States. The mine is a whitish blotch mine in the upper side of the leaf, and contains a single larva; but often a single leaf contains many of these mines (Fig. 758). The young larv^a is remarkable in resembling more the larv^a of a beetle than the ordinary type of lepidopterous larv'se (Fig. 758, 6). It is nearly flat ; the first thoracic segment is much larger than any of the others; the body tapers towards the hind end; and there are only the faintest rudiments of legs discernible. The larv^ae molt seven times. At the seventh molt the form of the body undergoes a striking change. LEPIDOPTERA 619 It now becomes cylindrical in form, there is a great change in the shape of the mouth-parts, and the fourteen feet are well developed. The full-grown cylindrical larva measures about 5 mm. in length. It spins a cocoon, which is simply a delicate, semi-transparent, circular sheet of white silk, stretched over a part of the floor of the mine. The pupa is dark brown in color, and bears a toothed crest upon its head (Fig. 758, n, 0), which enables it doubtless to pierce or saw its way out from the cocoon. The moth is a delicate little crea- ture, whose wings expand a little more than 6 mm. The fore wings Fig. 758. — Phyllonorycter hamadryadella: a, mine; b, young larva; c, full-grown, flat -form larva; d, head of same, enlarged; e, antenna of same, enlarged; /, round-form larva from above; g, same from below; h, head of same, enlarged; i, antenna of same, enlarged; k, maxilla and palpus of same, enlarged; /, labium, labial palpi, and spinnerets of same; m, pupa; n, side view of pupal crest; 0, front view of same; g, cocoon; Q, moth. (From the author's Report for 1879.) are white, with three, broad, irregular, bronze bands across each, and each band is bordered with black on the inner side. The hind wings are silvery. As this insect passes the winter as a larva within the dry leaves, the best way to check its ravages when it becomes a pest is to rake up and bum such leaves. Another common oak-leaf miner in the East is Phyllonorycter cincinnatiella. The larvce form large blotch mines on the upper surface of leaves. In this species the larv^ae are social, one mine often containing from several to a dozen larvae. The loosened epidermis is brownish yellow, somewhat puckered, and often covers nearly the 620 ^iV INTRODUCTION TO ENTOMOLOGY entire leaf. This species like most other gracilariids passes the winter as pupffi. A common miner in the leaves of locust is Parectopa rohiniella. The lar\^a makes on the upper surface of the leaf what has been termed a digitate mine, that is a blotch mine with a number of lateral galleries running out from it on each side. Several members of this family make tentiform mines in the leaves of apple and other fruit trees; but these species are rareh' of economic importance. Family COLEOPHORID^* Moths with a smooth head, without ocelli, and without maxillarv'- palpi. The labial palpi are of moderate size. The antennas are held extended forward in repose. The wings are very narrow. The discal ^^^ Cu, .J/3 ^J/i+2 Fig. 759. — Wings of Coleophora laricella. (After Forbes). cell of the fore wing extends obliquely ; vein Cui and vein Cuo when present are very short (Fig. 759). The larvae are usually leaf-miners when young or feed within seeds; later, with few exceptions, the}" are case-bearers. Nearly all of our species belong to the genus Coleophora, of which about ninety species have been found in this country. The two follow- ing species are those that have attracted most attention on account of their economic importance. The pistol case-bearer, Coleophora malivorella. — The larva of this species infests apple especially but is also found on quince, plum, and cherry. The larvae hatch in mid-summer from eggs laid on the leaves and eat little holes in the leaves. They soon construct little pistol- *The typical genus of this family is commonly known as Coleophora, the name used for it by Hubner in his "Tentamen." But those writers who do not recognize the "Tentamen" as a published work use the later name Haploptilia for the genus, and name the family the Haloptilhd^. LEPIDOPTERA 621 shaped cases composed of silk, the pubescence of leaves, and excre- ment. The larva projects itself out from the case far enough to get a foothold and eats irregular holes in the leaf, holding the case at a considerable angle with the leaf. About Sep- tember first the larvas migrate to the twigs where they fasten the cases to the bark (Fig. 760) and hibernate till April, spending about seven months in hiber- nation. They then pass to the swelling buds, expanding leaves and flowers, where they continue feeding. They become full-grown in the latter part of Aiay, and then fasten their cases to the smaller branches. After the case is fastened to the branch the larva turns around in it, and changes to a pupa; conse- quently the moth emerges from the curved end of the case. The cigar case-bearer, Coleo- phora fletcherclla. — This species, like the preceding one, is a pest of apple and other fruit trees, and resembles that species to a con- siderable extent in habits. In this species the young larvee are miners in the leaves for two or three weeks before making their cases. The case (Fig. 761) is com- posed of fragments of leaves fastened together b}^ silk. Fig. 760. — Coleophora nialivorella: a, apple twig showing larval cases and work on leaves; b, larva; c, pupa; d, moth; b, c, d, enlarged. (After Riley.) Fig. 761. — Cases of the cigar case bearer. (After Hammar.) Family ELACHISTID^ The head is smooth. The scape of the antennse does not form an eye-cap. The venation is but slightly reduced (Fig. 762). The hind wings are lanceolate, with a well formed discal cell. The larvas have sixteen legs. Most of the known species make blotch mines in grasses. And some at least when full-grown leave 622 AN INTRODUCTION TO ENTOMOLOGY -V.-/ S/ yl ill 2 Fig. 762. — Wings of Elachista guadrella. (After Spuler.) the mine and weave a slight web from which the pupa hangs sus- pended, like the pupa of a butterfly. This is a small family; most of our Si ___.-^ ' ^ ' 'J^'^—p'^'--^^ , species belong to '^\^ti::^:^^^^^^ the genus Elachista. Family HELIOZELID^ The antennas are from one-half to two-thirds as long as the front wings; the scape is short and not enlarged so as to form an eye-cap. The wings (Fig. 763) are lan- ceolate; in the hind wings there is no discal cell, owing to the coales- cence of the radial sector and media for nearly the entire length of the wing, vein Rg sep- arating near the apex of the wing. The habits of the larvse are well- illustrated by the following species. The resplendent shield -bearer, Cop- todisca splendorij- erella. — This spe- cies infests the leaves of apple, pear, quince, thom- apple, and wild cherry. The larva is both a miner and a case-bearer. It at first makes a linear Fig- 763-- mine; but later this ^^^-^ is enlarged into a blotch mine. When full-grown the larva makes an oval case cut from the walls of its mine and lined with silk. It then seeks a safe place in which to fasten this case. This is usually on the trunk or on a branch of the infested tree (Fig. 764, d). There are two genera- tions annually. The second generation pass the winter as larvae K*+5 .y^^ ^e/^ -Wings of Antispila pfeifferella. (After Spu- LEPIDOPTERA 623 within their cases. The adult (Fig. 764. g), is a brilHantly colored, golden-headed moth. The basal half of the front wings is leaden- gray with a resplendent luster and the remainder golden with silvery and dark brown streaks. It expands about 5 mm. Fig. 764. — Coptodisca splendoriferella: a, leaf of apple showing work; b, summer larva; c, larva in case travelling; d, cases tied up for winter; e, hibernating larva; /, pupa; g, moth, h, parasite. (From the Author's report for 1879.) The sour gimi case-cutter, Antispila nysscBfoliella. — This species infests the leaves of Nyssa sylvdtica. Its habits are similar to those of the preceding species. Family DOUGLASIID/E The scape of the antennae is small and does not form an eye-cap. The first segment of the labial palpi is small. The ocelli are large. The hind wings are lanceolate and without a discal cell, owing to the coalescence of the radial sector and media. Vein Rg sep- arates from media near the middle of the length of the wing (Fig. 765) . 