et tak A sh: Sa pes iS} 3! Saat Rs ieee ia heated fetveray 7 eastrenps bebe bs ie i 1 =. 4 (24813—5M—12-70) wie of Common and Economic Illinois Ants, with Keys to the Genera (Hymenoptera, Formicidae) ILLINOIS NATURAL HISTORY SURVEY Biological Notes No. 71 Urbana, Illinois JANUARY, 1971 STATE OF ILLINOIS DEPARTMENT OF REGISTRATION AND EDUCATION NATURAL HISTORY SURVEY DIVISION HERBERT H. ROSS GEORGE L. ROTRAMEL WALLACE E. LABERGE A Synopsis of Common and Economic Illinois Ants, with Keys to the Genera (Hymenoptera, Formicidae) Herbert H. Ross, George L. Rotramel, and Wallace E. LaBerge TO THE ILLINOIS HOMEOWNER, gardener, or farmer, ants are probably the best known of all insects. They invade houses in search of food, hollow out house timbers to make nests, make mounds and bare spots in gardens and lawns, tend aphids that injure some of our crops, and the more pugnacious ones bite picnickers. However, ants that intrude upon our privacy are not the only ones living in Illinois. Many live in the house, in the garden under stones, or in the soil, and they forage chiefly at night. Many other species inhabit woodlands, some living in the ground, others in rotten logs, and still others in dead trees. To date over 90 different kinds or species of ants have been taken in Illinois. Another 20 are known from neighboring states and will likely be found in Illinois with further collecting. These midwestern ants are classified into genera and these are grouped into six large categories called subfamilies. A seventh subfamily is more southern and western in distribution. These seven subfamilies constitute the North American rep- resentatives of the family Formicidae, which contains several thousand different species in the entire world. Although superficially ants may look much alike, those belonging to different genera and species exhibit a remarkable number of differences in such characters as the shapes of the mandibles, sizes of the eyes, pro- jections on the body, and contours of various parts. These characters are most marked between the genera. The species within many genera are frequently difficult to diagnose, and many complexes have not yet been thoroughly studied. As a result, it is not practical to give identification characters for every species occurring in Illinois. The genera and certain of the common and economic species can be identified readily, and these are the units that are treated in this synopsis, intended as a useful guide to the householder, gardener, farmer, and hiker. LIFE HISTORY All ants are social insects living in colonies or nests, and they have evolved a highly developed social pattern This paper is published by authority of the State of Illinois, IRS Ch. 127, Par. 58.12. The authors are one-time colleagues in the Section of Faunistic Surveys and Insect Identification of the Illinois Natural History Survey. Dr. Herbert H. Ross was formerly Assistant Chief of the Survey and Head of that section, George L. Rotramel was formerly a Technical Assistant in that section, and Dr. Wallace E. LaBerge is a Taxonomist in that section. Dr. Ross is now Professor of Entomology, University of Georgia, Athens. Mr. Rotramel is com- pleting work for the Ph.D. degree in the Department of Entomology and Parasitology, University of California, Berkeley. COVER ILLUSTRATION: Ann Prickett. A worker of Polyergus lucidus, the pale slave-making ant. associated with the production and rearing of the young and the maintenance of the nest. Developmental Stages Ants belong to the large group of insects that have four distinctive stages in the life history: (i) the egg, (11) the larva, (iii) the pupa, and (iv) the adult, the latter represented by males, females, and workers (Fig. 1). Typical males and females have well-developed wings and sexual organs; the workers are much smaller adult stages that lack wings and sexual organs and differ from the winged adults in many details of morphology. A typical ant nest centers around a queen, a female that has been fertilized and lost its wings. The queen stays in the nest and lays eggs that hatch into larvae. The larvae are whitish, legless maggots, somewhat egg shaped but tapered toward the head end. They are completely helpless and must be moved about in the nest and fed by the adult ants. When full grown, the larvae transform into whitish