/ c^^T% 1930 MBL/WHOI Library 0' ■ bles and the gnathochilarium there is a pair of one-jointed lobes, which have not been found in other diplopods; these are the "max- illulee" (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. 2t. — The second pair of jaws, maxillulae, 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: mb, 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; mx. lo, lobe of the maxilla; mx. p, maxillary palpus; h, tongue or hypopharynx; m.xl, maxillula; fl. flagellate process (After Carpenter). 18 AN INTRODUCTION TO ENTOMOLOGY Class PAUROPODA The Pauropods 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 tcrga of the body-segments are usually fused in couples, the legs are not grouped in double pairs as in the Diplopoda. The antennre 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 antennas 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 paiiropod Pauropus huxleyi, dor sal aspect (After Ken yon). Fig. 23. — Pauropus huxleyi, ventral aspect (After Lubbock). CHARACTERISTICS OF INSECTS AND THEIR RELATIVES 19 Fig. 24 — Eurypauropus spino- sus; face showing the base of the antennae, 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 allied 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 antennas, which differ from those 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 BrachypauropodidcB, is found in Europe. In this family the pairs of terga consist each of two distinct plates. Our two ^. , . , ^ . families are the fol- Fig. 26. — Antenna of Eurypauropus sptnosus (After Kenyon) . lowmg : Fig. 25. — Mouth-parts of Eury- pauropus ornatus; md, man- dible; mx, second iaws; /, lower lip (After Latzel). 20 AN INTROD UCTION TO ENTOMOLOG Y Family Paiiropodidce. — 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 Paiiropiis (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. Family Eurypaurdpidce. — 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 familiar representative is Enrypauropus spinosus Fig. 27. —Eurypauro- (pj^^ 27). This, unlike Panropus, is slow in its pus spinosus (After ^ ^ ' ^ -f ' 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 function 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 coxae united on the middle line of the body (Fig. 29,3,6), 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 ('11) as sub-classes, the Pleuro- stigma and theNoto- stigma. The names A'^y^ W^¥\ C of the sub-classes refer to the position 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 multi- dentalus. Fig. 29, — Mouth-parts of a centipede, Ceophilus 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 Scutigera and its Allies In the genus Scuttgera 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. (V 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 conserv^atories, living among the stored pots and about the heating pipes. It is much more common in the South than in the North Fig. 30. — Scutigera forceps. CHARA CTERISTICS OF INSECTS A ND THEIR RELA TI VES 23 The body of the adult measures an inch or a little 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- thmoiis region. Most of the body-segments bear a single pair of legs. The antennce 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 down 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 antenna are long and vary greatly in the number of the segments. There are no eyes. The mandibles, the "maxillulse" (paragnatha) , the maxillae, and the sec- ond maxillae or labium are present. Fig . 31 . — Scolopendrella (After Latzel). Fig. 32. — Mouth-parts of Scolopendrella seen from below; vtd, mandible; mx, maxillas; s, stipes; p, pal- pus; /, second maxillae or labium. The mandible on the right side of the figure 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 or hypopharynx (Fig. 33, h); they are hidden when the mouth-parts are viewed from below as represented in Figure 32 ; the maxillce (Fig. 24 AN INTRODUCTION TO ENTOMOLOGY of ScolopendreMa (After Hansen). 32, mx) resemble in a striking degree the maxillas of insects, consisting of a long stipes, (5), which bears a minute palpus, (^), and an outer and inner lobe; Vae second maxillce 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 nimiber of their segments. The other legs '^pophlVynx ^ (h) consist each of five segments; the last segment andmaxillulae(m) bears a pair of claws. Excepting the first two 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 P'^^^'f^^'^ with the cerci of insects (Fig. 35, c). A striking peculiarity of the symphylids is that Fig- 34- \^% °^ they possess only a single pair of tracheal tubes, Scolopendrella; f^ , ^ . f f . •. . -i • -•. p, parapodium. which open by a pair of spiracles, situated m the head beneath the insertion of the antenna. 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: Fig. 35.— The caudal Scolopendrella and Scutigerella. In the former the ^n^, o^ the body of Scolopendrella; i, posterior angles of 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 Myrientomatids The members of this class are small arthropods in which the body w elongate, as in the Thysanura, fusiform, pointed behind, and depressed; it may be greatly extended and retracted. The antenncB and cerci are CHA RA CTERISTICS OF INSECTS A ND THEIR RELA TI VES 25 absent. The oral apparatus is suctorial, and consists of three pairs of gnathites. There are three pairs of 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 proposed 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 I NT ROD UCTION TO ENTOMOLOG Y 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 Pauropoda, Symphyla, 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 Acerentomidae, charac- terized by the absence of spiracles and tracheae; and the Eosentomidae the members of which possess two pairs of thoracic spiracles and simple tracheae. 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 of antenncs, three pairs of legs, and usually one or two pairs of wings in the adidt 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 essentially 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 (?0i six; pons {irovs), a foot. CHA RA CTERISTICS OF INSECTS A ND THEIR RELA TI VES 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 directly or indirectly, upon insects for food, and the destruction of many flowering plants that depend upon insects for the 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 part. 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 antennse, 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 frequently bears other appendages at 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 Fig. 37. — Wasp with head, thorax, and abdomen separated. Fig. 38. — Nymph of the red- legged locust. 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 larv^ai of bees, wasps, flies, and many beetles are legless and more or less worm-like in form (Fig. 4) ; while the larvae 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 which 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 Coccidse (Fig. 40), and the females of the canker-worm moths. In fact, wingless forms occur in 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- dermis, 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- dermis (Fig. 41, 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 tracheae, 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 epithelium. 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 ^ A^ I NT ROD UCTION TO ENTOMOLOG Y larly stratified. This is due to the fact that the nuclei of the different cells are at different levels. The Trichogens. — Certain of the hypodermal cells become highly- specialized and produce hollow, hair-like organs, the setae, with which they remain connected through pores in the cuticiila. Such a hair-forming cell is termed a tnchogen (Fig. 41, tr); and the pore in the cuticula is termed a Mchopore. 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 on p. 171, 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 boiling or soaking it in an aqueous solution of this substance. Chitin. — This word was introduced into entomology by Odier in 1823 for the colorless, flexible covering of the arthropods after the integument had been boiled in caustic potash and the albuminous, oily, coloring and mineral substances had been removed thereby. By a not unusual turn in the use of words, chitin has come to mean, as stated by Newport (1836-1839): "The peculiar substance that constitutes the hard portion of the dermo-skeleton [in insects]." From 1870 and onward the words chitinize and chitinization have come to mean the hardening of the cuticula by the incorporation of chitin; and they are used with that meaning throughout this work. (For references to chitin, see p. loio). Rigid and flexible cuticida. — When freshly formed by the hypo- dermis, 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 in adult insects, usually becomes firm and inelastic ; this is due to a change in which the hardening substance is developed within or upon the original soft cuticula. What the exact nature of this change is or how it is pro- duced is not known. This change is usually spoken of as chitinization ; and the hard parts of the cuticula are then said to be chitinized, and the soft parts, as at the nodes, non-chitinized. The hardened or chitinized cuticula is rigid and inelastic while the soft or non-chitinized cuticula is flexible and elastic. The elasticity of the soft cuticula is well shown by the stretching of the body wall after a molt. It is also strikingly shown by the expansion of the soft, intersegmental cuticula to accommodate the growing eggs, as in the queens of Termites. THE EXTERNAL A NA TOMY OF INSECTS 3 1 The formation of chitin is not 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- tricuius 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 cuticula (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 , (i) . The basement membrane. — The inner ends of the hypodermal 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 different species of insects, and are frequently of taxonomic 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 set£e 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 aculeffi. 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 seise are what are commonly called the hairs of in- sects. Each seta (Fig. 42, s) 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 inchopore; 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 setae 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 cuticula. 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 setce. — 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 setse v\ith which the body is clothed. A classification of 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 wings 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 *• c ^1. 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 termed a conjunctiva. These con- junctivae may be distinguished from others described later as the transverse conjunctives. The conjunctivae 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 conjimctiva, 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 3F tergum; 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 sternites. 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 conjunctivae. Like the transverse conjunctivae, the lateral ones are more or less infolded. The sclerites. — Each definite area of chitinization of the cuticula is termed a sderite. 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 occur which can not be thus homologized. 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 the«^e regions ; it bears the mouth-parts, the eyes, and the antennae. Tiu: I horax 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. 11. 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 observed 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 ommatidium. The number of ommatidia of which a compound „. T^ . J- eye is composed varies greatly; there may be not Fig. 44.— Part of a -^ , ^ , . . ^, cornea of a com- more than fifty, as m certam ants, or there may pound eye. -[^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 EX TERN A L 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 larvse 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 cricket. sclerite between the arms of the epicranial suture (Fig. 45, F). 38 ^A^ INTRODUCTION 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 l^-rge (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, Cy) and the second clypeus being that next the labrum (Fig. 45, Co). The suture between the clypeus and the epicranium is termed the clypeal sutiire. The labrum. — The labrum is the movable flap which constitutes the upper lip of the mouth (Fig. 45, L). The labrimi 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 ig. 47. — Head of a larva of Corydalus, 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 included 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 epicranium; or, more specifically, that portion which is next the front and between the compound eyes is known as the vertex (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 postgenae 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 ocw/ar 5c/m^^5 (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. — Head and neck of a cock- roach. Fig. 49. — Head of Corydnliis, adult, ventral aspect. 40 AN INTROD UCTION TO ENTOMOLOG Y 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, tr). 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- fterior 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 were so named by Huxley ('78); pj -o. Head of a recently they have been termed the zn/^r^cg- cricket, ental surface mental plates by Crampton ('17), who con- of the dorsal wall. . , .■, , -i ■, 1 •.■, 1 •■ siders them to be 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 m.outh- parts. The antennae. — The antennae 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 naines 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. Tne Ring-joints. — -In certain Fig. 51.— Antennaofachalcis-fly. j^^^^^g (g_g_^ Chalcididae) 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 Filnide. — 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 antennae 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. Filiform or thread-like, in which the segments are of nearly uniform thickness. 3. M'omliform 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. Cldvite 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. Wheit 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 antennae. 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 maxillcB. 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-parts of a locust will serve as an example of the typical 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 maxillae, 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 is 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 sucking 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 insects. Fig- 53- — Mouth-parts of a locust: la, lab- rum; md, mandible; mx, maxilla; h, hypo- pharynx; /, labium. THE EXTERNAL ANA TOMY OF INSECTS 43 The lahrum. — The Idbrum 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 Scarabseidas, each mandible consists of several more or less distinct sclerites. The pardgnatha. — In some insects there is between the mandibles and the maxillse a pair of more or less appendage-like organs borne by the hypopharynx. These are the "paraglossse" of writers on the Thysanura and CoUembola and the "superlinguas" of Fol- som ('00). They were termed the maxillulse, 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 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, Corrodentia, the naiads of Ephemerida, and the larvse of Coleoptera. The MaxillcB. — The maxUlcs are the second pair of jaws of insects. Like the mandibles they are the appendages of one of the segments of the head. The maxillae 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 for foot- stalk, the palpifer or palpus-bearer, the suhgalea or helmet-bearer, and the lacinia or blade. The appendages are the maxillaty 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) . the paragnatha of Crustacea. In 44 AN INTRODUCTION TO ENTOMOLOGY or superior lobe, and the digitus or finger. The maxilla may also bear claw-Uke 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~. 55 and Fig. 56, which represent the two aspects of the maxilla of Ilydrophilus. Excepting Fig. 56, the figures of maxillaj 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, hov/ever, it is not the only part directly joined to the body ; for frequently muscles extend direct to ilie Jtibgalea, without passing tlirough the cardo. The stipes or footstalk (6) 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 side, and the subgalea on the other, may become united to the stipes without any 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 tlie 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 helmet-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 subp;alea 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 Ilydrophilus. Fig. 56. — Dorsal as- pect of a maxilla of Hydrophilus. THE EXTERNAL ANATOMY OF INSECTS 45 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 cases the galea resembles a palpus in form (Fig. 57). The galea is also known as the outer lobe, the upper lobe, or the superior lobe. The lacmia 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 iymer lobe, or the inferior lobe. The digitus or finger (h) 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 Fig. 57.— MaxiUa oiCicindela. ^^^i^^ (pjgg^ ^^ ^^^ ^6). The labium or second maxillcB. — The labium or under lip (Fig. 53), is attached to the cephaUc 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 line of the body. In the Crustacea the parts corresponding to the labitmi of insects consists of two distinct organs, resembling the maxillae; and in the embryos of insects the labium arises as \ \ ^VY, ,^ -T \ i-i^ d- a pair of append- \\,-A-V~V4A------'"^r^ X''^ ./■ V .' 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 siibvienlnm, the mentum, and the ligida; the appendages are the labial palpi. The suhmentum. The basal part of the labitun consists of two transverse sclerites; the proximal one, which is attached to the cephalic border of the gula, is the suhmentum (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 cephalic border of the suhmentum, and is often so slightly developed that it is concealed by the submentum. The ligula 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 paraglossa (c^). Sometimes, how- ever, the paraglossae 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 to the parts of the maxillje 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 maxiUa-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 the palpiger, and is the homologue of the palpifer of 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 (c^) is the par agio ssa, and obviously corresponds to the galea. The mesal one {c") corresponds to the lacinia or inner lobe. This part is probably wanting in those insects in which the glossa consists of an undividec: part; and in this case the glossa probably represents the united and more or less elongated sabgaleae. The epipharynx. — In some insects there is borne on the ental sur- face of the labrum, within the cavity of the mouth, an unpaired fold, which is membranous and more or less chitinized • this is the epi- phdrynx. Fig- 59- — Labium of a cockroach. THE EXTERNAL ANA TOMY 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 paragnatha 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 (18 16), 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 two 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 vestiges 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 INIilne-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 ocular 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 deutocerebrum, and the tritocerebriim. And it has also been shown that the protocerebrum innervates the co:npound eyes and ocelli; the deutocerebnim, 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 antennas 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. Folsom ('00) in his work on the development of the mouth-parts of Anurida 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 superlingiice; 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 mesothorax, and the metathorax. — The thorax is the second or intermediate region of the body ; it is the region that in nymphs, naiads, and aduhs 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 very 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 Acridiidae, 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 alitnmk. — ^When, as in the Hymenoptera, the intermediate region of the body includes more than the three true thoracic seg- ments it is designated the dlitrunk. The propodeum or the median segment. — ^When the alitnmk 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 h). 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 the prothorax is designated the proscutxim; while the term prescutum is applied to the sclerite immediately in front of the scutiim in each of the thoracic segments. This system leads to the UL-e 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 notum. 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 pronohtm, 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. 6i, 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 postnotmn or postsciitellum. — 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 postsciitellum, 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 prescHtum (Fig. 61, Psc), the scutum (Fig. 61, Set), and the scutellum (Fig. 61, 5cZ). 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 postscutellum. But the investigations of Snodgrass indicate that in its more genera- lized form the tergum contains a single sclerite, the notum; that the postscutellum ^^_ or postnotum is a secondary tergal chitini- zation in the dorsal membrane behind the j^- notum, in more specialized insects; and that iP" the separation of the notum into three parts, the prescutum, scutum, and scutellum, is a still later specialization that has arisen independently in different orders, and does not indicate a division into homologous parts in all orders where it exists. The patagia. — In many of the more specialized Lepidoptera the pronotum Fig. 61.— Diagram of a generalized is produced on each side into a flat ^^^^^if"" segment (From Snod- lobe, which in some cases is even con- stricted at the base so as to become a stalked plate, these lobes are the patagia. Mh THE EXTERNAL A NA TOMY 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 pleunim 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 of the episterna are divided by a distinct suture into an upper and a lower part. These two parts have been designated by Crampton ('09) as the an epister- 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. 6 1 , 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 ('09) as the anepimerum and the katepimerum respectively (Fig. 62). 4 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. — In 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. Fig. 62.— Lateral aspect Snodgrass (10 a) has shown that there are in of the meso- and meta- . 1 • , • , 1 • • 1 • 1 thorax of Mantispa some insects two sclentes m this region, which, rugicollis; 1,1, anepis- j^^ designates the episternal paraptera or ternum;2,2,katepister- ,^. ^ „ 1 7-,\ 1 xi j. num; J, 3, anepimer- preparaptera (Fig. 61, iP and 2F); and that urn; 4, 4, katepimerum; one or occasionally two are similarly situated c, c, coxa. , , . 1 1 1 J- A.1 • between the epimerum and the base 01 the wing, the epimeral paraptera or postparaptera (Fig. 61, 3P). 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 ntimber 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 cavity. When the epimera of the prothorax extend behind the coxae and reach the prosternum, 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 sternum of a wing-bearing segment may consist of three or four sclerites. These have been designated, beginning with the anterior one, the presternum (Fig. 61, Ps), the sternum or eusternum (Fig. 61, 5), the siernellum (Fig. 61, 57), and the poststernellum (Fig. 61, Psl). In the more special- ized insects only one of these, the sternum, re- mains distinctly visible. It is an interesting fact that while in the speciali- zation of the tergum there is an increase in the number of the scleri- tes in this division of a segment, in the specialization of the stemimi there is a reduction. It is a somewhat unfortunate fact that the term sternum 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 Fig. 63. — Prothorax of Harpalus, ventral aspect; c, coxa; em, epimerum; es, episternum; /, femur; n, pronotum; s, s, s, prosternum. THE EXTERNAL ANATOMY OF INSECTS 53 into the composition of this division when it consists of more than a single sclerite. To meet this difficulty Snodgrass has proposed that the term eusternum be applied 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 OP THE APPENDAGES Fig. 64. — Prothorax of Penthe; c, coxaj cc, coxal cavity; /, femur; 5, prosternum; ^ 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, ie. in the area Cui; this intercalary vein is desig- nated as ICui. The adven- titious veins . — In certain in- sects there are secon d ary 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 Syrphidce. 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-flies. 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 occm"; these are the following: The humeral cross-vein Qi) 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 (5) 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+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 M2 and 2d M2; see Figure 87 where the cells are lettered. The medio-cubital cross-vein {m — cu) extends from media tc cubitus. 72 AN INTRODUCTION TO ENTOMOLOGY R^M Cw- ■M1+1+ y Fig. 86. — Diagram of an arculus of a dragon-fly. 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 i?i. 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 Ri and R3 coalesce, as in the wings of Rhyphus (Fig. 87), the cell Ijdng behind vein i?2+3 is cell R3, and not cell R2+3, 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 with the proximal one. Thus in Rhyphus (Fig. 87), cell M2 is divided by the medial cross-vein into cell istM^. and cell zdMi. 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 fiat 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 cuhito-anal fold. Convex and 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 number of veins in the different orders of insects. The axillary furrow is a line that scr\-es as a hinge which facilitates the folding of the posterior lobe of tlie wing of many insects under that part of the wing \ \ ^\^ J^C^~'*"^^~"'~~''"~->-.^^^^^ wing where they VJ^---__X,^ ^X/^"^---^..^ ^^^"--~~ y^ are crossed by ^^^"~~--~_N_____;;i----'''^''^ furrows. The ^. „„ „,. , ,, . bullee are usually Pig. 88. — -Wings 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 himieral 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 Diptera is cell ist M2; and that of the Trichoptera is cell R2+3. THE EXTERNAL ANATOMY OF INSECTS 75 The anal area and the prea)ial 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 conjunctivas. 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 (Chrysididffi) there are usually only three or fotir 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 pygldium; the tergite cephalad of the pygidium, especially in beetles with short elytra, the propygidium; and the last abdominal sternite, the hypopygium. The term hypopygium is also applied to the genitalia of male Diptera by writers on that oi"der 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 Collembola, and in some larvae. 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 structtue of the collophore is described more fully later in the chapter treating of the Collembola. The spring of the Collembola. — 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 claspers and in females the ovi- positor; to them have been applied the general term genitalia, they are also known as the gonapophyses. The genitalia, when all are developed consist of three pairs of appendages. Writers vary greatly in their views regarding the seg- Fig.89.-Em- bryo of Hy- drophilus 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 Fig. 90.— Ventral aspect of Machilis; c, cer- of Uniformity in the terms cus; ip, labial palpus; w/ median caudal applied to homologous parts nlament; w/>, maxillary palpus; 0, oviposi- . , ,.„ , . . tor; s, s, styli. That part of the figure m the different Orders of m- representing the abdomen is after Oude- ggcts; such of these terms aS mans. 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 presemt. 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 78 AN INTRODUCTION TO ENTOMOLOGY many jointed; while in others they are short and not segmented. The function of the cerei is different in different insects; they are beHeved 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 lilvc the cerci. The prolegs of larvae. — The question whether the prolegs of lan-ae represent true appendages or are merely h^^Dodermal outgrowths has been much dis- cussed. Several embryologists have shown that in embry'os of Lepidoptera and of saw-flies limb-rudi- ments appear on all or most of the abdominal seg- ments; and that they very soon disappear on those segments which in the lan^a 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. Fig. 91. — Lepis- ma saccharina. V. THE MUSIC AND THE MUSICAL ORGANS OF INSECTS Much has been written about music; but the greater part of this literature refers to mtisic made by man for human ears. Man, how- ever, is only one of many musical animals; and, although he excels all others in musical accomplishments, a study of what is done by our humbler relatives is not without interest. The songs of birds command the attention of all observ^ers. 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 inten^als 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 rh}^hmic 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 the 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 Anobium. 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 Psocidae, Clothilla 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 htmian 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, prestraiably 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 htmis 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 htrnis 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 number inferred from the note produced. 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 himi 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 observed. 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 Acridiidae, Locustidae, 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 Acridiidse abdominal stridulating organs exist. a 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 Qidipodinae; 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 margih 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 toeusts consists in rubbing the inner surface of the hind femora, upoh 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 violin-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 simidtaneously. When about to stridulate, the insect B- Fig. 92. — A, hind femora of Stenobothrus ; B, file greatly enlarged. Fig- 93- — Fore wing of a male of Stenobothrus. C, costa. R, rkdius; Sc, subcosta; THE EXTERNAL ANATOMY OF INSECTS 83 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- bothrus. : .. . The stridulating organs of the Gryllidae and the Tettigoniidae. — The stridulating organs of the Gryllidae and the Tettigoniidse 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 wijigs 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:l!tfc£tfcM vibrating areas, the tympana (Fig. 94, -i, /). As ^i^&^^^m^ the file of either wing can be used to set the C tympana of the wings in vibration, we may say Fig.94. — Fore wing -of that Gryllus is ambidextrous. Gryllus; A, as seen „_, , . , . , ^ 1 1 • hi from above, that When the cricket wishes to make his call, he P^''.^, 9^ *^® 7^^"S elevates his fore wings so that they make an angle which IS bent down . , . ^1 -1^111.1 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;/, . 1 ^1 r 1 1 1 j.i t, tympana. B,base of one rests on the file of the other, he moves the of wing seen from ^ings back and forth laterally, so that the file and below; s, scraper; ° 1. ^1. -t-i,- ^u +1, /.file. C, file great- scraper rasp Upon each other, ihis throws the ly enlarged. wings into vibration and produces the call. _^^,. It is easy to observe the chirping of crickets. If one will movp^ 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, and especially those of the tree crickets. The rate of chirping 84 AN INTRODUCTION TO ENTOMOLOGY is often influenced by temperature, being slower in cool nights than in warm ones; and becomiijg slower towards morning if the tem- perature falls. In certain genera of crickets as Nemobius 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 Locustidae 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 Locustidas 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 unused 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 nymphs (Comstock and Needham, 'gS-'gp). The results obtained by a study of the wings of CEcanthus will serve as an illustration. Figure 95 represents the wings of a female nymph 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 wing of a male nymph of CEcanthus (From Comstock and Needham). The homologies of the tracheae 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 Cu2. 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, t); and the scraper is formed at the outer end of the anal area (Fig. 97,5). 86 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 fea- ture and one characteris- tic of the fam- ily, is that the musical organ occupies an area near the base of the wing which is small com- pared with the area occupied by the musical organs of the Gryllidas. But here, as in the Gryllidse, the file is borne by the basal part of Cua, Fig. 97. — Fore wing of an adult male of CEcanthus;f, vein bearing the file; s, scraper; i, t, tympana. Fig. 98. — Wings of a male nymph of Conocephalus, (From Comstock and Needhapi). ' ■ the tympana are formed between the branches of cubitus, and the ler 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 form 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 beetlS^ dfte of' Fig. 100. — Stridulating organ of an arit, Myrmica rubra (From Sharp after Janet); d, scraper; e, file. the two parts of the stridulating organ ig situated upon 'the elytra;' and it is quite probable that in these cases the'felytra acts as vibratitt^i'' surfaces, as do the wings of locusts and ci'ickets. But in rriany 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 dorsvim of the following segment. It is quite conceivable that in this case 88 AN INTROD UCTION TO ENTOMOLOG Y 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 Acridiidae, 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, Phonapate, 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 purposes is that of the larvae of certain Lucanidae 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 stridulating organ is possessed by the larvae of Passalus, in which the legs of the third pair are so much shortened that the /-^■— ) . larvae 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 larvae; and the col- ony is able to keep together by stridu- latory signals. d. THE MUSICAL ORGANS OF A CICADA Fig. loi. — 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). 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 90 AN INTRODUCTION TO ENTOMOLOGY Fig. 102. — -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; sp, spiracle; t, timbal; vc, ventral cavity (After Carlet). from the hind border of the thorax and overlap the basal part of the abdomen; these are the opercula (Fig. 102, o). The opercula are expansions of the ster- nellum of the meta- / thorax, and each 1 serves as a lid covering V^!^^v%?:'nV%:/^^ y'l^^-^'-r'^i-^^ ^P a pair of cavities, con- taining the external parts of the musical apparatus of 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, /. 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, i); the other two mem- branes are in the ventral cavity. The folded membrane is in the anterior wall of the ventral cavity (Fig. 102, /. 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- abdominal air chamber, which comnliinicates with the exterior through a pair of spiracles (Fig. 102 5^); 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 former 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 delicate 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 insect^. 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 himiming ring, which lies close under the opening of the spiracle; and is foimd within two 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 found 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 the 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 ellipse elongated ver- tically; the contraction of the muscles transforms it to an ellipse 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 number 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 removed 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 staflE 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 f, or a quarter rest 1, repre- sents a quarter of a second ; a sixteenth note t. or a sixteenth rest i 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 off obliquely at one end. *This view was maintained by Siebold at a much earlier date in his Anatomy oj 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 soimd, like gni or greeu, repeated in a trill indefinitely, but seldom grtt grfl grg grO grfl grft gra jrrfl grO^ grtt^ -f-g-gr p g g I r g r g g rtrrrrf r-rgTTtrgtTrrr Fig. 103. — The chirp of Gryllotalpa horealis (From Scudder). for more than two or three minutes, and often for less time. It is pitched at two octaves above middle C." XT\ rr\ XT!. xt\ 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 auttmm 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 III 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; c, alimentary canal; /t, heart; m, muscle; «, nervous system; r, reproductive organs. idea of the relative positions of some of the more important organs. The parts sho\yi\ 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 chitin, 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 oth^r directions. The alimentary canal (a) occupies the centre of the body, and extends from one end to the other. The heart {h) is a tube open at both ends, and lying between the alimentary canal and the muscles pf the back. The central part of the nervous system (m) 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 Ental surface of the pleurites of the meso- and metathorax of Melano- plus, showing the lateral apodemes, ap, ap. 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, Melanoplus. Each of these {ap and ap) is an invagination of the body- wall, between the epistemtim 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. The nimiber of apodemes may be very '^t\ie^ d1 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 tentorium there extend a variable nvtmber of processes or chitinized tendons. The posterior arms of the tentorium. — The posterior arms of the tentoriimi (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 Fig;. 109. — Head of Melanophis, cau- dal aspect. 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 from 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 tentoriimi (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 (Fig. 46, at). The dorsal arms of the tentorium. — Each dorsal arm of the tentorium arises from the side of the body of the tentoriiun 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 tentoriimi; 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- tions that are derived from tergites are termed phragmas; those derived from the pleurites, lateral apodemes; and those, from the stemites, furccB. 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 meta- phragma; but, as they do not arise one from each segment of the Fig. I 10. — Ten- torium of Mela- noplus, C2phalic aspect. Thedistal end of the dorsal arms detached. 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 prephragnia 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 stemiim and the stemelliim (Fig. 1 1 1) ; when the sternel- liim 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. h. 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, usually of many cells. In these cases the glandular area usually becomes invaginated, and provided with an 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 Fig. 112. — Ventralaspectof the m3so — and metathorax of Grylltis; the positions of the f ircae wit'iin the boiyare indicated by dotted lines. THE INTERNAL ANATOMY OF INSECTS 99 -fe..,,.... . i:..... J -—Id ■■--■ . -'- — ■ -•;"*--'.'-±.'f^. _ ^y Fig. 113. — Moltinpj-fluid glands of the last larval instar of Lept molar sa decimlineata, just before pupation; le, larval epidermis; Id, larval dermis; mf, molting fluid; pe, forming pupal epidermis; h, hypoder- mis; g, molting fluid gland (After Tower). 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 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 Itmien 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. 114. — Glandular s^ta; 5, seta; c, cuticula; h, hypodermis; bm, basement membrane; oreS is de- sensillum basiconicum; 5cc, sensillum coeloconicum. . . Three sense-organs are figured ; a surface view of the scnbed m the COnclud- first is represented, the other two are shown in sec- jj-^g section of this tion. (From Berlese). ^ 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 larvae 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 ommatidiiim 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 whtre they are present in this group they are of a highly developed type and not rudimentary^; the compound eyes of Machilis, for example, are as perfect as those of winged insects. The absence cf compound eyes in larvae. — The absence of com- pound eyes in larvae 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 with n^nnphs and naiads. While the development of the compound eyes as a whole is retarded in larvag, a few ommatidia may be developed and function as ocelli during larval life. h. 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. 13G AN INTRODUCTION TO ENTOMOLOGY When there are three ocelli, the double nature of the median ocel- lus is shown by the fact that the root of the nerve 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 larvae, as those of the Tenthredinidae, 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 larvag 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 larvee, 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 larva, while the development of the greater ntimber 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 larvae 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 tliree 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 of Gastropacha rubi, 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 featiu-e 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 more of them are united to form what is known as a rhabdom or optic rod. A group of two visual cells with the rhabdom 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 niimber 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 as described by Hesse ('01). 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 illustrated by the 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; nil, 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). 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 forming 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. 153), 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 thd retinulae 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 oceUi 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 Seller ('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 ormnatidia, 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 structure 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 twc? 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-cells. — Next to the corneal hypodermis there are four cells, which in one type 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, t). 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, t')- The retinula. — At the base of each ommatidium, there is a group of visual cells forming a retinula (Fig. 155, 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, rh). The distal end of the rhabdom abuts against the proximal end of the crystalline-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 nimiber of accessory pigment -cells (Fig. 155, ap), which lie outside of and overlap them. From the above it will be seen that each ommatidiiun of a eucone eye is composed of five kinds of cells, three of which, the corneal hypo- dermis, the crystalline-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 ommatidiuni contains a true crystaUine-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 important 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 i42 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 tlie pigment of the eye and are absorbed by it ; in each ommatidiimi the cornea transmits to the crystalline -cone light from a very limited field of vision, and when this light reaches the apex of the crystalline- 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 num- ber and size of the ommatidia. It can be Fig. 156.— Diagram iUustrat- readily seen that the image formed by mg the theory of mosaic ° vision. many small ommatidia will represent the details of the object better than one formed by a smaller number of larger ommatidia ; the smaller the portion of the object viewed by each ommatidimn the more 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 ommatidiiim, 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 ommatidium is so complete that only the light that has traversed the cornea and crystalline -cone THE INTERNAL ANATOMY OF INSECTS 143 B of that ommatidkim reaches its rhabdom. The image formed in such an eye is termed by Exner an apposed image; because it is formed by apposed points of Hght, falling 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 Hght 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 wih 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, A), each rhabdom is surrounded by an envelope of pigment, so that it can receive only Fig. 157.— Ommatidia ^^^ ^^^^^ passing through the crystalline-cone of from eyes of Colym- the ommatidiimi of which this rhabdom is a part. hetes; A, day-eye /pj^jg -g ^^^ condition found in the individual condition; B, nignt- eye condition (From killed in the light, and illustrates well the struct- ■'^'''^^^)- ure of a day-eye. In the other preparation (Fig. 157, B), which is from an individual kiHed in the dark, it can be seen that the pigment has moved up between the cry stalHne -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 158). The tapetum. — In the eyes of many ariimals 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 eyes of cats and in the eyes of moths 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 tapetum 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 tapetimi 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 Fig. 158. — Front of head of Cloeon, showing divided eyes; a, night-eye; b, day- eye; c, ocellus (From Sharp). THE INTERNAL ANATOMY OF INSECTS 145 small crystals that reflect the light ; and in insects it is a mass of fine tracheas 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 jumping 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 Acridiidae, there is a tympanum on each side of the first abdominal segment (Fig. 159); and in the Locustidas and in the Gryllidae, 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 tympanimi 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.- num. -Fore leg of a katydid; t, tympa- 146 AN INTRODUCTION TO ENTOMOLOGY structures of insects is a more or less peg-like rod contained in a tubular nerve-ending (Fig. i6i, A and B); this nerv^e-ending may or may not be associated with a specialized tympanum. 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- Fig. 161. — Diagrammatic representation of the auditory organs of a locustid (After Graber). 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 (s) 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 Fig. 162. — A scolopo- phore of the i n t e g u - mental type (From Hess). THE INTERNAL ANATOMY OF INSECTS 147 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 scolopalee 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, efe). 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 enlarged (From figured here 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 ner\^ous system Fig. 163. — Part of the scolopophore shown in Figure 162 more 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 the T; 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-lik e structure between two points in the wall of a single segment. It is believed that in cases of this kind the pjg jg^ Diagram integument acts as Fig.i64.