624 AN INTRODUCTION TO ENTOMOLOGY Fig. 765. — Wings of Tinagma obscurofasciella. Chambers.) (After This family is represented in this country by a single species, Tinagma obscuro- Sc c> fasciella, the larva of which is a leaf- miner in Rosaceas. Family CECOPHORID^ The head is usu- ally smooth, with appressed scales sometimes with loose scales and spreading side tufts. The antennffi usu- ally have a comb of bristles on the scape. The labial palpi are well- developed, generaly curved upward; the terminal segment is acute- ly pointed. The maxillary palpi are vestigial. The wings are fairly broad, sometimes ample Sc y? ^^ ^^ (Fig. 766). The venation is but little reduced. In the fore wings veins R4 and R5 are stalked or co- alesce throughout; veins R2 and Cu2 arise well back from the end of the discal cell; and vein ist A is preserved. In the hind wings veins Rs and M: are well separated and extend parallel. The posterior tibiag are cloth- ed with rough hairs above. The larvae have sixteen legs ; they are often prettily marked with dark tubercles on whitish or yellowish ground. The different species vary in their habits; the majority of them either live in webbed- together leaves or blossoms or feed in decayed wood; one species, Endrosis lacteella, is a stored-food pest in California and in Europe. About one hundred species have been described from our fauna; many of them are common. A generic revision of the American species was published by Busck ('09 a). The following one is a well- known pest. The parsnip webworm, Depressdria heraclidna. — The larvae of this species web together and devour the unfolding blossom-heads of parsnip, celery, and wild carrot. After the larvae have consumed the flowers and unripe seeds and become nearly full-grown, they burrow Fig. 766. — Wings of Depressaria heracliana. LEPIDOPTERA 625 into the hollow stems and feed upon the soft lining of the interior. Here inside the hollow stem they change to pupse. The moths appear in late July and early August, and soon go into hibernation in sheltered places. Family ETHMIID^ This family includes a small number of moths, which were former- ly included in the family CEcophoridae. The family Ethmiidas was established by Busck Cogb), who states that the main structural character of the imago by which this family can be distinguished from the CEcophoridae is the proximity of vein M2 in the hind wings to vein Ml instead of to vein M3 as in the CEcophoridae, it being radial not cubital. Fracker ('15) describes larval characters distinctive of the tvpical genus Ethniia. The members of this family have broad wings. The fore wings are usually bright colored, with striking patterns, often black and white. The larvje, as a rule, are social, living in a light web. They feed chiefly on plants of the family Borraginaceae. ^ Most of the species belong to the genus Ethmia of which about thirt}' are now known. Family STENOMID^ This family includes large moths as compared with most "micros." The wings are broad, especially the hind wings. In the fore wings all of the branches of the branched veins are typically present. In the hind wings vein Mi is joined at its base to vein Rg. The larvae live in webs on leaves, especially of oak. There are about twenty North American species, most of which belong to the genus Stenoma. A common species in the Atlantic States is Stenoma schlcegeri. This is one of our larger species, having a wing-expanse of 30 mm. The moth is of a dirty white color with the fore wangs mottled with darker bands and spots, and with a conspicuous patch of brown scales near the base of the inner margin. When at rest on a leaf the insect folds its wings closely about its body, and resembles in a striking manner the excrement of a bird. Family GELECHIID^ The head is smooth or at most slightly ruffled. The labial palpi are long, curved, ascending, and usually with the terminal seg- ment acutely pointed. The maxillary palpi are vestigial or wanting. The venation of the wings (Fig. 767) is more or less reduced; the stem of vein M is wanting; vein ist A is wanting in the fore wings; and sometimes in the hind wings also. In the fore wings the second anal vein is forked at the base, i. e., the tip of the third anal vein 626 AN INTRODUCTION TO ENTOMOLOGY Fig. 767. Busck. -Wings of Pectinopliora gossypiella. (After unites with it ; and in some forms, veins R4 and R5 coalesce through- out their length , but they are usually stalked. The hind wings are usually more or less trape- zoidal; and the outer margin is usually sinuate or emarginate below the apex. The larvae vary greatly in habits ; some are leaf-min- ers; but more feed in rolled or spun to- gether leaves or in stems orseed heads; and one is a serious pest of stored grain. This is the larg- est family of the Microf renatae ; more than four hundred species have been described from our fauna. A revision of the American moths of this family was published by Busck ('03). The Angou- mois grain-moth, Sitoiroga cerealel- la.- — The larva of this moth feeds upon seeds, and especially upon stored grain. It occurs through- out our country ; but it is especial- ly destructive in the Southern States. In that part of the coun- try it is extreme- ly difficult to keep grain long on account of this pest and cer- Fig. 768. — Paralechia pinifoliella: larva, pupa, adult, and leaves mined by the larva. (From the Author's Report for 1879.) LEPIDOPTERA 627 tain beetles that also feed on stored grain. The adult moth is of a very light grayish-brown color, more or less spotted with black; it expands about 12 mm. The common name is derived from the fact that it has been very destructive in the province of Angoumois, France. The most effective method of destroying this pest is by the use of carbon bisulphide in the manner in which it is used against the grain-weevils, already described. The pine-leaf miner, Paralechia pinifoliella: — It often happens that the ends of the leaves of pine present a dead and brown appear- ance that is due to the interior of the leaf having been eaten out. This is the work of the pine-leaf miner (Fig. 768). At the right season it is easy to see the long, slender larva in its snug retreat by holding a leaf up to the light and looking through it; and later the pupa can be seen in the same way. Near the lower end of the tunnel in each leaf there is a round hole through which the larva entered the leaf and from which the adult emerges. We have found this insect in several of the stouter-leaved species of pine, but never in the slender leaves of the white pine. In the North it is most abundant in the leaves of pitch-pine. The peach twig-borer, Andrsia line- atella. — This pest is generally distribut- ed throughout the United States and Canada, and sometimes it destroys a large part of the crop in some localities. The young larvae hibernate in small cavities which they excavate in the bark of young twigs. In the spring the larvae burrow into the tender shoots; the leaves of the buds unfold and then wither. There are several generations annuallv. The summer generations attack both twigs and fruit. The solidago gall-moth, Gnorimo- schenia gallcesoliddginis . — There are two kinds of conspicuous galls which are enlargements of the stems of golden- rod ; one of these is a ball-like enlarge- ment of the stem and is caused by the larva of a fly, Eurosta solidaginis, de- scribed in the next chapter; the other is spindle-shaped (Fig. 769) and is caused by the moth named above. The adult moth hibernates. The eggs are laid upon the young goldenrod plants. The young larva eats its way into the center of the stalk, and causes the growth of the gall. The larva becomes full-grown about the middle of July ; then before changing to a pupa it eats a passage-way through the wall of the gall at its upper end, and closes the opening Fig. 769. — Gall of the solidago gall-moth. (After Riley.) 