pupae, the transformation stage between larva and adult. Some larvae spin cocoons around themselves before pupating, but some do not. The pupae also are helpless. If the nest is badly dis- rupted, the workers will carry the larvae and pupae out of the nest to hiding places in the soil or under stones. In nests with an active queen, the larvae usually develop into workers or certain workerlike forms. The eggs, larvae, and pupae are cared for by the workers, who handle the immature stages inside the nest and forage for food outside the nest. The workers — obtain enough food for themselves, the queen, and the growing larvae. Most of the larvae grow up to be workers. When these workers are mature, they take up their activities of foraging for food and feeding the queen and the larvae, collectively called the brood. The development from egg to adult takes several weeks. Castes and Their Duties Depending on the species, a nest or colony may consist of several hundred to many thousands of in- dividual ants, including a considerable number of differ- ent forms or castes in addition to the queen. The commonest caste is called the worker, and these may be of two sizes; the smaller are minor workers and the larger are major workers. In the major worker the head is considerably larger in proportion to the re- mainder of the body than in the minor worker. In Drawn by Mrs. Alice Fig. 1.—The little black ant, Monomorium minimum. A, male; B, pupa; C, female; D, female with wings; E, worker; F, larva; G, eggs; H, group of workers in line of march. A to G much enlarged; H, about three times natural size. some kinds of ants an even larger type of worker, the soldier, is present. The soldiers are very much larger than any of the other workers and usually have ex- tremely long mandibles armed with sharp teeth. The primary function of the soldier caste is to protect the nest; the soldiers do not take care of the brood. In some ant species individuals that look like soldiers because of their larger eyes and much enlarged heads are actually specialized forms that crack plant seeds gathered for food. These nutcrackers are sometimes called the miller caste. Ants in other regions have evolved differ- ent castes that are modified workers; that is, they never have wings and cannot reproduce. All worker and soldier castes are females. Colony Formation At specific times of the year (different times for different species) a large number of winged males and (From USDA) females are produced in each colony. These winged ants appear to take no part in the colony activities except for being fed. After they have matured in the nest, these winged forms fly out in great swarms, and it is during these flights that the males and females mate. The males take no further part in the history of the nest, but the fertilized winged females alone start new colonies. The males die soon after mating, usually by being devoured by birds, other ants, or predaceous insects. Colony formation is extremely interesting. The fertilized female first nips off her wings, then burrows into wood or soil, makes a small cavity, and begins laying a few eggs. When these hatch into the first larvae of the colony, the female feeds them by re- gurgitation. The food stores used by the female are her fat bodies, formed while she was maturing in the parent nest, and the large wing muscles that are digested 4 by internal body fluids and converted into food. These first larvae tended by the queen develop into workers. As soon as these workers are mature, they start to forage, and from then on they and not the queen provide food for the colony. Caste Development One of the most interesting questions concerning ants is, why does one egg develop into a worker, another into a soldier, another into a winged, reproductive queen, and yet another into a winged, reproductive male? Entomologists who study ants have been sure for some time that some regulatory system determines the number of members of each caste produced within a colony. However, the mechanisms of this regulation are not clearly known as yet. The males arise from unfertilized eggs. This is true also of all ant relatives such as wasps and bees. The queens and worker castes develop from fertilized eggs. When an ant queen mates, she receives enough sperm to last her entire lifetime and keeps it