-Chordotonalorgan a tympanum or of a larva of Chironomus sounding board. (From Graber). representing the chordotonal organs of a larva of Chiro- nomus (After Gra- ber). h. THE CHORDOTONAL ORGANS OF LARV^ Chordotonal organs have been observed in so many larvae that we may infer that they are commonly present in larvee. These organs are very simple compared with those of certain adult insects, described later. Those figured in the preceding paragraphs will serve to illus- trate 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 tympana, but extend between distant parts of the body-wall, which probably acts as a sounding board. In certain larvae, however, the scolopophores are attached to specialized areas of the body-wall. Hess ('17) has shown that the pleural discs of cerambycid larvae, 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 THE LOCUSTID^ In the LocustidcE there are highly specialized ears situated one on each side of the first abdominal segment. The external vibrating THE INTERNAL ANATOMY OF INSECTS 149 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 M tiller's organ {go), first described by Miiller (1826). This gan- glion contains many Fig. 166. — Side view of a locust with the wings removed; t, tympanum. ganglion-cells and scolopalae and is the termination of a nerve extend- ing from the central nervous system, the auditory nerve (n). Figure 168 represents a section of Miiller's organ, showing the ganglion-cells and scolopalte. Intimately associated with the Miiller's organ are two horny processes (Fig. 167,0 and u) and a pear-shaped vesicle (Fig. 167, hi) ; and near the margin of the tympanimi, 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 Miiller's or- gan are attached to the tympanum, it is a chordotonal organ of the integumental type; it is attached to a vibratile mem- brane, between two air-spaces. Fig. 167. — Ear of a locust, Caloptenus italicus, seen from inner side; T, tympanum; TR, its border; 0, u, two horn-like processes; bi, pear-shaped vesicle; n, audi- tory nerve; ga, terminal ganglion or Miiller's organ; st, spiracle; M, tensor muscle of the tympanum (From Packard after Graber). a. THE CHORDOTONAL ORGANS OF THE TETTIGONIID^ AND OF THE GRYLLID^ In the long-homed grasshoppers and in the crickets, there is a pair of tympana near the proximal end of the tibia of each fore leg. In 150 AN INTRODUCTION TO ENTOMOLOGY many genera, these tympana are exposed and easily observed (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- --S tailed accounts of these organs have been published by Graber ('76), Adelung ('92) and Schwabe ('06); in this place, for lack of space, 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, Fig. 168.— Section of Muller's organ; g, passing through the tympana and ganglion-cells; n, nerve; s, s, scolo- ^-^q air-chambers formed by the pate (After Graber). folds of the body- wall. In the fol- lowing account the references, in most cases, are to both of these figures. Fig. 169. — Fore leg of a katydid; t, tympa- a Fig. 1 70. — Tibia of a locustid with covered tympana; o, front view; fc, side view; 0, 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 ANATOMY 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 supemumery spir- acles, differing in this respect from the tra- cheae 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 ■^ 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 tracheae (t), muscles (m) , the tibial nerve (Ntb), and a tendon (Tn). The interstices of the outer andinnerspaces 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 tympana, there is a ganglion (Fig. Fig. 171. — Longitudinal section of a fore tibia of Decticus verrucivorus (From Berlese after Schwabe). 152 AN INTRODUCTION TO ENTOMOLOGY I J I, Os) composed of nerve-endings, which are scolopophores of the integumental type. Two nerves extend to this gangHon, one from 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 hav^e 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.— Immediately below the supra-tympanal organ, and between it and the organ described in the next paragraph, is a ganglion composed of scolopophores of the subintegumental type; this is termed the ititermediate 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 Stebold's organ or the crista acustica. 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, used by some writers. Fig. 172. — Transverse section of the fore tibia of Decticus verrucivorus (From Berlese after Schwabe). In comparing this figure with the preceding, note that in that one the external parts are at the left, in this one, at the right. e. THE JOHNSTON S ORGAN There has been found in the pedicel of tlie 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 serve 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 by 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 setce; 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 Itmien of the pedicel is largely occupied by a ganglion composed of scolopophores, the attachment fibers of which are attached to the chitinous processes of the conjunctival plate. Fig. 173. — ^Antennae of mosquitoes, Culex; female; s, scape; p, pedicel. P— s -'^ F M, male; F, 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 whoris of setse 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. C « .^f^'^%^g^^ ^^ "^^^ formerly h /m ^Altkkt\. 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 mosqui- toes and of midges -Longitudinal section of the base of an anten- in which the males na of a male mosquito, Corethra culiciformis (After J^^ye this org'an hiijh- ly Specialized the fe- males seek the males. 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 scolopalae, which is the dis- tinctive characteristic of the auditory organs of other insects. Fig. 174. 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 applied to the organs of this type; of these that of sense domes is as appropriate as any, unless the conclusions of Mclndoo, referred to on the following page, are confirmed, in which case his term olfactory pores will be more descriptive. THE INTERNAL ANATOMY OF INSECTS 155 a b Fig. 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). AUof 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 17s, i>, 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 INTROD UCTION TO ENTOMOLOG Y present, but the sense-fiber of the sense-cell pierces the bottom of the cone and enters the round, oblong, or slit-like 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 antennal organs." XV. THE REPRODUCTIVE ORGANS a. THE GENERAL FEATURES In insects the sexes are distinct. Formerly Termitoxenia, 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 gynandroniorph; 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 abdomen 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- ing of the two sexes are common, especially in the Lepidoptera. In many insects the antennas of the male are -more highly specialized than those of the female; and this is true also of the eyes of certain insects. These are merely a few of the many known secondary sexual characters found in insects. r\ Fig. 178.— Repro- ductive organs of Japyx, female (After Grassi), b. THE REPRODUCTIVE ORGANS OF THE FEMALE The general features of the ovary. — In the more usual form of the ovaries of insects, each ovary is Fig.177.— Diagramofthereproduc- a compact, more or less spindle- tive organs of a female insect; 0, , jv j 1 <• ovary; o(i, oviduct; c, egg-calyx; v, shaped body composed of many paral- vagina; _5,spermathcca; 6c, bursa lei ovarian tubes (Fig. 177, o) , which copulatrix; sg, spermathecal . , ^ , 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 ntun- 158 AN INTRODUCTION TO ENTOMOLOGY ..A' H-{ ber of ovarian tubes differs greatly in different insects; in many Lepidoptera there are only four in each ovary; in the honey bee> 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 many insects, cells whose function is to furnish nutriment to the developing eggs; these are termed nurse-cells. Depending upon the presence or 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. 1 79, 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 epithelium lining of the ovarian tube becomes invaginated between the eggs in such a way that each egg is fa: ABC Fig. 179. — Three types of ovarian tubes; e, e, e, eggs; n, n, n, nurse-cells (After Berlese). THE INTERNA L ANA TOM Y OF INSECTS 1 59 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 epithelium serves a nutritive function. But 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. 177, 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 full- grown and each is provided with a shell before leaving the ovarian tubes. 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 micropyle, which is described in the next chapter (Figs. 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, &c); 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 copulatrbc 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 Fig. i8o.-Reproductive organs of the I'eceived by the bursa copulatri.x femaleof the milkweed butterfly; a, at the time of pairing, later it anus; 6, opening of the bursa copula- . ^u onprmathera and trix; ov, ovarian tubes; t, terminal passes to tne spermatneca, ana filaments of the ovary; v, opening from here it passes to the vagina. of the vagina (After Burgess). ^ ^^^^^ copulatrix is said tO 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, 5g). 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 16l In the more common form, each testis is a compact body (Fig. i8i, t) 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 volume. Fig. l8i. — 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; t, 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 Gryllidae, 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. iSi, 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. i8i, sv); the invaginated portion of the body- wall, correspond- ing with the vagina of the female, is the ejaculatory dtict (Fig. i8i, ed); accessory glands, corresponding to the colleterial glands of the female, are present (Fig. i8i, 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; the 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 i'lg. 182. — Diagram show- a>i. 1 ^ 1 • r ^.i.- j- u ing the relation of the h^e. i he lateral margms 01 this diaphragm do.-sal diaphragm and are attached to the sides of the body by a the ventral diaphragm ... , , . , • 1 1 to other viscera; a, series of triangular prolongations, which have ahmentary canal; d, been commonly known as the wings of the dorsal diaphragm; h, , .^. n ^1 1 , i- 1 heart; n, ventral nerv- heart (Fig. I ^g, c). The dorsal diaphragm IS ous system; v, ventral composed largely of very delicate muscles, diaphragm. -r , • ,1 ■ ■^^ 1 , .1 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 ANA TOMY 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 laterad 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, v. This diaphragm has been described as a ventral heart; but I believe that its function is to protect the abdominal ganglia 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 cenocytes. — The term oenocytes is applied to certain very large cells, that are found in clusters, often metamerically arranged, and connected with the tracheae and the fat body of insects. The name was suggested by the light 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 other 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 serv^e 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 albuminoids 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 leucocytes. 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 ANA TOMY OF INSECTS 165 The most commonly observed examples of light-producing insects are certain members of the Lampyridac, the fireflies and the glow-worms, and a member of the Elateridre, 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 larvae of mosquitoes, and certain lepidopterous larvae. 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 Photinns 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 account of the origin and development of the light-organs of Photurus pennsyhanica is given by Hess ('22). CHAPTER IV. THE METAMORPHOSIS OF INSECTS Many insects in the course of their lives 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 graceftil 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 diuing postembryonic 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 epitheliimi of the ovarian tube in which the egg is developed; 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'.tere are other vivi- parous insects, which are discussed later. In th'*s place is discussed (166) THE METAMORPHOSIS OF INSECTS 167 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 t)f 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 siihidatum; 4, Hydrometra martini. Fig. 184.— Egg of the cotton- worm moth; the micropyle is shown in the center of the lower figure. 168 AN INTROD UCTION TO ENTOMOLOG Y 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 papilla; (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 number 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 n 185.— Egg of peculiar mode of development of the larva of the Vrosoplnla meLan- . ogaster; m, micro- sheep -tick withm the body of the female makes Py^^- 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 true 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 solitary 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 number; 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 number 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 polyemhryony . 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 laying 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 solid 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 Megarhyssa lunator, which is parasitic 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 pro- tected 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 Hemerocampa covertheir egg-clusters with a frothy mass. Fig. 186. — Megarhyssa 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, Hydrophilidse, make egg-sacks out of a hardened silk-like secretion (Fig. i88) ; the locusts, Acridiidae, lay their eggs in oval masses and cover them with a ,..► '^,.. -. .,^ tough substance; the scale-insects r ,! , , - of the genus Pulvinaria excrete a i"' •. ' V- _ \ large cottony egg-sac (Fig. 189); Fig. 187 — Egg- mass of the squash-bug. Fig. 188. — Egg-sacoi Hydrophilus (After Miall). Fig. 189. — Pulvinaria innumerabilis, females on grape with egg sacs 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 Gotheca, 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 summit of a stiff stalk of hard silk (Fig. 192). Duration of the egg-state. — In the life-cycle of most insects, a few days, and only a few, intervene between the laying of p. an egg and the emergence of the nymph, naiad, or larva from — E g g- it. In some the duration of the egg-state is even shorter, the ™ f- ^ I hatching of the egg taking place very soon after it is laid, or pray- even, as sometimes in flesh-flies, before it is laid. On the ^ ^ 2 other hand, in certain species, the greater part of the life of an tis. individual is passed within the egg-shell. The common apple-tree tent-caterpillars, Clisiocampa americana, 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 are said to remain unhatched for two years; and a similar statement is made regarding the eggs of ovtr common walking-stick. 6. THE HATCHING OF YOUNG INSECTS Only a few accounts have been published regarding the manner in which a yoimg insect frees itself from the embryonic envelopes. In '^^^c ockroadT*^^^^ °^ ^ 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- 9 „ o ^[Mks/ ^;^%5^, cribed under several names. It was termed an egg-burster by Hagen, the ruptor ovi by C. V. Riley an egg-tooth by He3rmons, and the hatching spines by Wheeler. Fig. 192. — Eggs, larva, cocoon, and adult of Chrysopa. C. THE MOLTING OF INSECTS The young of insects 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 pltiral noun being used as in English is the word clothes. 172 AN INTRODUCTION TO ENTOMOLOGY Coincident with the formation of the new epidermis, new setae are formed beneath the old epidermis; these lie closely appressed to the outer surface of the new epidermis until released by the molting of the old epidermis. In the above account only the more general features of the process of molting are indicated, the details, according to the observations of Tower ('06) are as follows. (See Figure 1 13, p. 99). In the formation of the new epidermis it appears 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 ecdysis and has been found in all insects examined by him in varying degrees. It is said that the Collembola molt after reaching sexual maturity, in this respect agreeing with the Crustacea and the "Myriapoda," and differing from the Arachnida and from allother 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. gg) 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 Maj^-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 applied 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 larvae. — 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 measiu-ement 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 follows: .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) = 725 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. 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-'f93-— A spider in of the observed examples of the reproduction which lost legs we: e . . , . , , j j being reproduced. of appendages has an entu-e leg been reproduced. 174 AN INTROD UCTION 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 Collembola, which in other respects, also, are the most generalized of insects. The nature of the changes in form undergone by an insect with an ametabolous development is illustrated by the development of Machilis allernata, 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 that are correlated with the development of wings. In addition to the Thysanura and the Collembola there are certain insects that develop without metamorphosis, as the Mallophaga and the Pediculidas. But their ametabolous condition is believed to be an acquired one. In other words, it is believed 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 (1815), who included under it the lice as well as the Thysanura and Collembola. But with our present knowledge, if it is used it should be restricted to the Thysanura and Collembola, those insects in which a development without metamorphosis is a primitive not an acquired condition. *Ametabolous: Greek a, without; metahole (nera^oX-^) , change. 2 HE METAMORPHOSIS OF INSECTS 175 e. GRADUAL METAMORPHOSIS {Paurometaholous* 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). Fig. 197. — Nymph of Melano- plus, fourth instar (After Emerton). Fig. 199. adult. ■ Melanoplm, 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 paurometabolotis development. The characteristic features ot paurometaholous development are correlated with the fact that the mode of life of the young and of the *Paurometabolous: pauros {TraOpos) , Utile; metabole {fJ-era^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 -homed grasshopper will serve as an example of gradual metamorphosis. Each of the instars of our common red-legged locust, Melanoplus femur-riibrum, 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 eg^-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. — Thoseorders of insectsthat are characterized by a gradual metamorphosis are grouped together as the Paurometa- bola. This is not a natural division of the class Hexapoda but merely 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 t3rpe. — 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- horned 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 Coccidae the mode of devel- opment 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 Fig. 200. — disks. But the wings are developed externally. ^7™P^, °? ^ The AleyrodidcB. — In this family the type of meta- Riley). morphosis corresponds quite closely with that described later as complete metamorphosis; con- sequently 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 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. The adult emerges through a T-shaped opening on the dorsum of the pupariiim. Both sexes are winged. The AphididcB. — In the Aphididee there exists a remarkable type of development known as heterogamy or cyclic reproduction. This is characterized by an alternation of several parthenogenetic generations 178 AN 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 nourishment. This instar is commonly described as the pupa. /. INCOMPLETE METAMORPHOSIS (Hemimetabolous* Development) In three of the orders of insects, the Plecoptera, Ephemerida, and Odonata, there exists a type of metamorphosis in which the changes Pig. 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 metamorpJiosis 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 immature 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. *Hemimetabolous: hemi (^mO. l^alf ; tnetabole (/iera/SoXi)), 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 larvae. 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 metamorphosis 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 larvae. "Cenogenesis: kainos {Kalvoi}, new; genesis. 180 AN INTRODUCTION TO ENTOMOLOGY Deviation from the usual type of incomplete metamorphosis. — The more strikinj:^ 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 {Holometaboljis* 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 holometdbolous 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 behef 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 immattu"e stages of all insects; but more recent writers restrict its use to the immature in- *Holometabolous: holos {Ji><'Oi), complete; metahole {tiera^oX-o), 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 larvas 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 larvae and adults are augmented by the fact that not only have larvae 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 offspring. This tendency is termed homochronoiis 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 MuUer, in his "Facts for Darwin", to make the aphorism "There were perfect insects before larvse 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 larvae 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 larvae live under widely differing situations, various types of larvae have been developed; the more important of these types are described later. The greater or less reduction of tJie 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 larvas of certain Neuroptera, as Corydalus for example, have as perfect *Hom6chronous : homos (d/xo's), one and the same; chronos (xp<5»'oi), time. 182 AN INTRODUCTION TO ENTOMOLOGY legs as do naiads of insects with an incomplete ni etamorphosis. The larvae of Lepidoptera have short legs which correspond to only a part of the legs of the adult. While the larvas of Diptera have no external indications of legs. The development of prolegs in some larvce. — A striking feature of many larvas 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 believed 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, were redeveloped into functional organs. The development of tracheal gills. — A striking feature of many larvas 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 independently many times; for they exist in widely separated families belonging to different orders of insects that are chiefly aerial. They are possessed by a few lepidopterous larvse, and by the representatives of several famihes of Neuroptera, Coleoptera and Diptera. On the other hand, in the Trichoptera the possession of tracheal gills by the larvas 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 larvas. 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 dtu-ing larval life. 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 larvse of the most generalized Lepidoptera, the Hepialidse, are borers; the larvae of the Siricidas, which are among the more generalized of the Hymenoptera are borers; so too are many Coleoptera; most larvas of Diptera are burrowers; and the larv« 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 the 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 larvae 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 exhib- ited by the larvae of the more specialized Diptera. Here not only are the legs and wings developed internally but also the head. This phenomenon is discussed later. The different types of larvae. — 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 (Pamidae, Coleoptera), the slug-caterpillars (Cochlidiidae, Lepidoptera) , and the larvae of Microdon (Diptera) . To understand the variations in form of larvae 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 larvag 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 \arv^ of many Coleoptera (Cara- bidse, Dysticidae, and the first instar of Me- loidas). Eruciform. — The eruciform type of larvse is well-illustrated by most larvae of Lepidoptera and of Mecoptera; it is the caterpillar form (Fig. 203). In this type the body is cylindrical ; 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 larv® move freely, their powers of locomo- tion are much less than in the campodeiform type. Scaraheiform. — The common white grub, the larva of the May- beetle (Fig. 204) is the most familiar example of a scaraheiform larva. Fig. 202. — Campodea staphylintis (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 larvag of the Scarabasidag, hence the name ; but it occurs in other groups of insects. The movements of these larvae are slow; most of them live in the ground, or in wood, or in decaying animal or vegetable matter. Fig. 204. — Larva of Melolontha vulgaris (After Schiodte). Vermiform. — Those lar\^ce 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 larvae of butter- flies suspend themselves, and most larvae 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 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 Hnration in different insects, in which the wings are really Fig. 205. Larva of crane-fly. 186 AN INTRODUCTION TO ENTOMOLOGY Fig. 206. — ■ Lan'a of Platygaster (After Ganin.) outside of the body although still covered by the last larv^al cuticula; this period is the prepupal stadiiim. The prepupal instar differs markedly from both the last lan^al one and from the pupa ; for after the shedding of the last larval cuticula important changes in the form of the body take place before the pupal instar is assumed. The pupa. — The most obvious characteristics of the pupa state are, except in a few cases, inactivity and help- lessness. The organs of locom.otion are functionless, and may even be soldered to the body throughout their entire length, as is usual with the pupae 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 Linnaeus 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- pjg_ 207.— Pupa of a moth, cure of the body take plane at this 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 rneta- 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 structure. These changes take place during the period of apparent rest, the prepupal and pupal stadia. The chrysalis.— The term chrysalis is often applied to the pup^ 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, chrysalis, the plural of which is chrysalides; and second, chrysalid, the plural of which is Fig. 208 Pupa of a beetle . THE METAMORPHOSIS OF INSECTS 187 chrysalids. The singular of the first form and the plural of the second are those most often used. Active pii-pcB. — The pup£e of mosquitoes and of certain midges are remarkable for being active. Although the wings and legs are func- tionless, as with other pupag, 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 pupee of the carpenter- moths (Cossidae) the pupa is armed with rows of backward projecting teeth on the abdominal segments, which facilitate the movements within the burrow. The cremaster. — Many pupae, 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 often 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 diiring 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, 6); 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 larvai 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 Bonibyx, 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. 210.^ the cocoons of the sphecids appear like a delicate foil. cocoon^ of While in the more common type of cocoons the Trichostibas wall is a closely woven sheet, there are cocoons that from ^ which are lace-like in texture (Fig. 210). the adult has 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 inclosure; a problem which is solved in greatly varied ways. THE METAMORPHOSIS OF INSECTS 189 JV- 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 Cynipidce, 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 pupas 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 adult cuts a slit in the cocoon through which the moth emerges, this was observed by Packard in Tropcea 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. 2 12. — Cocoon of Megalopyge oper- cularis. ^m Fig. 211. — Longi- tudinal section of a cocoon of Callosamia pro- methea ; V ,va\ve- 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 larvse of Samia cecropia and Callosamia promethea. These lan^ae 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. 211, v). 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 stadium of most Diptera is passed within the last larval skin, which is not broken till the adult fiy is ready to emerge. In this case the larval 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 larva; in others the body of the larva shortens, assuming a more or less barrel-shaped form, before the change to a pupa takes place (Fig. 214). Modes of escape front 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 split at the front end of this (Fig. 215), or ^^iiS^ rarely, through a cross-wise split between the seventh Fig. 214. — Pupa- and eighth abdominal segments. In the more special- num of Try-^^Q^ 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 ptilinum is withdrawn into the head. The Different types of pupae. — Three types of pupag are commonly recognized; these are the following: Fig. 215.— Puparium of a Exarate pupce. — Pupse which, like those ^ ^^ ^ ^" of the Coleoptera and Hymenoptera, have the legs and wings free, are termed exarate pupae. THE METAMORPHOSIS OF INSECTS 191 Obtected pupce. — Pups which like the pupag of Lepidoptera, have the hmbs glued to the surface of the body, are termed obtected pupae. Coarctate PupcB. — Pupse that are enclosed within the hardened larval skin, as is the case with the pupae of most of the Diptera, are termed coarctate pup«. 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 larvae. 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 larvae 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 literatufe. 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 pseudovtmi 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 born when very young to those in which the entire lar\^al Hfe 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 larv^ae, pupse, and apparently in adults. Padogenetic LarvcB. — In 1862 Nicholas Wagner made the remark- able discovery that certain larvag belonging to the Cecidomyiidas give birth to living young. This discovery has been confirmed by other observers, and for this type of reproduction the term pcedo genesis, 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 Micromalthidse. Pcedogenetic pupcE. — The most frequently observed examples of paedogenetic reproduction are by larvas; but that pupas also are some- times capable of reproduction is shown by the fact that Grimm ('70) found that eggs laid by a pupa of Chironomus gtimmii, 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 from 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 stmcture and of development. Thus Leydig ('67) found a certain aphid to be both ovipar- ous and viviparous; the eggs and the individuals born as nymphs being produced from n3ighboring 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 born 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 oothecre as do other cockroaches. Among the recorded examples of this type of viviparity are representatives of the Ephemerida, Orthoptera, Hemiptera, Lepi- doptera, Coleoptera, Strepsiptera, and Diptera. Sexual viviparous insects giving birth to old larva;. — The mode of reproduction exhibited by these insects is doubtless the most excep- tional that occurs in the Hexapoda, involving, as it does, very impor- tant changes in the structure of the reproductive organs of the fe- males. With these insects the larvae reach maturity within the body of the parent, undergoing what is analogous to an intra-uterine develop- ment, and are born 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 families, 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, Melophagiis 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 belongs. The giving birth to old larvae is not restricted to the Pupipara. Surgeon Bruce (quoted by Sharp, '99) has shown that the Tsetse fly, Glossina morsitans, reproduces in this way, the young changing to pupae immediately after birth. An intermediate type of development is illustrated by Hylemyia strigosa, a dung-frequenting fly belonging to the Anthomyiidse. This insect, according to Sharp ('99), produces living larvs, 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 accomplished 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 (v^os), youthful; teinein {rtLvetv), 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 n3anphs and naiads, the latter with larvae.* 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 larval skin is shed. The development of the wings of the cabbage butterfly {Pontia rapes) 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 fiisu 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 stadiimi 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 '18, a). 196 AN INTRODUCTION TO ENTOMOLOGY portions of ine 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 larval 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 the Lepidoptera be- 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 respiratoiy organs, consisting of bundles of tracheoles, are developed (e and/) ; and later, near the close of the larval period, the tracheae 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-tracheae 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-veins 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 the 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). b. THE DEVELOPMENT OF LEGS The development of the legs pioceeds in widely different ways in different insects. In the ^. „,.,,.,, ,. Fig. 217. — Wing-bud m the larva of the more generahzed forms, the giant crane-fly, Holorusia rubiginosa; legs of the embryo reach an ?>"' hypodermis; pm, peripodal mem- j , r 1 1 brane; /, 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 larvae, 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 larvee that the development of their legs is retarded to a greater or less extent. This retardation is least in campodeiform larvs, more marked in cruciform larvae, and reaches its extreme in vermiform larvas. The development of the legs of insects with campodeiform larvae. — Among the larvee 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 larvas 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 larv^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 advlt leg ; but studies of the development of the legs of adults have shown that the divisions of the larval leg have no relation to the five divisions of the adult leg. TH^ 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 resiilts 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^se 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 larvce 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 Musca, the different segments telescope into each other. At the close of the larval period, the evagination of the legs takes place. C. THE DEVELOPMENT OF ANTENNAE I. The Transformation of the Antennce 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 mimber of the segments of the antennas takes place ; but in the Ephemerida, a reduc- tion in number of the antennal segments occurs. 2. The Development of the Antennce in Insects with a Complete " Metamorphosis One of the marked characteristics of larvae is the reduced condition of the antennae ; even in the campodeiform larvas of the Neuroptera, where the legs are comparatively well-developed, the antennae are greatly reduced. In cruciform larvas the development of the antennae follows a course quite similar to that of the legs. The larval antennae are small,* 200 AN 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 larvffi (Fig. 218). d. THE DEVELOPMENT OP Fig. 218. — Sagittal section through headof old THE MOUTH-PARTS lan^a oi Simtdiiim, showing forming imaginal head parts within. Ic, larval cuticula; id. Great differences exist imaginal head- wall; la, larval antenna; ia, ^mong insects with refer- miagmal antenna; re, imagmal eye; Imd, ** larval mandible; imd, imaginal mandible; ence to the comparative Imx larval maxilla; fmx, imaginal maxilla; structure of their mouth- lu, larvai labium; ih, imagmal labium (From Kellogg). parts in their immature and adult ins tars. In some insects the immature instars have essentially the same type of "*^""' -parts as the adults; in most of these cases, the mouth-parts are of the biting types, but in the Homoptera and Heteroptera both nymphs and adults have them fitted for sucking; in many other insects, the mouth-parts of the larvae are fitted for biting while those of adults are fitted for sucking; and in still others, as certain maggots, the development of the mouth-parts is so retarded that they are first functional in the adult insect. Correlated with these differences are differences in the method of development of these organs. In those insects that have a gradual or incomplete metamorphosis and in the Neuroptera, the Coleoptera, and the Hymenoptera in part, the mouth-parts of the immature and adult instars are essentially of the same type. In these insects the mouth-parts of each instar are developed within, the corresponding mouth-parts of the preceding instar. At each ecdysis there is a molting of the old cuticula, a stretching of the new one before it is hardened, a result of the growth in size of the appendages, and sometimes an increase in the number of the segments of the appendage. In a word, the mouth-parts of the adult are developed from those of the immature instar in a compara- tively direct manner. In some cases, however, where the mouth- THE METAMORPHOSIS OF INSECTS 201 parts of the larva are small and those of the adult are large, only the tips of the developing adult organs are within those of the larva at the close of the larval period, a considerable part of the adiilt organs being embedded in the head of the old larva. In a few Coleoptera and Neuroptera (the Dytiscidse, Mjrrme- leonidse, and Hemerobiidae) the larvas, although mandibulate, have the mouth-parts fitted for sucking. In these cases the form of the mouth-parts have been modified to fit them for a peculiar method of taking nourishment during the larval life. The mouth-parts of the adults are of the form characteristic of the orders to which these insects belong. In those insects in which the larvae have biting mouth-parts and the adults those fitted for sucking, the development is less direct. In the Lepidoptera, for example, to take an extreme case, there are great differences in the development of the different organs; within the mandibles of the old larvae there are no developing mandibles, these organs being atrophied in the adult; but at the base of each larval maxilla, there is a very large, invaginated histoblast, the developing maxilla of the adult; these histoblasts become evaginated at the close of the larval period, but the maxillae do not assume their defini- tive form till after the last ecdysis. The extreme modification of the more usual course of development of the mouth-parts is found in the footless and headless larvae of the more specialized Diptera. Here the mouth-parts do not appear externally until during the pupal stadium and become functional only when the adult condition is reached. See the figures illustrating the development of the head in the Muscidas (Fig. 220). It should be noted that the oral hooks possessed by the larvae of the more specialized Diptera are secondarily developed organs and not mouth-parts in the sense in which this term is commonly used. These oral hooks serve as organs of fixation in the larvae of the CEstrids and as rasping organs in other larvae. e. THE DEVELOPMENT OF THE GENITAL APPENDAGES The development of the genital appendages of insects has been studied comparatively little and the results obtained by the different investigators are not entirely in accord ; it is too early therefore to do more than to make a few general statements. In the nymphs of insects with a gradual metamorphosis rudimen- tary genital appendages are more or less prominent and their develop- 202 AN INTRODUCTION TO ENTOMOLOGY ment follows a course quite similar to that of the other appendages of the body. In insects with a complete metamorphosis the genital appendages are represented in the larvas by invaginated histoblasts; the develop- ing appendages become evaginated in the transformation to the pupa state and assiime their definitive form after the last ecdysis. III. THE DEVELOPMENT OF THE HEAD IN THE MUSCID^ In the more generalized Diptera the head of the larva becomes, with more or less change, the head of the adult ; the more important of these changes pertain to the perfecting of the organs of sight and the development of the appendages, the antennas and mouth-parts. But in the more specialized Diptera there is an anomalous retard- ing of the development of the head, which is so great that the larvae of these insects are commonly referred to as being acephalous. This retarded development of the head has been carefully studied by Weis- man ('64), Van Rees ('88) and Kowalevsky ('87). The accompanying diagrams (Fig. 220) based on those given by the last two authors illus- trate the development of the head in Musca, which will serve as an illustration of this type of development of the head. The larvas of Musca are conical (Fig. 219); and the head-region is repre- sented externally only by the minute apical segment Fig.219— Larva of the house-fly, M«5ca of the conical body. It domeshca (After Hewitt). .,, , , ■, ^ . Will be shown later that this segment is the neck of the insect, the developing head being invaginated within this and the following segments. This invagina- tion of the head takes place during the later embryonic stages. In Figure 220 are given diagrams, adapted from Kowalevsky and Van Rees, representing three stages in the development of the head of Musca. Diagram A represents the cephalic end of the body of a larva; and diagram B and C, the corresponding region in a young and in an old pupa respectively; the parts are lettered uniformly in the three diagrams. The three thoracic segments (1,2, and 3) can be identified by the rudiments of the legs (/', P, and P). In the larva (A) the leg-buds are far within the body, the peripodal membrane being connected with THE METAMORPHOSIS OF INSECTS 203 the hypodermis of the body-wall by a slender stalk-like portion. In the young pupa (B) the peripodal membranes of the histoblasts of the legs are greatly shortened and the leg-buds are near the surface of the body; and in the old pupa (C) the leg-buds are evaginated. The wing-buds are omitted in all of the diagrams. In the first two segments of the body of the larva (A) there is a cavity (ph) which has been termed the "pharynx" ; this is the part in which the oral hooks characteristic of the larvae of the Muscidae develop. The name pharynx is unforttmate as this is not a part of the alimentary canal; it is an invaginated section of the head, into the base of which the oesophagus (ce) now opens. In the figure of the larva (A) note the following parts: the oesophagus (cr) ; the ventral chain of ganglia (vg) , the brain (6) , and a Fig. 220. — Development of the head in the Muscidae. A, larva; B, young pupa; C, old pupa (From Korschelt and Heider after Kowalevsky and Van Rees). sac (ba) extending from the so-called pharynx to the brain. There are two of these sacs, one applied to each half of the brain, but only one of these would appear in such a section as is represented by the diagram. These sacs were termed the brain-appendages by Weismann. In each of the "brain-appendages" there is a disc -like thickening near the brain, the optic disc (od) ; this is a histoblast which develops into a compound eye; in front of the optic disc there is another prominent histoblast ; the frontal disc (Jd) , upon which the rudiment of an antenna (at) is developed. In the larA^a the brain and a considerable part of the "brain- appendages" lie within the third thoracic segment. In the young pupa (B) these parts have moved forward a considerable distance; and in the old pupa (C) the head has become completely evaginated. The part marked p in the two diagrams of the pupa is the rudiment of the proboscis. 