628 AN INTRODUCTION TO ENTOMOLOGY with a plug of silk, which is so formed that it can be pushed out by the adult moth when it is ready to emerge. Some members of the family are leaf-rollers. Figure 770 represents a leaf rolled by a gelechiid larva, probably Anacampsis innocella. This species infests poplar. The pink bollworm, Pectinophora gossypiella. — This species is regarded as one of the most destructive cotton insects known and ranks among the half-dozen most important insect pests of the world. It often reduces the yield of lint fifty per cent, or more and materially lessens the amount of oil obtained from the seeds. The adult is a small dark -brown moth, with a wing- expanse of from 15 to 20 mm. Figure 767 represents the shape and the venation of the wings. The larva eats the seeds and tunnels and soils the lint, causing the arrest of growth and the rotting or premature and imperfect opening of the boll (Busck). A detailed account of this pest, illustrated by many figures was published by Busck ('17). Family BLASTOBASID^ The scape of the antenna? is armed with a fringe of strong bristles, or pecten. The labial palpi are slender and upturned or vestigial. The discal cell of the fore wings(Fig. 771) is long compared with the lengths of the apical veins (R2 to Leaf rolled CU2) ; and these veins arise from the extreme end of by a gele- the cell. As vein Ri arises near the base of the wing it child larva, jg unusually distant from vein R2; to make up for the resulting weakening of the wing, the membrane is more or less thickened along the costa; this thickening is the so-called stigma. The hind wings are lanceolate, and rather narrower than the fore wings. Veins Rs and Mi are well separated at the end of the discal cell. Veins M2, M3 and Cui are close together or coincident. About one hundred species have been described from our fauna; among them are the following. The acorn-moth, Valenthiia glmidulella. — The larva of this species lives as a scavenger in acorns that have been destroyed by acorn- weevils, Balanius. The moth lays an egg in the destroyed acorn after the beetle has left it, and the larva hatching from this egg feeds upon the crumbs left by the former occupant. The larva passes the winter within the acorn. The moths emerge at various times throughout the summer. 70 LEPIDOPTERA 629 The oak-coccid blastobasid, Zenodochium coccivorella. — The larva is an internal parasite in the gall-like females of the coccid genus Kermes. I found it common at Cedar Kevs, Fla. -"^•^ IS/ A Cm C,i, Mi Fig. 771. — -Wings of Holcocera. (After Forbes.) Family COSMOPTERYGID^E The moths grouped together in this family vary greatly in structure. The fore wings are lanceolate, sometimes caudate, i. e. with the apex greatly prolonged. Vein ist A arises out of vein 2d A or is lost. The hind wings are lanceolate or linear. Vein Ri is separate from vein Sc. Veins Rs and Mi are close together. The following species will serve as examples of members of this family. The palmetto-leaf miner, Homaledra sabalella. — This species oc- curs only in the South where the saw-palmetto grows; but it is of general interest as illustrating a peculiar type of larval habit. The larvaj can hardly be said to be leaf -miners; for they feed upon the upper surface of the leaf, destroying the skin as well as the fleshy part of the leaf. They are social, working together in small companies, and make a nest consisting of a delicate sheet of silk covering that part of the leaf upon which they are feeding; this sheet is covered with what appears like sawdust, but which is really a mass of the droppings of the larvae (Fig. 772). The full-grown larva attains a length of 12 mm. The pupa state is passed within the nest made by the larvae. The moth expands 15 mm. Its general color is a delicate silvery gray, with a tinge of lavender in some individuals. The cat-tail moth, Lymncecia phragmitella. — The larva of this species feeds in the heads of cat-tail, Typha. It winters in the head, which presents a tattered and frayed appearance. The larvae spin an abundance of silk, thereby tying the down or pappus together and 630 AN INTRODUCTION TO ENTOMOLOGY keeping it from blowing away. The overwintering larvae are half- grown. When full-grown some transform in the heads, but many go down and bore in the stems and transform there. Cosmopteryx. — "The little moths belonging to the genus Cos- mopteryx are probably familiar to anyone who has collected and ob- served insects in nature. Who has not occasionally on a warm mid- sununer day met with a slender little streak of gold and silver sitting in the sunshine on a leaf in a protected comer and twirling its long white-tipped antennae in graceful motions If, when examined more closely, it is found to be a smooth shining little moth, brown with silvery lines on palpi and antennae, and with a striking broad golden Fig. 772. — Homaledra sabalella: larva, pupa, (From the Author's Report for 1879.) adult, and part of injured leaf. or orange fascia across the outer half of the wing, bordered on both sides by bright metallic scales, then you have a Cosmopteryx.'' "The larvas are leaf -miners, and the mines are easily distinguished from most others by the scrupulous cleanliness with which the larva ejects all its frass through a hole, so that the mine remains clear and white. At maturity the larva changes its color from green to a vivid purple or wine-red, leaves the mine, and spins a matted flattened cocoon of silk." (Busck '06). Among the better-known members of this family are the following : Stagmatophora gleditschiceella.- — -The larva burrows in the thorns of locust. Mompha Eloisella. — There are several species of Mompha that infest the fruit and pith of the evening primrose. The best-known of these is this one. Psacaphora terminella. — The larva is a miner in willow-herb, Epilobium. LEPIDOPTERA 631 Family SCYTHRIDID^ This family includes a group of genera that are closely allied to the Yponomeutida" and are included in that family by some writers. I do not find that any tangible characters of the adult insects separat- ing the two families have been pointed out ; but there appear to be differences in the setal characters of the larva? (see Fracker '15). The family is represented in our fauna by only two genera, Scythris- and Epermenia, including twenty-two species. None of these species has attracted attention on account of its economic importance. The larvae of Scythris magnatella feed on Epilohium. They are solitary when small, folding over half of the leaf to the midrib in the central part of its length, attached with web. Later they form con- siderable web among the leaves. The pupa is formed in a delicate, flossy web. (Dyar). The larva of Epermenia pimpinella feeds by forming a puffy mine on Pimpinella integerrima. The pupa is inclosed in a frail, open- meshed cocoon on the under side of a leaf or in angles of leaf -stalks. (Murtfeldt.) One of the more common representatives of this family is Scythris- eboracensis. The adult is a small black moth tinged with violet, with a wing-expanse of about 10 mm. It is found on flowers. Family YPONOMEUTID^* In this family the ocelli are small or absent. In the more typical forms the wings are comparatively broad, with the venation but little- reduced. In the fore wings all of the branches of the branched veins are usually separate, and vein R5 extends to the outer margin. In the hind wings veins Rs and Mi are well-separated. The first anal vein is distinct in both fore and hind wings. Writers differ greatly as to the limits of this family ; some include in it certain genera or groups of genera that by others are regarded as distinct families. In its restricted sense the family Yponomeutidae includes about fifty North American species; among these are the following. The cedar tineid, Argyresthia thuiella. — This is a small narrow- winged moth, which expands about 8 mm. Its ground color is pearly- white, with the fore wings dotted and marked with brown, especially on the outer half of the wing. The larva feeds on the leaves of cedar, and when full-grown spins a small, conspicuous white cocoon attached to a leaf. The apple fruit-miner, Argyresthia conjugella.- — The larva of this, species is a serious pest in the apple orchards of western Canada. It is pinkish white in color and about 9 mm. in length. It burrows in all directions through the fruit, causing it to decay. The winter is passed in the pupal state. The cocoons are made under the bark on the trunk of the tree or under leaves on the ground; they are white, *An emended form of this family name, Hyponomeutidas, is used by some writers. 