stored in special glands inside her body. The major factor in caste formation, therefore, is the control of the development of fertilized eggs and does not in- volve heredity directly. The clue to the differential development of the eggs seems to be found in certain feeding habits. When a worker feeds a larva or the queen or a soldier, the worker licks the body of the individual it has just fed. Apparently the bodies of these creatures exude certain secretions that are sought and enjoyed by the workers. It is believed that these secretions are actually hormones that control the behavior of the workers, primarily influencing the kind of food that they feed to the larvae. It has been found that larvae fed a high-protein diet develop into soldiers, whereas those fed a low-protein diet develop into workers. Presumably, similar dietary differences will cause a larva to develop into a reproduc- tive queen. TERMINOLOGY The anatomy of ants differs in several respects from those of many other insects such as grasshoppers and beetles. As a result, several terms used in the following keys may be unfamiliar to the general entomologist. To clarify these terms, many of them are indicated for the worker and queen caste in Fig. 2 and 3. Others are listed in the short glossary below. The most important morphological difference be- tween ants and many other insects concerns the divi- sions of the thorax and abdomen. In ants (and all other Hymenoptera) the first segment of the abdomen has become consolidated into the last or third segment of the thorax and forms an indistinct dorsal plate called the epinotum. This epinotal area sometimes bears dis- tinctive spines, epinotal spines. The main bulk of the abdomen (called the gaster) is joined to the thorax- epinotum by a constricted and often beadlike narrow portion called the petiole, which may consist of one or two segments (the second and sometimes third true segments of the abdomen). Unless one is referring spe- cifically to the epinotal area, the epinotum and thorax together are usually referred to simply as the thorax. Abbreviated Glossary clypeus—The “upper lip” of the front of the head (Fig. 3). dorsum—The upper surface or top. dorsal—Pertaining to the upper surface or top. frontal carina—A ridge of the head just to the mesal side of the base of the antenna; this may be elevated or form an overhang over the base of the antenna. funicle—The many-segmented portion of the antenna beyond the scape or basal segment. mesal—On or toward the midline of the body. node—A projection or elevation on the dorsal surface of one of the segments of the petiole. Fig. 2.—Worker ant of the genus Aphaenogaster, side view, showing terms used for diagnostic parts. EYE LABIAL PALP MAXILLARY PALP THORAX — —-—— ~———- ABDOMEN— — — — —~ I PETIOLE GASTER HEAD — WING STUBS THORAX SCUTELLUM EPINOTUM EPINOTAL SPINES PETIOLE <—_ —— ABDOMEN 4 eh Za GASTER < NS petiole—One of the small segments between the thorax and gaster. (If an ant specimen dies with the gaster elevated, the petiole and its structures may be diffi- cult to see, in which case the specimen should be relaxed and the gaster depressed until the entire body is about level.) scape—The first segment of the antenna. (When mea- suring this structure, one should not count the small socketlike end piece that actually articulates with the head.) sclerite—Any area of the body set off by ridges, grooves, or membranes. scrobe—A long, hollowed-out area on the head above the insertion of the antenna into which the antenna folds when in repose. striae—Minute, ridgelike ornamentations of the surface. suture—Any division between two sclerites. venter—The underneath side. ventral—Pertaining to the underneath side. DIAGNOSIS OF ANTS AND TERMITES Ants are members of the insect order Hymenoptera, which includes the sawflies, wasps, bees, and ants. Ants resemble some of the wasps, especially those having wingless forms that may resemble worker ants very closely in general appearance. Ants may be differentiated from wasps by the ants having one or two segments forming a distinct petiole between the thorax and the gaster, each segment of this petiole produced dorsally into an enlargement or node (Fig. 1 and 2). Some of the wasps have a petiole, but none of them has one bearing a dorsal node. Ants are also confused with termites, often called white ants, because termites also live in large colonies. Ants and termites may be differentiated as follows: \FRONT WING Fig. 3.