204 AN INTRODUCTION TO ENTOMOLOGY By comparing diagrams B and C it will be seen that what was the tip of the first segment of the larva and of the young pupa (++) becomes the neck of the insect after the head is evaginated. IV. THE TRANSFORMATIONS OF THE INTERNAL ORGANS Great as are the changes in the external form of the body during the life of insects with a complete metamorphosis, even greater changes take place in the internal organs of some of them. In the space that can be devoted to this subject in this work, only the more general features of the transformation of the internal organs can be discussed; there is an extensive and constantly increasing literature on this subject which is available for those who wish to study it more thoroughly. In insects with a gradual or with an incomplete metamorphosis there is a continuous transformation of the internal organs, the changes in form taking place gradually : being quite comparable to the gradual de velopment of the external organs ; but in insects with a complete metamorphosis, where the manner of life of the larva and the adult are very different, extensive changes take place during the pupal stadium. The life of a butterfly, for example, is very different from that it led as a caterpillar; the organs of the larva are not fitted to perform the functions of the adult ; there is consequently a necessity for the reconstruction of certain of them; hence the need of a pupal staditmi. Pupag are of ten referred to as being quiet ; but physiologi- cally the pupal period is the most active one in the post-embryonic life of the insect. In those cases where a very marked change takes place in the structure of internal organs, there is a degeneration and dissolution of tissue, this breaking down of tissues is termed histolysis- In the course of histolysis some cells, which are frequently leu- cocytes or white blood corpuscles, feed upon the debris of the disin- tegrating tissue ; such a cell is termed a phagocyte, and the process Is termed phagocytosis. It is believed that the products of the digestion of disintegrating tissue by the phagocytes pass by diffusion into the surrounding blood and serve to nourish new tissue. After an organ has been more or less broken down by histolysis, the extent of the disintegration differing greatly ir different organs and in different insects, there follows a growth cf new tissue; this process is termed histogenesis. THE ME TA MORPHOSIS OF INSECTS 205 The histogenetic reproduction of a tissue begins in the differentia- tion and multipHcation of small groups of cells, which were not affected by the histolysis of the old tissue; such a group of cells is termed an imaginal disc or a Mstoblast. They were termed imaginal discs on account of the disc-like form of those that were first described and because they are rudiments of organs that do not become func- tional till the imago stage ; but the term histoblast is of more general application and is to be preferred. The extent of the transformation of the internal organs differs greatly in different insects. In the Coleoptera, the Lepidoptera, the Hymenoptera, and the Diptera Nemocera, the mid-intestine and some other larval organs are greatly modified, but there is no general histolysis. On the other hand, in the Diptera Brachycera, there is a general histolysis. In Musca all organs break down and are reformed except the central nervous system, the heart, the reproductive organs, and three pairs of thoracic muscles. Regarding the extent of the transformations in the other orders where the metamorphosis is com- plete we have, as yet, but little data. SUPPLEMENTARY NOTE After the manuscript of this volume was sent to the printer there appeared a very important paper by Mr. R. E. Snodgrass on the "Anatomy and Metamorphosis of the Apple Maggot, Rhagoletis pomonella Walsh." This was published in the "Journal of Agricul- tural Research" Vol. 28, pp. 1-36, with six plates. This paper was received too late to make possible the incorpora- tion of the new material in the preceding pages. PART II THE CLASSIFICATION AND THE LIFE- . HISTORIES OF INSECTS CHAPTER V THE SUBCLASSES AND THE ORDERS OF THE CLASS HEXAPODA Insects constitute one of the classes of the Arthropoda, that division of the animal kingdom in which the body is composed of a series- of more or less similar segments and in which some of these segments bear jointed legs. This class is known as the Hexapoda. The distinctive characteristics of the Class Hexapoda and its relation to the other classes of the Arthropoda are discussed in the first chapter of this work; we have now to consider the division of this class into subclasses and orders. The orders that constitute the Hexapoda represent two well-marked groups; this class is divided, therefore, into two subclasses. This division was first proposed by Brauer ('85), who recognized the fact that while the wingless condition of certain insects, the fleas, lice, bird-lice, and. the wingless members of orders in which the wings are usually present, is an acquired one, the wingless condition of the Thysanura and Collembola is a primitive one. In other words, from the primitive insects, which were wingless, there were evolved on the one hand the orders Thysanura and Collembola, which remained wingless, and on the other hand, a winged form from which have descended all other orders of insects. An extended study of the wings of insects has shown that the wings of all of the orders of winged insects are modifications of a single type ; it is believed, therefore, that all of the orders of winged insects have descended from a common winged ancestor. As to the lice, bird-lice, and fleas, the relation of each of these groups to certain winged insects, as shown by their structure, has led to the belief that their wingless condition is an acquired one, being the result of parasitic habits. The lice or Anoplura are commonly regarded as closely allied to the Homoptera and Heteroptera ; the bird-lice or Mallophaga to the Corrodentia; and the fleas or Siphonaptera to the Diptera. Hence these wingless insects are placed with the winged insects in a single subclass. The two subclasses thus recognized were named by Brauer the Apterygogenea and the Pterygogenea respectively. The cumber- someness of these names led to the substitution for them of the shorter names Apterygota and Pterygota. The Apterygota includes the orders Thysanura and Collembola; and the Pterygota, all other orders of insects. Some writers regard the Thysanura and Collem- bola as suborders of a single order, which they term the Aptera. The distribution of insects into orders is based on the classification of Linnffius, as set forth in his "Systema Naturae" (1735-1768). Linnaeus, who has been called the Adam of zoological science, divided (209) 210 AN INTRODUCTION TO ENTOMOLOGY his class Insecta into seven orders; these he named Coleoptera, Hemiptera, Lepidoptera, Neuroptera, Hymenoptera, Diptera, and Aptera, respectively. Since the time of Linnaeus many modifications of his classification of insects have been proposed; and new ones are constantly appear- ing. The result is that now there is a great lack of uniformity in the classification used by different writers. The modifications of the Linna?an distribution of insects into orders are based on the belief that in certain cases Linnaeus grouped into a single order forms that really represent two or more distinct orders. The result has been a great increase in the number of orders recognized. Linnaeus included in his class Insecta, under the order Aptera, not only wingless insects but also arachnids, crustaceans, centipedes, and millipedes. The animals thus grouped by Linnaeus are now dis- tributed into several classes; and to the class composed of the animals now commonly known as insects, those characterized by the posses- sion of only six legs, the term Hexapoda is commonly applied. Some writers, however, apply the term Insecta to the class of insects as now limited. Some of the more recently recognized orders of insects are repre- sented among living insects by comparatively few species; but in each case the structure of the insects included in the group is so differ- ent from that of all other insects that we are led to believe that they represent a division of the class Hexapoda that is of ordinal value. -^ There are given below the names of the orders of insects recognized in this work. The sequence in which these orders are discussed is of necessity a more or less arbitrary one. In general the plan adopted here is to make the series an ascending one; that is, the more gen- eralized or primitive insects are placed first and the more highly specialized ones later in the series; but as the different orders of insects have been specialized in very different ways, the relative de- grees of their specialization cannot be shown by arranging them in a single linear series, as must be done in a book. To indicate the different ways in which the different members of a group have been specialized and the relative rank of those specialized in a similar way, use must be made of a diagram representing a genealogical tree. . Many such diagrams have been made, but no one of them has re- ceived general acceptance; much remains to be learned before such a diagram can be made that will inspire confidence in its accuracy. In the course of the preparation of a special treatise on the wings of insects (Comstock ' 1 8 a) , I wrote a table indicating the more strik- ing of the methods of specialization of the wings characteristic of each of the orders of winged insects; and in the discussion of the different orders, I followed the sequence indicated by this table. In doing this I did not advocate the basing of a classification of insects upon the characters presented by the wings alone, but merely made use of these characters for the purposes of that work. HEX A POD A 211 A renewed study of the relationships of the different orders to each other, in which an effort has been made to correlate other characters with those presented by the wings, has not indicated the desirabihty of changes in the sequence of the orders indicated in that table, ex- cept in the allocation of those orders in which wings are wanting. The importance of the wings of insects for taxonomic purposes was early recognized by entomologists, as is well shown by the fact that the names of the Linnsean orders are all drawn from the nature of the wings, except one, Aptera, and that from the absence of wings. The different methods of specialization of the wings arose very early in that part of the geological history of insects that is known to us. And as most of the fossil remains of the older insects consist of wings, we are forced to depend very largely on the characters presented by these organs for data regarding the separation of the primitive insects into the groups from which the orders of recent insects have been developed. But in characterizing the orders as they now exist all the results of the study of the structure of insects and of their transformations are available. Aside from the structure of the wings, the characters most used in characterizing the orders of insects are those presented by the structure of the mouth-parts and the nature of the post-embryonic development. While these characters are of value in defining the orders, but little use has been made of them, as yet, in working out the lines of descent of the various orders from the primitive insects. The primitive insects had chewing mouth-parts and this type has been retained in the greater number of the orders. But although many detailed accounts of the structure of the mouth-parts of chew- ing insects have been published, no one has worked out the various ways in which they have been specialized in such a manner as to in- dicate the phylogeny of the orders. Several different types of sucking mouth-parts exist among living insects; but these are apparently of comparatively late origin, and while they are of great value in defining the orders in which they occur, they do not afford characters for determining the primitive divisions of the Pterygota. The nature of the post-embryonic development of insects, like the structure of the mouth-parts, affords characters for defining the orders of recent insects, but is of little value in determining the phylogeny of the orders. The primitive insects doubtless developed without any marked metamorphosis as do the Thysanura and Collembola of today. With the development of wings, there arose that type of development known as gradual metamorphosis, and this type is retained by eight of the orders recognized in this work. Incomplete metamorphosis is the result of a sidewise development of the immature instars of the insects exhibiting it, in order to fit them for life in the water, and it doubtless arose independently in each of the three orders in which it occirrs; it is therefore an ordinal characteristic in each case and not one indicating a natural group of orders. This is also true of com- 212 AN ITRODUCTION TO ENTOMOLOGY plete metamorphosis, which also doubtless arose independently in different divisions of the insect series, as, for example, intheNeurop- tera, which it is believed is a very ancient order, the origin of which was much earlier than the attainment of complete metamorphosis. TABLE OF THE METHODS OF SPECIALIZATION OF THE WINGS CHARACTERISTIC OF THE ORDERS OF WINGED INSECTS* This table is merely the result of an effort to indicate the more striking of the methods of specialization of the wings characteristic of each of the orders of insects. It is not a key for determining the orders of insects. It is not avail- able for this purpose; because, in many cases, the wings of an insect do not show the type of specialization characteristic of the order to which the insect belongs. Thus, for example, while the most characteristic modification of the courses of the wing-veins in the Diptera and Hymenoptera is due to the coales- cence of veins proceeding from the margin of the wing towards the base of the wing, there is no indication of this type of coalescence of veins in some of the nemocerous Diptera. A. Wings specialized by the development of supernumerary veins in the preanal area. B. Supernumerary veins of the accessory type. C. Wings developed externally. D. Wings retained throughout life. Wings without a striking contrast in the thickness of the veins of the anterior part of the wing and those of the middle portion Orthoptera DD. Wings deciduous, there being near the base of each wing a trans- verse suture along which the wing is broken off after the swarming flight. Wings with the veins of the anterior part of the wing greatly thickened and those of the middle portion reduced to narrow lines ISOPTERA CC. Wings developed internally Neuroptera BB. Supernumerary veins of the intercalary type. C. Flight -function cephalized; the hind wings being greatly reduced in size Ephemerida CC. Flight-function not cephalized; the hind wings as large as or larger than the fore wings Odonata AA, Wings specialized by a reduction in the number of veins in the preanal area. B. Wings developed externally. C. The two pairs of wings similar in texture. D. With the tendency to develop accessory veins retained. . Plecoptera DD. With the tendency to develop accessory veins in the preanal area lost. E. With the courses of some of the longitudinal veins modified so that they function as cross-veins 'oRRonFNTTA EE. The transverse bracing of the wing attained in the usual way. F. The veins of the wing bordered with dark bands.. .Embiidina FF. The veins of the wing not bordered with dark bands. G. Wings long and narrow, supplemented by a wide fringe of hairs Thysanoptera GG. Wings not greatly narrowed and not supplemented by a wide fringe of hairs Homoptera CC. The front wings more or less thickened. D. The front wings not greatly reduced in length as compared with the hind wings. E. The front wings thickened throughout Homoptera EE. The front wings thickened at the base, the terminal portion membranous Heteroptera DD. The front wings greatly reduced in length Dermaptera *From "The Wings of Insects," pp. 120-122. HEX A POD A 213 BB. Wings developed internally. C. Fore wings greatly thickened. D. Fore wings modified so as to serve as covers of the posterior wings COLEOPTERA DD. Fore wings reduced to slender, leathery, club-shaped appendages Strepsiptera CC. The two pairs of wings similar in texture. D. With the tendency to develop accessory veins retained. . Mecoptera DD. With the tendency to develop accessory veins lost. E. The most characteristic method of reduction of the wing-veins of the preanal area being by coalescence outward. F. Anal veins of the fore wings tending to coalesce at the tip. Wings usually clothed with hairs Trichoptera FF. Anal veins of the fore wings not tending to coalesce at the tip. Wings clothed with scales Lepidoptera EE. The most characteristic method of reduction of the wing-veins of the preanal area being by coalescence from the margin of the wing inward. F. With only one pair of wings Diptera FF. With two pairs of wings Hymenoptera The sequence in which the orders of insects are discussed in the following chapters has been determined by the above table. This sequence, like all linear arrangements of groups of organisms, is more or less arbitrary. Thus while there is an effort to place first the more generalized orders and later those that are more specialized, the putting together of orders exhibiting the same type of specialization results in some cases in the placing of comparatively generalized forms after those that are obviously more highly specialized. The position of the Plecoptera is an illustration of this. The insects of this order are evidently more generalized than, for example, the Neuroptera or the Odonata, which are placed earlier in the linear series. The comparatively high position assigned to the Plecoptera is, however, only apparent. A reference to the table will show that the orders of insects are grouped in two series, "A" and "AA". Under "A" are placed those orders in which the wings are specialized by addition in the preanal area, and under "AA" those orders in which the wings are specialized by reduction in the preanal area. Each of these series includes some quite generalized insects and others that are highly specialized. The completion of the discussion of the first series before taking up the second series results in the generalized members of the second series following the highly specialized members of the first series. The more generalized members of these two series, the Orthoptera of the first series and the Plecoptera of the second series, are probably more closely allied to each other than is either of these orders to the more specialized orders of the series in which it is placed; the two series arose from a common starting point, the Palaeodictyoptera, but have widely diverged in the course of their development. An even more striking illustration of the difficulty of indicating the relative ranks of orders by the use of a single linear series is the position of the Isoptera in the above table. This order is a very 214 AN INTRODUCTION TO ENTOMOLOGY ancient one; it separated from the Palaeodictyoptera before definite cross-veins in the wings had been developed and has not attained them. It is placed in the table next to the Orthoptera because the wings are specialized by the development of supernumerary veins of the accessory type and are developed externally; but the peculiar specialization of the wings is very different from that of the Orthop- tera as is indicated in the table. And in other respects the termites have reached a stage of development far in advance of that shown by any of the Orthoptera. They have attained a social mode of life, with the correlated separation of the species into several castes and the development of remarkable instincts. In this respect they rival the social H^nmenoptera. In fact the living members of each of the orders of insects must be regarded as a group of organisms representing the results of speciali- zation in a direction different from that of any other order; and to attempt to decide which order is the "highest" seems as futile as the discussion by children of the question: "Which is better, sugar or salt?" The list below indicates the sequence in which the orders are discussed in the following chapters. THE SUBCLASSES AND ORDERS OF THE HEXAPODA SUBCLASS APTERYGOTA. — Wingless insects in which the wingless condition is believed to be a primitive one, there being no indication that they descended from winged ancestors. ORDER THYSANURA. — The Bristle-tails. p. 220. ORDER COLLEMBOLA. — The Spring-tails. p. 225. SUBCLASS PTERYGOTA. — Winged insects and wingless insects in which the wingless condition is believed to be an acquired one; i. e., those insects that have descended from winged ancestors. ORDER ORTHOPTERA. — The Cockroaches, Crickets, Grasshoppers, and others, p. 230. ORDER zoRAPTERA. — The genus Zorotypus. p. 270. ORDER isoPTERA. — The Termites or White Ants. p. 273. ORDER NEUROPTERA. — The Dobson, Aphis-lions, Ant-lions, and others, p. 281. ORDER EPHEMERiDA. — The May-flics. p. 308. ORDER ODONATA. — The Dragon-flies and the Damsel-flies, p. 314. ORDER PLECOPTERA. — The Stone-flies. p. 325. ORDER CORRODENTIA. — The Psocids. p. 33I. ORDER MALLOPHAGA. The Bird-lice. p. 335. ORDER EMBHDINA. — The Embiids. p. 338. ORDER THYSANOPTERA. — The Thrips. p. 341. ORDER ANOPLURA. — The LicC. p. 347. ORDER HOMOPTERA. — The Cicadas, Leaf-hoppers, Aphids, Scale-bugs, and others, p. 394. ORDER HEMiPTERA. — The True Bugs. p. 350. ORDER DERMAPTERA. — The Earwigs. p. 460. ORDER COLEOPTERA. — The Beetles, p. 464. ORDER STREPSIPTERA. — The Twisted Winged Insects, p. 546, ORDER MECOPTERA. — The Scorpion-flies. p. 550. ORDER TRICHOPTERA. — The Caddice-flies. p. 555. ORDER LEPiDOTERA. — The Moths, the Skippers, and the Butterflies, p. 571. ORDER DiPTERA. — The Flies. p. 773. ORDER siPHONAPTERA. — The Fleas, p. 877. ORDER HYMENOPTERA. — The Bees, Wasf)s, Ants, and others, p. 884. HEX A POD A 215 TA BLE FOR DETERMINING THE ORDERS OF THE HEXAPODA 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. Alouth-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 structtue. 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-like 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-lilce. 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-lilce 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. I. Antennae inconspicuous, awl-shaped, short and slender. J. First and second pairs of wings of nearly the same length; tarsi tliree-jointed. p. 314 Odonata JJ. Second pair of wings either small or wanting; tarsi foiu-- jointed, p. 308 Ephemerida IL Antennae usually conspicuous, setiform, filiform clavate, capitate, or pectinate. J. Tarsi two- or three- jointed. K. Second pair of wings the smaller, p. 331 . Corrodentia 216 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 May-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..C0RRODENTIA 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 JJ. Abdomen without many- jointed anal filaments. K. Prothorax horny. First wings larger than the second, naked or imperceptibly hairy. 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 (Sisyrids). 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 young individuals, with rudimentary wings. G. Lowerlip greatlyelongated, 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. Larvas, 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 APOD A 217 H. With paired lateral filaments on most or on all of the ab- dominal segments. (Sialidae). p. 281 Neuroptera See also Haliplidae 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.Te 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 opposed 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. (Campodeidae 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. Larvas 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 ocelli on each side of the head. p. 550 Mecoptera FF. Without abdominal prolegs. G. Body clothed with scales. (Machilidae and Lepismatidse). 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. {Boreiis). 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. (Mantidae). p. 230 Orthoptera NN. Prothorax not greatly lengthened. O. Cerci present; antennas usually with more than fifteen joints, often many-jointed. P. Cerci with more than three joints. Q. Body flattened and oval. (Blattidae). 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; anteimae usually with eleven joints, p. 464 COLEOPTERA HH. Antennae short, not pronounced; larval forms. I. Body cylindrical, caterpillar-like. p. 550.MECOPTERA II. 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 JJ. 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-Uke, 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 II.Beak arising from the back part of the head. p. 394. . . . HOMOPTERA HEXAPODA 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 larvas representing several of the orders, and the active pupae 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. (Coccidse). p. 350.HEMIPTERA DD. Pupag, the inactive stage of insects with a complete metamor- phosis; capable only of a wriggling motion, and incapable of feeding. E. Obtected pupae, pupag 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, pupas enclosed in the hardened larval skin. p. 773 DiPTERA EEE. Exarate pupae, 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 Vr 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 adidt insects resemble the young inform. 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 reduced in number and the cerci are usually filifortn 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 m/) . 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 Japyx (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 antenna are long and many- jointed. In the Machilidse Fig. 22 1 . — Machilis, ventral aspect : c, cer- cus; Ip, labial palpus; mf, median caudal filament: mp, maxillary palpus; o, ovi- positor; s, s, styli. *Thysanura: thysanos (dvpavos), a tassel; oura (ovpd), the tail. (220) THYSANURA 221 Fig. 222. — Japyx sol ifiigus. (After Lub bock.) (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 Lepismatidas (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 Campodeids and the Japygidas, 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 maxillae (Fig. 223, B) bear prominent palpi. In the Campodeidee 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 Machilidfe and the Lepismatidas the jaws are not overgrown; these two families are known, on this account, as the Ectotrophi or Ectotro- phous Thysanura; while the Campodeidse and the Japygidae are grouped together as the Ento- trophi or Entotrophous Thysanura. The over- growing of the mouth- parts by folds of the gense 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 -P The abdomen consists of eleven segments. The eleventh segment bears the cerci, which are filiform and many-jointed except in the Japygidffi, where they are forceps-like. In the Machilidae 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 number 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 Lepisma 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 Machilidag and Lepismatidse 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 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 S3anphyla, is an indication of the primitive condition of these insects. The generalized form of the reproductive organs of the Thy- Fig. 226. — sanura is another indication of this. Ovary of Ja- In Japyx the ovarian tubes have a p/x. (After metameric arrangement (Fig. 226); rassi.; ^^^ -^^ 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 Canipodea; 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 gense. (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^e Fig.227. — Ovary of Machilis: c, coxite of the eighth abdomi- nal segment; s, stylus ; o, ovi- positor. (After Oudemans.) 224 AN 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 saccharma (Fig. 228). It is silvery white with a yellowish tinge about the antennns and legs and measures about 8 mm. in length. It is often a troublesome pest in laundries, libraries, and mu- seums, 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 pyrethrum or by a poisoned bait, consist- ing of a thin boiled starch paste to which has been add- Fig- 228.—Lepisma ed from three to five per ^accMnna (After . . • xi. 4- Lubbock.) 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 fire-brat, Thermohia domestica. This species resembles the fish-moth in general ap- pearance except that it has dusky markings on its upper surface. It is remarkable for fre- quenting 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 legs and each consists of two or three segments. Family Japygid^. — This family is repre- sented by the genus Jdpyx, 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. 229. — Campodea staphylinus. (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 adnlt insects resemble the young in form. They differ Fig. 230. — Side view of Tomocerus plumhens: co, collophore; c, catch; s spring. (After Willem.) 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 inwalking on smooth surfaces; the fourth abdominal segment usually bears a pair of appendages, which constitute a spring- ing organ; and the third abdominal segment usually 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 Fig. 231. — An ommatid- ium of Podiira aquat- ica. (After Willem.) *Collembola: colla (k6XXo), glue; embolon (e/x^oXov), a bolt, bar; — -from their collophores. (225) 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 tergum of the mesothorax ; in theSminthuridae 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 antennae 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 . 2 3 o) . 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 aqtiatica, 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 of ^HzTnpana in the fore tibi« and in the ab- sence of stridulating organs even when the tegmina are present. Only a single spe- Fig. 256. — Camptonotus carolinensis, female. Blatchley.) (From 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 McAtee ('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 cave-crickets, 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-hof-ned 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, lilce other Tettigoniidae, 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. — Ceuthophihis uhleri, male. (From Blatchle}'.) 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 :oof 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 oi Ceuthophilus uhleri, and Figure 2 $g the female of Ceuthophilus maculdtus. Subfamily STENOPELMATIN^E The Sand-Crickets These are large, climisy creatures with big heads (Fig. 260). They live under stones and in loose soil. They are represented in our fauna by a single genus, Stenopelmdtus, several species of which are found in the Far West and especially on the Pacific Coast. Fig. 260. — Stenopelmatus. 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 fiat 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 Tridactylinae the antennas are short; in the Tri- gonidiinae the ovipositor is sword -shaped ; in the Gryllotalpinae and the Tridactylinas the ovipositor is wanting in our species; and in the Tridactylinas the tarsi are reduced. It is evident that one step in the reduction of the nimiber of tarsal segments is the growing together of the metatarsus and the second segment. This is shown in the hind tarsi of Anaxlpha, CEcanthus, 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 Tettigoniidae. In some genera one t^Tnpanum 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 distinct, depressed, and heart- shaped. B. Hind tibise armed with two series of spines without teeth between them. p. 243 Trigonidun^ BB. Hind tibiae with teeth between the spines, p. 244 Eneopterin^ 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 CEcANTHiNiE 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 tibiae 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 character- istics of the Gryllidae. 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 (Nemobius) , but unlike 244 AN INTRODUCTION TO ENTOMOLOGY them it does not live on the ground. The antennas 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>Tnpana 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 tibiae. This species is found from southern New England west to Minnesota and Nebraska and south to Florida and Texas. Faldcula hebdrdi.- — 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 tibiae are without visible tympana. 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 ■Anaxipha tegmina is 8.5 mm. Its range extends from "" Washington, D. C, to Florida and Texas. Phylloscyrtus pulchellus. — 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. Fig. 261.- exigua. (From Lug- ger.) 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 These represent Only a few species are found in our fauna, three genera: Orocharis, in which both tym- pana of the fore tibiae are present ; Hdpithus, with a tympanum on the inner face only of the fore tibiae; and Tajalisca, with no tympana and no stridulating organs. The most common species is Orocharis saltdtor (Fig. 262). This is usually pale reddish brown, but some individuals are grayish. The length of the body is 14-16 mm. It is found from New Jersey west to Nebraska and south to Florida and Texas. The only common species of Hapithus is H. agitator, which is found from Long Island west to Nebraska and south to Florida and Texas. Our only species of Tafalisca is T. lurida, which is found in southern Florida. Subfamily CECANTHIN^ The Tree-Crickets Fig. 262. — Orocharis sal tat or. (From These are delicate crickets, many of which are Lugger.) of a light green color, with the body and legs sometimes dusky. Figure 263 represents a male; in the females the front wings are miore 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, CEcdnthus, implying / dwell in flowers. Two genera of tree-crickets are represented in our fauna, Neoxabea and CEcanthus; these can be distinguished by differ- ences in the armature of the hind tibiae. Neoxdbea. — In this genus the hind tibi« 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). Neoxdbea bipunctdta 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. QLcdnthus. — In this genus the hind tibiee 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 antennae, in their song, and in the Fig. 263. — CEcatithus 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, CEcanthus calif ornicus, occurs in California; and one, QLcanthus 9. « h Fig. 264. — Basal segments of antennae of CEcanthus and Neoxabea. is explained in the text. (After Lugger and Fulton.) (The lettering argentinus, 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 antennae 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. angiistipennis BBB. Basal antennal segment with a straight club-shaped black mark. (Fig. 264, e) QL. 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. qiiadripunctatus CC. First antennal segment with black markings similar to above, but broader and usually coniluent, 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. nigricornis 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 ntveus (Fig. 263). The pres- ence of this insect, though usually unseen, is made very evident in late ORTHOPTERA 247 Slimmer and in the autumn by the song of th e males. This song is begun 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 cambium 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 CEcdnthus nigricornis. 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. Fig. 265. — Stem of black In such cases the dead canes should be cut out raspberry with the eggs J 1 J 1 • it, • u r xi 01 Ltcantnus mertcor- and burned early m the spring before the eggs „,-^, ^^ ^^ ^gg enlarged, hatch. (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 groimd, 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 Nemohius. 248 AN INTRODUCTION TO ENTOMOLOGY Fig. 266 sus. -Gryllus assimilis luctuo- 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 oirr faima; but now all of our native forms are believed to be merely varieties of one species, Gryllus assvnilis, 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 pennsylvdnicus . — 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 coimtry; 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, Nemobius. — To this genus belong the little field-crickets, which are the most abtmdant of all of our crickets. In these the hind tibiae are furnished with long, mobile, hairy spines. Fig. 267. — Gryllus assim- ilis pennsylv ani- cus. (From Lugger.) ORTHOPTERA 249 and the first segment of the hind tarsi is imarmed 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 12 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.- mesticus. ger.) -Gryllus do- (From Lug- Fig. 269. — -Nemo- bius fasciatus. (From Lugger.) Fig. 270. — Nemo- bius palustris. (Fom 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 Fig- 271 —MyrmecopMla pergandei. obtain this substance from the ^^'■°"' Lugger.) greasy walls of the ant-burrows. Apparently the ants derive no benefit from the presence of these 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 Long Island. Only four spe- cies have been described from the East and one of these is restricted to Florida. A few others are known from the western part of our coiintry. A monograph of the North American species was published by Rehn and Hebard ('12). Figure 272 represents the male of Cryptoptilum trigonipdlpum, a wingless species found from Virginia southward; and Figure 273, the male of Holosphyrum boredle, found in the Southwest. Fig. 272. — Cryptopti- lum trigonipalpum. {From Rehn and Hebard.) Fig. 273. — 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 tibia?, especially, are fitted for digging; they are greatly broadened and shaped some- ORTHOPTERA 251 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 of the type genus, Gryllotalpa, 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- ienscus, 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 ^^^-^l^- —Gryllotai. • ^ 77 ,v/7 7 7^ _. 7 /-rv- \ -T^i • pa hexadactyla. species IS Gryllotalpa hexadactyla {rig. 274). ihis species has been generally known in this country as Gryllotalpa 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 yarious plants, and also on other insects. The eggs are deposited in a neatly constructed subterranean chamber, about the size of a hen's egg. Fig. 275. — Front leg of a mole-cricket; A, inner aspect; B, outer aspect; e, ear-slit. (From Sharp.) 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 252 AN INTRODUCTION TO ENTOMOLOGY Fig. 276. — Tri- dactylus apica- lis. (From Lug- ger.) smaller, the larger species measuring only 10 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 horny, 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 tympana. The first four tarsi, in our genera, are two- jointed; the hind tarsi are one- jointed or want- ing. The hind tibiae are furnished 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 surface of water upon which they have jumped; they may also serve a similar purpose on land, mak- ing a firm planting of the end of the leg upon the ground. 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 only 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. Triddctylus. — 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^^n- Ellipes. — In this genus the hind tibiae are furnished with a single pair of "natatory lamellse"; and the hind tarsi are wanting. Our species is Ellipes miniita. 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 Tridactylidse. Family LOCUSTID^* The Locusts or Short-horned Grasshoppers The family Locustidae includes the locusts or short-horned 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-known insects. They differ from most of the members of th.e two preceding families in having the antennae much shorter than the body, and consisting of not more than twenty-five 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 tympanum, the external parts of the organs of hearing (Fig. 277, t). 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 imfortunate, the scientific name Locus- tidce has been applied by many writers to the long-homed grasshoppers. Locusts lay their eggs in oval masses and cover them with a tough substance. Some species lay their eggs in the ground. 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 Locustidag 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- tidae, 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 Qi^DiPODiN^. CC. Vertex and front of head meeting at an acute angle; vertex extending horizontally; front strongly receding, p. 259 Truxalin^. AA. Claws of tarsi without an arolium between them; pronotum extending over the abdomen, p. 259 AcRYDliNiE. diidae, based on the generic name Acrydium of Fabricius; and still others use the family name Acridiidse, based on Acridmm, an emended spelling of Acrydium, The oldest name given to this family is Acrydiana, applied to it by Latreille in 1802; but the group of insects that Latreille used as the type of the family is the Locusta of Linnasus (1758); for this reason the name given to the family by Latreille has been changed to Locustids. See also the footnote on page 234. 254 AN INTRODUCTION TO ENTOMOLOGY Subfamily LOCUSTIN.E . 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 locust or western grasshopper, Melanoplus spretus. — The most terrible of insect scourges that this coimtry has known have been the invasions Fig. 277. — Side view of a female locust with the wings removed. Pig. 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; / shovvs 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. — Melanoplus femur- rubrum. ORTHOPTERA 255 Fig. 280. — Melanopliis Riley.) bivittatus. (From The permanent home or breeding grounds 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. Fortimateiy, 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 yoimg, 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 . — Melanoplits bivitia- species generallv disappears within a year, (FVom iS^ e/) ^ ^^"^"''- extends east and south so as to include " ^' more than half of Mitmesota and Iowa, the western tier of counties of Missouri, the whole of Kansas and Oklahoma, and the greater part of Texas. The coimtry 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 land in 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.) by machines com- monly known as ' 'hopper dozers. ' ' The red-legged locust, Melanoplus femur-rubrum. — This is the Fig. 283. — Schistocerca americana. most common short -homed grasshopper 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 foimd 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 foimd 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 and has been found as far north as Con- (From Riley.) throughout the United Fig. 284. — Brachystola magna. (From Riley.) 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 marginicollis. — 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 foimd in the Southern States east of the Mississippi River. -^^S" ^^S-— Leptysma marginicollis. Subfamily CEDIPODIN^ The Band-winged Locusts In this subfamily the prostermmi 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 1 9- Fig. 286.— EncoptolopJnis sordidus. 22 mm. ; of the female, 24-32 mm. The northern green-striped locust, Chortophaga mridtfascidta. — This is a very common species in the United States and Canada east of the Rocky Moim tains. 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 ,. ,^ ^ . places. It takes flight Fig. 287.-Z)z5.«.tora.aro/.na. (From Lugger.) ^^^^.^^^ ^^^ ^j^^ ^^^^^ stridulate while in the air. The color of this insect varies greatly, simulating that of the soil upon which it is foimd. It is usually of a pale yel- lowish or reddish bro^vn, 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 Moimtains. 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 Y\g. 2^^. Spharagemon bolli. of our band-winged locusts (Fig. 289). (From Lugger.) 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 Rocky Mountains. ORTHOPTERA 259 Fig. 289. — Hippiscus apiculatus. (From Lugger.) Subfamily TRUXALIN^ • The Slant-faced Locusts In this subfamily, as in the preceding one, the prostemimi is unarmed but the head is of a different form. In the Truxalinag, 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, Chloedltis conspersa. — This is a veryabimdant 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 Y-ig.2()i.— Chloealtis conspersa, iQmaXe. (From darker brown. The teg- Lugger.) mina and hind wings are a little shorter than the abdomen in the male (Fig. 290), and much shorter in the female (Fig. 291). The males measure 15-20 mm. in length; the females, 20-28 mm. Subfamily ACRYDIIN^ The Pigmy Locusts The Acrydiinas includes small locusts of very imusual form. They differ so much from other locustids that some students of the 260 ^A^ INTRODUCTION TO ENTOMOLOGY Fig. 292.— A pig- my locust. Fig. 293. — Acrydium graniilatum. 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 prostemimi 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 found 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, greatly enlarged, with its wings closed. Family PHASMID^* The Walking-Sticks and the Leaf-Insects The Phasmidas is of especial interest on ac- count of the remarkable mimetic forms of the insects comprising it. In those species that are found in the United States, except one in Florida, the body is linear (Fig. 295), wingless, and furnished with long legs and antennas. 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. — A crydium 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 lichens, 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 Phyllium (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 Timema, 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 summer 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. Fig. 295. — Diapheromera fern orata. 262 AN INTRODUCTION TO ENTOMOLOGY Among the more striking in ap- pearance of the walking-sticks found in the South are Megaphdsmadentricus, our largest species, measuring from 125 to 150 mm. in length, and Anisomorpha buprestoides, a yellowish brown 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. 2g6.—Phyllium scythe. (From ognized by the imusual 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 coxas 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 form 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 Mantidas 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 Fig. 297. — Stagmomantis Carolina 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 oothecag on nursery stock, and have become established here. These are the Mantis religiosa of Europe, which was first observed in this covmtry 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 accoimt 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 pronotimi; the head is bent so that the mouth-parts project caudad between the bases of the first pair of legs; the antennas are long and bristle-like ; and the pronotum is shield-like. This family includes only the cockroaches ; but these Fig. 298. — Egg- insects are known in some localities as "black c^^^s of Stag- ,,,,,-, , • • j_i momanhs car- beetles, and our most common species m the ^^^^^ (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 AN 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- ings. In the warmer parts of the country, how- ever, native and foreign species alike swarm in buildings of all kinds, and are very common out of doors. Fig. 299. — Ootheca of a 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 devoiu* 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-like capsules (Fig. 299). These capsules, or oothecse, vary in form in different 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 oothecse. The nymphs 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 nymphs; 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 foimd in North America north of the Mexican boimdary, and ten of these are probably introduced species (Hebard '17). The cockroaches that are most often foiind 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 common wood-cockroach, male DD. Pronotum reddish-brown with two blotches of a lighter color. The American 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, Blatlella 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 4L .-*'*^^ "\ ^ — -^ 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 ^ , « all parts of the world, living upon ships, and Fig- 303- — The oriental cockroach: a, female; b, spreading from them, male, c side view of female; d, half-grown sped- 'p^e oriental cock- men. All natural size. (From Howard and Mar- i, r?;^j. • ,-i- J^^l- \ roach, Blatta onentaUs (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 f otmd in only a few places in Canada. It measures from 18 to 25 mm. in length. It is blackish browTi 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, Parcohldtta 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 affinities 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 campodeijormis. — In this the only species of the family known, the body is elongate, slender, depressed, and thysanuriform Fig. 307. — Grylloblatta campodeijormis. (After Walker.) (Fig. 307). The legs are fitted for rtmning, 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, 30 mm. As yet, this species has been found only in the vicinity of Banff, Alberta, and in Plumas Coimty, CaHfomia. 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 308. 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 yoimg 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 nms rapidly among the hairs and apparently also springs. In an early account of one of the species of Hemmierus 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 mentioned here on accoimt of their exceptional manner of development and mode of life. Fig. 308. — Hemimerus han s eni . (From Hansen.) CHAPTER IX ORDER ZORAPTERA* So little is known regarding the insects of this order, only a single genus having been fotind, 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 i g 13 . 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 foimd in this country. 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 antennas are moniliform and nine-jointed. Compound eyes and ocelli are wanting. The cerci are short, fleshy, and imsegmented. The winged adult female (Fig. 309, i) has large compound eyes, three ocelli, nine-jointed antennas, and two pairs of wings. The vena- *Zoraptera: zoros (sw/961), pure; apterous {dirrepoi), without wings. (270) ZO RAPT ERA 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. pig_ 309. — Zorotypus hubbardi: i, winged adult female; 2, adult female that had shed her wings; 3, nvmph of winged form; 4, wingless adult female. 5. An- tenna of adult wingless Zorotypus snyderi. (From Caudell, m Proc. Ent. Soc. Wash., Vol. 22.) I 272 AN INTRODUCTION TO ENTOMOLOGY Fip:ure 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 hubhardi and Zorotypus snyderi. Detailed descriptions of each of the forms of each of these species are given by Caudell ('20), and the external anatomy of Zorotypus hubhardi 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 genus, 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 flat 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 tennites 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 number 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 merely 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 Q-ffos), equal; pteron {irrepbv), a wing. (273) 274 AN INTRODUCTION TO ENTOMOLOGY The antennae are moniliform; in the winged adults the number of segments varies in different species from twelve to twenty-five or more. In newly hatched nymphs the number of antennal segments is less than in the later instars. The members of the winged sexual caste have pigmented compound eyes and a pair of ocelli. It is commonly stated that both the workers and soldiers of termites are blind; but in some species the soldiers have compound eyes; these, however, are not pigmented. There is an African species, the marching termite, in which both workers and soldiers possess eyes (Fuller '12). The median ocellus is wanting in termites; but in many forms there is in its place a more or less distinct opening of a gland, the frontal gland, whose secretion is used for defense; this opening of the frontal gland is termed the fontanel or fontanelle or fenestra. Fig. 310. — Wings of Termopsis angiisticollis. The wings are long and narrow, and, when folded on the back of the insect, extend far beyond the end of the abdomen. In the Aus- tralian genus Mastotermes, the anal area of the hind wings is broadly expanded; in other termites the fore and hind wings are similar in form (Fig. 310). In each case, the veins of the anterior part of the wing are greatly thickened and those of the middle portion reduced to indistinct bands or to narrow lines. Regular cross- veins are lack- ing, the membrane of the wings being strengthened by an irregular network of slightly chitinized wrinkles. The wings are deciduous, being shed after the swarming flight. The shedding of the wings is facilitated by the presence in each wing, except in the hind wings of certain genera, of a curved transverse suture, the humeral suture. ISOPTERA 275 The homologies of the wing-veins are discussed by the writer in his "The Wings of Insects," Chapter VIII. The abdomen consists of ten visible segments and bears a pair of two- to six-jointed cerci. The genitalia are vestigial and are concealed by a backward prolongation of the sternum of the seventh abdominal segment. If a colony of termites be examined, many kinds of individuals will be found. This multiplicity of forms is due partly to the fact that these insects undergo a gradual metamorphosis, and nymphs of various sizes and degrees of development will be foimd running about among the mature individuals. But even if only adults be considered, it will be foimd that each species consists of several distinct castes. With the termites the nuniber of castes is greater than with the social bees, social wasps, and ants; and each caste includes both male and female individuals. The termites differ also from other social insects in that there are at least two and sometimes three castes whose function is reproduction. The following castes have been foimd among these insects. The first reproductive caste.