632 AN INTRODUCTION TO ENTOMOLOGY and the outer layers have the threads arranged so as to form a beautiful openwork pattern. The adult moth has a wing-expanse of about 12 mm. It is figured by Slingerland and Crosby ('14). _ The suspended lace-cocoon, Urodus parvula. — This beautiful cocoon (Fig. 773) is not uncommon in Florida. It is found in various situations. I found the specimen figured here attached to an orange leaf. The adult is a brownish moth without markings and with a wing-expanse of 28 mm. The ailanthus webworm, Atteva aurea. — The lar- vae live in communities within a slight silken web on the Ailanthus; they feed on the leaves and also gnaw the leaf-stalks in two. When the larva is full- grown it suspends itself in the middle of a loose web and transforms there. The adults appear in Sep- tember and October and pass the winter in this state. The adult is very striking in appearance. The fore wings are bright marigold -yellow with four bands of round pale sulphur-yellow spots upon a brilliant steel-blue ground. The hind wings are transparent, with a dusky margin and blackish veins. The wing- expanse is about 25 mm. The ermine-moths, Yponomeuta.- — There are several species of the typical genus of this family that have received the common name ermine-moths, because of the color of their fore wings, which are snowy white dotted with black. One of these, Yponomeuta padella; is an introduced species which is an apple and cherry pest. The larvae live in a common web, and in this they spin their cocoons. The name ermine-moths is applied also, especially in England, to some of the Arctiidee that are white spotted with black. Fig. 773-— Co- coon of Uro- dus parvula Family PLUTELLID^ This family is closely allied to the Yponomeutidee and is regarded by many writers as a subfamily of that family. These moths differ from the Yponomeutidae in that they hold the antennae extended forward in repose; in this respect they resemble the Coleophoridae. The larvcB differ from those of the Yponomeutidae and the Scythrididae in that their prolegs are longer than wide. About fifty North American sepcies have been described; these represent nine genera. The most important species from an economic standpoint is the following one. The diamond-back moth, Plutella maculipennis. — The larva of this species infests cabbage and other cruciferous plants, eating holes of variable size and irregular form in the leaves. It is sometimes also a pest in greenhouses, infesting stocks, wall-flowers, sweet alyssum, and candytuft. The larva when full-grown spins a lace-like cocoon attached to a leaf. The moth expands about 15 mm. The fore wings LEPIDOPTERA 633 Fig. 774. — Wings of Clvphiptervx thrasonella. (After Spuler.) of the male are ash-colored, with a yellow stripe outlined by a wavy dark line extending along the inner margin. When the wings are closed, the united yellow stripes form a row of three diamond-shaped markings. These sug- gested the common name of the species. In the female the front wings are a nearly uniform gray . The hind wings in both sexes are a dull gra>'. Family GLYPHIPTERYGID.^ The ocelli are usually large. The maxillae are strong and clothed with scales. The maxillary palpi are vestigial or wanting. The labial pal- pi are upturned to the middle of the front or beyond, often beyond the vertex. In the fore wings veins R4 and Rs are usually separate and vein Cuo arises close to the angle of the discal cell. In the hind wings the second anal vein is strongly forked at the base. Nearly forty North American species are now known. These represent two subfamilies. Subfamily Glyphipterygi- N.'E. — This subfamily is composed chiefly of the species of the genus Glyphlpteryx. In this genus the wings are moderately broad (Fig. 774) and the fore wings have a lobe-like prolongation between veins R4 and R5. Ten species are now listed from our fauna. Subfamily Choreutin^. — In this subfamily the wings are broad and triangular (Fig. 775), and usually with narrow fringes. The moths bear a striking re- semblance to tortricids. The lar- vae live under webs on leaves or Fig. 775. — Wings of Simathis fabriciana. (After Spuler.) between leaves that are fastened together. 634 AN INRTODUCTION TO ENTOMOLOGY Family HELIODINID^ The hind wings are narrow-lanceolate and pointed or linear and much narrower than their fringe. The maxillary palpi are minute and porrect. The labial palpi are very short and drooping. The maxillae are strong. The tarsi are armed with more or less distinct whorls of bristles; the tibiae are also often armed with stiff bristles. Usually when at rest the imago holds the posterior pair of legs ele- vated at the sides above the wings. The larvae are not well-known ; those that have been described are of various habits. Cycloplasis panicijoliella.- — The larva of this species mines in grass, Panicum clandestinum. Its mine is at first a long thread-like line; towards the latter part of the life of the larva it is enlarged into a blotch. When the larva has reached maturity, it cuts a perfectly circular disk from the upper cuticle of the leaf, folds it along its di- ameter and unites the edges of the circumference, so as to make a semicircle. When completed the larva, enclosed in its semicircular cocoon, lets itself fall to the ground, where it attaches the cocoon to some adjacent object. (Clemens). Schreckensteinia erythriella. — The larva feeds on sumac bobs. It is common; the body is uniform dark green, but the frass is scarlet. When full-grown it makes a lace-like cocoon on the outside of the bob. Schreckensteinia festaliella. — The larva of this species is an external feeder on Ruhus; it is spiny, and when full- grown makes a lace- like cocoon. Euclemensia basset- tella. — The larva is an internal parasite in the gall-like females of the coccid genus Kermes. The adult is a beauti- ful greenish-black moth, which has its fore wings marked with reddish orange (Fig. 776). The genus Euclemensia is placed in this family provisionally. Family ^GERIID^ Euclemensia bassettella. The Clear-winged Moths The clear-winged moths constitute a very remark- able family, many of them resembling bees or wasps in appearance more than they do ordinary moths, a resemblance due to their clear wings and in some cases to their bright colors (Fig. 777). There are a few moths in other families, as the Fig. 777. LEPIDOPTERA 635 clear-winged sphinxes and certain euchromiids, that have a greater or less part of the wings devoid of scales; but they are exceptions. Here it is the rule that the greater part of one or both pairs of wings are free from scales; hence the common name, clear-winged moths. In a small number of members of this family the wings are scaled throughout. These insects are of moderate size; as a rule they have spindle- shaped antennae, which are terminated by a small silky tuft; some- times the antennae are pectinate; the margins of the wings and the veins of even the clear-winged species are clothed with scales; and at the end of the abdomen there is a fan-like tuft of scales. Fig. 778. — Wings of Synanthedon exitiosa. The fore wings are remarkable for their extreme narrowness and the great reduction of the anal area (Fig. 778) ; while the hind wings have a widely expanded anal area. The nimiber of anal veins in the hind wings varies greatly within the family, the number ranging from two to four; where there are four anal veins, it is probably the third anal vein that is forked. Another remarkable feature of the wings of these insects is that in the female the bristles composing the frenulum are consolidated as in the male; this condition exists in the females of a few members of other families. The females of the ^geriidas possess a frenulum hook; but this is not so highly specialized as that of the male. In addition to the presence of a highly specialized frenulum and a frenulum -hook, there is a unique provision for holding the fore and hind wings together. The inner margin of the fore wing is 636 AN INTRODUCTION TO ENTOMOLOGY folded under; and the radius of the hind wing is armed with setae, which hook into this fold. The adults fly very swiftly and during the hotter part of the day. They frequent flowers thus increasing their resemblance to bees or to wasps. The larvee are borers, living within the more solid parts of plants. Some species cause serious injury to cultivated plants. More than one hundred species have been found in America north of Mexico. Among the better known species are the following. The blackberry crown-borer or the raspberry root -borer, Bemhecia margindta. — The larva of this species burrows in the roots and lower