—Winged female ant of the genus Aphaenogaster, dorsal view, show- ing terms used for diagnostic parts. S HIND WING TARSAL CLAWS Winged or dark-bodied forms having the abdomen at- tached to the thorax by a narrow waist or petiole (Fig. 1); whitish, soft-bodied forms (larvae and pupae) found in the nest are grublike, nonambula- tory, and often without legs .............. ants Winged and dark-bodied forms having the abdomen joined broadly to the thorax; pale forms found in the nest all have well-developed legs and are ambu- latory Pig 4) shee oS oc pak ses Sega termites Termites constitute the insect order Isoptera, close relatives of cockroaches. Even the youngest stages have legs and are active. If a nest is disturbed, the older individuals do not carry the younger ones to a hiding place. Termites are not discussed further in this synopsis. If an ant nest is disturbed, the worker ants carry the inactive larvae and pupae to a hiding place. KEY TO ANT CASTES The castes of ants may be identified by the following key. In this key the soldiers, nutcrackers, and both major and minor workers are keyed out together under “workers.” 1. Tip of abdomen with a set of clasping structures that may be partially or completely retracted (Fig. 16P) ; wingless or with wings, but never with Gere Gib "3 wn On SOM Ole oomiae aoc ae males Tip of abdomen without clasping structures, some- times with a sharp sting (Fig. 7E and H) ora small cone having a ring of minute hairs (Fig. 6D) ; wingless or having wings or wing stubs . .2 2. Having either wings (Fig. 3) or wing stubs that are visible on the sides of the thorax where the wings have been broken off; dorsum of thorax having several transverse or curved sutures be- tween bases of wings or wing stubs, these sutures Fig. 4 (Right)—A common Illinois termite, Reticulitermes flavipes. A, winged queen; B, worker nymph; C, winged queen. B and C are natural size. (From Illinois Natural History Survey Circular 39) A, Labidus, front Fig. 6.—Diagnostic parts of worker ants. view of head; B, Labidus, enlarged view of bases of antennae; C, Camponotus, side view of petiole and gaster; D, Camponotus, nozzle-like anal opening at tip of abdomen. delineating several sclerites, always including a large V-shaped or U-shaped scutellum (Fig. 3) PSS. AED ME CaO aS OR ee AMES females Wingless, lacking wing stubs (Fig. 2); dorsum of thorax without a scutellum and associated scle- Mi fCSwrreqere here ceases ek oem eae attra: workers SYNOPTIC KEYS The following keys include all of the genera known from Illinois and a few others that are known to occur not far from this state and may ultimately be found here. Because most of the Illinois ants have a wide distribution, this synopsis should be helpful for the entire Midwest. The only North American subfamily not represented in these keys is the southwestern subfamily Cerapachyinae. Fig. 5 (Left)—Worker of Pseudo- myrmex. A, side view; B, front view of head (at right angles to greatest length). This subfamily contains only two genera in North Ameri- ca, Cerapachys and Acanthostichus, whose workers and queens may be distinguished by the spines on the lateral margins of the terminal abdominal sternum. The genera treated in this synopsis have been num- bered serially. To facilitate referring from the keys to the generic synopses, the genera have been given the same numbers in the keys as in the following synopses. KEY TO SUBFAMILIES AND GENERA (WORKERS) 1. Petiole two segmented (Fig. 2 and 5) .......... 2 Petiole one segmented (Fig. 7C, D,and E) ...... 4 2. Head with long, smooth eyes; antennae always close together at base; scape little more than half length of head (Fig. 5B) ; medium-sized to large ants of wasplike appearance (Fig. 5A) (sub- family Pseudomyrmecinae)................ 