— At a certain season of the year, late spring or early summer for omt most common species in the eastern United States, there can be foimd in the nests individuals with fully developed wings. These are sexually perfect males and females and constitute what is known as the first reproductive caste. In these the cuticula is black or dark chestnut in color, the eyes are fimctional, and the wings project more than half their length beyond the end of the body. A little later, these winged individuals leave the nest in a body ; sometimes clouds of them appear. After flying a greater or less distance they alight on the ground, and then shed their wings. At this time the males seek the females and they become associated in pairs ; but the fertilization of the females does not take place till later. It seems probable that in some cases swarms issue from different nests at the same time, as we know to be the case with the true ants, and that in this way males and females from different nests may pair, and thus the danger of inbreeding be lessened; but Holmgren and others doubt that this occurs. The greater number of individuals comprising one of these swarms soon perish ; they fall victims to birds and other insectivorous animals. Each of the more fortunate couples that have escaped their enemies, find a suitable place for the beginning of a nest and become the foimders of a new colony. Such a pair are commonly known as the king and the queen of the colony; they are also known as the primary royal pair to distinguish them from the second reproductive caste. The primary royal pair can be recognized by the presence on the thorax of the stimips of the wings that they have shed. After the nest has been begun, the abdomen of the female becomes greatly enlarged, as a result of the growth of the reproductive organs and their products; this is greater in certain exotic species than it is in those foimd in this country. Figure 311 represents 27G AN INTRODUCTION TO ENTOMOLOGY Fig. 31 I •— Queen ter- mite, Ter- mes gilvus. in natural size the queen of a species found in India. The dark spots along the rniddle of the dorsal wall of the abdomen are the chitinized parts of that region; the lighter portions are made up of the very much stretched membrane uniting the segments. This queen is a comparatively small one ; in some species the queens become from 150 to 200 mm. in length; of course such a queen is incapable of locomotion, but lives with its mate inclosed in a royal chamber ; their food is brought to them and the eggs are carried away by workers. In our native species the queens do not become so greatly enlarged and do not lose the power of movement. A remarkable peculiarity in the habits of termites is that the association of the male and the female is a permanent one ; the king and the queen live together in the nest, and there is repeated coition. The second reproductive caste. — There are fre- quently foimd in the nests of termites neoteinic sexual forms; that is, individuals which are sexually mature but which retain the nymphal form of the body, having short wing-buds which do not develop further. These individuals constitute the second reproductive caste, which is represented by both males and females. The members of this caste are pale in color; their compound eyes are only slightly pig- mented; and they never leave the nest unless by subterranean tun- nels. If a primary king or queen dies, its place is taken by individuals of the second reproductive caste. For this reason, the members of this caste are commonly known as substitute kings and queens or as complemental kings and queens. The substitute queens produce comparatively few eggs, and conse- quently it requires several of them to replace a pri- mary queen. Many pairs of substitute kings and queens are commonly foimd in orphaned nests. The third reproductive caste. — In some cases there have been foimd adult neoteinic sexual forms which resemble workers in lacking wing-buds. These are known as ergatoid kings and queens. The workers. — If a termite nest be opened at any season of the year there will be found a large nimiber of wingless individuals of a dirty white color, usually blind, and of the form represented by Figure 312. These are named the workers, for upon them devolve nearly all of the labors of the colony. A study of the internal anatomy of workers has shown that both sexes are represented in this caste; the reproductive organs are, however, only little developed as a rule; but occasionally workers capable of laying eggs are foimd. The worker caste is not always present; it is absent in the genera Kalo- Fig. 312. — A worker. I SOFT ERA 277 Fig. 3 13 -—A sol- dier. termes and Cryptotermes, where the nymphs of the reproductive forms apparently attend to the duties of workers; and in the genera Termopsis and Neotermes ordinary sterile workers are not foimd, but the third reproductive caste, large, worker-like, grayish brown, fertile forms, with no wing-buds, is present. The nymphs of this caste often perform the duties of the workers (Banks and Snyder '20). In some tropical species there are two types of workers, which differ in size. The soldiers. — ^Associated with the workers, and resembling them in color and in being wingless, there occur numerous representatives of another caste, which can be recognized by the enormous size of their heads and mandibles (Fig. 313); these are the sol- diers. They are so named because it is believed that their chief function is the protection of the colony; but they do not seem to be very effective in this. Among the soldiers, as among the workers, both sexes are represented ; but as a rule the reproductive organs are not functional. Sometimes, however, soldiers capable of laying eggs are found. In the genus Kalotermes soldiers with small wing-buds are often found. The soldier caste has not been found in the genus Anoplotermes, and in the genera Constrictotermes and Nasutitermes the soldier caste is wanting unless the nasuti, described in the next paragraph, are regarded as soldiers. In certain tropical species there are two types of soldiers which differ in size. The nasuti. — In certain species of termites there are foimd individuals in which the head is elongated into a nose-like process, from the tip of which a fluid ..xa;™^ exudes, which is used as a means of defense and also, 1^^^ it is said, as a cement in constructing the nest and y^!^ 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. ^( A f t e r regard them as constituting a distinct caste. Among 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 fotmd. 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 larvag that ordinarily would produce workers. According to this view the newly hatched termites are not differentiated into castes; but Sharp.) 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 from the older workers. According to the second view the yoiing 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 foimd by Thompson ('17 and '19) that although the newly hatched nymphs 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 fovmd 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 nymphs of Eutermes pilifrous, a Jamaican species, which were 2 nun. long and externally all alike, they were distinguishable, after staining, into worker nymphs with a small vestigial frontal gland, and soldier nymphs with a large frontal gland. In a study oi Reticulitermes (Leiicotermes)fiavipes , Thompson ('17) fotmd that the n3miphs 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 mounds 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 imdigested wood upon which the insects have fed. This is molded into the desired form and on drying it becomes solid. 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 under stones or other objects lying on the ground; some burrow only in I SOFT ERA 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 termites found north of Georgia and east of Nevada. These often infest the founda- 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, they eat out the interior, leaving a thin film on the outside. Thus a table may appear to be soiind, 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 foimd 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 groimd. 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 destruction of the seed-cane. Certain African termites have been found to cultivate fimgus- 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 AN INTRODUCTION TO ENTOMOLOGY the individuals that are fed; the feeding of the young 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 ' . the colony; and that the intensity of the licking and feeding of ^ e 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 eumenids that feed their larvae from day to day and while doing this feed upon saliva exuded by the larvae, 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 kno\vn species are described, seventeen of them for the first time. This brings the total number of our known species up to thirty-sLx, 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 {Tpo'ra. The habits of the larva are similar to those of Sisyra. Fig. 331. — Labia of Spongilla-flies : a, Climacia dictyona; b, Sisyra umbrata. (After 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 larvae of Sisyra and Climacia are the only known aquatic neuropterous larvs foimd in this coimtry. Family SYMPHEROBIID^ The Sympherohiids 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 Sympherobiidae 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 ^A^ INTRODUCTION TO ENTOMOLOGY Sympherobius. — In this genus 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 Sympherobius 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 country and in Europe. Its wing expanse is from 5 mm. to 6 mm. Family HEMEROBIID^ The Hemerohiids The Hemerobiidas include insects of moderate size; in most of our species the wing-expanse is between 12 mm. and 22 mm.; in one species of Megalomns 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. Fig. 333. — Wings of Hemerobius humuli As now restricted this family is composed of a group of genera that are characterized by a distinctive mamier 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 hamuli; in the fore wings of this species (Fig. 333), 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. 333). Here 296 AN INTRODUCTION TO ENTOMOLOGY vein R2+3-t-4 is bent forward near its base and is joined to vein Ri. The extendinjT of the union of veins Ri and R2+3+4 from the point where they now anastomose towards the base of the wing, so as to obhterate the small cell between them, and also towards the apex of Pig. 334. — Wings of Megalomus mcestus. 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 Megalomus mosstiis (Fig. 334), a more complicated one. Here there have been developed a larger number of definitive accessory veins and of marginal accessory veins. Under the title "A Revision of the Nearctic Hemerobiidae" 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 known at that time are described. NEUROPTERA 297 The larvse of the hemerobiids, as far as they are known, resemble in their general appearance aphis-lions (Chrysopidse) , and, like the aphis-lions, feed on plant-lice and other small insects. Their mouth-parts are formed for piercing and sucking (see page 282), and the posterior part of the alimentary ca- nal is transformed into a silk-organ, as in Sisyra (see page 283). They are found most often running about on trees, and especial- ly on coniferous trees. Some, like the aphis-lions, are naked ; but the lar- vse of some species, at least, of Hemero- hius cover them- selves with a cloak, composed of the empty skins of their victims and other debris (Fig. 335). These larvae are furnished at the sides with projections which serve as pedicels to elongate, divergent hairs that help to keep the cloak in place. There are thirty described American species belonging to this family; these represent four genera, Hemerobius, Boriomyia, Megalo- mus, and Micromus. Fig. 335. — Larva of Hemerobius: A, the larva bare; B, the same partially concealed by the remains of its victims, etc.; a portion of the covering has been re- moved in order to show the head. (From Sharp.) Family DILARID^ The Dilaridag is a small family, representatives of which are found chiefly in the Old World. In this family the antennas of the male are pectinate; and the female is furnished with an exerted ovipositor. Only a single, exceedingly rare species, Dilar americdnus, has been foimd in North America; and of this only a single female individual is known. This is a small insect ; the length of the body, not includ- ing the ovipositor, is about 3 mm.; the length of the ovipositor is a little greater than that of the body ; the expanse of the wings is about 14 mm. There is a single five-branched radial sector in both fore and hind wings. In several exotic species the radius of the fore wings bears two or more sectors. The type of our species was taken at Bee Spring, Kentucky, in June, 1874. 298 AN INTRODUCTION TO ENTOMOLOGY Family BEROTHID^ The Berothidae is a small family, which is represented in North America by a single genus, Lomamyia, of which only two species are Fig. 336. — Wings of Berotha insolita. known. Figure 336 represents the venation of the wings of the type species of the family, Berotha insolita, which is found in India, and to which our species are closely allied. The fore wings are falcate, which is not true of certain exotic genera ; the humeral cross-vein is not recurved ; many of the transverse veins between the costa and the subcosta are forked ; the radial sector bears definitive accessory veins; and there is a single series of gradate veins in the radial area. In the hind wings the first radio-medial cross-vein is transverse; vein Cu2 is wanting; and the area between the margin of the wing and veins ist A and Cui is narrow and largely occupied by the fanlike tips of the accessory veins. Nothing is known regarding the early stages of these insects. Family P0LYST(ECH0TID..E The family Polystoechotidas was established to receive the genus PolystCBchotes,oi which only two species, both American, are known. These are the members of the allied families. Fig. 337- tus. -PolysUechotes puncla- larger insects than are NEUROPTERA 299 measuring in wing-expanse from 40 mm. to 75 mm., varying greatly in size. They are nocturnal and are attracted to lights. The two species can be distinguished as follows : Polystoechotes punctdtus (Fig. 337). This is blackish, with three longitudinal lines on the prothorax, and with the lateral margins of this segment yellowish. Cu' Fig. 338. — Wings of Polyskechotes punci(t,tus. Polystcechotes vittdtus. — This is pale yellowish, with a black stripe on the sides of the thorax, and with the abdomen dark brown. The larva of neither of these species is known. This is a strange fact considering the size and the abundance of these insects. The wings of Polystcechotes punctatus (Fig. 338) represent the type of wing-venation characteristic of this family. In these wings the humeral cross-vein is recurved and branched; veins Sc and Ri co- alesce at the tip; the radial sector is pectinately branched; the ntmi- ber of cross-veins is greatly reduced; but there is in both fore and hind wings a very perfect series of gradate veins. In these wings the development of definitive accessory veins on the radial sector and the regularity of the border of marginal accessory veins have reached a very high degree of perfection. Family CHRYSOPID^ The Lacewing-Flies or Aphis-Lions The family Chrysopidas includes the insects commonly known as lacewing-flies; these and their larvae, the aphis-lions, are common 300 AN INTRODUCTION TO ENTOMOLOGY and well-known insects; they are found upon herbage and the foliage of shrubs and trees throughout the summer months (Fig. 330)- The adults are easily recognized by their deli- cate lacelike wings and their green or yellowish green color. Members of several of the preceding families have delicate lacelike wings; but with those insects the wings are more or less brown or are hyaline. While these insects are most commonly known as the lacewing- fiies, 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 Chrysopidse are characterized by a very re- markable and distinctive type of specialization, the details of which Fig. 339— Eggs, Chrysopa. larva, cocoon, adult Fig. 340.- cubitus. -Fore wing of Chrysopa nigricornis: M', 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 \^ein 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-cubitus~one or vein Cui', re- spectively (Fig. 340, M' and Cu/). Fig. 341. — Tracheation of the wings of a pupa of Chrysopa nigricornis. An examination of the tracheation of the wings of a pupa of Chrysopa nigricornis reveals the nature of the two serial veins M' and Cu/ (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 larvae of the lacewing-flies 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 larvas of Hemerobius. This has been observed by European writers (Sharp 302 AN INTRODUCTION TO ENTOMOLOGY '95); and recently Mr. R. C. Smith ('21) has found that the larvae 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 ^3+4 Mi+2 /?5 R^ ^1 '''''^+^^v"^^^r^ Fig. 342. — Diagram of the wings of Chrysopa nigricornis, 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. NEUROPTERA 303 Family- MYRMELEONID^ The Ant-Lions The members of the family Myrmeleonidce are commonly known as ant-lions. This name was suggested by the fact that the larvae 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 and with very many cross-veins. Fig- 343- — Larva, cocoon with pupa-skin projecting, and adult, of an ant-lion. both definitive and marginal, 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 Ascalaphidce. The determination of the homologies of the wing-veins of the Myrmeleonidse 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 often 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 larvEe 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 fift3^-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 larvae 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- em 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 Myrmeleon. 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). Incase 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 larva can be easily kept in a dish of sand, and their habits watched. The most common ant-lion in the North is Myrmeleon ini- maculdtus; the larva of this species makes a pitfall. The habits of the larvae of Glenunis, Dendroleon, and Acanthdclists, three genera that are repre- sented in this country, have been described by European writers. These larvas do not dig pitfalls, but partially bury themselves in the sand, from which position they throw themselves quickly upon their victims. 345. — Pitfall of an ant-lion. NEUROPTERA 306 Family ASCALAPHID^ The Ascalaphids The family Ascalaphidce 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 antennas (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. 346. — 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 mymieleon- r ca Fig. 347. — Wings of Ululodes hyalma. 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 larvse 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 Ascalaphidae 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 tropical insects, but a few species occur in the United States ; these represent three genera, which ) can be separated by the following table. Fig. 348. — Larva of Ululodes hyalina. (After McClendon. A. Eyes entire Neuroptynx A A. Each eye divided into two parts by a groove. B. Hind margin of wings entire Ululodes BB. Hind margin of wings excised Colobopterus " Cu- Mx^A Fig. 349. — Wings of Semidalis aleurodijormis. (After Enderlein.) NEUROPTERA 307 Family CONIOPTERYGID^ The Mealy-winged Neuroptera The Coniopterygidas 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 Hemerobiidae 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 fiat 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 of ten 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 siimmertime 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 350.— A May-fly. this state. The antennas 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 long, soft, and composed of ten Caudal end of abdomen of Siphlurus alternatus, male: g, 10, 11, abdominal segments; c, cerci; w/, median caudal filament ; ^, penis;/, forceps-limbs. (After Morgan.) *Ephemerida, Ephemera: ephemeron {i^ plus signs and con- Cy' \ l^i-fT'l^ \ \ \ \'^1„ \ \ 1 — r->^_ 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- 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 ephemeros, signifying 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 midsummer ; 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 albomanicatus. 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 evenly spread, and in mutual contiguity." (Eaton '83). Fig- 355- — Metamorphosis of a May-fly, Ephemera varia: A, adult; B, naiad. (After Needham.) 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 setse," that is, 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, -p. ^ feeding largely on the decaying stems and leaves of i^fd of a May- aquatic plants, the epidermis of moss and of roots, 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, like Ilexagetiia, Ephemera, and Po/ywiVarcj^areburrowers beneath the bottom silt. A few like Cccnis and EphemerclLa, are of sedentary habits and live rather inactively on the bottom, and on silt-covered stems. Many are active climbers among green vegetation; such are Callibcclis and Blasturus; and some of these can swim and dart about by means of synchronous strokes of tailand gills with the swiftness of a minnow. The species of Leptophlebia love the beds of tlow-flowing streams, and all the flattened nymjihs of the Heptageninse live in swiftly moving water, and manifest various degrees of adaptation to withstanding thft 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 hypopharynx bears a pair of lateral lobes, which are believed to be vestiges of paragnatha ; and sec- ond, the presence of accessory circulatory organs in the cerci and median caudal filament (Fig. 357)- 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 molt af- Fig- 357-— A, caudal end of abdomen of ter they have attained functional Cloeon dipterum: h, heart; a, acces- wingS. The term subimagoiaap- sory circulatory organs. B, twenty- piig^j ^^ ^^e instar between the sixth segment of a cercus : o, oriiice m ■ -, j ji £ ^ s i 4.u^ blood vessel. (After Zimmerman.) "aiad and the final fomi of the insect, 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 twent\'-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 simulans, 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 oraer 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 ars 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 fanned 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 large size (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 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 sharply 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 143. Three ocelli are present. The antennas 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 labnim is prominent; the mandibles and maxillae are both strongly toothed; and the labium consists of Fig. 358. — ^A dragon-fly, Plathemis lydia. (From San- born.) *Odonata: odous {65o^^/.+ \ \'^^^^0^^~::^Z^^^^V^ 0/3+4 \ \ NV^"^ ^"'^ \ ^>-^^ 2d A Fig. 376^. — Wings of Isogenus sp. ^^Sc^^ ^^'— - W. y^^^ - — \/?2+3 -A ^4+5 '7l/l+2 ^d A^st ^ vl/j + 4 Scx Sr, Ml+2 Fig. 376f. — Wings of Nemoura sp. 330 ^A^ 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.E In this family, as in the Nemouridae, the media of the fore wings separates from radius abruptly, the two forming a blunt angle (Fig. 3760?) ; but in this family there are in the anal area of the fore wings A'4+5 Fig. 376(/. — Wing of Capnia sp. only simple veins arising from the basal anal cell (Fig. 376^), and the cerci are well developed. This is a small family which is represented in our fauna by only three genera. The members of this family that are most often seen are the little black species of Capnia that appear on snow on warm days in the latter half of winter and in early spring. The naiads of these live chiefly in small brooks. Fig. 377. — A winged psocid, Cerastipsocus venosus. CHAPTER XV ORDER CORRODENTIA* The Psocids and the Book-Lice The winged members of this order have Jour membranous wings, with the veins prominent, but with comparatively Jew cross-veins; the Jore wings are larger than the hind wings; and both pairs when not in use are placed rooj-like over the body, being almost vertical, and not Jolded in plaits. The mouth-parts are formed Jor chewing. The metamorphosis is gradual. The best -known representatives of this order are the minute, soft-bodied insects which are common in old papers, books, and neglected collections and which have received the popular name book-lice. These low, wingless creatures form, how- ever, but a small part of the order. The more typical winged forms (Fig. 377) bear a strong resemblance to plant-Hce or aphids. The body is oval,the head free, and the protho- rax small. The fore wings are larger than the hind wings; and both pairs when not in use are placed roof- like over the body, being almost vertical, and not folded in plaits. The wing-veins are prominent, but the venation of the wings is reduced. The tarsi are two- or three-jointed. Cerci are wanting. The mouth-parts are of especial interest on account of the presence of well-preserved paragnatha. Fig- ure 378 represents the mouth-parts of the common book -louse, Troctes divinatdrius, as figured by Snodgrass ('05) . The mandibles {B) are of the ordinary, strong, heavy, biting type. The maxillag (w) consist each of a body piece, a weakly chitinized terminal lobe, and a four-jointed palpus. The paragnathus if, J) is represented in the figure at A, with the maxilla; it lies above the maxilla and is, therefore, in its typical position between the maxilla and the mandible of the same ^Corrodentia : Latin corrodens, gnawing. r33i) Fig. 378. — ■Mouth-parts of a book- louse, Troctes divinatorius : A , max- illa and paragnathus of right side, ventral view; m, maxilla; /, /, paragnathus; p, protractor mus- cle; r, retractor muscle. 5, man- dibles. C, labium, ventral view; p, palpus. (After Snodgrass.) 332 AN INTRODUCTION TO ENTOMOLOGY side. Note that the figure is a ventral view, hence the paragnathus is represented as passing beneath the maxilla. The paragnatha have Fig. 379. — The wings of a psocid. been known as the fur ccb maxillares. The labium {C) bears a pair of one-jointed palpi. The venation of the wings is distinctively characteristic in this order. The venation is more or less reduced; but its most characteristic feature is the bracing of the wing by anastomoses of the principal Fig. 380. — Fore wing of a full-grown nymph of a psocid. veins instead of by cross-veins. This is well shown by the wings of Psocus (Fig. 379). The determination of the homologies of the wing-veins in this insect was accomplished by a study of the trachea- tion of the wings of nymphs. Figure 380 represents the tracheation of a fore wing of a full-grown nymph of Psocus. There are no cross-veins in the wings of Psocus; the arculus (ar) in the fore wing is merely the base of media, and what appear as CORRODENTIA 333 cross-veins in the central portion of the wing are sections of media and cubitus. In some genera, however, the radial cross-vein is present, and in some, instead of an anastomosis of veins M and Cui, these veins are connected by a medio-cubital cross- vein. The metamorphosis is gradual. The nymphs resemble the adults in the form of the body, but lack wings and ocelli in those species that are winged in the adult; in the wingless species the differences between the young and the adult are even less marked. The Corrodentia of the United States and Canada represent two families, which can be separated as follows. A. Wings well developed; ocelli present Psocid^ AA, Wings absent or vestigial; ocelli absent AtropiD/E Family PSOCID^ The Psocids The family Psocidse includes the more typical members of the Corrodentia, those in which the wings are well developed (Fig. 377). Usually the wings extend much beyond the end of the abdomen ; but short-winged forms occur in species which ordinarily are long-winged. Of course the young of all are wingless, and there is a gradual develop- ment as the insect matures. The antennae consist of only thirteen segments ; this will enable one to separate the immature forms from the Atropidee, in which the antennse have a greater nvimber of segments. The psocids occur upon the trunks and leaves of trees, and on stones, walls, and fences. They feed upon lichens, fungi, and probabl / other dry vegetable matter. They are sometimes gregarious. I have often seen communities of a hundred or more closely huddled together on the trunks of trees, feeding on lichens. The eggs are laid in heaps on leaves, branches, and the bark of trunks of trees. The female covers them with a tissue of threads. It is believed that both sexes have the power of spinning threads. The silk is spun from the labium. More than seventy species, representing eleven genera, have been described from our fauna. Family ATROPID^ The Book-Lice and Their Allies The family Atropidse includes small Corrodentia, which are wingless or possess only vestigial wings. The most commonly ob- served species are those known as book-lice, which are the minute soft-bodied insects often found in old books (Fig. 381). Of these the two following species are the best known. Troctes divinatorius. — This is a wingless species which measures about I mm. in length ; it is grayish white, with black eyes. 334 AN INTRODUCTION TO ENTOMOLOGY Atropos pulsatdria. — In this species the fore wings are represented by small convex scales; it is of a pale yellowish white color and is a little more than i mm. in length. Each of these species has been known as the death-watch, as they have been believed by superstitious people to make a ticking sound that presaged the death of some person in the house where it is heard. It is not probable that such minute and soft insects can produce sounds audible to human ears. The sounds heard were prob- ably made by some wood-boring beetles, Anohiids, which are also known as the death-watch. Book-lice are found chiefly in damp, well-shaded rooms, not in general use. They do not attack man, but feed upon dead vegetable and animal matter, as the paste in book-bindings, wall-paper, and photo- graphs. They rarely occur in sufficient numbers to do serious injury. They can be destroyed by fumigating the infected room with hydrocyanic acid gas. This, however, should be used only by experienced persons. Ordinarily a prolonged heating and drying of the room will be sufficient to destroy them. Fig. 381. — A book-louse. Hi CHAPTER XVI ORDER MALLOPHAGA* The Bird-Lice The members of this order are wingless parasitic insects with chewing mouth-parts. Their development is without metamorphosis. The bird-lice resemble the true lice in form, being wingless, and having the body more or less flattened ; certain species that infest domestic fowls are well-known examples. These insects differ from the true lice in having chewing mouth-parts. They feed upon feath- ers, hair, and dermal scales, while the true lice, which constitute the order Anoplura, have sucking mouth- parts, feed upon blood, and infest only mammals. The Mallophaga infest chiefly birds, and on this accoimt the term bird-lice is applied to the entire group; a few genera, however, are parasitic upon mammals. Some writers term the Mallo- phaga the biting lice, which is a more accurate designation ; but the name bird-lice is more generally used. The bird-lice are small insects. The more common species range from I mm. to 5 mm. in length. The mouth-parts are on the imder side of the head, the most anterior .part of the head being a greatly enlarged clypeus ; they are of the mandibulate type; and paragnatha ("furcae maxillares") have been found in several species (Snod- grass '05). There is a pair of "simple eyes" located in the lateral margins of the head. The structure of these eyes has not been de- scribed; but judging from their position they are probably degenerate ommatidia and not ocelli. The front legs are shorter than the others and are used to convey food to the mouth. There is an interesting correlation between the habits of these insects and the structure of their feet. The tarsi of those species that feed on mammals are one-clawed and fitted for folding against the tibice; they are organs well adapted for clinging to hairs. Those species that feed on birds have two-clawed tarsi and are better fitted for running. The above distinction is not quite accurate, as a few two-clawed species feed on kangaroos, wallabies, and wombats. *Mall6phaga: mallos (/taWis), wool; phagein {(payeiv), to eat. (335) 336 ^A^ INTRODUCTION TO ENTOMOLOGY The accompanying figures represent some of our common species Fig. 382. — Goniodes stylif- er. (From Law.) Fig. 383. — Tricho- d e c t e s I a t u s. (From Law.) Fig. 384-— Trichodectes spheroceph- alus. (From Law.) Fig. 385- — Trz- chodectes sca- laris. (From Law.) Fig. 386. — Tricho dectes equi. (From Law.) Goniodes styUjer (Fig. 382) infests turkeys; Trichodectes Idtus (Fig. 383), dogs; Trichodectes spherocephalns (Fig. 384), sheep; Trichodectes scalar is (Fig. 385), domestic cat- tle; and Trichodectes equi (Fig. 386), horses and asses. The eggs of the Mallophaga are glued to the hairs or feathers of their hosts. The development takes place on the body of the host and is without metamorphosis. The young are not so dark in color as the adults and the cuticula is less densely chitin- ized. The ametabolous condition of these insects is believed to be an acquired one, a result of their parasitic habits. The bird-lice are well known to most people who have pet birds or who keep poultry. It is to free themselves from these pests that birds wallow in dust. When poultry are kept in closed houses they should be provided with a dust-bath. All poultry houses should be cleaned at least twice a year, and the old straw burned. Sprinkling powdered sulphur in the nests and oiling the perches with kerosene will tend to keep the pests in check. If a poultr^^ house becomes badly infected, it should be cleaned thoroughly, every part whitewashed, and the poultry dust- ed with either insect-powder or sodiirm fluoride. The Mallophaga is a small order. Professor V. L. Kellogg in his "Mallophaga" (Kellogg '08 b) estimates the mmiber of known species to be 1250; these represent twenty-seven genera. But there are doubtless many species not yet discovered, as comparatively few birds and mammals have been thoroughly searched for these pests. The work just quoted is the latest and most complete systematic treatise on this order. It followed a long series of papers on these insects published by this author. A more generally accessible ac- count of the species that have been found in North America is a MALLOPHAGA 337 chapter in Professor Herbert Osbom's "Insects Affecting Domestic Animals" (Osborn '96). The chief divisions of the order adopted by Kellogg ('08 b) are as follows. A. With filiform, 3- or 5-segmented, exposed antennae; no maxillary palpi; mandibles vertical Suborder Ischnocera B. With 3-segmented antennae; tarsi with one claw; infesting mammals. Family Trichodectid/e BB. With 5-segmented antennae; tarsi with two claws; infesting birds ., Family Philopterid^ AA. With clavate or capitate, 4-segmented, concealed antennae ; with 4-segmented maxillary palpi; mandibles horizontal Suborder Amblycera B. Tarsi with one claw; infesting mammals Family GYROPiDiE BB. Tarsi with two claws; infesting birds, excepting a few species that infest kangaroos, wallabies, and wombats Family Liotheio.^ CHAPTER XVII ORDER EMBIIDINA* The Emhiids This order is composed of small and feeble insects in which the body is elongate and depressed. The winged members of, the order have two pairs of wings, which are quite similar inform and structure; they are elongate, membranous, extremely delicate, and folded on the back when at rest; the venation of the wings is considerably reduced. The mouth- parts are formed for chewing. Cerci are present and consist each of two segments. The metamorphosis is of a peculiar type. This is a small order of insects; Enderlein ('12 a) in his monograph of the Embiidina of the world lists only sixty-one species. The body is elongate and depressed (Figs. 387 and 388). Only the males are winged ; and in some genera this sex also is wingless. The venation of the wings is re- duced ; this reduction has been brought Fig- 387. — Embia sabulosa, male. (After En- derlein.) Fig. 388. — Embia sabulosa, female. (After Enderlein.) about both by the coalescence of veins and by the atrophy of veins. Each of the veins of the wings extends along the middle of a brown band ; between these bands the membrane of the wing is pale in color. The alternating brown and pale bands give the wing a very characteristic *Embiidina: Embiidae, Embia, embios {tfi^Tos), lively. (338) EMBIIDINA 339 appearance (Fig. 3 89) . In those forms where the venation of the wings has been reduced by the atrophy of veins, the brown bands persist after the veins have faded out ; hence it is easy to determine by these bands the former position of veins that have been lost. A discussion of the venation of the wings of the Embiidina is given in my "The Wings of Insects." The antenncB are fihform and are composed of from sixteen to thirty -two segments . The compound eyes consist of many ommatidia, Fig. 389. — Fore wing of Oligotoma saundersi: A, the wing; B, outline of the wing showing the existing venation; C, outline of the wing showing the venation restored. (After Wood- Mason.) which are of the eucone type. Ocelli are always wanting. The mouth-parts are mandibulate; the maxillary palpi are five-jointed and the labial palpi three-jointed. The abdomen is composed of ten distinct segments and bears at its tig a pair of two-jointed cerci. Figure 387 represents the male of Enibia sabulosa, with the wing of one side removed; and Figure 388, the female of this species. The metamorphosis is of a type intermediate between gradual and complete. This was shown by Melander ('02 b), who studied the development of Enibia texdna. The young resemble the adults in the form of the body, except that the body is cylindrical instead of depressed; and the cuticula of the young is less densely chitinized and pigmented than is that of the adult. In the case of the females 340 AN INTRODUCTION TO ENTOMOLOGY and of those males that are wingless in the adult instar, it might be said that these insects develop without metamorphosis. But in the case of the winged males the development resembles that of insects with a complete metamorphosis in one important respect; that is, the development of the wings is internal until the penultimate molt is reached. Melander states that he sectioned the fully grown larva and found the wings as large invaginated pockets completely beneath the hypodermis. In the penultimate instar of the winged females there are well-developed, external wing-pads. This instar may well be termed a pupa. The embiids are very active insects both in running and in flight. They are often gregarious. They live in silken nests or galleries under stones or other objects lying on the ground, and burrow into the soil when the surface becomes too dry. Imms found in his studies of Embia major \nthe Himalayas that maternal care on behalf of the ova and larvag is strongly exhibited by the females, in much the same , manner as is known to occur among the Dermaptera. Writers differ as to the source of the silk of which the nests are made. Melander ('02 a) and others have described glands in the metatarsi of the forelegs, which open through hairs, and have ob- served that in spinning its nest the insect uses its fore feet. But Enderlein maintains that the chief source of the silk is from glands that open through a spinneret on the labium, although the secretion of the metatarsal glands may play a part in the formation of the silken tissues. The embiids are widely distributed in the warmer parts of the world. A few species have been found in Florida, Texas, and California. CHAPTER XVIII ORDER THYSANOPTERA* The Thrips The members of this order are minute insects with wings or wingless. The winged species have Jour wings; these are similar in form, long, narrow, membranous, not plaited, with but few or with no veins, and only rarely with cross-veins; they are fringed with long hairs, and in some species are armed with spines along the veins or along the lines from which veins have disappeared. The mouth-parts are formed for piercing and sucking. The tarsi are usually two-jointed and are bladder- like at the tip. The metamorphosis is gradual, but deviates from the usual type. These insects are of minute size, rarely exceeding 2 mm. or 3 mm. in length . They can be obtained easily , however, from various flowers , especially those of the daisy and clover. Ordinarily it is only necessary to pull apart one of these flowers to find several thrips. They are in many cases very active insects, leaping or taking flight with great agility. In case they do not leap or take flight when alarmed, they are apt to run about and at the same time turn up the end of the abdomen in a threatening manner, as if to sting. In this respect they resemble the rove-beetles. The body is long (Fig. 390) . The head is narrower than the thorax, without any distinct neck. The antennas are filiform or moniliform and consist of from six to nine segments; they are always much longer than the head and may be two or three times as long. The compound eyes are large, with conspicuous facets, which are circular, oval, or reniform in outline. Three ocelli are usually present in the winged forms, but sometimes there are only two ocelli ; wing- less species lack ocelli. The mouth-parts are fitted for piercing and sucking ; they are in the form of a cone which encloses the piercing or- gans. The cone is composed of the clypeus, _^ thrips. labrum, maxillary sclerites, and labium. The piercing organs consist of the left mandible (the right mandible is vestigial) and the two maxillae. Each maxilla is composed of two parts: first, the palpus-bearing maxillary sclerite; and second.the maxillary seta. For detailed accounts of the mouth-parts see Hinds ('02) and Peterson ('15). The above statement regarding the mouth- parts is based on the paper by Peterson. The mouth-parts of the Thysanoptera bear a striking resemblance to those of the Hemiptera *Thysan6ptera: thysanos {ddtravos), fringe; pteron {vTephv), a wing. (341) 342 AN INTRODUCTION TO ENTOMOLOGY and the Homoptera, which are described in detail in later chapters. The three thoracic segments are well developed. The wings are laid horizontally on the back when not in use; they are very narrow, but are fringed with long hairs (Fig. 391), which, diverging in flight, compensate for the smallness of the membrane. The fringing of the wings suggested the name Thysanoptera, by which the order is known. The two longitudinal veins that traverse the disk of the wing in ant Fig. 391. — Fore wing of ^lothrips nasturlii. (After Jones.) The lettering is original. the more generalized forms I believe to be the radius and the media respectively. The costal vein is continued by an ambient vein, which margins the entire preanal area of the wing (Fig. 391, am). The ambient vein is termed the "ring vein" by writers on this order, al- though the term ambient vein has been long in use for veins in this position. There is a short longitudinal vein separating the anal and preanal areas; this is doubtless the anal vein (Fig. 391, yl). An organ for uniting the two wings of each side, and consisting of hooked spines situated near the base of the wings and a membranous fold on the under side of the anal area of the fore wing, is described byHinds ('02). In some species one or both sexes are wingless in the adult state; and in others, short -winged forms occur. The legs are well developed, but are furnished with very peculiar tarsi. These are usually composed of two segments; the last seg- ment terminates in a cup-shaped or hoof-like end and is usually without claws. Fitted into the cup-shaped end of the tarsus there is a very delicate, protrusile, membranous lobe or bladder, which is withdrawn into the cup when not in use but is protruded when the tarsus is brought into contact with an object. This is one of the most distinctively characteristic features of the members of this order. It was this feature that suggested the name Physopoda which is ap- plied to this order by some writers.* The abdomen consists of ten distinct segments. The form of the caudal segments differs in the two suborders as indicated below. The manner of oviposition differs in the two suborders. In the Terebrantia the female cuts slits with her saw-like ovipositor and deposits her eggs singly in the tissue of the infested plant. In the Tubulifera it is evident that the eggs must be deposited on the surface. *Physopoda: physao {TTLmetrical, 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 clings 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 fiocculent 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 consumed. 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 stems of aquatic plants; but Ramphocorixa acuminata usually attaches its eggs to the body of a era} -fish. The males of most of the CorLxid^ 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 produced. These stridulating organs differ in form in different species. In addition to the stridulating organs of the fore legs there is in certain species a more or less currs'-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 Eg\'pt. 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 ion; 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 Notonectidae 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, Fig. 416.— Nolo- corresponds to the bottom of a boat, and is sloped necta undulata. , ,-, ui • r ^.i • i. /t^- ^\ so as to greatly resemble m form this part (rig. 410). 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 sharp and pro- HEM I PT ERA 363 jecting. The legs are all long ; the hind pair are much 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, studying it by 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 lid. 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 meso thorax; 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 tibiae 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 swimming. B. Last segment of the antennae much shorter than the penultimate segment. NOTONECTA BB. Last segment of the antennae longer than the penultimate segment. BUENOA AA, Legs quite similar Plea 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 commonly 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, carrying 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 siriola, 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 filaments together the grooves form a tube, which conducts the air to two spiracles situated at the caudal end of the abdomen. By means of this ap- paratus these insects are able to rest on the bottom of a shallow pond, or among rubbish or plants in water, and by projecting this tube to the surface obtain what air they need. With regard to the form of the body, two very different types exist in this family. In one, repre- sented by the genus Nepa, the body is a long oval, Pi„ Ai-j—Nepa fl^^' ^"^ ^^^^ (^^g- 417); in the other, represented apictdata. by the genus Ranatra, the body is almost linear and cylindrical (Fig. 418). An intermediate fonn, 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 tibias 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 Rdnatra 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 fikn (Bueno); and also upon floating dead leaves and stallcs of cat-tail, where the}^ 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 Nepidas of North America was published by Hungerford ('22). Fig. 418. — Ranatra fusca. Family BELOSTOMATID^ The Giant Water-Bugs 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. — Lethocertis 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 from 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 many parts of the country as "electric-light bugs." The family Belostomatidae is repre- sented in this country by four genera. Recent studies of the nomenclature of the genera of this family 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. ..Lethocerus 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 Lethocerus americdnus. 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 Fig. 420. — Belos- insects in our literature the gener- toma fluminea. ic xisxaQ Belostoma is used. pjg ^21. Male of Benacus. — Only a single spe- Abedus, with eggs. HEMIPTERA 367 cies of this genus, Bendcus griseus, is found in our fauna. This close- ly resembles /L^if/zoc^rM5 ammca«M5 (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. Abedus. — 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-Bugs The Naucoridffi 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 antennae are very short, and well concealed beneath the eyes; the beak is three-jointed and covered at the base by the large labrum ; and the hemelytra are furnished with a distinct emboliirm. 