part of the canes of blackberries and raspberries, sometimes completely girdling the cane at the crown. The peach-tree borer, Synanihedon exitiosa. — This is the most important enemy of the peach-tree,except perhaps the San Jose scale in the North and the plum curculio in the South. In some parts of the country it is difficult to find a peach-tree that is not infested by it. The eggs are laid on the bark of the tree near the ground. The larvae bore downward in the bark of the trunk just below the surface of the ground. Their burrows become filled by a gummy secretion of the tree. As this oozes out in large masses the presence of the borer is easily detected by it. The insect always passes the winter in the larval state. When full-grown the larva comes to the surface of the ground and makes a cocoon of borings fastened together with silk. The perfect insects appear from May till October; -^ y^ the date at which most of them appear varies in ^--4^ ^— ^ different sections of the country. There is a ^B|^HH|^^^^ single generation each year. The adults differ ^^^^|H^^^^ greatly in appearance. The general color of jwl both sexes is a glassy steel-blue. In the female ) " 1 (Fig. 779) the fore wings are covered with scales, p-g yyg^^synanthedon ^^^ there is a bright orange-colored band on the exitiosa, iemale. abdomen. In the male both pairs of wings are nearly free from scales. The usual method of fighting this pest is to carefully watch the trees and remove the larvae with a knife as soon as discovered. Recently the use of a toxic gas, paradichlorobenzene, has been found available on trees six years of age and older; and experiments are now being made to determine the practicability of its use on younger trees. See U. S. Dept. of Agr. Bull. 1 169, and later bulletins when pubhshed. The Pacific peach-tree borer, Synanthedon opalescens. — On the Pacific Coast there is a peach-tree boier that is distinct from the above, and appears to be an even more serious pest. The larva is more difficult to remove from the tree, as it bores into the solid wood. The female of this species lacks the orange-colored band on the abdomen. The lesser peach-tree borer, Synanthedon ptctipes. — The larvae of this species infest peach, plum, cherry, june-berry, beach-plum, and chestnut. They do not confine their attacks to the crown but more LEPIDOPTERA 637 often occur on the trunk and larger branches. This borer rarely attacks perfectly sound, uninjured trees and is not a serious pest in orchards that receive good care. Both sexes of the adult resemble the male of the peach-tree borer, having both fore and hind wings transparent. The imported currant borer, CamcBsphecia tipuliformis.- — This is a small species, the adult having a wing-expanse of only about i8 mm. There are but few scales on either pair of wings except on the tip and discal vein of the fore wings and the outer margin of the hind wings. The eggs are laid on the twigs of currant. The larvae penetrate the stem, and devour the pith ; in this way they make a burrow in which they live and undergo their transformations. The perfect insects appear in June. Before this time the leaves of the infested plant turn yellow. If such plants be cut and burned in A4ay the pest will be destro3^ed. The squash-vine borer, Melittia satyriniformis- — The larva of this species (Fig. 780) does great damage by eating the interior of squash- vines; it also sometimes in- fests pump- kin-vines and those of cu- cumber and melon. It is most destruc- tive to late squashes . When full- grown the lar- vae leave the vines and enter the ground, where they make tough silken cocoons, a short distance below the surface, in which the winter is passed.- The adults appear soon after their food-plants start growth. The fore wings of the adult are covered with scales and the hind legs are fringed with long, orange-colored scales. To check the ravages of this pest, the vines should be collected and destroyed as soon as the crop is harvested in order to destroy the larvae that are still in them; the land should be harrowed in the fall to expose the cocoons and then plowed deeply the following spring in order to bury them so deeply that the moths can not emerge. If the vine is covered with earth two or three feet from its base it will produce a new root system which will sustain the plant in case the main stem is injured at the base. Where late squashes are grown early squashes can be used as trap plants. Borers can be removed from the vines with a knife; when this is done the vine should be cut lengthwise, and, after the larva is removed, the vine covered with earth; if this is done carefully the wound will soon heal. The pine clear-wing moth, Parharmonia pmi. — Frequently there may be seen on the trunks of pine-trees large masses of resinous gum satyriniformis, squash-vine 638 AN INTRODUCTION TO ENTOMOLOGY mingled with sawdust-like matter. These are the results of the work of the larvae of this insect, which bore under the bark and into the superficial layers of the wood. The adult resembles the female of the peach-tree borer, but the abdomen is more extensively marked with orange beneath. i'^^ 2d A ^stA Fig. 781. — Wings of Archips cerasivorana. K, Rj^ R, /?^ SUPERFAMILY TORTRICOIDEA The Tortricids The tortricids are generally small moths ; but as a rule they are larger than the mem- bers of most of the families of the Micro- frenatas. They have broad front wings, which usually end squarely. The costa of the front wings curves forward strong- ly near the base of the wing. When at rest the broad front wings fold above the body like a roof. The moths are variegated in color, but are usually brown, gray, or golden rather than of brighter hues. As a rule the hind wings are of the color of the body and without markings. The venation of the wings of a common species is represented by Figure 781. The larvae vary greatly in habits. Many of them are leaf -rollers. It was this habit that suggested the name Tortrix for the typical genus, from which the names of one family and of the superfamily are derived. A large portion of the rolled leaves found upon shrubs and trees are homes of tortricid larvcC ; but it should be remembered that the leaf-rolling habit is not confined to this family. While many are leaf-rollers probably a larger niimber are borers in stems, buds, or fruits. About eight hundred North American species of the Tortricoidea have been decribed. This superfamily includes four families, which, can be separated by the following table. A. Both veins Mi and M2 of the hind wings lost. p. 644 Carposinid^ AA. Vein M, of the hind wings present, vein M2 either present or lost. B. With a fringe of long hairs on the basal part of vein Cu of the hind wings, on the upper side of the wing. Do not mistake a bunch of long hairs arising from the wing back of vein Cu for this fringe. LEPIDOPTERA 639 C. Fore wings with veins R4 and R5 stalked or united, veins M^, M3, and Cui diverging or parallel. (A few species only), p. 642 .... . Tortricid^ CC. Fore wings with veins R4 and Rs separate, or with veins M2, M.,, and Cur converging strongly toward the margin of the wing. p. 639 OLETHREUTID.E BB. Without a fringe of long hairs on the basal part of vein Cu of the hind wings. C. Fore wings with the distal part at least of vein 1st A preserved. Vein CUi of the fore wings arising from a point before the outer fourth of the discal cell. D. Veins Mi and M2 of the fore wings somewhat approximate at the margin of the wing {Laspeyresia lautana) p. 639 Olethreutid^ DD. Veins Mi and M2 of the fore wings divergent or parallel, p. 642 TORTRIGID^ CC. Both fore and hind wings with vein istA lost, vein Cuj of the fore wings arising from the outer fourth of the discal cell. p. 643 Phaloniid^ Family OLETHREUTID^* As a rule the members of this family are easily distinguished from all other tortricids by the presence of a fringe of long hairs on the basal part of cubitus of the hind wings, on the upper side of the wing. This fringe is lacking in a few members of this family and is present in a few members of the next family. This is the largest of the families of tortricids; more than four hundred North American species have been described. The following species are among those most likely to be observed, and will serve to illustrate the differences in habits of the different species. The codlin-moth, Carpocdpsa pomonella.