20 Head shorter, eyes no larger than in Fig. 10; bases of antennae frequently well separated (Fig. 10) ; antenna usually with scape longer, frequently longer than head 3. Compound eye represented by only one facet or ab- sent (Fig. 6A); a pair of high, sharp ridges arising from head between antennal bases (Fig. 6B) (subfamily Ecitoninae) Compound eye represented by more than a single facet (Fig. 10); head without high ridges like those in Fig. 6B (subfamily Myrmecinae) .. .21 4. Genital opening small and circular, surrounded by stiff hairs forming a terminal nozzle (Fig. 6C and D) (subfamily Formicinae) Genital opening slitlike or inconspicuous (Fig. 7) . .5 5. Gaster with a distinct constriction between first and second segments; abdomen with a well-developed sting (Fig. 7) (subfamily Ponerinae) Gaster without a constriction between first and sec- Fig. 7—Diagnostic parts of worker ants of the subfamily Ponerinae. A, Proceratium, dorsal view of thorax; B, Ponera, dorsal view of thorax; C, Sysphincta, side view of body; D, Ponera, side view of thorax and petiole; E, Proceratium, side view of thorax and abdomen; F, Amblyopone, front view of head; G, Ponera, front view of head; H, Amblyopone, side view of thorax and abdo- men. ond segments (Fig. 8) ; abdomen without a sting (subfamily Dolichoderinae) ............... 10 Subfamily ECITONINAE 6. Tarsal claw toothed (Fig. 17A) ....... 1. Labidus Tarsal claw without a tooth (Fig. 17B) =f ote one Abeta Eien ee 2. Neivamyrmex Subfamily PONERINAE 7. Thorax with no sutures visible in dorsal view (Fig. AN ee iaeet ee jet shean tea faicie tiie tlaovidbie Rice. sacs 8 Thorax with two sutures visible in dorsal view (Fig. LIB) Mere rewire ae acta cole sasksone Sones save 9 8. Terminal portion of abdomen arising near anterior end of ventral margin of end of second gastric segment; petiole moderately long and low in lateral view (Fig. 7C) ......... 6. Sysphincta Terminal portion of abdomen arising from near pos- terior end of second gastric segment; petiole high and short in lateral view (Fig. 7£) 3 5 ano ape ROR gaa Oe een eee 5. Proceratium 9. Mandibles as long as head (Fig. 7F) ; petiole almost square in lateral view (Fig. 7H) enema ara Riksta peaks aa Asal 3. Amblyopone Mandibles only about half length of head (Fig. 7G) ; petiole rectangular and high in lateral view (Fig. TED. ae" nck Cxerose Cor fc Behe eeCR oe a 4. Ponera Subfamily DOLICHODERINAE 10. Epinotum with a flat, U-shaped dorsal projection extending posteriorly (Fig. 8B and £) ae eee art coe ae 7. Dolichoderus Epinotum with either a conical projection (Fig. 8D) Or mone (Riggi8 Gi) ae aciocsnty hearer eer 11 11. Epinotum with a conical process (Fig. 8D) ; man- dible with a prominent bladelike terminal tooth, maxillary palp with segment 3 as long as seg- ments 4, 5, and 6 combined (Fig. 8F) Bch te hoes om caetee 8. Dorymyrmex No conical process on epinotum (Fig. 8C) ; man- dible without a bladelike tooth, maxillary palp with segment 3 much shorter than segments 4-6 COMPINER yo aryana cis ee ee tna oreene + ce er 12 12. Node of petiole vestigial (Fig. 8A) .. 10. Tapinoma Node of petiole as prominent as in Fig. 8C Pie rhniuai a ee aa is aweratees meage ke ave 9. Iridomyrmex Subfamily FORMICINAE 13. Antenna with 9 segments ..... 11. Brachymyrmex Antenna with 12 segments (Fig. 2) ............ 14 14. Mandibles sickle shaped, their inner margins with a series of minute bumps or crenulations but no WGA (UB, GAD) socsockscss wone 16. Polyergus Mandibles stouter and toothed (Fig. 14B—D) ...15 Fig. 8—Diagnostic parts of worker ants of the subfamily Dolichoderinae. A, Tapinoma, side view; B, Dolichoderus, side view of thorax and abdomen—f, dorsal process; C, Iridomyr- mex, side view of thorax and abdomen; D, Dorymyrmex, side view of thorax and abdomen; FE, Dolichoderus, dorsal view of thorax and petioles—p, dorsal process; F, Dorymyrmex, side view of head—1, labial palp; m, maxillary palp. 15. Maxillary palp with three or four segments BR ey eye eee NRE re ete 12. Acanthomyops Maxillary palp with five or six segments ........ 16 16. Mesopleuron with a distinct ridge near anterior ven- tral portion (Fig. 9B) ....... 15. Camponotus Anterior margin of mesopleuron rounded, without Ig | XSi: SH. rel os AEA ORR OD py ONG Pep PAO Ore Gee il7/ 17. Node of petiole low and sloping anteriorly, the whole petiole forming a low triangle (Fig. 9D, E, and GC) Pitac. cecter a tec ktaarat occ pee ocean he cs assy eT 18 Node of petiole upright, petiole forming a high tri- avorelle (lis, SIC eiael J8)) Gockacnsacugsescaugcs 19 18. Thorax viewed from the side having a distinct con- striction or “neck” near middle (Fig. 9G) ess ote ie eters a tS RON ONAN 17. Prenolepis Thorax viewed from the side having no such distinct constriction or “neck” (Fig. 9D and £) Save Reset eatin toyota ect ete 18. Paratrechina 19. Clypeus shorter, as in Fig. 14C, with an indistinct transverse swelling; dorsum of epinotum some- what angulate (Fig. 9F) .......... 