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 predacious and are fond of reedy and grassy, quiet waters, where they creep about like the dytiscid beetles, creeping and swimming around and Fig. 422. — Pel- between the leaves and sprays of the submerged plants, ocoris femor- seeking their prey. Only two genera of this family are represented in our fauna; these are Pelocoris and Amhrysus. 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 species of this genus are found in this country and these are restricted to the eastern half of the United States. The most common one is Pelocoris femordtus (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. Ambry sus. — Ten species of this genus have been found in this coimtry; they are restricted to the Far West. 368 AN INTRODUCTION TO ENTOMOLOGY Family GELASTOCORID^ The Toad-shaped Bugs The GelastocSridae was formerly known as the GalguHdce; 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 Galgidus, 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- tenna; 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 -—Ge/- ^j^g color of the soil on which they live. Hungerford latus. ' h^s 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 Gelastocoris oculdtiis (Fig. 423). Two other species of Gelastocoris 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, Mononyxfuscipes, is found in California, the hemelytra are free, but the fore tarsi are one-clawed. The genus Nerthra is also represented in this country by a single species, Nerthra stygtea, 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 antennas exposed. They resemble the following family, the Saldidas, in having the beak long, reaching the hind coxa;. The eyes are prominent, and tvvo ocelli are present. The family includes a single genus, Ochteriis, 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 309 The widely distributed species is Ochterus americdnus . 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 Shore-Bugs With the Saldidae 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- tennas are four-jointed; there are two ocelli; the rostrum is three- jointed and very long, reaching to or beyond the middle coxcC. The membrane of the wing-covers is furnished with looped veins, forming io\xr 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- ^^\ ^~^' ^ ened and almost as coriaceous as the corium proper. ^ °^^" "^' 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 VELIIDyE The Broad-shouldered Water-Striders The Velliidae 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 Veliidce 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 Gerridee. The intermedi- ate legs are about equidistant from the front and hind pairs, except in Rhagovelia. 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 characterized by the long, deeply split, terminal segment of the tarsi of the middle legs. Our most common species of this genus is Rhagovelia obesa (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 „. „, ,. countr^^ 'fj^2' '''^'"'^*" 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, Macrovelia harrisii, which is restricted to the Far West. Family GERRID.E 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 antennge 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 that were flying near them. HEMIPTERA 371 Twenty species of water-striders have 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 Gerrinae). 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. Antennas not half as long as the body, not extending beyond the thorax; sixth abdominal segment of the male doubly emarginate. Gerris CO. First segment of the antennae longer than the second and third taken together Gerris BB. Pronotum glabrous, shining; antennae long and slender. . .Tenagogonus AA. Inner margin of the eyes convexly rounded. Body comparatively short and broad ; abdomen so short as to appear almost nymphal 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 antennae 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 segm.ent 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; antennae 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. Limnoporus. — ^We have only a single species of this genus, L. ru- foscuiilldtus. 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 foimd 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 yellow 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. serheus off the coast of California. Family MESOVELIID^ 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 ver>^ small plump-bodied bugs, measuring less than 3 mm. in length. The antennas 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 ^^^1^427-— Hemelytron of ^gjj^g ^Y\g. 427). Two genera of this family ^ '^"'^' are found in the United States. HEMIPTERA 373 Hehrus. — 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 antenuEe 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^ 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 antennae 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), is widely distributed. The other two, 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- Fig. 428. — Hydrome- tra martini. 374 AN INTRODUCTION TO ENTOMOLOGY ognized by the form of the antennas (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 Schizopteridas 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 deflexed; the fore coxal cavities are very prominent and tumidly formed. The beak is short. Fig. 429.— Glyptocomhussaltator: The Schizopteridae is represented in c, dorsal aspect; b, antenna, our fauna by a single species, Glyptocom- (After Heidemann.) bus saltator (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 jimiping, 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 Dipsocoridae the head is extended horizontally or slightly deflexed, 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- tocombus, 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 Isometopids This is a family of limited extent, there being very few species known in the entire world. It includes very small bugs, those found in this country ranging from 2 mm. to 2.6 mm. in length. HEMIPTERA 375 The Isometopidas is closely allied to the following family, the Miridag; by some writers it has been classed as a subfamily of that family. In both families the antennas are fonr-jointed; the beak is four-jointed; the hemelytra are composed of clavus, corium, cuneus, and membrane; at the base of the membrane there are one or two cells ; otherwise the membrane is with out veins. The Isometopidae 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 (Fig. 430). Both are exceedingly rare in- sects. Family MIRID.E The Leaf-Bugs Fig. 430. — Isometopus pulchel- lus. (After Heidemann.) This family, which has been known as the Capsidce, is more large- ly 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 antennae 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, PoEcilocdpsus linedtus. — This is a bright Fig. 431. — Hemelytron of Pcecilocapsus lineatus. 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 hemelytra (Fig. 432). There is in many 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 numerous 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 Moimtains. 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, fil'^^~t> the destruction of the nymphs by the use of kerosene Uneatus. 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 dark-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 scutelliim; 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, Heterocordylus 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 Jime or early in July; they hatch in the following spring soon after the opening of the leaves of the fruit-buds. The n^inphs 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 HEMIPTERA 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 antennas 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, by 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 Anthocoridae, 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 Termatophylidas 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 Fig. 433. — Hcmelytron of Triphelps. 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 antennae, of four; and the tarsi, of three. The species are small. They are found in a great variety of situations, often upon trees and on flowers, sometimes under bark or rubbish. They are predacious. 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 insididsus. — 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 corium, at the tip of which is a large, triangular, blackish spot; the membrane is milky 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.E 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 antennas 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 coxae. B. Pronotum with the anterior margin very deeply sinuate. The genus Clmex. C. Body covered with very short hairs; second segment of the antennae shorter than the third; hemelytra with the inner margin rounded and shorter than the scutellum. The common hedhxxg . . .C . lectuldrius CC. Body covered with longer hairs; second and third segments of the an- tennee 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 slightly sinuate or nearly straight in the middle. Species found in swallows' nests. . .CEciacusvicdrius PiA.. Beak long, reaching to the posterior coxae. Infests poultry in southwest United States and in Mexico Hamatoslphon inodorus The common bedbug, Cimex lectuldrius. — ^The body is ovate in outline and is very flat (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- HEMIPTERA 379 Fig.434.— Q'wex lectularius. turnal insect, hiding by day in cracks of fumitiire 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 I^^^jT^ the cracks of the bedstead and other places in which "^^JK^ it hides with corrosive sublimate dissolved in alco- m^^^ hoi. This is sold by druggists under the name of /^^^r \ 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^ The Many-combed Bugs The Polyctenidas 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. 435. — 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 436. — Hemelytron of Nabis Jems. 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 NABID^ The Nahids 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 Nabis; 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 Conscus; and most of the references to these insects are under this name. Nabis ferus. — This is one of our most common species. It measures about 8 mm. in length. It is pale yellow with nimierous minute brown dots; the veins of the membrane are also brownish. 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. Nobis 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 yellowish. The hemelytra barely extend to the second abdominal segment. The long-winged form of this species is not common; it is ^^f.j^'^;~^^j^^ much narrower behind, and the hemelytra and the ab- domen are rather dusky, or piceous, instead of jet-black. bis subcole- optratus. Family REDUVIID^ The Assassin-Bugs The Reduviidag is a large family, including numerous genera of diverse forms. Many 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 cristatiis. (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 prostemum, which is grooved to receive it. Except in a few spe_ cies, ocelli are present in the winged forms. The anten- nae 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 family. The wheel-bug, Arilus cristdtus. — 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 n5nmphs when young are blood-red, with black marks. The masked bedbug-hunter, Reduvius persondtus. — The adult of this species is represented by Figure 439; it measures from 15 to 20 mm. in length, and is black or very dark brown in colo^- Fig. 439-— Re- duvius per- sonatus. 382 AN 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 antennae 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, Tridioma sanguisuga. — 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 Reduviidse that received the name of "kissing-bug" as a result of sensational newspaper accounts which were widely published in the summer of i8gg 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 Triatonia was renamed Conorhinus and most of the references to this species are under this generic name. The thread-legged bug, Emesa brevipennis. — This is our most common representative of one of the subfamilies of the Redu- viidas in which the body is slen- der and the middle 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 Yi^. ^^o— Emesa brevipennis. 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 brevipennis 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 Reduviidae of North America has been published by Fracker ('12). Family PHYMATID^ The Ambush-Bugs The Phymatidae is poorly represented in this country but some of the species are very common. Here we find the body extended HEMIPTERA 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 pronotiim in Phymata there is on each side a groove into which the antenna fits. Only two genera are represented in our fauna, each Fig. 441. — by six species. These are Phymata and Macrocephalus. Phymata er- 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 yellow 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^ The Unique-headed Bugs 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 antennse 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 Enicocephalus formicina, found in California, and Systelloderus bleeps, 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 culicis) flying in small swarms near Ithaca, N. Y. Their manner of flight resembled that of chironomids. They were observed 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 TINGID^ The Lace-Bugs The Tingidag are doubtless the most easily recognized of ail 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 very small insects. But they occur in great ntunbers 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- Fig- 443- — Corythucha tcUimi is usually wanting or vestigial, replaced arcuata. }^y. ^j^g angular hind portions of the pronotum; and the tarsi are two-jointed. About seventy-five species of lace-bugs, representing twenty-three genera, are now listed from this country. There are two well-marked subfamilies. Subfamily TINGING This division includes nearly all of the known species. Here the scutellum is usually covered by an angular projection of the pronotimi ; 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 Crataegus. The infested leaves have a brown and sunburnt appearance. Eggs, n^-mphs, 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^E In this subfamily the scutellum is not covered; the hemelytrb, 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- tvinged 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- thticha arcuata. The Cotton-Stainer Family In this family the antennae are four-jointed; the beak is also foiu--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 Pyrrhocoridas can be dis- tinguished from the Lygaeidce 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 succinctus. 386 ^A^ INTRODUCTION TO ENTOMOLOGY oblong-oval in form, of a red color; the hemelytra and an arc on the base of the prothorax, and also the scutellum, are pale brown. The hemel}i;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 16 mm. in length. The young bugs are bright red with black legs and antenna. 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. Pig. 446. — Dys- dercus suturellus. The species whose range extends farthest north is Euryophthdlmus SMccinctus. This is found from New Jersey south to Florida and west to Arizona. It is brownish black, with the lateral and 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-Bug Family the costal margin of the hem- Fig. 447. — Hemelytron of LygcEus kalmii. The Lygasida 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 numerous microscopic hairs. In Figure 448 this insect is represented natural size and enlarged. The species is dimorphic, there being a short-winged *- rK\^ form. There are two generations of the chinch-bug each pjg ^^g — BUssus 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 globuliferum, which is the cause of a contagious disease of the chinch-bug. 388 AN INTRODUCTION TO ENTOMOLOGY Family NEIDID.E The Stilt-Bugs The family Neididae consists of a small number 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 the tip of the first segment enlarged. The beak is four-jointed; and the membrane of the hemelytra is furnished with a very few veins. Only eight species of this family have been found in our fauna ; 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 woods and in meadows and pastures. Jdlysus spinosMS. — 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 irom the base of the scutelliim, and another from each side of the mesopleura, just in front of the posterior coxse. The body is about 8 mm. in length. Jalysus perclavdtus. — 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 antennas ; and the last segment of the antennae is shorter and thicker than in /. spinosus. Neides mUticus. — Like 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 hom. The other representatives of this family in our fauna are found in Florida, Arizona, New Mexico, and California. Fig. 449. — Jalysus spinosus. 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 antenna are four-jointed ; the tarsi are two-jointed; and the beak is four-jointed, but often apparently three-jointed. These insects are supposed to feed upon fimgi or upon the juices of decaying wood and bark. The family is well represented in this countr}-; fifty-nine species, repre- senting nine genera, are now known, and doubtless many remain to be discovered. Fig. 450.— /I r- adus acutiis. Fig. 451. — Hemelytron trivittafus. Leptocoris 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 antennse 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- pressed; the ocelli are present; the beak is four-jointed; the scutellum is small or of medium size; the hemelytra are usually complete and composed of clavus, coriiim, 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 twent}^- 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, Anzsa tnstis. — 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 ochre-yellow, darkened by ntunerous minute black punctures. Upon the head are two longitudinal black stripes; the lateral margins of the pro thorax ar3 yellow, owing to the absence of the punctures along a narrow Fig. 452. — Anasa tristis. 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 summer 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 species each year. This is one of the most annoying of the many pests of the kitchen-garden; 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 nymphs 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-Bug Family With the Pentatomidas we reach a series of families, three in number, 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 Pentatomidas is well shown by Figure 454. It is broad, short, and but slightly convex; the head and prothorax form a triangle. The scutellimi 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 Coreidas, 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 Fig. 454-— A pentatomid. HEMIPTERA 391 stink-bugs 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, Murgdntia histrionica. — 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.- Poenis,Cyrtomenus mirdbilis, a species found in the South and the Southwest. Fig. 456.— Cyrtome- nus mir- abilis. Subfamily THYREOCORIN^ The Negro-Bugs The subfamily Thyreocorinse is represented in our fauna by a single genus, Thyreocoris, of which sixteen species have been found in this countr}^ 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 scutelliim is very convex and covers nearly the whole of the abdomen. These insects infest various plants, and often in- jure raspberries and other fruits by imparting a dis- 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. Fig. 457-— Thy re 0 oris ater. Family SCUTELLERIDvE 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 scutelliim is very large, covering nearly the whole of the abdomen. The lateral margins of the scutellimi are not furnished with grooves for receiving the edges of the hemelytra as is the case in the two preceding families. The tibiae are smooth or furnished with small spines. Figure 458 represents Eurygaster alterndtus somewhat enlarged, and serves to illustrate the typical form of members of this family. The family is represented in this country by Fig. 458. — Eury- fourteen genera including twenty-six species. I have gaster altema- met no account of any of our species occurring in ^"•^" sufficient numbers to be of economic importance. 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 Coccidce; the wings are of the same thickness throughout, and usually are held sloping at the sides of the body when at rest. The mouth-parts are formed for piercing and sucking; the beak arises from the hind part of the lower side of the head. The metamorphosis is gradual except in some highly specialized forms. Although the Homoptera is a well-defined order, the families of which it is composed differ greatly in the appearance of their members. For this reason there is no popular name that is applied to the order as a whole. The Homoptera was formerly regarded as a suborder of the Hemip- tera, that order being divided into two suborders, the Heteroptera and the Homoptera. But these two groups of insects differ so mark- edly in structure that it seems best to regard them as distinct orders. The Hemiptera is, therefore, restricted to what was formerly known as the suborder Heteroptera, and the suborder Homoptera is raised to the rank of a separate order. The wings of the Homoptera are usually membranous, but in some the front wings are subcoriaceous. In these cases, however, the}^ are of quite uniform texture throughout, and not thickened at the base as in the Hemiptera. Many wingless forms exist in this order; in the family Coccidas the females are always wingless; and in the family Aphididas the males may be either winged or wingless, while the sexually perfect females and certain generations of the agamic females are wingless. In the Coccidae the males have only a single pair of wings, the hind wings being represented by a pair of club-like halteres. Each of these is furnished with a bristle, which is hooked and fits in a pocket on the hind margin of the fore wing of the same side. In several of the families of the Homoptera the wing-venation is greatly reduced ; and even in the case of the more generalized forms, if only the wings of adults be studied the venation of these wings appears to depart widely from the hypothetical primitive type; but by examining the tracheae that precede the wing-veins in the wings of the nymphs, it is easy to determine the homologies of the wing-veins. This has now been done in the case of representatives of each of the families. The most generalized condition was found in the wings of a cicada, which will serve as the type of homopterous wing-venation. *Hom6ptera: homos (6fj.6s), same, pteron (irTepdv), a wing. (394) HOMOPTERA 395 Figure 459 represents the tracheation of the fore wing of a young nymph of a cicada. The dotted hne a-h indicates approximate- ly the line along which the hinge of the wing of the adult is formed. In this wing the only departures from the typical branching of the tracheas are the following: trachea Ri coalesces with the ra- dial sector to a point beyond the separation of trachea R 4+5 from the sector; the first anal trachea coalesces with trachea Cu for a short distance; and the second and third anal trachese are unit- ed at the base. These differences are remark- Fig. 459. — Tracheation of a fore wing of a young nymph of a cicada. ably slight compared with the great changes that have taken place in the specialization of the mouth-parts and other organs of the adult cicada. Figure 460 represents the fore wing of a mature nymph of a cicada. In this wing trachea Ri is completely aborted. In fact one of the Fig. 460. — Tracheation of a fore wing of a mature nymph of a cicada. most characteristic features in the venation of the Homoptera, and of the Hemiptera also, is the absence or very great reduction of vein Ri in the adult wings of most members of these two orders. In the stage represented in this figure the developing cross-veins appear as pale bands. 396 AN INTRODUCTION TO ENTOMOLOGY Figure 461 represents the wings of an adult cicada. In this figure, where the veins are not ntunbered their homologies are indicated by the numbering of the cells behind them. In the adult wing there is a massing of several veins along the costal margin of the wing, and the cross-veins have the same appearance as the branches of the primary veins. Further details regarding the development of the wings of a cicada, and accounts of the development of the wings of representatives of other families of the Homoptera, are given in "The Wings of Insects" (Comstock '18). In the Homoptera the front part of the head is bent under and back so that the beak arises from the hind part of the lower side of the head. There is no distinct neck; and so closely is the head applied to the thorax that usually the front coxse are in contact 4r The wings of a cicada. with the sides of the head, and in many forms the beak appears to arise from between the front legs. The mouth-parts are formed for piercing and sucking. The piercing organs consist of four long, bristle-like setae, the mandibular and maxillary setae; these are enclosed in a long, jointed sheath, which is the labium. The labium and the enclosed setas constitute what is commonly termed the beak. The beak, however, corresponds to only a portion of the mouth- parts of a chewing insect, each mandibular and maxillary seta being only a part of a mandible or maxilla; in each case another part of the organ enters into the composition of the head-capsule. As an example of the homopterous type of head and mouth-parts those of a cicada are probably the most available, on account of the large size of these insects and the comparative ease with wh^ch the HOMOPTERA 397 parts of the head can be distinguished. Figure 462 represents a lateral Fig. 462. — Head and prothorax of a Fig. 463. — Head of a cicada, front view: cicada, lateral aspect: a, antenna; md, mandibular seta; mx, maxillary c, clypeus; e, compound eye; ep, seta; other letters as in Fig. 462. epipharynx; /, labrum; 0, ocelli; 2, (After Marlatt, with changes in the 3, second and third segments of the lettering.) labium. (After Alarlatt, with changes in the lettering.) view of the head and prothorax of a cicada, and Figure 463 a front view. The corresponding parts are lettered the same in the two figures. The compound eyes (Figs. 462 and 463,^), the an- tennce(Figs. 462 and 463, a), and the three ocelli (Figs. 466 and 467,0), can be easily recognized and need not be described in detail. The front is a small scle- rite near the summit of the head. It can be most easily recognized by the fact that it bears the median ocellus. In the adult insect the su- ture between it and the ver- tex is indistinct; but in the exuviae of a nymph, where the epicranial suture has been opened by the emergence of the adult, the outline of this sclerite is evident (Fig. 464). In many homopterous insects the front is vestigial or wanting. The vertex (Figs. 462 and 463, v) bears the paired ocelli. The clypeus (Figs. 462 and 463, c) is very large, occupying the greater part of the anterior surface of the head. In several of the Fig. 464. — Part of the exuviaa of the head of a nymph of a cicada: a, antennae; as, antennal sclerite; c, clypeus; e, e, com- pound eyes; /, front; v, v, vertex. (After Berlese.) 398 AN INTRODUCTION TO ENTOMOLOGY CO " published accounts of the head of homopterous insects the clypeus has been incorrectly identified as the front. The labrum (Figs. 462 and 463, /) is joined to the lower end of the clypeus; at its distal end it forms a sheath covering the base of the labium and the enclosed seise. This part is described as the clypeus by those who have incorrectly identified the clypeus as the front. The epipharynx (Figs. 462 and 463, ^) arises at its normal position on the ental surface of the labrum; but it is greatly developed and projects beyond the end of the labrum. The projecting part has been mistaken for the labrum by some writers, those who have failed to recognize the front and have termed the clypeus the front and the labrum the clypeus. The mandibular sderites are easily recognized in the cicada. On each lateral as- pect of the head there are two quite distinct sclerites; the one that is next to the clypeus and the base of the labium is the mandibular sclerite(Figs.462and 463,:?;). This sclerite is termed the lora by some writers on the Homoptera. The mandibular sclerites are believed to be in each case the basal part of a man- dible. They were first rec- ognized as such by Profes- sor J. B. Smith ('92); and this conclusion has been adopted by Marlatt ('95), Heymons ('99), Meek ('03), Berlese ('09), and Bugnion and Popoff ('11). On the other hand, Muir and Ker- Fig. 465. — Caudal view of the head of a cicada, with part of the head-capsule and muscles re- moved so as to show the left mandible and the right maxilla. (Prom Meek.) shaw ('12) regard the loree as "lateral developments of the clypeal region" and not parts of mandibles. The structure of the mandible as a whole has been worked out by Meek ('03) and is shown in the left half of Figure 465. Within the cavity of the head the maxillary seta is enlarged, and to it are attached a retractor muscle (mdr) and a protractor muscle (mdp). The seta is attached to the dorsal end of the mandibular sclerite (Fig. 465, mds) by a quadrangular sclerite (Fig. 465, co). The maxillary sderites (Figs. 462 and 463, y) are closely parallel with the mandibular sclerites, but extend farther down, joining the HOMOPTERA 399 terminal part of the lab rum. Each maxillary sclerite is a part of a maxilla. This is clearly shown by the fact that in the embryo each maxilla is at first a bilobed appendage; from one of these lobes the maxillary sclerite is developed, and from the other the maxillary seta (see Heymons '99). In the adult insect the maxillary sclerites are not separated from the epicranium by sutures as are the mandibular sclerites (Figs. 462 and 463). The form and relations of the different parts of a maxilla, as worked out by Meek ('03), are shown in the right half of Figure 465. From the enlarged base of the maxillary seta a crescent-shaped sclerite (Fig. 465, ca) extends to the maxillary sclerite (Fig. 465, mxs). In this figure the maxillary retractor muscles {mxr), the maxillary protractor muscles (mxp) , and a tendon (mc) connecting the crescent- shaped sclerite with the tentorium, are also represented. It is interesting to note the similarity in the structure of the mandibles and the maxillas. Each consists of a basal part which forms a portion of the wall of the head; a terminal piercing organ, the seta; and a sclerite connecting these two parts. The labium forms the outer wall of the beak ; it consists of three segments; the second and third are lettered in Figures 462 and 463. The proximal segment is probably homologous with the submentum of the chewing insect mouth ; the second segment, with the mentum; and the third segment, with the ligula (see footnote, page 354). The dorsal surface of the labiimi, which is the lower surface, is deeply grooved, forming a channel which enclos- es the mandibular and maxillary setae. The labium, which is all that is commonly seen of the beak in either hemipterous or homopterous insects, is not a piercing or- gan; it is not pushed into the food sub- stance of the insect, but serves merely as a sheath for the mandib- ular and maxillary setae, which are the piercing organs and which are worked by the protractor and retractor muscles within the head (Fig. 465). Figure 466 represents a cross-section of the third segment of the beak of a cicada as figured by Meek ('03), and shows the relation of the labium to the mandibular and maxillary setae. Each seta is crescent-shaped in cross-section; the mandibular setae lie outside of the maxillary setae ; the maxillary setae, which extend side by side at Fig. 466. — Cross-section of the third segment of the beak of a cicada: lab, labium; md, mandibular seta; mx, maxillary seta; /, /, lumina in the seta. (From Meek.) 400 AN INTRODUCTION TO ENTOMOLOGY the base of the beak, are twisted so that at this point one lies above the other. The two are fastened together by interlocking grooves and ridges ; and between them is a channel for the passage of the food. Within each of the four setae, there is a Itimen (Fig. 466, /, /). The hypopharynx is a funnel-shaped, chitinized organ found near the base of the ental surface of the labium, at the end of the pharynx. The nature of the metamorphosis differs to a considerable degree in the different families; in most cases it is gradual, but marked modifications of this type have been developed in the Aleyrodidce and in the Coccidas. The members of this order feed on vegetation and to it belong some of our more important insect pests. This order includes ten families, which are designated as follows : The Cicadas, Family Cicadid^, p. 401. The Spittle-insects, Family Cercopid^, p. 402. The Tree-hoppers, Family Membracid^, p. 404. The Leaf-hoppers, Family Cicadellid^, p. 406. The Lantern-fly Family, Family Fulgorid^, p. 408. The Jumping Plant-lice, Family Chermid^, p. 410. The Typical Aphids, Family Aphidid^, p. 415. The Adelgids and the Phylloxerids, Family Phylloxerid^, p. 428. The Aleyrodids, Family Aleyrodid^, p. 437. The Scale-bugs, Family Coccid^, p. 440. ^ TABLE FOR DETERMINING THE FAMILIES OF THE HOMOPTERA A. Beak evidently arising from the head; tarsi three- jointed; antennae minute, bristle-like. B. With three ocelli, and the males with musical organs. Usually large insects, with all the wings entirely membranous, p. 401 Cicadid^ BB. Ocelli only two in number or wanting; males without musical organs. C. Antenn:s inserted on the sides of the cheeks beneath the eyes. p. 408 FULGORID^ CC. Antennae inserted in front of and between the eyes. D. Prothorax not prolonged above the abdomen. E. Hind tibiae armed with one or two stout teeth, and the tip crowned with short, stout spines, p. 402 Cercopid^ EE. Hind tibiae having a row of spines below, p. 406 . Cicadellid^ DD. Prothorax prolonged into a horn or point above the abdomen, p. 404 Membracid^ AA. Beak apparently arising from between the front legs, or absent ; tarsi one- or two- jointed; antennae usually prominent and threadlike, sometimes wanting. B. Tarsi usually two-jointed; wings when present four in number. C. Wings transparent. D. Hind legs fitted for leaping; antennae nine- or ten-jointed, p. 410.. Chermid^ DD. Legs long an slender, not fitted for leaping; antennas three- to seven-jointed. 412 Superfamily Aphidoidea CC. Wings opaque, whitish; wings and body covered with a whitish powder, p. 437 Aleyrodids HOMOPTERA 401 BB. Tarsi usually one- jointed ; adult male without any beak, and with only two wings; female wingless, with the body 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, p. 440 Coccid^ Family CICADID^ The Cicadas The large size and well-known songs of the more common species of this family render them familiar objects. It is only necessary to refer to the periodical cicada and to the harvest- flies, one of which is represented by Figure 467, to give an idea of the more striking character- istics of this family. We have species of cicadas much smaller than either of these; but their characteristic form is sufficient to distinguish them from members of the other families of this order. The species are generally of large size, with a subconical body. The head is wide and blunt, with prominent eyes on the outer angles, and three bead-like ocelli arranged in a triangle be- tween the eyes. The structure of the mouth- parts is described on an earlier page and illus- trated by several figures; and the form and venation of the wings are shown by Figure 461. But the most distinctive peculiarity is the form p. , ™ ., . , . of the musical organs of the males; an example of f/^j these is described and figured on pages 89 to 91. The family Cicadidae is well represented in this country ; seventy- four species, representing sixteen genera, are now listed from our fauna. The two following species will serve as illustrations. There are several species of cicadas that are commonly known as dog-day cicadas or harvest-flies; the most abundant of these is the species that has received the popular name of the lyreman; this is Tibicen linnet (Fig. 467). The shrill cry of this species, which is the most prominent of the various insect sounds heard during the latter part of the summer, has brought its author into prominent notice. This insect varies both in size and colors. It commonly measures 50 mm. to the tip of the closed wings; it is black and green, and more or less powdered with white beneath. The transformations of this insect are similar to those of the following species, except that it probably completes its development in a much shorter period. It 402 AN INTRODUCTION TO ENTOMOLOGY differs also in seldom, if ever, occurring in sufficient numbers to be of economic importance ; but a brood of it appears each year. The member of this family that has attracted most attention is the periodical cicada, Tibicina septendecim. This species is commonly known as the seventeen-year locust; but the term locust when applied to this insect is a misnomer, the true locusts beings members of the order Orthoptcra. The improper application of the term locust to this species was doubtless due to the fact that it appears in great swarms, which reminded the early observers in this country of the hordes of migratory locusts or grasshoppers of the Old World. This species is remarkable for the long time required for it to attain its maturity. The eggs are laid in the twigs of various trees; the female makes a series of slits in the twig, into which the eggs are placed. Sometimes this cicada occurs in such great numbers that they seriously injure small fruit trees, by ovipositing in the twigs and smaller branches. The nymphs hatch in about six weeks. They soon volun- tarily drop to the ground, where they bury themselves. Here they obtain nourishment by sucking the juices from the roots of forest and fruit trees. And here they remain till the seventeenth year following. They emerge from the ground during the last half of May, at which time the empty pupa-skins may be found in great numbers, clinging to the bark of trees and other objects. It is at this period that the cicadas attract attention by the shrill cries of the males. The insects soon pair, the females oviposit, and all disappear in a few weeks. More than twenty distinct broods of this species have been traced out; so that one or more broods appear somewhere in the United States nearly every year. In many localities, several broods co-exist; in some cases there are as many as seven distinct broods in the same place, each brood appearing in distinct years. There is a variety of the species in which the period of development is only thirteen years. This variety is chiefly a southern form, while the seventeen-year broods occur in the North. Family CERCOPID^ The Spittle-Insects or Frog-Hoppers During the summer months one often finds upon various shrubs, grass, and other herbs, masses of white froth. In the midst of each of these masses there lives a young insect, a member of this family. In some cases as many as four or five insects inhabit the same mass of froth. It is asserted that these insects undergo all their trans- formations within this mass ; that when one is about to molt for the last time, a clear space is formed about its body and the superficial part of the froth dries, so as to form a vaulted roof to a closed chamber within which the last molt is made. The adult insects wander about on herbage, shrubs, and trees. They have the power of leaping well. The name frog-hoppers has HOMOPTERA 403 doubtless grown out of the fact that formerly the froth was called "frog-spittle" and was supposed to have been voided by tree-frogs from their mouths. The name is not, however, inappropriate, for the broad and depressed form of our more common species is somewhat like that of a frog. The origin and formation of the froth of spittle-insects has been discussed by many writers. Guilbeau ('08) found by many experi- ments that the froth is derived from two sources. The greater part of the fluid is voided from the anus ; to this fluid is added a mucilagi- nous substance which renders it viscous and causes the retention of air bubbles, which are introduced into it by the insect by means of its caudal appendages. The mucilaginous substance is the excretion of large hypodermal glands, which are in the pleural region of the seventh and eighth abdominal segments. These are known as the glands of Batelli; they open through numerous minute pores in the cuticula. It is evident that the covering of froth protects the spittle-insects from parasites and other enemies. In this family the antennas are inserted in front of and between the eyes; the prothorax is not prolonged back of the abdomen, as in the Membracidae ; the tibias are armed with one or two stout teeth, and the tip is crowned with short, stout spines, as shown in Figure 468. The Cercopidffi is represented in our fauna by six genera, which include twenty-five species. The follow- Fig. 468. — Le- ing species will serve as examples. p y rom a One of the more common and very widely distribut- |j"^_5 '^"natu- ed species is Lepyronia quadranguldris (Fig. 468). The ral size, and adult of this species is a brownish insect, densely one tibia en- covered with microscopic hairs, and black beneath; larged. the hemelytra are marked with two oblique brown bands, which are confluent near the middle of the costal margin; the htimeral region is dusky; and the tip of each hemel>i:ron is marked with a small blackish curve; the ocelli are black, but indistinct. This species measures from 6 mm. to 8 mm. in length. Somewhat resembling the preceding species, and also common and widely distributed, is Aphrophora quadranotdta. In this species the body is pale ; the hemelytra are dusky, each with two large hya- line costal spots, margined with dark brown; the ocelli are blood-red; and the head and pronotimi are furnished with a slightly elevated, median, longitudinal line. To the genus Clastopiera belong certain other common members of this family. In this genus the body is short and plump, some- times nearly hemispherical; the species are small, our common forms ranging from 3 mm. to 6 mm. in length. Clastopiera proteus is a conspicuous species on account of its bright yellow markings. It varies greatly in color and markings; but the most striking forms . are black, with three transverse yellow bands, two on the head and one on the thorax, and with the scutellum and a large oblique band 404 AN INTRODUCTION TO ENTOMOLOGY on each hemelytron yellow. Another common species is Clasioptera ohtusa. This occurs on black alder in summer and autumn. It is of a claret-brown color above, marked with two pale bands on the vertex, two on the prothorax, and a wavy, broader band on the hemelytra. The membrane is often whitish, the waved band is extended exteriorly, and there is a pale V-shaped figure on the end of the scutellimi. Family MEMBRACID^ Fig. 469. — A, Spongophorus ballista; B, Spongophorus querini. The Tree-Hoppers The most useful character for distinguishing members of this family is the prolongation of the prothorax backward above the abdomen; some- times it extends back to the tip of the abdomen and completely cov- ers the wings. This develop- ment of the prothorax re- sembles that which occurs in the pigmy lo- custs, the sub- family Acrydiinse of the order Or- thoptera. In many of the Membracidse, however, the prothorax is not only prolonged backward but is extended sidewise or upwards, with the result that in some cases the insect presents a most bizarre appearance ; this is especially true of certain tropical forms ; Figure 469 represents two species found in Central America. Many species of the Membracidce live upon bushes or small trees; others inhabit grass and other herbaceous plants. Although these insects subsist upon the juices of plants, they rare- ly occur in sufficient nimibers to be of economic impor- tance. Sometimes the females injure young trees by lay- ing their eggs in the bark of the smaller branches and in buds and stems. Many members of this family excrete honey-dew and are attended by ants, especially in the nymphal stages, as are the aphids. The adults are good Fig.470. — Cer- leapers ; hence the common name tree-hoppers. esa bubalus. This family is well represented in this country; one hundred eighty-five species, representing forty-three genera, are now listed. Among our more common species are the following. The Buffalo tree-hopper, Ceresa bubalus. — The popular name of this species refers to the lateral prolongations of the prothorax, which suggest the horns of a buffalo (Fig. 470). The life-history of HOMOPTERA 405 this insect has been worked out by Funkhouser ('17). The nymphs feed on succulent herbs, particularly sweet clover; the eggs are laid on young trees, particularly elm and apple, the stems of which are injured by the egg-punctures. Oviposition occurs most commonly in early September, at Ithaca, N. Y. The eggs hatch early in the following May. The young nymphs 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-homed tree-hopper, Ceresa di,ceros .—This, species re- sembles the buffalo 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 hinotdta.- — 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 pronotum. Another very common species, and one that is closely allied to the preceding, is Campylenchia Idtipes. 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 p. „ , is a grass-inhabiting species and is common in pastures wnona. ^ ' ^^^ especially on alfalfa. It is often taken by sweeping. Telamona. — To this genus belong our humpback Fig. 471.- chenopa notata. En- bi- 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; they 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 niimber of species that are very injurious to cultivated plants. The members of it are of small or moderate size. The antennas 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 tibiae are the most salient characters of this family. The form of the body is jl i commonly long and slender, often spindle-shaped ; but p. 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 theUnited States and Canada. Among the more important members of the family from an economic standpoint are the following. The destructive leaf-hopper, Euscelis exitidsus, which is repre- sented, greatly enlarged, in Figure 474, sometimes infests winter wheat to a serious extent. It is a widely 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 conies, 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 resumed for a short time in the spring they change to a light lemon-yellow. The darker markings on the *Tliis family has been commonly known as the Jassidae, but Cicadellidae is the older name. HO MO PT 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,^ £mpoa roscB, 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, Empoasca JahcB. — Al- though this species is named the apple leaf- hopper, it infests to an in- jurious extent many 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 pronotiim. 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. undata (Fig. 476) is a common species. Its body, head, fore part of the thorax, scutel- lum, and legs are bright yellow, with circular lines of black on the head, thorax, and scutellum. The fore 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 Gyponinae, includes forms which resemble certain genera belonging to the Cercopidasby their Fig- 475- — Erythroneura comes: a and b, female and male of the typical conies variety; c, the vitis variety. (From Slingerland.) Fig. 476. —On- cometopia undata. 408 AN INTRODCUTION TO ENTOMOLOGY pltimp proportions. Among these are Penthima americdna, which is a plump, short -bodied insect, resembhng a Clastoptera; and the genus Gypona includes a large ntmiber 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.E 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 phos- 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, Laternaria 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 Merian, a careful observer, who wrote more than two hundred years ago (1705), stated that this prolongation of the head is luminescent. This statement was ac- cepted by Linnaeus 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 Megamelus notula. Hansen.) (Aftei 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 Merian were infested by luminescent bacteria, as has been observed to be the case occasionally in certain other insects. No member of this fam- ily is known to be liimi- nescent. The Chinese candle- fly, Fulgoria candeldria, 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 s>body characteristic of this family. The different genera differ 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 antennce. 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 niunerous 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- bertii (Fig. 480) is a gay lemon-yellow or cream-colored species, with Fig. 480.- ler.) -Otiocerus coquebertii. (From Uh- 410 AN INTRODUCTION TO ENTOMOLOGY wavy red lines on the fore wings. It measures about 8 mm. to the tips of the wings, and Hves upon the leaves of grape-vines, oaks, and hickor}^ Ormenis. — In our common representatives of this genus the wing -covers are broad, and closely 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. Fig. 481. — Ormenis sep- tentrionalis. 