- — This is the best known and probably the most important insect enemy of the apple. The larva is the worm found feeding near the core of wormy apples. The adult (Fig. 782) is a beautiful little creature with finely mottled pale gray or rosy fore wings. There is a large brownish spot near the end of the fore wing, and upon this spot irregular, golden bands. The moth issues from the pupa state Fig- 782.— tar- in late spring and lays its eggs singly on the surface onlua of the fruit or on adjacent leaves. As soon as the larva hatches it burrows into the apple and eats its way to the core, usually causing the fruit to fall prematurely. When full grown the larva burrows out through the side of the fruit, and undergoes its transformations within a cocoon, under the rough bark of the tree, or in some other protected place. The number of generations annually varies in different parts of the country. As a rule there is in the North one full generation and usually a partial second ; where the season is longer there are two or three generations. The larvae winter in their cocoons transforming to pupae during early spring. The method of combating this pest that is most commonly em- ployed now is to spray the trees with a solution of arsenate of lead, four to six pounds of arsenate of lead in one hundred gallons of water, just after the petals fall and before the young apples are heavy *This family is the Eucosmidae of some writers, and the Epiblemidce of others. 640 AN INTRODUCTION TO ENTOMOLOGY enough to droop. The falling spray lodges in the blossom end of the young apple, and many of the larvae which attempt to enter at this point, the usual place of entrance, get a dose of poison with their first meal. The pine-twig moths, Evetria. — The genus Eve- rtia includes many spe- cies that infest the twigs and smaller branches of various species of pine. Some of our best known species were described under the generic name Retinia but now the old- er name Evetria is applied to them. The following species are well-known. Evetria ccmstockidna. ■ — This species (Fig. 783) illustrates well the hab- its of the boring species. The larva infeststhe small branches of pitch-pine. It is a yellowish-brown caterpillar, which makes a burrow along the cen- tre of the branch. Its presence may be detect- ed by the resin that flows out of the wound in the twig and hardens into a lump. Two of these lumps are shown in the figure, one of them split lengthwise, and the oth- er with a pupa-skin pro- jecting from it. The lar- va, pupa, and adult are also figured. The moth is represented natural size; the darker shades are dark rust-color, and the lighter, light-gray. The insect winters as a larva; the adult emerges in May and June. Evetria frustr ana. — This species infests the new growth of several species of pine, spinning a delicate web around the terminal bud, and mining both the twig and the bases of the leaves. The larva, pupa, and adult are represented somewhat enlarged in the figure. An in- fested twig is also shown (Fig. 784). The grape-berry moth, Polychrosis vitedna.- — The most common cause of wormy grapes is the larva of this moth. The moth emerges Fig. -j^T,.— Evetria adult, and work. for 1879.) 'oiiislockiaiia: larva, pupa, (From the Author's Report LEPIDOPTERA 641 in the spring from its cocoon on a fallen leaf where it has passed the winter in the pupa state. The first generation of larvae make a slight web among the blossom buds into which they eat destroying many embryo grapes. When full-grown the larva passes to a leaf and makes a very peculiar cocoon. It cuts a semicircular incision in the leaf, bends over the flap thus made, fastens its free edge to the leaf, and lines the cavity thus enclosed with silk; here it trans- forms to a pupa. The moths of the second and later generations lay their eggs on the berries, and the larvae bore into them and feed on the pulp and seeds. The most efficient method of control of this pest is by spraying with a solution of arsenate of lead, six pounds of the poison in one hun- dred gallons of water. The first applica- tion should be made shortly after the fruit sets, and one or two more at intervals of ten da vs. Fig. 784. — Evetria frustrana: larva, pupa, adult, and work. (From the Au- thor's Report for 1879.) The bud-moth, Tmetocera ocelldna. — The larva of this insect is a pest infesting apple-trees. It works in opening fruit-buds and leaf-buds, often eating into them, especially the terminal ones, so that all new growth is stopped. It also ties the young leaves at the end of a shoot to- gether and lives within the cluster thus formed, adding other leaves when more food is needed. Sometimes so large a proportion of the fruit-buds are destroyed as to seriously reduce the amount of the crop. The pupa state is passed within the cluster of tied leaves or within a tube formed by rolling up one side of a leaf, and lasts about ten days. The moth expands about 1 5 mm. ; it is of a dark ashen gray, with a large, irregular, whitish band on the fore wing. The clover-seed caterpillar, Laspeyresia inter stinctdna. — This is a common pest which feeds in the heads of clover, especially red clover, destroying many of the unopened buds and some of the tender green seeds, and spoiling the head as a whole. It sometimes greatly dimin- ishes the crop of seed. There are three generations annually. The last generation passes the winter in the pupa state as a rule; but some larvae hibernate under rubbish. The adult is a pretty brown moth, with a series of silvery marks along the costal margin of the fore wings, and two on the inner margin, which form a double crescent when the wings are closed on the back. This moth expands 10 mm. If the hay is cut early and stored the larvee will be destroyed while still in the heads. Nest of Archips rosana. w/m Fig. 7^.— Arch- ips rosana. Q42 AN INTRODUCTION TO ENTOMOLOGY Family TORTRICID^ The Typical Tortricids The tortricidae differ, as a rule, from the preceding family in lacking a fringe of long hairs on the basal part of the cubitus of th^ hind wings. In the fore wings the distal part of the first anal vein is preserved, and vein Cu2 arises from a point before the outer fourth of the discal cell In a recent list 165 North American species are enumerated; these represent 15 genera. Several of our better-known^ members of this family belong to the genus Archips. This is the genus Caccecia of those writers who do not recognize the names proposed by Hubner in his "Tentamen." These insects have been named the ugly-nest tortricids; ugly dwelling being the meaning of Caccecia, and also descrip- tive of the nests of the larvae of these insects. The four following species are common. The rose ugly-nest tortricid, Archips rosana. ■ — The larva of this species feeds within the webbed-together leaves of rose and a number of other plants. Figure 785 represents the nest of a larva in a currant leaf; and Figure 786 the adult of this species. This moth expands about 20 mm. The fore wings are olive-brown, crossed by bands of darker color; the hind wings are dusky. This species differs from the two following in that each larva makes a nest for itself. The cherry-tree ugly-nest tortricid, Archips cerasivordna. — This species lives upon the choke-cherry and sometimes upon the culti- vated cherry. The larvae, which are yellow, active creatures, fasten together all the leaves and twigs of a branch and feed upon them (Fig. 787), an entire brood occupying a single nest. The larvee change to pups within the nest; and the pupa, when about to transform, work their wa\^ out and hang suspended from the outer portion of the nest, clinging to it only by hooks at the tail end of the bodv. Fig. 787. — Nest of Archips cerasivor- ana. Here thev transform, LEPIDOPTERA 643 im leaving the empty pupa skins projecting from the nest, as shown in the figure. The moths vary in size, the wing ex- panse of those we have bred ranging from 20 mm. to nearly 30 mm. The wings are bright ochre- \-ellow; the front pair marked with irregular brownish spots and numerous transverse bands of leaden blue (Fig. 788, male; Fig. 789, female), p. —Archips The oak ugly-nest tortricid, Archips fervidana. f^ /^ ^ j- ^ or ana — The nests of this species are common on our male. oak-trees in late summer. They are merely a wad of leaves fastened together. Each nest contains