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 antennas being ten -jointed or rarely nine- or eleven-jointed. The terminal segment of the antennae bears two thick setae 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 fioccosa are indi- cated in Figure 4S3 . Fig. 482 lia. -Psyl- itf.+2 Fig. 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 coxa. *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 Phylloxeridae. 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 nimi- bers to attract attention, except in case of the pear- tree Psylla. The family Chermi- dae 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- mamma. — This is a gall- making species which in- fests the leaves of hack- berry {Celtis occidentdlis) with galls, and a single gall and a nymph enlarged (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: c, leaf with galls, from under-side; Z>, section of gall enlarged and insect in cavity; c, nymph, enlarged. (From Riley.) Figure 484 represents an infested leaf The adult insect Pig. 485. — Pachypsylla celtidis-mamma. (From Packard.) Fig. 486.— Psyllia pyricola. tant species from an economic standpoint, being a serious enemy of the pear. It is a small species (Fig. 486) ; the stimmer generations 412 AN INTRODUCTION TO ENTOMOLOGY measure to the tips of the folded wings from 2.1 mm. to 2.8mm., the hibernating form 3.3 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 young nymphs migrate to the axils of the leaf petioles and the stems of the forming fruit; later they spread to the imder 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 young fruit in midsinnmer. In some cases orchards have been so badly injured by this pest that they have been cut down by 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 nymphs; this spray- 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 antennse, which appear on various plants in the house and in the field. Usually, at least, in each species there are both winged and wingless 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, ab) , but are laid flat on the abdomen in some genera. The beak is four-jointed and varies greath- HOMOPTERA 413 in length; in some species it is longer than the body. The antennae 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 antennae 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 antennas are usually provided with sense-organs, the sensoria, which vary in niunber and shape in different species and are ||* i^'''"' ■■'•''■< '/'I'lii'i ^"^^^^^GgaarTTTy^-^ CUZ'. Fig. 488. — The melon aphis, Aphis gossypi: a, winged agamic female; aa, en- larged antenna of same; ah, winged agamic female, with wings closed, sucking juice from leaf; b, young nymph; c, last nymphal instar of winged form; d, wingless agamic female. (Prom 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 materialis 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 Se*R^^M+Cu,+ tstA Fig. 489. — The wings of Eriosoma americana. (From Patch.) surface of the body, or it may be in large flocculent or downy masses; every gradation between these forms exists. The superfamily Aphidoidea includes two families, the Aphididas and the Phylloxeridce. 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) APHiDlDi*; AA. Both the sexually perfect females and the parthenogenetic forms lay eggs. Vein Ri of the fore wings is wanting; and the outer part of the stigma is bounded behind by the radial sector (Fig. 490) Phylloxeridce ;Se.il+M.C«J_;f^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 Aphididffi 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 nonnally 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 summer months. The stem-mother. — In the spring there hatches from an over- \5intering egg a parthenogenetic, viviparous female, which lives on the primary host. As this female is the stock from which the simmer 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 aptercs* 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. * Spuria (New Latin, fem. 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 spuricB alatce 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 established 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 sexuparcB. 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 igi. 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 they 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 summarized 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 MO PT 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. — Wingless 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 sexuparae. 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- rnoved as soon as born, 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 number 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 pseudogalls. True galls formed by aphids are described in the accounts of the last two subfamilies. 418 ^A^ 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 APHIDIN^ The following species will serve as an example of the bark-feeding species belonging to this subfamily, and also of the maximum size reached by any aphid. The giant hickor}'-aphid, Longistigma cdryce. — This is a ver\- 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 ^% ^^ma^^arTI^' ^^^^t to the tip of the wing. The top of the thorax '^^' and the 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 lilce 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. h. 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 fiiiit 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 Sorhus. It is a migrating spe- cies. HOMOPTERA 419 The appie-bud aphis, Rhopalosiphum prunifdlicB. — This is the species that most commonly infests the opening apple-buds, often nearly covering them. It also infests pear, pltim, 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, Anuraphis maidi-radlcis . — This is a serious pest of com throughout the principal corn-growing States, sometimes totally ruining fields of com. Broom-corn and sorghum 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 americanus) , 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 com, 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 Lasius americanus should recognize the importance of preserving the eggs from which their herds are to develop ! The strawberry -root aphid, Aphis forbesi. — 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^E 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 ahietinus, 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 egg, 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 b, the gall-making Erisomatins. 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 Aphididae, 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 lamgera. — 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 Schizoneura 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 itlmi, a European species, which in Eiu-ope has been found to migrate to Ribes. The alder-blight, Proctphilus tesselldtus. — A woolly aphid that is foimd in dense masses on the branches of several species of alder is known as the alder-blight. Colonies of this species are easily foimd 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 butterfl}^ Feniseca tarquinius, which feeds on the aphids. In the late summer 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 acerjdlii, which name must now be regarded as a s^monym of Proclphilus tesseUdtus, 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 Si?,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. h. 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 Eriosomatin^ that are most likely to attract attention are the following. The cockscomb elm-gall colopha, Colopha uhmcola. — 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 HOMOPTERA 423 the gall is an excrescence resembling a cock's conib in form, which rises abruptly from the upper surface of the leaf (Fig. 493, a). It is compressed, and has its sides wrinkled perpendicularly and its summit 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 ,b). In the spring the stem-mothers ^t=C?F^ Fig. 493. — Colopha ulmicola: a, leaf showing galls from above and beneath; b, 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, Tetranetira gramlnis. — The life-cycle of this species is quite similar to that of the preceding one. The primary 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, Thecdbius 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 midsimimer becomes the mother of nimierous 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, Mordwilkoja vagabunda. — 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 life-cycle of this species. Fig. 494. — The vagabond poplar-gall. Walsh and Riley.) (From Subfamily HORMAPHIDIN^ The members of this subfamily are usually gall-makers, resembling in this respect certain members of the Eriosomatinffi, 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 Hormaphidina?, 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; J, 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 offspring of the migrants, is broadly oval, with the entire margin of the body 426 AN INTRODUCTION TO ENTOMOLOGY 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 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. (From Pergande.) 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, Hamamelhtes spindsus. — 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.) HO MO PT ERA 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; ^ /, 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 PHYLLOXERIDiE • 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^^M^cu + /«<-^ s« Fig. 500. — Wings of Adelges. (From Patch.) In this family the cornicles are always wanting; and the males and sexually 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 by 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 winge is separate from vein 1st A (Fig. 500). The sexual forms have a beak. The alimentary canal is normal, producing a fluid excrement. The species infest only conifers AoELGiNiE AA. The wingless agamic females do not secrete a waxy flocculence, but in the genus Phylloxerina they excrete a waxy powder. The winged forms have three-jointed antennae, the second segment of which bears two sensoria. The wings when at rest are laid flat upon the abdomen. The free parts of veins Cu HOMOPTERA 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 PHYLLOXERINiE Sa^E+M+Cu + istA 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 Chermidas, formerly known as the Psyllidas. 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 number 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 strohilohius 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 {PtCeo) 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 fortn; 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. Second 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 gallicolce, 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 stem-mothers of the one-year cycle are hatched; and second, tiie 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 exsules, that is, exiles. Some writers term the first of this series of generations false stem-mothers {fundatrices spunce) 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 offspring of the third generation two types are recognized by Marchal ('13): first, nymphs which remain undeveloped for a time, the sistens 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 offspring are the sexual forms, this generation is known as the sexuparce. C. A GENERATION ON SPRUCE The completion of the second year of a two-year cycle. Fifth generation. — From eggs laid by the sexuparae 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 known. 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 pinifdlicB. — 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 {Pinus strobus) . 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 *Si.stens, Latin sislo, to stand; progrediens, Latin pro, forth, gradior, to go. 432 AN INTRODUCTION TO ENTOMOLOGY Fig. 502. — Gall of Adelges pinifolicB on spruce. protected by the remains of the body and closed wings of the dead insect. It has been determined that these plant- lice 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 Chermes abieticolens; but piniJoUcs 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 primary host and pine its secondary host. The green-winged adelges, Adelges able- tis. — This species causes the growth of pine- apple-shaped galls on several species of spruce (Fig. 503). It is a European species and its life-history has been the subject of m^uch 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 viridis). Dr. Patch Cog) has studied Adel- ges abietis 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 pine-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 P ,, c A, , 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 summer. Return migrants to the pine have not been observed; but there must be a generation of these, the parents of the wingless hibernating Fig. abietis. HOMOPTERA 433 generation, if, as stated, the pines are free from the pest during the summer. 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 foimd 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- loxerince; 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-histor>' 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 summer. They are termed the gallicolcB. The radicicoloB 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 3^ear 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 gallicolae. The migrants or sexuparce. — During the late simimer 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 swelhngs 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 hatched 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-inhabiting form: a, roots of Clinton vine showing 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 matiu-e lice; h, granulations of skin; i, tubercle; j, transverse folds at border of joints; k, simple eyes. (From Riley.) HOMOP TERA 437 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 Coccidae, 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 Fig- 5o8. —An aleyrodid are scale-like in form and often resemble somewhat certain species of the genus Lecanium of the family Coccidas. Except during the first stadiimi, the laryag 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 (oXeu/jciSijs), like flour. 438 AN INTRODUCTION TO ENTOMOLOGY thus the body is lifted away from the leaf and is perched upon an exquisite palisade 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 antennse 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 paronychium. 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 larvae during the first stadium are active, after which they remain quiescent. There are four larval 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 puparitmi, 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 HO MO PT ERA 439 from the caudal end of the body. The excrement is in the form of 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. — Asterochito7i vapor ariorum: 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 vapor ariorum. — 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 after 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, h), 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 440 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 strawberr^^ 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 e^^ state out of doors. The citrus white fly, Dialeurodes cUri. — This is a well-known pest in the orange-growing sections of our countr>% 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 wa^^s: 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 camellice), 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 forbesii. — Figure 509 represents this species, which is fairly common on maple, but rarely in sufficient nimibers to do serious injury. Family COCCID.E The Scale-Insects or Bark-Lice, Mealy-Bugs, and others The family Coccidse 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 Pig. 512. — Chionaspis furfura: 7, scales on pear, natural size; /o, 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 themaniifacture of candles, before the introduction of parafiin. 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 always greatly 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- 513-— Wing of Pseudococcus. (From Patch.) ^^^^ -g fu^^jghed 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 setce, the digitules (Fig. 514) ; these are tenent hairs ; some of the digi- tules arise from the tip of the ^^-"--i ^.""'X^ — —.^ d tarsus, and some from the claw. The caudal end of the ab- domen of the male usually bears a slender tubular pro- 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 serv^es 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 o£ 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. Fig. 514. — Leg of a female Lecanium: digitules. d, d. HOMOPTERA 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 development 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 possessed 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 bram 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 long and slender, and consist of from six to thirteen segments ; in some of the Margarodinas they are branched or fiabellate. The antennse 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 clypeus, _ -Mouth-parts of a ^^e labrum,and the mandibular and maxillary Swnted'arealn tafSj sclerites In cleared specimen, there can te the beak; B, the beak; /, seen withm this area a complicatea endo- labrum; 0, oesophagus; skeleton (Fig. 516, A). s, loop of mandibular and 'p^e labium (Fig. 516, B), which is com- Z^^. iSter" B*!monly termed the beak or rostrum consists jese.) of three segments m a few forms found m Fig. 516. 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 setas 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 labiimi. The crumena 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 setae 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 Coccidae there are to be found most re- markable variations in struc- 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. Th ese 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 araucaricz: r^^nz\ ring;^, anal-ring j^^ ^-^is place, only sufficient setae; /, anal lobe; as, anal seta. Be- u \i- 1 j. j ^ tween the bases of the anal-ring sets space can be taken to define there are openings of wax-glands. the more important Struc- HOMOPTERA 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 setae, the anal-ring setce (Fig. 517, ^)- 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 setcB. — Each anal lobe bears one or more prominent setse, the anal setce (Fig. 517, as). The anal plates. — In the subfamily Lecaniiuce, 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. 5 1 8, 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 Diaspidinse is given later. The spines and the setce. — The position and number of spines and of setce 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 Coccidae ('81, '82, '83) termed certain spine-like setse 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. Unfortimately different authors use quite different terms, Fig. 518.— A Leca7iium, enlarged : ap, 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 cerattibcB. — In the Diaspidina? 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 Diaspidinaj, bears a perforated knob. This invaginated cuticular tube is termed a ceratuba. The ceratuba) vary greatly in length and in shape ; in some the greater part of the tube is reduced to a fine thread, with a bulb-like inner end. A few ceratubas are represented in a diagram given later (Fig. 522). The openings of most ceratubas are flush with the body-wall, but some of them open through plates in the marginal fringe. The dif- Several types of openings of ferent types of ceratubas have re- ceived distinguishing names formed by combining a prefix with the word ceratubae. 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. 520.- cerores 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; />/, plate; .s, setae; f, 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 Diaspidinas (Fig. 52 1 , g) are termed genacerores. The features of 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, ceratubae opening through plates; e, linear ceratubae; /, /, /, 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, v). 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 different groups are distinguished as the median group {me so genacerores), the cephalo-lateral groups, one on each side (pregnacerores) , 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 ceratubas, and the types of ceratubas 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 (incisures) in the margin of the pygidium (Fig. 521, i). 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, ;P). The presence or absence of a thickening of the lateral margin of the pygidium cephalad of the region in which the lobes are situated, and resembling the lobes in structure (Fig. 523, m). The number 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 Chrysoniphalus tenebricosus, ventral aspect, with the paraphyses (pp) of the dorsal wall showing through: /, /, /, lobes; m, thickened margin; s, spine-like setse. The metamorphosis of coccids. — In this family the two sexes are indistinguishable during the first nymphal stadium. Both are fur- nished with legs, antennae, and functional mouth-parts. It is during 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 antennas when they assume the quiescent form ; and in some the mandibular and maxillary setffi are wanting in the adult. The number of n^nnphal 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 v^aries 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 Diaspidinse the formation of the scale begins either at the close of the first stadium or immediately after the first molt. With the molt at the beginning of the quiescent period the male loses its legs, antennae, and mandibular and maxillary setae. The setae are not replaced; and, consequently, the adult males can take no food. The legs and antennas 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 Coccidae 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- lian species, and has been subdued Fig. 524.- adults, -Icerya purchasi: females, and young on orange. 450 AN INTRODUCTION TO ENTOMOLOGY to a great extent by the introduction of an Australian lady-bug, Rodolia cardindlis. Subfamily COCCIN.E 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 Cactacea^. 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^ Fig. 525- larged. -Orthezia, greatly en- The Ensign Coccids ' Members of this subfamily occur not uncommonly on various weeds. They are remarkable for the sym- 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 born, 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 HOMOPTERA 451 Fig. 527. — Pseudococcus cilri. Fig. 526. — Pseudococcus longispinosus. novcie mealy-bugs 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 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 Riper sia 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 pig_ ^28.— Lecanium hesperidum, adult fe- of the body in many species. males, nattiral size. 452 ^A^ 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 countr}^ it lives out of doors. The adult female is nearly flat (Fig. 528), and is viviparous. HO MO PT ERA 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 hemisphoerica .- — 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 53 1 represents several adult females with their egg-sacs on a cane of grape. The maple-leaf pulvinaria, Pulvindria ac ertcola . — This .species is also found on maple. It differs from the preceding 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, Fig. 530. — Saissetia hemisphcerica: 3, adult females on orange, natural size; ja, adult female, enlarged. Fig. 531. — Pulvinaria vitis. 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 the\' 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 Qiiercus 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 Fie. 532. — Ceroplastes cirripedi- ^, t^. • ■,■ ■ ■, -, ■, formis. The Diaspidmae 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 Diaspidinc-e 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 nyinphal 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. HO MO PT ERA 455 In a few genera the female does not molt the second exuvise* ; the body shrinks away from it, and transforms within it. In such cases is it termed a puparhwi. Figure 535 represents the scale of Fiorhiia fiorhiicB; here the puparium can be seen through the trans- parent scale. Fig. 533. — Kermes sp. on Quercus agri folia : 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 Diaspidinse. 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 exuvicB 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 pinncBjorniis. — This scale-insect is well known in the orange-growing sections of this and of other JbmM. Fig. 534. — Chionaspis phiifolice: 2, scales on Pinus strobus, natural size, leaves stunted; 2a, leaves not stunted by coccids; 26, scale of female, usual form, enlarged; 2c, scale of female, wide form, enlarged; 2d, scaXe 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, zaand j6); 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 ustmlly 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 Mytilaspis citncola. Fig- 535-— ■'^*- orinia fiorinia. 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 uhni. — 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 pygidiimi. 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 Mytilaspis pomonim. The scurfy scale, Chiondspis furjura. — 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 , ic) . 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 piniJdlicB. — 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, 2b; 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 rosdyos) , 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 famil}- 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 larv£e (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 faima; these represent four genera, which can be separated as follows : A. Posterior coxas contiguous; eyes large, prominent. B. Third joint of the maxillary palpi shorter than the fotirth. . .Cicindela BB. Third joint of the maxillary palpi longer than the fourth Tetracha AA. Posterior coxae 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 Teiracha, 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 virghiica. These beetles are nocturnal, hiding dttring the day and hunting by night. Amblycheila. — The best-known representative of this genus is Amblycheila cylindrifdrmis , 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 da}'time. 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 rabbish, where they hide by day. At night they roam aboixt 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 TenebrionidaO , 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 antennas 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 antennas 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 larv^ 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 y'ip. 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, Calosoma 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. Calosoma sycophdnta, 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, Calosoma calidum, is easily recognized by the rows of reddish or copper-colored pits on the wing-covers (Fig. 560). The bombardier-beetles, Brachinus. — There are many species of beetles that have at the hind end of the body little sacs in which 558. 480 AN INTRODUCTION TO ENTOMOLOGY 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 very 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 which 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. Galenta jdnus is still another species that bears some 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 caligindsus, which is represented natural size in Figure 563. It is of a pitchy black color, and is one of the most common of 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 genns Diccelus 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. Fig. 561. 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 Pcecilus lucubldndus. 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 Amphizoa, which occur in California, Vancouver, and Alaska, clinging to logs or stones under the surface of streams. In these beetles the metasternimi is truncate behind, not reaching the abdomen, and has a very short antecoxal piece. The family OMOPHRONID.^ consists of a single genus, Omophron, 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 coxae 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 tibise 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 simmier, and contain filamentous algas and other aquatic plants. They swim poorly but crawl over the stems of aquatic plants. Little is known regardingthe feeding habits of the adults. Matheson ('12) found that several species feed on the contents of the cells of A''z/^//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 larvce 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 larvse of Peltodytes each of these spines bears a long, jointed filament, which is a tracheal gill. The larvae of this genus have no spiracles ; but the larvas of Haliplus possess both thoracic and Fig- 565. abdominal spiracles. The larvas of the Haliplidce feed on filamentous algce; 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-lilce form of the antennas. 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 nimiber of deep furrows (Fig 567), while others of the same species have them smooth. The diving-beetles abound in our streams and ponds, but they are more often fotmd 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 larvas 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 roimded, 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 commimicates 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 terminated 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 imdergoes its trans- formations. The pupa state lasts about three weeks in summer; but the larvas 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. The best 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 Cyhtster, Dyttscus, and allied genera. In Cyhister the little cups on the under side of the tarsal disks of the male are similar, and arranged in four rows. In Dyttscus and its allies the cups of the tarsal disks vary in size. Figure 569 represents a common species of Dyttscus. 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 diving-beetles which are of about the same size as the preceding, but which have the wing- covers marked with numerous very fine transverse strias; 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.E 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 found in large numbers, either swimming or resting motionless near together. They rarely dive, except when pursued; but are so agile that it is extremely difficult to catch them without a net. Many 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 by 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 larvse 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 rounded at the tip. In DineUtus 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 Fig. 574. — Ventral aspect of part of thorax and abdomen of Enchro- ma gigantea: ist A, first abdom- inal segment. 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 im- movably 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 larv£e vary greatly in form ; some are campodeiform, some are scarabeiform, and others are vermi- form ; in none are the legs more than 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 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 sweeping 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 antennas 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 antennee. 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 appear- ance when seen from below. They obtain the air by bringing the head to the surface of the water and pro- jecting the antennae, 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 secre- tion. 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 *Polyphaga: polyphagus, eating many kinds of food. Fig. 572. 486 AN INTRODUCTION TO ENTOMOLOGY 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 larvse 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 larvse resemble somewhat those of the Dytis- cidse; but the body is much more plump, 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 . 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 common species is Hydrophilus ohtusdtus; this measures about 1 5 mm. in length. Some of the smaller 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. Fig. 573- Family PLATYPSYLLID^ The Be aver -Parasite Only a single representative of this family is known; this is Platypsylla cdstoris, 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 Brathlnus, of which three species are described, two from the East and one from California. These beetles are somewhat elongate, with the outline COLEOPTERA 487 of the prothorax and of the elytra elliptical; they measure from 3.6 mm. to 5 mm. in length. The Calif ornian 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, Leptinus 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 bimible-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 Leptimllns vdlidus, found in Hudson Bay territory, and Leptinlllus aplodontice, 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 antenuce 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 Fig. 575. 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 SUpha. The burying-beetles, Necrophorus. — To this genus belong the larger members of the famil}^ The body is very stout, almost cylin- drical (Fig. 575). Our common species have a reddish spot on each 488 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 grotmd. This they will continue until the object is below the surface of the ground. 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 accounts 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 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 imder dead animals instead of for performing deeds requiring great strength. Silpha bituberosa, which is known as the 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 foimd upon the ground, under stones or other objects. COLEOPTERA 489 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 if 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 19) 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 larvcc 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. Staphylinus 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 scutellvim black, and a row of obscure, square, blackish spots along the middle of the abdomen. Staphylinus 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^E includes certain very small beetles, the larger ones not exceeding 3 mm. in length. They resemble rove- 490 AN INTRODUCTOIN TO ENTOMOLOGY beetles in the shortness of the wing-covers and in having the dorsal part of the abdominal segments entirely homy; but they differ from them in that the abdomen is not flexible, and in having fewer abdominal segments, there being onh' five or six on the ventral side. The species are chcstnut-bro^^^l, dull yellow, or piceous, and are usualh' slightly pubescent. The antenna) are usually eleven-jointed, rarely ten-jointed. The elytra and abdomen are convex and usually wider than the head and prothorax. These beetles are usually found under stones and bark, or flying in the twilight; a few species have been foimd 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 Pselaphida2 in the char- acters given above except that the antemiee 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 antennse, 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 ova fauna. The family SCAPHIDIIDvE, or shining fmigus-beetles, includes small, oval, very shining beetles, foimd in fungi, rotten wood, dead leaves, and beneath the bark of logs. The elytra are broadly truncate 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, Sphcsrites glahrdtus, 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 SPHvERIID^ 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 found 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 L y hundred described North American species. i« The family LYCID^ includes certain nH|\ beetles that were formerly classed in the w fire-fly family; but they differ from the Fig. 578. Lampyridse in having the middle coxas distant, and in that the elytra lack epi- pleuras. The elytra are usually furnished with several longitudinal ribs and a network of fine elevated lines. pjg^ ^^g 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 simimer 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 antennee. 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 AN 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 Lampyrida3 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 the prothorax, though rounded in front, does not cover the head, which is exposed. The antennas are usually pliunose or flabellate in the males. The females of some species, at least, are glow-worms, re- sembling the larvae in form, and are photogenic. Only twenty -three American species have been described ; most of these are foimd in California, Texas, and Arizona, but some occur in the East. Family CANTHARID^ The Soldier-Beetles and others The family Cantharidce includes those genera that were formerly included in the family Lampyridce as the subfamily Telephorinas. For the distinctive characters separating this from the allied families, see the table, page 473. The application of the name Cantharidce 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, Chauliognathus. These are very abundant in late summer and autumn on various flowers, but especially on 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- p-. gined soldier-beetle, C. margindtus. ig- 5 I- "Yhxs, 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 ground 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 i, the body and which are supposed to be scent organs for A" 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 locahties. The family is represented in our faima by more than three hundred species. The family CLERID.^, or the checkered beetles, includes a con- siderable number of predacious species which are found on flowers and on the tnmks 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 carnivo- rous, living under 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 by nearly two hundred species. Figure 584 represents one of our more common species, Trichodes nuttdlli. The family CORYNETID^ has recently been sep- arated from the Cleridse, which they closely resemble. In this family the fourth joint of the tarsi is atrophied; this character distinguishes these beetles from the Cleridas. About forty American species have been described. To this family belongs the red-legged ham-beetle, Necrdhia rufipes. This is a small steel-blue beetle with reddish legs; it measures from 3.5 mm. to 6 mm. in length. It is found 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 antennas. Only two species have been found in this country and these are rare. To this family belongs the ship- timber beetle, Lymexylon navdle, of northern Europe. The larva of this species was at one time a very serious pest in ship-yards, on account of i.tfs 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 ovi- position of the beetle was suggested by Linnaeus. The family MICROMALTHID^ includes a single species, Micromdlthtis 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 accotmt 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). Briefly, this author's observations indicate that eggs are produced by larva: as well as by the adult females; that there are seven or eight forms of larva? ; that the two sexes of adults are developed through two distinct lines of larv^a?; and that viviparous as well as oviparous pccdogenesis occurs in the life-cycle. The larv^ae 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 found under 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 found on plants, but some live on the ground near water. The larvae live for the most part in decaying wood. The family MORDELLID^ includes a large number jfO^ of small beetles which are easily recognized by their pe- /fZ-^ culiar form (Fig. 585). The body is arched, the head Fig. 58s. being bent down; 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 usually found on flowers ; the larv^ae live in rotten wood and in the pith of various plants, upon which they are su pposed to feed. Nearly one hundred fifty 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 very 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 fiabellate in the males, and frequently serrate in the females. The adult insects are foimd on flowers. The larvae that are known are parasites, some in the nests of wasps, and some on cockroaches. COLEOPTERA 495 Family MELOID^ The B lister-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 naiTOwer 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 knowTi as the Spanish-fly; but our Ameri- can species possess the same blistering property. The postembryonic development of those blister-beetles of which the complete life-history is known is a very remarkable one; for it has been found that in each of these cases there is a complicated hypei-metamorphosis. 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 lai-vee 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 triungulm, a term applied to the first instar of blister-beetle larvse. 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 trimigulins are very active. In the case of those that feed on the eggs of short -horned grasshoppers, they run over the ground 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 tritmgulin, 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 yoiuig. 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 triunj^nihns 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 yqty 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 scarabseid 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 scarabacoid inform; these two instars can be distinguished as the first scarabceoid /an;aandthe second scarabceoid larva respectively. The second scara- COLEOPTERA 497 bceoid 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 temied 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 larvag 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 Epicaiita. 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 larv«, so far as is known, are parasitic in the egg-pods of locusts (Melanoplus). In addition to Epicanta vittdta, discussed above, our more common 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 umcolor. 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. 588. 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 maxillae developed into a long sucking-tube, which is some- ig- 590- 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, Eiirystethus subopdcus, was found by Professor VanDyke on the seashore, in crevices of inter-tidal rocks. The faniily OTHNIID^ 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^E includes less than a score of North American species. Some of these live iinder bark, and are said to prey on bark -beetles ; others are found under stones. Seetable, 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 bod}^ is elongate; the head and prothorax are narrower than the wing- covers; the antennas are serrate or subpectinate in the females and usually flabellate in the males (Fig. 591). The beetles are found about decaying trees, beneath the bark of which the larvas 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^ 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 coxae are not laminated, and the trochanters of the middle and posterior legs are very long. The family CEBRIONID^ includes a few species found in the South. They were formerly included in the Elateridas; but they differ from that family in that the abdomen consists of six or more ventral segments. This family differs 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 famity, 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 foimd on cedars. The antennse are serrate in the females, frequently flabellate in the males. The anterior and middle coxae 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 coiuitry 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 imtil it succeeds in striking on its feet, and then it runs off. Pig, cq2. 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 imiform brownish color; some are black or grayish, and some are conspicuously spotted 500 AN INTRODUCTION TO ENTOMOLOGY (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 ■^^ \BV/' ventral side; and the hind coxsc are each furnished 'Jk y3lK ^^^^^ ^ groove for the reception of the femur. -^wV /HPlA 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 Fig- 59 3 -—A family, is due to two facts: first, the prostemum is Aeolus dorsalis Prolonged into a process which extends into a groove natural size and ^^ ^^^ mesostemum; 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 larvce live in various situations; most of them are phytophagous, but some species The larvaj are long, narrow, Fig_ ^g_^_ 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. 595. 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 gromid, 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 ground, 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 himdred 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 larvae 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 Corn- stock and Slin- gerland ('91) in an effort 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 grotmd; 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 fotmd that if the cells containing pupae 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 pups or yoimg adults would be broken. The eyed el- ater, Alaus ocu- latus .- 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 AN INTRODUCTION TO ENTOMOLOGY insect varies greatly in size, some individuals being not more than half as large as others. The larvae 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 EUCNEMIDiE was formerly regarded as a subfamily of the Elateridee. It differs from the Elateridas, as now restricted, in having the labrum concealed, and in that the antennae 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 Buprestida^, 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 prostemum pro- longed behind into a process, which is received in the mesostemiim. They differ from the elaters in having the prothorax firmly joined to the mesothorax, and the front coxal cavities closed behind by the meso- sterniun instead of by the prostemum; and from the buprestids in having the ventral abdominal segments all free. The adult beetles are found on flowers. Family BUPRESTIDS The Metallic Wood-Borers 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 antennse 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 very 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 very 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 Fig. 598. Fig- 599- Fig. 600. These "flat-headed" larvae 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 larv^ce 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 by nearly three hundred species; among the more important of those that infest cultivated plants are the following. The Virginian buprestid, Chalcophora virgmica. — 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 larvse bore in the wood of pine, and are often very injurious. Diccrca divaricdta is 1 8 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). The lar- va bores in peach, cherry, beech, and maple. The flat-headed apple-tree borer, Chrysobothris 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 larvas at first bore into the bark and sap-wood, and later into the solid wood. The transforma- tions are completed in one 3'ear. 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 ruficollis. — 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 larv^a bores in the stems of raspberry and blackberr>^ causing a large swelling, known as the 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 Fig, 601. 504 AN INTRODUCTION TO ENTOMOLOGY Fig. 602. California. This genus was formerly included in the following family ; but it differs from the Dryopida; 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 Paminag of the old family Pamidae, in which were included the preceding family and the following family. The Dryopidce differ from the Psephenidae in that the members of it have only five ventral abdominal seg- ments, and from the Elinid^ in that in the Dr^^opidae the anterior coxas 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. 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 Dryopidae. Fig. 603. 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 greatly 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 foimd in our faima. 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 browm 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 Georfssus, 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 DASCILLID^ includes certain beetles that live on plants, usually near water. The legs are short, with slender tibias; The tarsi are five-jointed; the anterior coxas bear a distinct trochan- tin ; the posterior coxse 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 DascUlus cervinus 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 Dascyllidas. In the Eucinetidse the anterior coxce do not bear a trochantin; the posterior coxae 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 fatma; seven of these belong to the genus Eucineius. The larva of a European species of Eucinetus lives on fimgoid matter on wood. The family HELODID.^ includes small beetles, less than 6 mm. in length, foimd 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 larvas 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 family CHELONARIID^ is represented in our fauna by a single species, Chelonarium lecontei, found in Florida. See table, page 471, for distinguishing characters. Family DERMESTID^ The Derniestids 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 Dermestidee, 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 larddrius.— 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 /^m^ band of black spots, three on each wing-cover (Fig. 605). Vwl 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^g^j^ jg scored. 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 scrophuldrice. — This is a well-known household pest. It is an introduced European insect, which was first recognized as a serious pest 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 margin 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 aboimds 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 museiim pests, Anthrenus verhdsci and Anthrenus museorum. — 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 larvae 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 ^A^ 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 very 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. Nearly one hundred species have been found in this country. The family NOSODENDRID^ includes two species of Noso- dendron, one found in the East and one in California. They were formerly included in the Byrrhidas, 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 coxce. 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 five-jointed, with the fourth segment very small; they are more or less dilated; the posterior coxae are flat, not sulcate; the anterior cox£e 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 ffrom North America. One of the most common species is Glischrochlus (I ps) fasctdtus (Fig. 606). This is a shining black species, with two conspicuous, interrupted, reddish bands across the wing-covers, p. gQg The family RHIZOPH AGID^ includes only the genus 7?/jz2(5^AagM5, 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 MONOTOMID^ 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 CUCUJID^ The Cucujids The insects of this family are very flat 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 clavipes (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 tibiag and tarsi dark. The most important member of this family is the com silvanus, Silvdnus 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 feed 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. 607. Fig. 608. ^ Fig. 609. length. Some of our more common species are conspicuously marked with shining black and red. To the genus Megaloddchne 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. Jascidta is about 12 mm. in length. The genus Languria includes long, narrow species, which resemble click-beetles in form. Figure 609 represents Languria mozdrdu 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 larvae are destroyed whenever clover is cut at the proper time. The larvffi o£ some species of this family feed on fungi. The familyDERODONTID^ 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 Byturus, of which there are five species in our fauna. This genus was formerly included in the Dermestidas, 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 umcolor. — 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 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. COLEOPTERA 511 The family MURMIDIID^ includes five introduced species ■representing five genera. They are very small, oval beetles, differing trom the Colydiidge in having the antennas inserted on the front, and in having the anterior coxae inclosed behind by the metastemum. 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 Endomychidas 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 antennas are about half as long as the body ; the prothorax is nearly square, and usually has a wide, 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 CompositcC. More than one hundred North American species have been described. Family COCCINELLID^ The Lady-Bugs 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 yellow spots. The larvce occur running about on foliage ; they are often spotted ^ith 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 lavYse 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 512 AN INTRODUCTION TO ENTOMOLOGY Fig. 613. has been incorrectly known as Veddlia cardindlis, has proved of very great value in subduing the cottony -cushion scale {Icerya purckasi). This lady-bug was introduced from Australia. The larva of BracJiyacantha 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 wing-cover. It frequently passes the winter in our dwellings, and is found on the walls and windows in early spring. Under such circimistances 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 scutellum (Fig. 613). Although almost all of the Coccinellidae are predacious, there are some that are herbivorous. One of these is found in the East. This is the squash -ladybird, Epildchna horedlis. 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- ish, with large, 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- lady bug, Epi- ldchna corriipta, which is found in the South and Southwest, is an- other herbivo- rous species. The family ALLECULI- D^, 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- Fig. 614. 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 illustrate 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 pupee are used for bird-food and are grown in quantity by bird-supply houses. The forked fungus-beetle, Boletotherus cornutus, is common in the northeastern United States and in Canada about the large toadstools (Polyporus) 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 Eleodes 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 climisily, and carrying the hind end of the body as high as possible. The most common species are large, smooth, club-shaped beetles (Fig. 617), and are commonly known as pmacate-hugs. These beetles and those belonging to several closely allied genera lack hind wings. Fig. 617. 514 AN INTRODUCTION TO ENTOMOLOGY The family LAGRIID^^, 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 A rthromdcra cenea (Fig. 6i8) ; this species measures from 9.1^ 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 antenna; are received in grooves on the under side of the prothorax. Except one species found in Florida, our species belong to the genus Hyporkdgits. 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. P^w//?^ o6/zg'Ma/a is distinguished by having the scutellimi clothed with rust-red hairs (Fig. 619). Penthe pimelia closely resembles this species, except that the scutellum is black. The family PTINID^ has been restricted recently to one of the subfamilies of the old family Ptinidag, which included, in addition to the insects now retained in it, those classed in the three following families. In the Ptinidas, as now restricted, the antennas 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 speciesare retained in this family. They are all small beetles and some of them are household pests, infesting stored provisions, clothing, and books. The best-known species is Piinusfur. 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 ANOBIID^, or the death-watch family, includes a large part of the old family Ptinidas, there being more than two hundred species in our fauna. In this family the antenuce 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 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 ,v^\\\c\\ infests dried tobacco and destroys cigarettes and cigars by boring holes through them. To this family belongs the death-watch, Xestohium rufovillosum, which bores in the timbers of buildings and makes a ticking sound by strilving its head or jaws against the walls of its burrows. This sound heard in the night by 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 cylindrical burrows or beneath the bark. Sometimes they infest timbers to such an extent that the wood is largely reduced to powder, hence the common name, powder-post beetles. The adult of one species, AmpJncerus hicauddtus, 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 nimiber 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^E 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 CISIDiE 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 SCARAB^ID^ The Scarabcsids 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 ENTOMOLOG} these insects is the lamellate form of the club of the antennae, 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 Trogidas, which has recently been separated from this family, the antennae are lamellate. The two families can be separated by the fact that in the Scarabaeidae the epimera of the mesothorax extend to the coxas, while in the Trogidas 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 tumble-bugs remove the food for their larvas 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 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 s}Ttnbolism. 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 timible-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 IcBvis is our most common species (Fig. 620). In Copris and Phancsiis the middle and posterior tibias are dilated at the ex- tremity. In Phanceus the fore tarsi are wanting, and the others are not furnished with claws ; the species are brilliantly colored. Phanceus 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 numbers 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. III. The earth-boring dung-beetles.- — -These beetles are of a rounded convex form (Fig. 621). They differ from all other dung-beetles in having the antennae eleven-jointed, and in the labrum and mandibles being visible from above. This is a small group, only p. ^ twenty-two North American species having been de- scribed. The popular name is derived from that of the typical genus, GeotrUpes, which signifies earth-boring. Those species the habits of which are known, live in excrement. The females bore 518 AN INTRODUCTION TO ENTOMOLOGY Fig. 622. 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 tumble-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 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-bugs. — 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 summer. 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 polished 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 injury 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 under the name "white-grubs." They are often great Fig. 623. COLEOPTERA 619 Fig. 624. 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 inethod 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, Macrodactylus sub- 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-like hairs, which give it a yellow color; the legs are long, slender, and of a pale rod color. These beetles appear in early stmimer, and often do great injury to roses and other flowers, 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 group belong the most beautiful beetles known, many appearing as if made of burnished gold or silver, or other metal. The goldsmith-beetle, Cotdlpa 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- 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 i^Tape. The larva feeds upon decaying roots and sttunps of various trees. The Japanese beetle, PopUlia japonica. — This is a very serious pest which feeds in the adult state on the foliage of man^v-- cultivated Fig. 625. 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 larvee 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- tes 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, Dyndstes grdntii, in which the large horn on the thorax is twice as long as in D. tityrus. In the West Indies there occurs a species, Dyndstes 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 latter type. The sugar-cane beetle, Euciheola rugiceps . — This beetle is a serious pest in the cane-fields of Louisiana, and it sometimes injures com. 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 2 5 mm. in length. It is purplish black, and the wing-covers are rough- ened with irregular, coarsely punctured striae. 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- suming 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 More than one hundred species Fig. 627. — The sugar-cane beetle. unnecessary 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 mda. — 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, black spots (Fig. 629). It is one of the first insects to appear in the spring. It flies near the surface ot the ground with a loud himiming sound, like that of a bumble-bee, for which it is often mistaken. During the summer months it is not seen ; Fig. 628. 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 corn 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 nttida. — 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 Fie 62Q °^ ^^^ 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 larvae are also often troublesome 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 niimbers 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 scarabaeids by the fact that the epimera of the mesothorax do not extend to the coxas as they do in the Scarabaeidae. The members of this family are oblong, con vex. 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 mediimi 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 Family LUCANID^ 523 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 antennae, which is composed of flattened plates ; but these plates are not capable of close appo- sition, as in the antennas 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 stimips. 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 biiishes 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 larvae 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 dania. — The most common of our stag-beetles is this species (Fig. 631). It flies by night with a loud buzzing sound, and is often 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 figured here is a male; in the female the mandibles are shorter. The giant stag-beetle, Lucdnus elaphus, is a large species found in the South. It measures from 35 inm. 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- tudinal strife and the teeth on the outside of the fore tibiffi much smaller (Fig. 632). Several species of stag-beetles that are much smaller than Dorcus are found in this country. Fk Fig. 632. 524 AN INTRODUCTION TO ENTOMOLOGY Family PASSALID^ The members of this family resemble the stag-beetles in the form of the antennae, 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, Passalus 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 larv^a 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 8g. The beetles of this genus are common through- out the tropics of both hemispheres. According to the observations of Ohaus, which have been ^33- 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 larv£e, 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 Ceranihycids 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 antennae are long, often ABC Fig. 634. — Tarsi of Phytophaga: A, typical; B, Spondylis; C, Parandra. 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 nmners; 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 larvae 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 p. ^ 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 Prionin^e AA. Prothorax not margined. B. Front tibiae not grooved ; palpi never acute at tip. p. 526 . CerambyciN/E BB. Front tibiae obUquely grooved on the inner side; palpi with the last segment cylindrical and pointed, p. 528 Lamiin^ Subfamily PRIONIN^E 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-homed beetles. — ^The beetles of the genus Pa- mwiira exhibit some strikingdifferences from the more typical ceramby- cids, and were formerly placed in a separate family, the Spondylidce; 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 ^A^ 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 Pardndra hriinnea (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 laticollis. — 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 antennas 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 imhricornis, is very similar to the preceding species but can be distinguished at a glance by the form of the antennse. In the antennae of the male the number 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 briinneus, is also a common spe- cies. The body is long, narrow, and some- what flattened ; it measures from 2 5 mm. 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. 638. Subfamily CERAMBYCIN^ The Typical Ceranibycids 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, Glycobius speciosus. — This is a handsome insect, p. marked with black and yellow, as indicated ^^" ^'^' in Figure 641. It lays its eggs in midsimi- 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- hmcB. — 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 autimm 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 larvae 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. 642. Fig. 641. 528 AN INTRODUCTION TO ENTOMOLOGY The painted hickory-borer, Cyllene caryce. — 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 autumn. 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, Hypermdlliis villosus. — The work of this insect is much more likely to attract attention than -the insect itself. Fre- quently, in the autimm, 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 lan^a 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 autumn 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 autumn and burning them before the beetles have escaped. Subfamily LAMIIN^E The Lamiids As in the preceding subfamily, the prothorax is rounded with these beetles; but the lamiids are distinguished by hav- ing the fore tibia? 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- chanius notdtus. — This beautiful brown and gray beetle is about 30 mm. long, with antennas 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 flat-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 Fig- 644- 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 larvee throw out at the entrances of their burrows. The two-spotted oberea, Oberea bimaculdta, 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 about 12 mm. in length and of a deep black color, except the protho- rax, which is yellow. There are usu- ally two or three black spots on the pronotum, but frequently these are Fig. 645. Fig. 646. wanting. By cutting and burning all the canes after the crop has been picked, the borers in them can be 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. tetraophthdlniMS . In this species there are four black spots on each wing-cover, and the antennae are black and not ringed with a lighter color. The larva bores in the roots and the lower parts of the stems of milkweeds. I 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 larvae and adults. They are usually short-bodied, and more or less oval in outline; the antennas 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 Dondcia, 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 antennae, 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 larvas feed. Many of the larvffi 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 antennse (Fig. 647). They measure from 6 mm. to 1 2 mm. in length, and are of a metallic color — 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 larvos 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 larv^ 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 pupa?. 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 larv« hatching from such eggs will not have a chance to mature. The grape root-worm, Fidia 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 larvae drop to the ground and burrow down to the roots, which they destroy, causing the death of the vine. Most of the larvas 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, Leptinotdrsa 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 (Solamim 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 ot 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 itwasmore 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 larvas and adult beetles feed on the foliage of the potato. The larvse 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 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 (Asdepias) . 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 .vittataihsiS two black stripes on each wing-cover. The adult feeds on the leaves of cucumber, squash, and melon; and the larva, which is a slender, worm-like creature, bores in the stems and roots of the same plants. The twelve-spotted diabrotica, D. duodecimpunctdta, and Diabrotica sdror, agree in having six black spots on each wing- cover. The former is very 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 com 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 com 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 prune 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 flea-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 destroyed with kerosene emulsion. COLEOPTE RA 533 The cucumber flea-beetle, Epitrix cucumeris, is a common pest of melon and cucumber vines; it also attacks the leaves of potatoes, raspberry, turnip, cabbage, and other plants. This is a minute black spe- cies, meas- uring less p. g than 2 mm. -t^^g- ^53- 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 antennae 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 larvae on the roots of the infested plants. The grape fiea-beetle, Haltica 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 vine}'ards, 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 larvss feed externally upon the leaves and bear a parasol composed of their excrement; Fig. 652. 534 AN INTRODUCTION TO ENTOMOLOGY Fig. 655. Other species are leaf-miners. Baliosus rubra is a good representative of this group (Fig. 654). It varies in length from 3 mm. to 5 mm. It is of a reddish color, with the elevated portions of the elytra more or less spotted with black. The larva mines in the leaves of apple, forming a blotch-mine; the transformations are undergone within the mine. We have also found this species mining the leaves of basswood in great numbers. 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, morning-glory, 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 melted gold when one is happy ! Unfortunately 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 very 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, Physondta unipunctdta. — 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 five 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 Mnipunctata. We have found the larvae abun- dant in July on the same plant with the adults. The milkweed-tortoise, Chelymorpha casstdea, 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 {Asclepias) and various other plants. COLEOPTERA 535 Family MYLABRID^ The Pea-Weevil Family These are small beetles, the larvae of which live in the seeds of leguminous 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 eighty-one belong to the genus Mylahris. The pea-weevil, Mylahris pisonim. — "Buggy peas" are /^Hf^ t M' well known in most sections of our country; but just how 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 larvce hatch pjg 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, Mylahris ohtectus. — This species resembles the preceding quite closely; but it is a little smaller (Fig. 656), and lacks the whitemarkings 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 two *Rhynchophora: rhynchos (New Latin), snout; phoros {(p6po%), bearing. 536 AN INTRODUCTION TO ENTOMOLOGY families, the bark-beetles and timber-beetles, in which the beak is either wanting or extremely short and broad. The most distinctive features characterizing this series of families are the following: the suppression of the gula, the gular sutures being confluent (Fig. 657, gs); the absence of sutures between the prostemimi and the epistema and epimera; the meeting of the epimera of the pro- thorax on the middle line behind the prostemum (Fig. 657, em)\ and the palpi being usually short and rigid. A volume entitled "Rhynchophora or Weevils of North Eastern America" was published by W. S. BlatchleyandC. W. Lengin 19 16. This work includes descriptions of the then known species found in this region, with analytical keys, and many figures. Family BRENTID^ The Primitive Weevils Fig- 657- This family is confined chiefly to tropical re- gions; only six species are found in the United States, and but one of these in the North. The northern brentid, EUpsalis minUta. — In the female the head is prolonged into a slender snout ; but in the male the snout is broad and flat, and is armed with a pair of powerful jaws (Fig. 658). These are weapons of offence, for the males fight desperately for their mates; and too, the males are generally larger than the females. In these respects these insects resemble the stag-beetles, the males of which also fight for their mates. The northern brentid is found beneath the bark of recently felled or dying oak, poplar, and beech trees, in the solid wood of which the larvae bore; and is widely distributed over the United States and Canada. Family PLATYSTOMID^* The Fungus Weevils This fp,mily includes a small number of snout-beetles in which the beak is short and broad, and the labrum is present; the antennas are not elbowed, and the terminal segments rarely form a compact club; the palpi are flexible; and the prothorax bears a transverse elevated ridge at or near its base. The larvas of many species infest woody fungi, others breed in the smut of corn and wheat, and still others bore in dead wood. The *This family is the Anthribidas of many authors. COLEOPTERA 537 larvas of one cosmopolitan species, known as the coffee-bean weevil, Arceocerus fasciculdtus, attack seeds of various plants. Sixty-two species of this family are known to occur in America irorth of Mexico. Family BELID^ The New York Weevil The family Belidas is represented in our fauna by a single species, the New York weevil, Ithycerus novehoracensis . This is a large species, measuring from 1 2 mm. to 1 8 mm. in length. It is black, rather sparse- ly clothed with a mixture of ash-gray and pale brown prostrate hairs which give it a black-spotted appearance. The beak is short and broad. The mandibles are prominent, not very stout, and emarginate at the tip, with an inferior cusp. The antennae are not elbowed; the first segment is longer than the second; and the terminal segments form a small, oval club. This species breeds in the twigs and tender branches of oak, hick- ory, and possibly other forest trees. The adult beetles appear in early spring, and sometimes do much damage to fruit-trees by eating into buds, and gnawing the tender bark on new growth. They can be caught by jarring them on to sheets or by the use of a plimi-curculio catcher. Family CURCULIONIDiE The Curculios or Typical Snout-Beetles The Curculionidee is a very large family; it is represented in America north of Mexico by more than eighteen hundred species; to it belong four-fifths of all our Rhynchophora. This family includes the typical snout -beetles, the head being prolonged into a well-defined beak, which is usually long and curved downward. The family Curculionidse is divided into thirteen subfamilies; but several of these are very small. The seven subfamilies mentioned below will serve to illustrate the more important variations in structure and in habits, and they include the more important species from an economic standpoint. The subfamily Rhinomacerin^, or pine-flower snout-beetles, in- cludes a small number of snout-beetles in which the elytra have no fold on the lower surface near the outer edge, and in which the labrum is distinct. The head is prominent, not deflexed; the snout is as long as the prothorax, rather flat, narrowest about the middle, wider at base and tip; the elytra are rounded at the tip, and entirely cover the abdomen. These beetles infest the staminate flowers of coniferous trees, in which the eggs are laid. Six species are found in our fauna. The subfamily Rhynchitin^, or toothed-nose snout-beetles, in- cludes snout-beetles in which the elytral fold is feeble, the labrum is wanting, and the mandibles are toothed on both the outer and the inner side. The mandibles can be spread widely, and when closed the outer tooth at the end of each projects forward so that two small, acute teeth seem to project from the mouth. 538 AN INTRODUCTION TO ENTOMOLOGY The most common member of the family is Rhynchltes bicolor (Fig. 659). This is red above except the snout, and black below; the body, not including the snout, is about 6 mm. long, ^^^ the snout is half that length. The adults are often abun- .^^^^^ dant on wild roses, and less frequently on cultivated roses. ' ' The larvae infest the hips of roses. Fig- 659. The subfamily Attelabin^, or leaf-rollmg weevils, is composed of beetles which have neither an elytral fold nor a labrum, and in which the mandibles are flat, pincer-shaped.and toothed on the inner side. The elytra 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 th.egenns,AUelahus. 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 groimd 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 b}^ a single species, the sweet-potato root-borer, Cylas fonnicd- 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 Brentidae. 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 the more important species are the following. The imbricated snout-beetle, Epiccerus imbri- cdtus, is usually a dull, silvery^ white beetle with brown markings; but the species is quite variable in color. It is represented, somewhat enlarged, in Figure 661. It is omnivorous, gnawing holes in va- 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 fiilleri. — This is an oval, black snout-beetle, lightly covered with dark brown scales, and about 6 mm. 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, Brachyrhlnus 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 larvae 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 sulcdius. — 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 larvee destroy the roots of strawberries; and both larvae 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 antennae 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 larvae 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 Baldninus. Figure 662 represents Balaninus rectus resting on an acorn ; the specimen figured, when found, had her snout inserted in the acorn up to the antenna. Of the closely allied species Balaninus naslcus breeds in hickory-nuts, and Balaninus probosctdeus in chestnuts. The following are some of the more important Fig. 60^. pests belonging to this subfamily: The plimi-curculio, Conotrachelus nenuphar. — This is tiie 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 AN 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 larvae 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 larvag 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 quadrigihhus , infests the fruit of apple, often in company with the plum-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, blackberry, 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- ig- 3- Yelops 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 larvee. 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. Very 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 larvse of the larger species feed upon the roots and bore in the stems of plants, especially grass and com, while those of the smaller species infest grains and seeds. Most of our larger species belong to the germs Sphenoph- orus; one of these is represented in Figure 664. These are of mediiun or rather large size, and are often marked in a very characteristic manner by longitudinal elevated bands of darker color; frequently, when collected, they are covered with a coat of clay. They are commonly known as the bill-bugs. One species, Sphenophorus maidis, is an ^^^- ^^4- important pest of corn 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. COLEOPTERA 541 Among the smaller members of this subfamily are two exceedingly- important pests of stored grains; these are the granary-weevil, Caldndra grandria, and the rice-weevil, Caldndra oryzaz. 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 South and the Far West. Formerly this group was classed as a subfamily of the ScolytidcC. It is distinguished from the Scolytidag 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 liimber useless. The eggs are de- posited in the galleries; and the lan^as feed on a fimgus, 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 ; Fig. 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- phlcens liminaris. The Engraver-Beetles and the Ambrosia-Beetles The members of the family Scolytid^ 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 antennae are elbowed or bent in the mid- dle, and are clubbed at the tip; the tibias 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 obscurus. ■ — ^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 summer after seeding. In these regions it is the common practice to seed with clover and timothy mixed; after the clover disappears the field becomes a timothy meadow. No practical method of control of this pest has been found. Fig, 667. — Work of clo- 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 larvse 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 rugulosus. — This species in- fests apple, quince, pliun, 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 cherry. 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 Scolytidas 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 mali 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 was developed. The excrement of the larvas 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. Themouth 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 larvse 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- metam orphosis . The order Strepsiptera comprises insects that were formerly classed as a family of the Coleoptera, the Stylopidas; 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 stadiiim the young larvae 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 stylopids 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 cylindrical body, it is the head end of the pupariimi of a male. Adult male stylopids can be bred by keeping alive stylo- pized insects containing male pupse. Fig. 670. — Abdo- men of stylo- pized insect: s, s, stylopids. *Strepsiptera : strepsis (ffrpexpis), a turning; pteron (irrepSv), a wing. (546) STREPSIPTERA 547 Fig. 671. — Opthalmochlus diiryi. (After Pierce.) Figure 671 will serve to illustrate the appearance of an adult male stylopid. The more striking features are the flabellate antennae; 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-s h a p e d appendages; and the large size of the hind wings. The an- tennas 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 flabel- 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 AcroscMsmus bruesi (Fig. 672,0) the mandibles are slender, curved, and scimitar- like; beneath the mandibles are the maxillse; these are two-jointed; the second segment is believed to be the reduced palpus. In Pento- zocera australensis (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 (Mengeid^), and furnished with two claws; Fig. 672. — Mouth-parts of male stylopids: a, Acros- cMsmus bruesi. (After Pierce.) b, Pentozocera austral- 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 number 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 •jonsolidated 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 larvae 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 iriun- 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 triim- 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 hrood 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 lar/a or a n>Tnph 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 STREP SIPTERA 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 triungulinids 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 nymph 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 scarabcci- 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 lar\^al 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 headand 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 pupariiun, 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) lists ninety-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 mouth-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,^,5^7); and on each side of the submentum 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, maxillas; 0, ocelli; sm, submentum; st, stipes. (After JMiyake.) 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 labium 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 antennae 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 (yu^/coj), length; pteron (irTepdv), 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 very 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 ^L_^, I St A Fig. 676. — Wings of Pa?iorpa. 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 larvas 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 H^-menoptera. This order is represented in our fauna by 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 Pan6rpodes 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 ocelH; 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 "^^^^Xl ' Fig. 678.— Pan- orpa, female. Fig. 679. — Abdomen of Panorpa rufescens. last two segments of tarsus of Bittacus, ap- posed; c, last three seg- ments of tarsus of Bittacus. part of a scorpion, and suggested the common noxne scor- 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. MECOPTERA 553 The females lay their eggs in crevices in the earth. The larvs 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. 68 1 ) ; the larvee 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 Ale- coptera, our species measuring from 2.5 mm. to 5 mm. in 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 Fig. 682. — Merope tuber, slightly- enlarged. (Photographed by J. G. Needham.) Fig. 68 1. -Larva of Panorpa rufes- cens, first instar. (After Felt.) 554 AN INTRODUCTION TO ENTOMOLOGY Panorpa; and, like the scorpion-flics, 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 capttire 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, h, 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. Apterohlttacus . — This genus includes a single known species, Apterobittacus 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-Flies The members of this order have Jour wings; these are mem.branous 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 of 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 specialized 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 Leptoceridas and some Hydropsychidas. 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 {6pl^, rpTx^s), the hair; pteron {irrepdv), a wing. (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 AI3 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 antennae are setaceous, and frequently several times as long as the bod}'; the compound eyes are usually 5a 5£2 Ri_R. 2d A isl A Cm2 ^«i Fig. 685. — Wings of Rhyacophila fuscula. small and with small facets; the ocelli are either present or absent; when present they are three in number; the mandibles are mere tubercles at the base of the labnmi ; 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 tibice and tarsi are often furnished with black or brown, some- times yellow, spine-like setas. 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-fliesra, Phryganea interrupta; b, Tricenodes sp. (From Lloyd.) distance before the apex ; these are larger than the spine-like sets and are usually differently colored. The ntimber of these spurs is much used in classification. The eggs of caddice-fiies are round or slightly oval in form. They are laid either in water or upon objects above water from which the larvcB 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 cadd ice-flies, except some of the Rhyacophilidas, 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 larvse of most caddice-flies, the caddice-worms, are somewhat caterpillar-like (cruciform) 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 larvas do not build port- able cases. In the eruciform larvae the head is bent down, as in a caterpillar; in the campodeiform larvse 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- himips," 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 larvce 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 wherever 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; some 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 larvae, the pupee being as truly aquatic as the larvee. 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 merely 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 pupae are of the exarate type, that is, the wings and legs are free (Fig. 688). Some pupas 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-fiies 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 larvae 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. -A, pupa Phryganea pi- losa. (After Pic- tet.) B, mandi- bles of pupa of Molanna angiis'.a- 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; antennae 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; antennse 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 tibise with two or three spurs, middle tibise 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 tibise 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 CALAMOCERATIDiE 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 Ri and R2 confluent apically or connected by an apical cross-vein in the fore wing. Females, p. 567..0dontocerid^ HH. Veins Ri and R2 not connected apically. p. 569 SERICOSTOMATIDiE 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^ DD, Ocelli wanting. E. Front tih'iss. with three spurs, p. 563 Polycentropid^ EE. Spurs of front tibi^ fewer than three. 560 AN INTRODUCTION TO ENTOMOLOGY F. Anterior branch of the radial sector in the fore wings forked. p. 562 HYDROPSYCHIDyE FF. Anterior branch of the radial sector simple, p. 564 PSYCHOMYIDiE BB. Maxillary palpi with fewer than five joints. C. Maxillary palpi with four joints; ocelli present. Males, p. 564... PHRYGANEIDiE 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/E DD. Maxillary palpi hairy or scaly, appressed against and often covering the face; fore tibiae with two spurs. Males, p. 569. . SERicosTOMAXiDiE 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 RHYACOPHILIDiE 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. Fronslong, extending back to the caudal margin of the head. p. 563 POLYCENTROPID^ FF. Frons normal, p. 564 Psychomyid^ 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^ 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 PHRYGANEIDyE 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 Sericostomatid^ GG. p. 566 MOLANIDiE Family RHYACOPHILID^ The larvae 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 Rhyacophilinae, TRICHOPTERA 561 do not build cases, but crawl about naked beneath stones seeking their food ; they feed on small larvae and filamentous algffi. The larva of our most common species, Rhyacophila fuscula, 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- r^. ^ , , , „, ,.,,.,,. tic of the "Rhvaronhilirl3--nn1v ^^^' 6^9-— A larva of Rhyacophila building tic 01 tne xnyacopnnia^e.only ^^^ ^^^^-^ chamber, exposed by lifting off atewothercaddice-wormsspm the stone beneath which it was. (From cocoons. Needham and Lloyd.) The members of the subfamily Glossosmatinae 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; b, ventral view. (After Lloyd.) Family HYDROPTILID^ The Micro-Caddice-Flies This family is composed of minute caddice-fiies, which resemble tineid moths in appearance. The larvas are found in both quiet water and rapid streams, and often occur in very great nimibers. They build cases which differ in form in the different species, but are usually flat; 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 confusa : i , 2, case. Lloyd.) 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 confilsa, 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 family Hydropsychid^ of the older authors ^'!:„&i"r{'^^lar^r^^^^ ^^^^ divided into four families by Ulmer,— (After Hydropsychidffi, Philopotamid^, Polycentropid^e, and Psychomyidas. 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 larvas 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 \^i ul Ilxdropsyche. TRICHOPTERA 563 the net is built up from a horizontal surface its sides are supported by bits of wood. Algae, larvee, 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 larv£e 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, Chimdrrha aterrima, has been published (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, and a smaller opening at the hind end. The nets are fastened in 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 entangled in it. The full-grown larva covers itself with an inegular dome of pebbles in which to transform, and spins about its body a delicate cocoon. Fig. 693. — Nets of Chimarrha aterri- ma, natural size. (From Noyes.) Family POLYCENTROPID^ The larvaj 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 Polyceniropus live in still or slowly- flowing water with sandy or muck bottoms. These larvae 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 lan^ al 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 larvae 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 form^ are abundant in the stomach contents." (Noyes.) Fig. 694. — Dwelling of Polyceniropus sp. Noyes.) (From Family PSYCHOMYID^ The lavvse 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 larvae 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 larvae 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 a which the following brief notes are compiled. This author discusses three species of Neuronia and three species of Phryganea. Neurdnia. — The larvae are found in slowly moving streams of spring water; rarely they 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 larvae 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 larvae 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 larvae 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 larvae often fail to cut the leaf-fragments used in the construction of the case into the rectangular form seen in the cases of old larvae; but the bases of the untrimmed fragments are arranged in a spiral (Fig. 695, c). In pre- paring to pupate, the larvae 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.) 56G AN INTRODUCTION TO ENTOMOLOGY Family MOLANNID^ Fig. 696. — Case of Mo lanna. (After Lloyd. The only memSers of this family the larvae and cases of which have been described in this country belong to the genus Moldnna. The larvaj 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.E The larvas 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. Set odes 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. Leptocenis 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 larvae 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 Trianodes. (After Lloyd.) TRICHOPTERA 567 at Ithaca, N. Y., made cases in the form of cm-ved cornucopias (Fig. 697, b); 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. Tricenddes. — The larvae 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, &), 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 larvae 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 larvae 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 larv^ are free-moving, crawling separately over the bottom of the stream. But in the early spring, just before pupation, the larvae Fig. 698. — develop a remarkable gregarious habit. Almost all of C a s e o f the larvffi within certain areas of the stream congregate Psilotreta on the sides of a few selected stones in such numbers (After that their cases are sometimes piled one on top of another Lloyd.) 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 sillc. 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 LIMNOPHILID^ The larvce 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 larvce 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 larvse 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 larvee that change the form of their case when full- grown is Limnophilus combindtus, which is described by Lloyd. Dur- Fig. 699.-Case of Ganonema anie 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 TRICHOPTERA 569 the log-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 larv^ 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. Larvs 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 SERICOSTOMATID^ Fig. 702. — Case ot Limnophilus combinatus. (After Lloyd.) Fig. 703. — Case of Helicopsyche. (From Lloyd.) The larv« 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 bor edits. — The larvae 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 larvse 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. 1 Goera calcarata. — ^The Bxvse. 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 Fig. 704.— Case of Goera larval case (Fig. 704) is a (After ^ubg made of fine grains of sand on each side of which calcarata. Lloyd.) Fig. 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 theremarkable 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 wdth 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 larvas 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 of a wing of a butterfly, greatly magnified. Fig. 707. — Scales of Euclea delphinii. (After Kellogg.) *Lepid6ptera: lepido (Keirls, \eirlSos), scale; pteron {irTepdv), a wing. (571) 572 AN INTRODUCTION TO ENTOMOLOGY Fig. 7o8.