several larvce; later the empty pupa-skins may be found clinging to the outside of the nest as in the preceding species. The fruit-tree ugly-nest tortricid, Archips argyrosptla. — This is one of the most destructive of the leaf -rollers infesting fruit trees. It is a very general feeder attacking both fruit and forest trees. The eggs are laid on the bark of the twigs in June. Fig. 789— Archips The larvaj hatch about May ist of the following female "' "'^ '^ ""' ^'^^^ ^^^ ^^^^^ ^^^ Opening buds, w^here they roll and fasten the leaves loosely together with silken threads. After the fruits set, they are often included in the nests and ruined by the caterpillars eating large irregular holes in them. The pine-leaf tube-builder, Eulia pinatubdna. — One of the most interesting of tortricid nests occurs commonly on white pine. Each nest consists of from six to fifteen leaves drawn together so as to form a tube, and is lined with silk. This tube serves as a protection to the larva, which comes out from it to feed upon the ends of the leaves of which the tube is composed; in this way the tube is shortened. I bred the moth from nests collected at Ithaca, N. Y.; and have found similar nests as far south as Florida. The moth expands 12 mm. Its head, thorax, and fore wings are of a dull rust-red color, with two oblique paler bands crossing the fore wings, one a little before the middle, the other a little beyond and parallel with it. Family PHALONIIDtE In this family and in the following one the first anal vein is lost in both fore and hind wings and vein Cuo arises from the outer fourth of the discal cell. In this family vein Mi of the hind wings is pre- served, usuallv stalked with vein Rg. The palpi of the two sexes are alike. More than one hundred North American species have been de- scribed, and constantly others are being found. Comparatively little is known about the habits of our species ; but most of the European species whose habits are known are borers, chiefly in herbaceous plants. The juniper web-worm, Phalonia rutildna. — This is an imported species which has attracted attention by its injuries to junipers, the 644 AN INTRODUCTION TO ENTOMOLOGY leaves of which it fastens together with silk. In this way it makes a more or less perfect tube within which it lives, but from which it issues to feed. Themoth expands about 1 2 mm. andhas bright, glossy, orange fore wings, crossed by four reddish brown bands. Family CARPOSINID^ This family is distinguished from the preceding one by the fact that in the hind wings both vein Mi and vein M2 are completely lost, and the palpi of the male are short while those of the female are long. This is a small family, only five North American species are now listed, and very little is known regarding the habits of these. The currant-fruit-worm, Carposina Jernalddna. — In the unpub- lished notes of the late Professor M. V. vSlingerland, I find an account of this insect. The larva feeds within the fruit of the currant, eating both the pulp and the seeds. The infested fruit soon drops. When full-grown the larva leaves the berry and goes into the ground to transform. The adult emerges in the following spring about the time the currants are turning red. SuPERFAMiLY PYRALIDOIDEA The Pyralids and their Allies This group of families includes a very large number of small or moderate-sized moths, of fragile structure, normally with firmly and finely scaled wings, and with the anal area of the hind wings broad. The first anal vein of the fore wings is almost always lost, and there is no accessory cell. In the hind wings there are usually three anal veins; and veins Sc and R are separate along the discal cell, but grown together or closely parallel for a short distance beyond the cell. The maxillee are scaled at their base; and the maxillary palpi when present are of the porrect type. The labial palpi often project beak-like. The larvae are characterized by the presence of only two setae on the prespiracular wart of the prothorax, and by setae IV and V of the abdomen being close together. This superfamily includes the five following families, which can be separated by the characters given in Table A, page 584. Family PYRALIDID^ The Pyralids The members of this family found in our fauna are mostly small moths, but a few are of moderate size ; some tropical species, however, are quite large. So large a portion of the species are small that the family has been commonly classed with the preceding families as Microlepidoptera. LEPIDOPTERA 645 The members of the different subfamilies of this family differ so greatly in appearance that it is not possible to give a general descrip- tion that will serve to distinguish it ; a very large portion of the species have a special look, due to their thin and ample hind wings with large anal areas; it is necessary, however, to study structural characters to find evidences of a common bond. The body is slender ; the head is prominent ; the ocelli are usually present; the antennge are almost always simjjle, but frequently the antennae of the male have a process on the scape or a notch and tuft on the clavola; and the palpi are usually moderate in size or long; but very often they project beak-like; for this reason the name snout-moths is often applied to this family. Id A Fig. 790. — Wings of Nomophila noctuella. Fig. 791. — Wings of Tlascala redtictella. As a rule there are three anal veins in the hind wings and one in the fore wings. The discal cell is always well-formed, but there is no accessory cell. In most cases the pyralids can be recognized by the fact that the subcosta and radius of the hind wings are separate along the discal cell, but grown together for a short distance beyond the cell, after which they are again separate (Fig. 790). In some genera these two veins do not actually coalesce, but extend very near to- gether for a short distance (Fig. 791). The two types, however, are essentially the same. This is one of the larger families of the Lepidoptera ; nearly one thousand species have been described from America north of Mexico alone. The family is divided into many subfamilies, representatives of fifteen of which are found in our fauna. The best known species, those that have attracted attention on account of their economic importance, belong to the subfamilies discussed below. 646 AN INTRODUCTION TO ENTOMOLOGY Fig. 792. — Des- mia funeralis. Subfamily PYRAUSTIN^ The Pyraustids This is one of the larger of the subfamiHes of the Pyrahdidae; about three hundred species have been described ^^-s,^,>^^^ from America north of Mexico. This subfamily in- ^HmUSr eludes many small moths; but it contains also the ^^Bxf^^r majority of the larger species of pyralids; some of I the species are very striking in appearance. The members of this subfamily differ from other pyralids by the following combination of characters. There is no fringe of long hairs on the basal part of vein Cu of the hind wings; veins R2 and R5 of the fore wings arise from the discal cell distinct from vein R4 (Fig. 790); and the maxillary palpi are never very large and triangular. Among our better known species are the following. The grape leaf- folder, Desmia fun- eralis.— This is a common species throughout the United States, the larva of which feeds on the leaves of grape. The larva folds the leaf by fastening two portions to- gether by silken threads. When full grown it changes to a pupa within the folded leaf. The moth is black with shining white spots. The male (Fig. 792) differs from the female in having a knot-like enlargement near the middle of each antenna. There is some vari- ation in the size and shape of the white spots on the wings. In some specimens the white spot of the hind wings is sep- arated into two or three spots. There are two generations of this species in the North and three or more in the South. The basswood leaf-roller, Pantogrd- pha limdta.- — -Our basswood trees often present a strange appearance in late summer from the fact that nearly every leaf is cut more than half way across the middle, and the end rolled into a tube (Fig. 793) . Within this tube there Fig- 793- — Nest of larva of Pa7i- tographa limata. LEPIDOPTERA 647 Fig. 794. — Pantographa limata. lives a bright green larva, with the head and thoracic shield black. When full grown the larv^a leaves this nest and makes a smaller and more simple nest, which is merely a fold of one edge of the leaf, or sometimes an incision is made in the leaf extending around about two-thirds of a circle and the free part bent over and fastened; in each case the nest is lined with silk, thus forming a delicate co- coon. Here the larva? pass the winter in fallen leaves. At Ithaca, N. Y., Professor Slingerland found that the larvas did not pupate till the following July, and that adults emerged in August. The adult moth expands about 33 mm.; it is straw-colored with many elaborate markings of olive with a purplish iridescence (Fig. 794). The melon-worm, Diaphaniahyalindta. — This beautiful moth (Fig. 795) is often a serious pest in our Southern States, where the larva is very destnictive to melons and other allied plants. The young larvae feed on the foliage; the older ones mine into the stems and fruit. The insect passes the winter as a pupa in loose silken cocoons in dead leaves or under rubbish. The moth is a superb creature, with glistening white wings bordered with black, and with a spreading brush of long scales at the end of the abdomen. This species appears to be injurious only in the Gulf States, but the moths have been taken as far north as Canada. The most practicable method of protecting cantaloupes and cucimi- bers from this pest is by planting stmimer squash- es among them as a trap crop at intervals of about two weeks so as to fur- nish an abundance of buds and blossoms dur- ing July and August. The earlier squash vines should be removed and destroyed before many worms have reached maturity on them; and after the crop is harvested the vines and waste fruits should be gathered and destroyed. Fig- 795- — Diaphania hyalinala: larvae, cocoon', and adults. (From the Author's Report for 1879.) 648 AN INTRODUCTION TO ENTOMOLOGY The pickle-worm, Diaphdnia nitiddlis. — This species is closely allied to the preceding one. The wings of the moth are yellowish brown with a purplish metallic reflection; a large irregular spot on the front wings and the basal two-thirds of the hind wings are semi- transparent yellow. The tip of the abdomen is ornamented with a brush of long scales, as in the preceding species. The range and habits of this species are quite similar to those of the melon-worm; and it should be fought in the same way. The Wehworms.- — The larvae of many pyralids have the habit of spinning a silken web beneath which they retreat when not feeding, and on this account have been termed webworms. Several species of these webworms belong to this family; among them are the follow- The cabbage webworm, Hellula midalts.- — This species infests various cruciferas in the Gulf and South Atlantic States. The larva is about 12 mm. in length, of a grayish yellow color, striped with five brownish-pur[3le bands. The garden webworm, Loxostege siniildlis.- — This species is most injurious in the Southern States and in the Mississippi Valley. It infests various garden crops and corn and cotton. The larva varies in color from pale and greenish yellow to dark yellow and is marked with numerous black tubercles. The European corn-borer, Pyraiista nubildlis. — This is a greatly feared pest which has recentlv appeared in this country. It is a borer in the stems of plants, in which it winters as a partly grown larva. Its favorite food appears to be corn and especially sweet corn ; but it infests other cultivated plants, as dahlias and gladiolus, and many large-stemmed weeds. The full-grown larva measures about 20 mm. in length; the adult moth has a wing-expanse of from 25 to 30 rmn. As this is written, efforts are being made by the National Government and by several State Governments to prevent the spread of this pest ; and many circulars and bulletins are being published regarding it. Subfamily NYMPHULIN^ The Aquatic Pyralids This subfamily is of especial interest as the larvse are nearly all aquatic, differing in this respect from nearly all other Lepidoptera. The larvae of most of the species live upon plants, like water lilies and pond weeds, that are not wholly submerged; but in some species the larva has a true aquatic respiration, being furnished with tracheal gills. In our best known species, these trachael gills are numerous and form a fringe on each side of the body of long slender filaments, which are simple in some species and branched in others. The larvae vary greatly in habits ; some species live free upon the plants they infest; in some species, each larva makes a case of two leaf fragments fastened together at the edges; most of the described larvae live in quiet waters, lakes, ponds, or pools, but the larva of LEPIDOPTERA 649 Elophila fidicdlis was found by Lloyd ('14) to live beneath sheets of silk spun over exposed surfaces of current-swept rocks, in a rapid stream. In the case of several species whose life-history has been deter- mined the pupal stadium is passed in a cocoon beneath the surface of the water. An exception to the usual habits of larva of this subfamily is presented by Eurrhypara urttcdta, introduced from Europe to Nova Scotia; this species is not aquatic, but feeds on nettle. Subfamily PYRALIDIN^ The Typical Pyralids This is a small subfamily; only twenty-four species are now enu- merated in our lists, and these are mainly from the far Southwest. The best-known species are the two following: The meal snout-moth, Pyralis farindlis. — The larva of this species feeds on meal, flour, stored grain, and old clover hay. It makes little tubes composed partly of silk and partly of the fragments of its food. It rarely occurs in sufficient numbers to do serious injury; and its ravages can be checked by a thorough cleaning of the infested places, or when practicable by the use of carbon bisulphide. The moth is commonlv found near the food of the larva, but is often seen on ceilings of rooms sitting with its tail curved over its back. It expands about 25 mm. ; the fore wings are light-brown, crossed by two curved white lines, and with a dark chocolate-brown spot on the base and tip of each. The clover-hay worm, Hypsopygia costdlis. — The larva of this species sometimes abounds in old stacks of clover-hay, and especially near the bottom of such stacks. As the infested hay becomes covered with a silken web spun by the larva, and by its gunpowder-like excrement, much more is spoiled than is eaten by the insect. Such hay is useless and should be burned, in order to destroy the insects. The moth expands about 20 mm. It is pig. 7^5. Hy- a beautiful lilac color, with golden bands and fringes p s 0 p y gi a (Fig. 796). c 0 s t all s . Subfamily CRAMBIN^ The Close-wings Although this is not a large subfamily, there being only about one hundred and thirty species known in our fauna, the members of it are more often seen than any other pyralids. The larvse of most of the species feed on grass; and the adults fly up before us whenever we walk through meadows or pastures. When at rest, the moths wrap their wings closely about the body; this has suggested the name close- 650 AN INTRODUCTION TO ENTOMOLOGY wings for the insects of this family. When one of these moths aHghts on a stalk of grass it quickly places its body parallel with the stalk, which renders it less conspicuous (Fig. 797). Many of the species are silver}^ white or are marked with stripes of that color. About seventy of our species belong to the genus Crambus. The moths of this genus are often seen; but the larvae usually escape observation. They occur chiefly at or a little below the surface of the ground, where they live in tubular nests, constructed of bits of earth or vegetable matter fastened together with silk. They feed upon the lower parts of grass plants; and sometimes on other crops planted on sod land infested by these insects. Thus Crambus caliginosellus is known as the corn-root webworm on account of its injury to young com plants which it bores into and destroys ; it is also known as the tobacco stalk -worm, on account of similar injury to young tobacco plants. Another species of this genus, Crambus hortuellus , is known as the cranberry girdler. This sometimes does Crambus. considerable injurv^ in cranberry bogs by destroying the bark of the prostrate stems of the vines. To this subfamily belong the larger com stalk-borer, Diatrcea zeacolella, which sometimes bores into the stalks of young corn in the Southern States, and the sugar-cane borer, Diatr