-Scale of S e r y da c onstans. (After Kel- It is well known that these scales are merely modified setae. That is, they are setae which, instead of growing long and slender as setae usually do, grow very wide as compared with their length. Every 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 nearly two hundred years ago; and in recent times the morphological iden- tity of setae 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 setae, the scales, like setae, 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 of many very fine longitudinal ridges (Fig. 707) ; or they may be series of transverse ridges between the longitudinal ones (Fig. 708). A cross-section of certain scales indicates that the ) ridges are produced by foldings of the outer wall {i. e the wall of the scale that is exposed when the scale is in place on the wing). Figure 709 represents cross-sections of a scale illustrating this condition. In some scales, however, the lumen of the scale has been filled to a considerable extent by chitin, and the origin of the ridges is not so obvious. Fig. 709. — Cross-section of scales of Par- nassius smintheus. (After Kellogg.) The scales of the Lepidoptera were probably developed from that type of setae 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 stiffness, 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 stiff'ness 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 value 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 thesame way as does a diffraction grating, producing the beautiful iridescent colors. Kellogg ('94) found that on certain scales from a species of Morpho the strias 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 will 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 purpose 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 Jugatas and in some of the more generaHzed families of the suborder Frenatffi, there are, in addition to the more obvious setse and scales, many very small, hair-like structures, which differ from setse in being di- rectly continuous with the cu- ticula, and not connected with it by a joint (Fig. 710); these are termed the fixed hairs or aculecB. Fig. 710. — Part of a wing of an aculeate moth, with most of the scales re- 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 Cui. If this is true, the vein that is commonly desig- nated as vein Cui is really vein 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 nimiberof branches of radius or of media M^hich 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 Jugatee 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 united by a frenulum (see p. 61). In ~Ss J?, _ 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 ancestors, the frenulvun 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. Fig. 711. — Wings of Obrussa ochrefasciella, male. (After Braun.) LEPIDOPTERA 575 c m Fig. 712. — 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 In some of the more generalized Lepidoptera there is a series of slightly curved, spine-like setae 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 r tP s.i especially in the Noc- 3 t.a 0 ^^U^r-ij 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). — This is a band extending halfway across the wing near its base. The transverse anterior band (Fig. J12 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 second 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 stadium, the mouth-parts are vestigi- al; and in one family, the Micropterygidas, which is doubtfully in- cluded in this order, the mouth-parts are of the mandibular type. ^^ .,^,y,,„^ .jrfBflsiBJi^ -^^ those families in "^W ■?* "^^'^ 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 vestiges. Wheii only one pair of palpi are developed they 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- „. „ r. .. t .„ amined, there will be Fig. 714. — Cross-section of maxillae. x j 1 1 • 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 maxillae, greatly elongated, and fastened to- gether side by side. In Figure 713 there is represented a side view of the maxilla 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 maxillag 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 antennse are always conspicuous ; they differ greatly in form in different 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 antennas is greatly enlarged and forms what has been termed the eye-cap. The pro thorax 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 577 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 type is that of the Geometridee; it appears superficially as a hollow bulla located immediately below the spiracle, opening forward against the coxa of the hind leg. Some Pyralidse 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 Thyatiridas and Drepanidse. The third type presents a variety of appearances. Its essential part is a mem- branous disk, the tympanum proper, on the metathorax just below the root of the wing. In the Dioptidse, Notodontidse, Agaristidae, 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 Arctiidag, Pericopidce, 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 (Euteliinse, 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 larvag are known as caterpillars ; they vary 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 nu- merous 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. 715. — Larva of a hawk-moth. 578 AN INTRODUCTION TO ENTOMOLOGY -Types (a and b from The hooks or crotchets 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, biserial; 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, mnUiordinal. The tip of a proleg on which the hooks or crochets are borne is termed the planta. In most lepidopterous larvae 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 larvse, each seg- ment of thebody, when not too highly special- ized, is armed with a definite nimiber 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 f otmd in the more generalized families. In some of the more specialized families the tubercles are larger and many-haired (Fig. 716, 6) ; 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 Arctiidffi. In the larvae of the Satumioidea 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 numerous setae which are scattered and which have no constant position ; such setae are termed secondary seta, in contradistinction to those borne on setiferous tubercles which are of a definite nvmiber 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 subprimary setce. Fig. 716.- Dyar.) LEPIDOPTERA 579 In order to make use of the primary and subprimary setee in classification, it is necessary that each of these setag 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 larvae 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 nimibered with Roman numerals beginning with the one nearest the middle line of the back; the number 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 ('10) 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 Dyar, 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- ^^2- 717— Arrangement of setiferous tu- J -1 ^ r ji bercles m a noctuid larva: a, tubercles dommal segments of the same ^f ^ metathorax; b, tubercles of a insect. 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 larvae, 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 ntmiber of setal maps. This writer proposes a mcw terminology for the setae, using Greek letters instead of Roman nimierals. *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 fiat. The anterior edge is to the left, and the mid-dorsal line at the up- per edge. In Figiu-e 717 the positions of the spiracle and of the legs are also indicated. 580 AN INTRODUCTION TO ENTOMOLOGY Schierbeck ('i6 and '17) proposes still another terminology for the setae, applying a Latin name to each. Most caterpillars, except, as a rule, the larvas 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 pupae of the Lepidoptera are typically of the obtected type; that is, the developing wings, legs, mandibles, maxillae, and antennas 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- jugate, which are provisionally in- cluded in this order, these append- ages are free, the pupae resembling those of the Trichoptera ; but in the Hepialidas the appendages are glued to the surface of the body as in the specialized Frenatas. In some of the more generalized Frenatas, as the Fig. 718.— Pupa of a moth. Nepticulidas, and in the Heliozelidae, the appendages are all free ; between this condition and that of the truly obtected pupa of the more specialized Frenatas, 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 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 Frenatas; 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 tk" 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 antennse 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 Jugatse, 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 Frenatae, the two wings of each side are united by a frenulum in the more generalized forms and by a substitute for a frenulum 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 1 806, 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), Supple- 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^e. C. The Mandibulate Jugates. p. 592 Family Micropterygid^e CC. The Haustellate Jugates. p. 593 Family ERiocRANiiDiE BB. The Macrojugat^. The Swifts, p. 594 Family Hepialid^ *Heter6cera: hetero (^repos), other, different; ceras (/c^pas), a horn. *Rhopal6cera: rhopalon {p6iTQ\ov), a club; ceras {Kipas), 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 Frenatae the form of the primitive Frenatas, those that were the first to appear on earth. C. The Aculeate Frenate. — Moths in which the aculeae are distributed over the general surface of the wings. The Incurvariids. p. 598 Family Incurvariid^ The Nepticulids. p. 600 Family NEPTicULiDiE 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 C0SSID.E The Smoky Moths, p. 604 Family Pyromorphid^e The Dalcerids. p. 605 Family Dalcerid^ The Flannel-moths, p. 606 Family MEGALOPYGiDyE 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 Specialized Microfrenat^e. — 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 winga 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^ The Tineids. p. 611 Family Tineid^ The Bag-worm Moths, p. 613 Family Psychid^ The Tischeriids. p. 615 Family Tischeriid^ The Lyonetiids. p. 616 Family Lyonetiid^ The Opostegids. p. 617 Family Opostegid^ The Oinophilids. p. 617 Family Oinophilid^ The Gracilariids. p. 617 Family Gracilariid^e The Coleophorids. p. 620 Family Coleophorid^ The Elachistids. p. 621 Family Elachistid^ The Heliozelids. p. 622 Family Heliozelid^ The Douglasiids. p. 623 Family DouglasiidvE The aicophorids. p. 624 Family CEcophorid^ The Ethmiids. p. 625 Family Ethmiid^ The vStenomids. p. 625 Family Stenomid^ The Gelechiids. p. 625 Family Gelechiid^ The Blastobasids. p. 628 Family Blastobasid^ The Cosmopterygids. p. 629 Family Cosmopterygid^ The Scythridids. p. 631 Family Scythridid^ The Yponomeutids. p. 631 Family Yponomeutid^ The Plutellids. p. 632 Family Plutellid^ The Glyphipterygids. p. 633 Family Glyphipterygid^ The Heliodinids. p. 634 Family Heliodinid^ 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^ The Carposinids. p. 644 Family Carposinid^e CC. The Pyralids and Their Allies Superfamily Pyralidoidea The Pyralids. p. 644 Family Pyralidid.* The Plume-moths, p. 652 Family Pterophorid^ LEPIDOPTERA 583 The Many-plume Moths, p. 653 Family Orneodid^ The Window-winged Moths, p. 653 Family THYRiDiDiE The Hyblseids. p. 655 Family Hybl^id^ CCC. The Specialized Macrofrenat^. — Specialized Frenatae which are 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 Frenulum-conservers . — Specialized JMacrofrenatse in which the two wings of each side are typically united by a frenulum; but in some highly specialized genera o^ some families (Sphingidee, Geometridas, and Dre- panidae) 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 SpHiNGlDiE Superfamily Geometroidea The Geometrids. p. 663 Family Geometrid^ The Manidiids. p. 673 Family MANiDiiDiE 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 Noctuids The Foresters, p. 697 Family Agaristid^ The Pericopids. p. 698 Family Pericopid^ The Arctiids. p. 699 Family Arctiid^ The Euchromiids. p. 706 Family Euchromiid^ The Eupterotids. p. 707 Family Eupterotid^ The Epiplemids. p. 708 Family Epiplemid^ The Thyatirids. p. 709 Family Thyatirid^ The Drepanids. p. 710 Family Drepanid^e DD. The Frenulum-losers. — Specialized 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-losing 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 antennas 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.e The Giant Silk-worms, p. 719 Family Saturniid^ The Silk-worms, p. 727 Family Bombycid^ The Lasiocampids. p. 728 Family Lasiocampid^ EE. The Skippers. — These are day-fiying 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 antennae are enlarged into a club towards the tip. Superfamily 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 differ from 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.^ 584 AN INTRODUCTION TO ENTOMOLOGY The Pierids. p. 744 Family Pierid^ The Four-footed Butterflies, p. 750 Family NvMPHALiDiE The Metal-marks, p. 767 Family Riodinid^ The Gossamer- winged Butterflies, p. 768 Family Lvc^NlDiE 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. 613. PsvcHlDiE 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^ CCC. In addition to the above there are some arctic species of the Noc- tuidse and of the Arctiid^ 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 Jugate). 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 MiCROPTERVGiDiE DD. Mandibles of the adult vestigial; maxillae formed for sucking; subcosta of fore wings forked near its apex. p. 593 ERiocRANiiOi^ CC. Moths of medium or large size, without functional mouth-parts, p. 594 Hepialid^ 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. (Microfrenatae.) Pass to Table B. DD. Hind wings much broader than their fringe, and not lanceolate. E. Wings fissured deeply. F. Each wing divided into six lobes, p. 653 ORNEODiDiE PP. Wings never more than four-lobed; usually the fore wings. bilobed and the hind wings trilobed. p. 652 PTEROPHORiDiE 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 JEgerubm 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. {Agdisiis.) 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 i". not counted as a vein. LEPIDOPTERA 585 I. Veins Sc + 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^. . . . PYRALiDioi li. Veins be + R, and Rs 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 m rubbed specimens) ; the spurs of the tibia; more than twice as long as the width of the tibiae. (Microfrenatse.) Pass to Table B.* ' JJ. The fringe on the anal angle of the hind wings not longer than elsewhere or but slightly so ; the spurs of the tibiaj about as long as the width of the tibiae. K. Veins Sc + Rr and Rs of the hind wings grown to- gether 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 T 1 }J ^^^^^^ '^''}?^- P- ^°4 Pyromorphid^ I.L. Moths ot medium size, and densely clothed with long, woolly hairs, which are light-colored or brown VTT ^\f^-^ ■ Q ■ ,■ D • ■ • V T, ■■;•,•• ; MeGALOPYGID^ KK. Veins Sc -f R, and Rs of the hind wings separate or grown together for only a short distance. L. I St and 2d anal veins of the fore wings united bv a cross-vein. M. Accessory cell present (Hypoptina;). p. 603. MM. Accessory cell absent, p. 613. Psychid.^ LL 1st and 2d anal veins not united by a cross- vein M. Vein M, of the fore wings arising from the discal cell nearly midway between veins Mj and M 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^ JNN. Veins M3 and Cui not coalesced beyond the end of the discal cell. O. Veins R, and R3 coalesced at base, but separate from veins R, and R„ which also coalesce at base. p. 712 Lacosomid^ 00. Vems R„ R^, R,, and R^ united at base. MM. Vein M, of the fore wings ' emer^nrfrom the discal cell nearer to cubitus than to radius causmg cubitus to appear four-branched. N. Fore wings with an accessory cell. O. Moths with heavy, spindle-shaped bodies nn Ai''l'?°'^' ^^JP^S wings, p. 601. Cossmi UU. Moths m 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. ■or)' ■ tV;- Dalcerid^ pp. Wings more or less oblong, usually twice as long as wide; mouth-parts usually developed with scaled tongue. (Micro- irenatee.) Pass to Table B. NN. Fore wmgs without an accessory cell _*A few of the Eucleidas present these characters; but with these moths thp wmgs are broad and the base of media extends through the middle of The discal 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. (Microfrenatag.) Pass to Table B. MM. Veins Sc and R of the hind wings fused for a greater or less distance. N. Ocelli present, p. 683 N0CTUID.E NN. Ocelli absent, p. 704 Lithosiin^ 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 M2 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 M, of the hind wing joined to radius at or beyond the apex of the discal cell. Q. Tongue (maxillae) wanting; fore wings with Rj + 3 and R4 + s stalked together,north- ern species with hyaline dots on fore wings. p. 707 EuPTEROTIDyE QQ. Tongue present, often weak; fore wings fully scaled; usually with accessory cell, or with veins Rj and R4 stalked together. p. 674 NOTODONTID^ 00. The basal part of the subcosta of the hind wings joined to radius for a short distance and then making a prominent bend towards the costal margin (Fig. 909). (See also OOO.) P. Veins R3 and R4 of the fore wings widely separated from each other, stalked respec- tively with R2 and R5. p. 712 LACOSOMIDiE PP. Veins R3 and R^ long-stalked with each other, widely separated from Rs which is stalked with Mj. p. 708 Epiplemid^ 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. Antennas 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 So 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 distinct and parallel to the point where vein R sepa- rates from the discal cell, and then approach- ing very close or fusing for a short distance. (See also PPP.) Q. Small moths with snow-white wings (Eudeilinia). p. 710 DrepaniD/E QQ. Moths that are not white. R. Vein R5 of the fore wings stalked with veins R3 and R4 (Chrysauginse). p. 644. Pyralidid^ RR. Vein Rj free (Meskea). p. 653 Thyridid^ PPP. Vems 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^ 5SS AN INTRODUCTION TO ENTOMOLOGY QQ. Antennae 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^ RR. Hoods of the tympana less con- spicuous dorsally and more widely separated. S. Veins So 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. NOCTUID^ 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 also SSS.) p. 679. Lymantriid^ 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 (Arctiinse). p. 700. Arctiid^ TT. Ocelli absent. U. Fore wings with raised tufts of scales (Nolinas). p. 705. Arctiid^ UU. Fore wings smoothly scaled. V. Vein AI2 of the hind wings well developed and aris- ing slightly nearer to vein JMj than to vein Mi {Menopsimus). p.683 NOCTUID^ VV. Vein M2 of the hind wings arising much nearer to vein M3 than to vein jVIi, or wanting (Lithosiinaj). p. 704. Arcthd.(E 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 Saturnioidea LL. Small moths with slender bodies and weak wings (Dyspteris). p. 667 Geometrid/E CC. Antennae 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 antennas usually terminated by a re- curved hook. The skippers, p. 732 Hesperioidea DD. With some of the branches of radius of the fore wings coalesced be- yond the apex of the discal cell ; club of antennae 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 antennas enlarged and concave beneath, forming an eye-cap. B. Fore wings with radius, media, and cubitus unbranched. p. 61 7.0postegid^ 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 antenna 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. 61 1 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. Aculeae absent, or present only in a small area at the base of the discal cell; ovipositor membranous, retractile; antennas typically rough, with an outer whorl of erect scales on each segment, rarely as in D. p. 611 T1NEID.E 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^ 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 fiat. G. Aculeae present, etc., as in D under C above, p. 598 iNCURVARIIDiE 590 AN INTRODUCTION TO ENTOMOLOGY GG. AculesD 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^ 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 M2 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 Cua 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. laiitana). p. 639, 642 Olethreutid^ and Tortricid-E HH. Vein Cuz of the fore wings arising from the outer fourth of the discal cell, save in a few Glyphipterygidae, 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 Mr 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 R5 are stalked and both run to the costa. p. 625 Gelechiid^ JJ. Palpi with third segment short and blunt, roughly scaled; vein R5 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 Rs 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 Mi. p. 624 CEcophorid^ LL. Veins R.4 and Rs long stalked; vein Rj running to outer margin. (See also LLL.) M. Ocelli very large and conspicuous {Allononyma.) p. 633 Glyphipterygid.,e MM. Ocelli small or absent. N. Vein M2 of the hind wings arising nearer to vein Mi than to M3. p. 625 Ethmiid^e NN. Vein M2 of the hind wings arising nearer to vein Mj than to Mi. p. 624 . . .CEcophorid^ LLL. Veins R4 and Rs separate, vein Rs 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, Solenohia). p. 614. . . .Psychid^ 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 Plutellid.« LEPIDOPTERA 591 KK. Wings broad, ample, not falcate; maxillary palpi of folded type, inconspicuous, invisible in Setiostoma. p. 625 Stenomid/E FF. Hind wings with pointed apex and excavated below, rarely bifid. (vSee also FFF.) p. 625 Gelechiid^ FFF. Hind wings narrow-lanceolate and pointed 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 ELACHiSTiDiE 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^ n. Vein Rs of hind wings separating from media near the apex of the wing. p. 634 Heliozelid^ GG. Hind wings with vein R closely parallel with or fused to Sc near base. In the broad-winged Gracilariidce, veins Sc and R are fused and the base of vein M is preserved, simulating the con- dition in G, but the combined base of Sc and R curves strongly into the lobed basal half of costa, and then approaches or fuses with M at middle of wing, unlike the relation of Sc and R in G. H. Hind tarsi with strong spinules, usually near apices of seg- ments, as well as tibiae; posterior legs displayed when at rest. p. 634 Heliodinid^ HH. Tarsi smooth-scaled, the spinules concealed in the scaling; the tibiae often hairy, but rarely (Acrocercops, Epermenia) bristled. I. Fore wings with only four veins running from the discal cell to the costa, and five or six to the inner margin. p. 631, 632 Yponomeutid^ and Plutellid^ II. Fore wings with five veins running to costa, or only four to inner margin. J. Discal cell oblique in wing; vein Cu2 very short, running directly across to inner margin. K. Antenn£e turned forward in repose; fore tibiae slender, with a small epiphysis at the apex or none. p. 620. C0LEOPHORID.E KK. Antennae turned back in repose; fore tibiae with the epiphysis conspicuous, and often more than half as long as the tibia; the tibiae rarely slender. L. Hind wings with veins Sc and R usually fused near base; fore wings with a stigma, and with Ri ansilig near the base of the discal cell and R2 near the apex of the cell. p. 628 Blastobasid^ LL. Hind wings with veins Sc and R not fused; fore wings with the space between the origins of veins Ri and R2 only three or four times that between veins R2 and R3. p. 629 Cosmopterygid^ JJ. Discal cell not set obliquely in wing; vein Cu^ nor- mally long and parallel to the medial veins. K. Male antennae heavily ciliate; accessory cell of fore wings extending halfway to base of wing; head with a large, loose, but often obsctue, semierectile tuft. p. 615. TlSCHERIID^ KK. Male antennas rarely ciliate; accessory cell small or absent. L. Palpi minute and drooping; vertex tufted; hind wings linear (Bedellia). p. 616 Lyonetiid^ LL. Palpi moderate, with fusiform third segment; maxillary palpi often well developed and porrect. (See also LLL.) p. 617 GBACiLARiiDiE 592 AN INTRODUCTION TO ENTOMOLOGY LLL. Palpi upturned, with acuminate third segment, often exceeding the vertex; maxillary palpi of folded type but very 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 Cosmopterygid^ MM. Vein Ri of the fore wings but little longer than vein R2, and arising beyond the middle of the discal cell. p. 631 SCYTHRIDIDyE Suborder JUGATE This suborder includes those Lepidoptera in w^hich 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 Jugatse 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 Jugatse, as now more commonly limited, in- cludes several families, representatives of three of which have been found in America; these are the Micropterygidae, the Eriocraniidge, and the Hepialidce. The members of the first two of these families diflFer 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 Microjugatas. 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 frenulimi ; 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 Macrojugatas. Family MICROPTERYGID.^ The Mandibulate 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 Jugatse, 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 Micropterygidce 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 antennse, 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 Jugaies The members of this family, like those of the preceding one, are small insects which resemble tineid moths in general appearance. 594 AN 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. The females lack a bursa copulatrix but have 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 w^ing 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 auricyanea. The structure and transformations of this species have 5f. Sc, Ri 2d A I St A Fig. 720. — Wings of Mnemonica. been described by Busck and Boving ('14). The adult has a wing- expanse of from 12 to 14mm. 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 w4th 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 2 5 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 day. 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 Jugatae, the Hepialidse may be dis- tinguished as the Macrojugatas. In the Hepialidas 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 pur purascens . 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- plied. (Figs. 74 and 75.) The larvae 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 pupse 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 purpurascens, 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^E 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 si A jcfA 2d A ' Fig. 722. — Wings of Prionoxystus robinice. 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 Gracilariidas and of the Cosmopterygidas, vein Ri of the hind wings is free, not co- alesced with vein Sc. The essential characteristic of the Frenatae is that they are descendants of those primitive Lepidoptera in which the two wings of each side were united by a frenulum. This fact should be clearly understood, for in many of the Frenatae the frenulum has been lost. The loss of the frenulum in these cases is due to its having been supplanted by a substitute for it, by an enlarged htuneral 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 frenulimi 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- ulum of the male is com- posed of several setae, as is that of the female, but these setae are grown together Fig. 723. — Wings of a hook. moth: f h, frenulum- 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 frenulimi-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, / /i). As a rule the frenulum-hook arises from the membrane of the wing near the base of cell C ; but in some moths (Castnia) 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 Frenatae the form of the primitive Frenatee, 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 Frenatae ; 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 AN INTRODUCTION TO ENTOMOLOGY There are also included in this group of families those families in which the fixed hairs or aculeas are retained over the general surface of the wings, even though in some cases, as in the Nepticulidce, the venation of the wings may be greatly reduced. The presence of aculeae 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 Jugatas. 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 aculeas are confined to small areas of the wing surface or have been lost. Family INCURVARIID^ This family and the following one differ from all other Frenatce and agree with the Jugatas in having retained aculeae distributed over the general surface of the wing (Fig. 710). In this family the venation of the wings is but little reduced; the antennas 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 lan'^ae 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. Sofne of the species are also conspicuous on account of their striking colors and markings. The larvse 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 Adda. Subfamily Incurvariin^. — An interesting representative of this division of the family Incurvariidse is the following well-known species. The maple-leaf cutter, Paraclemensia acerifoliella. — The larva in- fests the leaves of maple, and occasionally is so abundant that it does serious injury. 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 5rucca-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 Yucca filamentosa, a plant not fitted for self- pollination or for pollination by insects in the ordinary ways; in fact, it is poUinized 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 maxillae 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- ment of seeds, upon which the larv^ 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 below the 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 yucca- 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 yucca-moths. The larvae of Prodoxus Fig. 725. — Tegeticula alba: a, side view of head and neck of female denuded ; i , load of pollen ; 2, maxil- lary tentacle; 3, maxillae; 4, maxillary palpi; 5, antennas; b, maxillary tentacle and palpus; c, an enlarged spine ; d, maxillary palpus of male ; e, scale from front wing; /, front leg; g, labial pal- pus; h, i, venation of wings; j, last segment of abdomen of female, with ovipositor extruded. All enlarged. (From Riley.) 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. Family NEPTICULID^ In this family, as in the preceding one, fixed hairs or acuieae are distributed over the general surface of the wings. In the Nepticulidas 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 frenulum 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 oiEctcedcmia, the lar- vae 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 on 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 Nepticulidse of North America was monographed by Braun ('17). Fig. 726. — Wings of Ohrussa ochrefasciella, male. (After Braun.) Family COSSID.E The Carp enter -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 larvse are borers; many of them live in the solid wood of the trunks of trees. The wood-boring habits of the larvce 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-skin? can be found projecting from the deserted burrows. 602 AN INTRODUCTION TO ENTOMOLOGY The carpenter-moths are of medium or large size. The antennas of the males are mostly bipectinate; those of the females are either very slightly bipectinate or ciliate. In a few species the antennae 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 preserved, and is forked within the discal cell. In the fore c. /?■ />, Fig. 727. — Wings of Prionoxystus robinice. wing the veins R3 and R4+5 anastomose, forming an accessory cell. The frenuliim is vestigial in this genus ; but in some other genera it is well developed. Atithors 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- frenata?; but I place it here at the beginning of the Non -aculeate Generalized Frenatce 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 : LEPIDOPTERA 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; antennae of male pectinate throughout CossiNiE BB. Veins Rs and Mj of the hind wings widely separate; antennae 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 wings. Nearly one-half our species belong to this si A Fig. 734. — Wings of Lagoa crispata. LEPIDOPTERA 607 In the female the an- 735, — Lagoa crispata, male. Fig. 736. — Old cocoon Megalopyge opercularis. 735; the female is larger expanding, 40 mm. tennis are very narrowly pectinate. Thelar- Vce feed on many trees and shrubs, including oak, elm, apple, and raspberry. They are short, thick, and fleshy, and are covered with a dense coat of long, silky, brown hairs, which project upward and meet to form a ridge or crest along the middle of the back ; interspersed among these fine hairs are venomous setae. The cocoons are of a firm, parchment-like texture, covered with a thin web of rather coarse threads. Mixed with the silk of the cocoon are hairs of the larva. The cocoon is provided with a hinged lid. This species is found in the Atlantic States. Megalopyge opercularis. — This species is somewhat smaller than the preceding one; the male has a wing-expanse of about 25 mm., and the female of about 3 7 mm. The fore wings are umber brown at base, fading to pale yellow outwardly; they are marked with wav^'' lines of white and blackish hairs, and the fore margins are nearly black. The larvae 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. Fig- 737- opyge. -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 ENTOMOLOGY 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 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 sets. The larvae 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 maxillcB 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 the coalescence of the m is/ A Fig. 739. — Wings of Adoneta spintdoides. 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 Sc *This family is termed the Cochlidiidae by some writers, and by others the Limacodidae. 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 larvce 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, Sihlne 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 setae. The spiny oak-slug, Euclea delphhiii. — 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. (Fig. 743) is cinnamon-brown, with a variable number green spots on the fore wings. The hag-moth, Phobetron pithecium. — The common name ha^- moth is applied to the larva of this species on account of its remark • Fig. 740. -^ I St A —Wings of Packardia geminala. Fig. 74 1-— ^' i b ine stimulea, larva. Fig. 742. — Euclea delphinii, larva. Euclea The moth of bright 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 larv^a 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, Prolimacddes hadia. — 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. Family EPIPYROPID^ Fig. 744. — Phobetron pithe cium, larva. (After Dyar.) Fig. 745. — Prolima- codes badia, larva. 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 barherimia. Another species, Eptpyrops anomala, has been described from China ; and larvjE 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 Fulgoridae. 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 larvae 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- atffi" 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 of 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 theMicropterygidae and theEriocraniidae, now placed in the suborder Jugatee; the Incurvariidas and the Nepticuli das, placed at the beginning of the Frenatse; 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 Cossidae. The families of the Microfrenatas 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.E 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. Fort\^-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 larvae 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 com when planted on sod. They surround the base of each plant with a fine web mLxed 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 antennae are shorter than the front wings. The maxillas are usually small or vestigial. The maxillar>^ palpi are usually large and folded. 612 AN INTRODUCTION TO ENTOMOLOGY •Wings of Tinea parasitella. (After The labial palpi are short and clothed with but three or four bristles. In the typical genera the venation of the wings is quite generaHzed (Fig. 747), the base of media being pre- ? >^f >? served in both fore ~~ and hind wings and all of the veins char- acteristic of the Frenatas being pres- 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, espe- cially those that con- Fig- 747-— tain much wool; few Spuler.) 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 hisselliella. — This is our most common clothes-moth. Although the larva spins some silk wherever it goes, it makes neither a case nor a gallery; 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 dift'ers greatly in appearance from the other two species, the fore wings being black from the base to near the middle, and white be- yond. 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 the silken sacs made by the larvae, 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-vitae, 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- tennee, 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 oi Otkettcus some species nearly naked; when clothed with scales " ^^' they are usually of a smoky color without markings. The venation of the wings varies I? 3^ J^ 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 obsen^ed. Abbot's bag-worm, Otkettcus abboti. — 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 sable brown, with a 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. Fig. 749. — Wings of Thyridopteryx ephemercB- formis. 614 AN INTRODUCTION TO ENTOMOLOGY The evergreen bag-worm or the bag-worm, Thyridopteryx ephe- mer^formis. — This species prefers red cedar and arbor-vitas, 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 mosthkelyto 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 Psych idae. 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- vitse, 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 Fig- 750-— Thyridop- the male. She is entirely destitute of wings and teryx ephemerce- j r^^^ genitalia of the male can be greatly extended, makmg 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 larvse 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. Fig. 752. Solenohia 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 larvce are found on the trunks of trees and feed LEPIDOPTERA 615 Fig- 753.- ler.) -Wings of Solenobia. (After Spu- upon lichens. Figure 753 represents the venation of the wings of a European species of this genus. Family TISCHERIID^ The vertex of the head is clothed with erect, broad, and short scales. The an- tennas 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 2d A Fig. 754. — Wings of Tischeria marginea. Spuler.) (After 616 AN INTRODUCTION TO ENTOMOLOGY to pupae 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 purjjlish and dusted with pale yellowish scales. To control this pest, plow the orchard after the leaves have fallen, or rake and burn the fallen leaves. Fig. 755. — Wings of Bedellia somnulentella. (After Clemens.) Family LYONETIID^ Moths with the head smooth, at least on the front. The scape of the antennse usually forms an eye-cap. The ocelli and the maxillary palpi are wanting. The labial palpi are usually very small. The wings are very 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 fore wings are usually warped up or down. The larvee are leaf -miners or live in webs between leaves. The following species will serve 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 pomifoli- ella. — The larva 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 numbers, 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 i-eveal 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 Bucculatrtx, to which the above species belongs, is placed by some writers in a separate family, the Bucculatrigidcs . 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, and with 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 antennee, 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-off, fusiform, terminal joint as in the Tineidas, 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 sabtnella, 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 larvse 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. I'he 618 AN INTRODUCTION TO ENTOMOLOGY 2(iA Cii2 Ah On ^3 Fig. 757. — Wings of Gracilaria. (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 pi-esent in the genus Parornix. The tiinn 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 maxillce 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 parench\Tna. The young larvae always make a flat 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 larvas 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 Lithocolletis, but which is termed Phyllonoryc- ter by those who recognize the names in the "Tentamen" of Hiibner. The following species will serve 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 of ten a single leaf contains many of these mines (Fig. 758). The young larva is remarkable in resembling more the larva of a beetle than the ordinary type of lepidopterous larvae (Fig. 758, b). It is nearly fiat ; 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 larvae 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, o), 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; w, side view of pupal crest; 0, front view of same; q, cocoon; Q, moth. (From the author's Report for 1879.J 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 larvee form large blotch mines on the upper surface of leaves. In this species the larvae 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 AN INTRODUCTION TO ENTOMOLOGY entire leaf. This species like most other gracilariids passes the winter as pupae. A common miner in the leaves of locust is Parectopa robiniella. The larv^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 nmning 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 rarely of economic importance. Family COLEOPHORID^* Moths with a smooth head, without ocelli, and without maxillary palpi. The labial palpi are of moderate size. The antennas are held extended forward in repose. The wings are very narrow. The discal Fig. 759. — Wings of Coleophora laricella. cell of the fore wing extends obliquely; vein Cui and vein Cu2 when present are very short (Fig. 759). The larvag are usually leaf-miners when young or feed within seeds; later, with few exceptions, they 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, pliim, and cherr\^ 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 Hiibner 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 HAPLOPXiLnD^. 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 larvce 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 May, 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 fletcherella. — 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 larvae 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 by silk. Fig. 760. — Coleophora malivorella: a, apple twig showing larval cases and work on leaves; b, larva; c, pupa; d, moth; b, c, d, enlarged. (After Riley.) Fig. 761 bearer. —Cases of the cigar case- (After Hammar.) Family ELACHISTID.^ The head is smooth. The scape of the antennas 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 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 species belong to the genus Elachtsta. /?, A"., Fig. 762. -Wings of Elachtsta guadrella. (After Spuler. ) Family HELIOZELID^ The antennae 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 Rs sep- arating near the apex of the wing. The habits of the larvae are well- illustrated by the following species. The resplendent shield -bearer, Cop- todisca splendorif- erella. — This spe- cies infests the leaves of apple, pear, quince, thorn- 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 -Wings of Anlispila pfeifferella. (After Spu- LEPIDOPTERA 623 within their cases. The adult (Fig. 764, g), is a brilliantly 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 gum case-cutter, Antisplla nysscBfoUella. — This species infests the leaves of Nyssa syhatica. Its habits are similar to those of the preceding species. Family DOUGLASIID^ The scape of the antennas 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 Rs sep- arates from media near the middle of the length of the wing (Fig. 765). 624 AN INTRODUCTION TO ENTOMOLOGY This family is represented in this country by a single species, Tinagma obscuro- Sc j^ fasciella, the larva of which is a leaf- miner in Rosaceas, Family (ECOPHORID^ The head is usu- ally smooth, with appressed scales; sometimes with loose scales and (After spreading side tufts. The antennas usu- The labial palpi are well- Fig. 765. — Wings of Tinagma obscurofasciella. Chambers.) ally have a comb of bristles on the scape developed, generally curved upward; the terminal segment is acute- ly pointed. The maxillary palpi are vestigial. The wings are fairly broad, sometimes ample Sc /? M, (Fig. 766). The venation is but little reduced. In the fore wings veins R4 and R5 are stallced 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 Ml are well separated and extend parallel. The posterior tibice are cloth- ed with rough hairs above. The larvas 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 larvas have consumed the flowers and unripe seeds and become nearly full-grown, they burrow id A 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 pupee. The moths appear in late July and early August, and soon go into hibernation in sheltered places. Family ETHMIID^ This family includes a small ntmiber of moths, which were former- ly included in the family CEcophorids. The family Ethmiidag was established by Busck ('09b), who states that the main structural character of the imago by which this family can be distinguished from the CEcophoridas is the proximity of vein M2 in the hind wings to vein Ml instead of to vein M3 as in the CEcophoridse, it being radial not cubital. Fracker ('15) describes larval characters distinctive of the typical genus Ethmia. The members of this family have broad wings. The fore wings are usually bright colored, with striking patterns, often black and white. The larvffi, as a rule, are social, living in a light web. They feed chiefly on plants of the family Borraginacese. Most of the species belong to the genus Ethmia of which about thirty 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 larvse 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 wings 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. — Wings of Pectinophora gossypiella. Busck.) (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 larva? 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 Microfrenatae ; 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, Sitdtroga cerealel- la. — The larva of this moth feeds upon seeds, and especially upon stored grain. It occurs through- out our countr>^ ; 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 1 2 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- atclla. — 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 annually. The summer generations attack both twigs and fruit. The solidago gall -moth, Gnorimo- schema gallcBSoliddginis. — There are two kinds of conspicuous galls which are enlargements of the stems of golden-rod; one of these is a ball-like enlargement of the stem and is caused by the larva of a fly, Eurosta solidaginis, described in the next chapter ; the other is spindle-shaped (Fig. 769) and is caused by the moth named above. The eggs are laid on the old plants in the fall and hatch in spring. The young larva crawls to a new shoot and boring down into it 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 l^af rolled by a gelechiid larva, probably Anacdmpsis innocuella. 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 antennae 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 Fie 770— 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 chiid 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 Rg 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, Valentmia glandulella. — The larva of this species lives as a scavenger in acorns that have been destroyed by a,com- weevils. Balaninus. 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. 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 Keys, Fla. Fig. 771. — Wings of Holcocera. (After Forbes.) Family COSMOPTERYGID^ 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 occasionally 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 sahalella. — This species oc- curs only in the South where the saw-paknetto grows; but it is of general interest as illustrating a peculiar type of larval habit. The larvce 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 oE 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, Lymncscia 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 awa}^ 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- summer day met with a slender little streak of gold and silver sitting in the sunshine on a leaf in a protected corner 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 IUU