13. Lasius Clypeus longer, as in Fig. 14D, with a slight mesal crest or angulation for most of its length; dorsum of epinotum smoothly rounded (Fig. 9C) ee eer oa eee 14. Formica Subfamily PSEUDOMYRMECINAE 20. Includes only one genus in North America (Fig. 5) Pie baka cade se ee 19. Pseudomyrmex Fig. 9.—Diagnostic parts of worker ants of the subfamily Formicinae. A, Polyergus, front view of head; B, Camponotus, side view of thorax and petiole—r, ridge; C, Formica, side view of thorax and petiole; D, Paratrechina, side view of thorax and petiole; E, Paratrechina, side view of thorax and petiole; F, Lasius, side view of thorax and petiole; G, Prenolepis, side view of thorax and petiole. Subfamily MYRMECINAE 21. Pedicel attached to dorsal surface of gaster, which is flattened dorsally and markedly heart shaped (Bigs Zoic sehacon onic 26. Crematogaster Pedicel attached near center of anterior end of gaster, which is ovoid in shape (Fig. 2) ..... 22 22. Dorsum of thorax with tubercles, as in Fig. 23B Saat eee ae eae 21. Trachymyrmex Dorsum of thorax without tubercles ........... 23 23. Front part of mesonotum with long spines projecting forward (Pig 23) eee eee 20. Atta Front part of mesonotum without spines (Fig. 10C, DG; Handi) coke ce eee 24 24. Head somewhat wedge shaped in full-face view (Pig 24) cee eetel ee ee eee ee 25 Head not wedge shaped in full-face view (Fig. 104 andtE in seach cee Ree ee eee 26 25. Mandibles as long as in Fig. 24A and B Se See ero eters 8 Aeron Ohl spo 22. Strumigenys Mandibles shorter, as in Fig. 24C and D Bh ace meatceae ite Ree eke ere 23. Smithistruma 26. Epinotum with dorsal margin smoothly rounded, without spines or angulation (Fig. 1Z) ..... 27 Epinotum with spines (Fig. 10C, D, G, and H) or with an angulate posterior dorsal margin (Fig. 27. 28. NOV) 5, Beare dt eekener ceca ee cin eee nie eee 28 Antenna with 10 segments, the last two forming a distinct club (Fig. 10B)........ 27. Solenopsis Antenna with 12 segments, club either not distinctly set off or having three or more segments (Fig. WAN preee pe sates acne hse 28. Monomorium Antennal scrobes well developed, extending beyond the posterior margin of the eye (Fig. 10H and Te) i exco ec Cone CACACEO OR ARE CREA ere ae ear 29 Antennal scrobes not reaching the posterior border Fig. 10—Diagnostic parts of worker ants of the subfamily Myrmecinae. antenna; C, Pheidole, side view of thorax and petiole; D, Tetramorium, side view of thorax and petiole; EF, and F, Harpagoxenus, side and front views of head; G, Myrmica, side view of thorax and petiole; H, Leptothorax, side view of thorax and petiole; J, Myrmecina, side view of thorax and petiole; J, Myrmica, tangential view of head; K, and L, Pogonomyrmex, side and front views of head; M, Pheidole, front view of head: N, Tetramorium, front view of head; O, Leptothorax, front view of head; P, Aphaeno- gaster, front view of head; Q, Stenamma, front view of head. 29. 30. A, Monomorium, front view of head; B, Solenopsis, Or ins GO (be NO/FONE gases oocsccccc 30 Minute yellow ants, at most 1.5 mm long 5 eee, > epee nairact 24. Wasmannia Brown ants about 2.5 mm long. . 25. Harpagoxenus Posterior border of clypeus with a distinct, semi- circular, deep, sharp depression (Fig. 10/) ; epinotum with a large lateral flange covering part of base of petiole (Fig. 10G). .34. Myrmica Posterior border of clypeus with a short, shallow depression (Fig. 102) or its margin merging 10 smoothly into the rest of the head (Fig. 10K) ; out spinelike flange above each posterior spine epinotum with a smaller or inconspicuous flange (Gates MOS IDS (Es Bhocl Ia) Gaescodoecccsos-- 32 at base of petiole (Fig. 10D)) ........... 31 32. Mesal portion of anterior margin of clypeus concave 31. First segment of petiole slightly shorter than second; (Fig. 10Z); ventral side of head with long epinotum with an almost spinelike flange above curved hairs (Fig. 10K) ... 29. Pogonomyrmex each posterior spine (Fig. 107). .31. Myrmecina Mesal portion of anterior margin of clypeus pro- First segment of petiole longer than second, its duced, convex, or bilobed (Fig. 10M-—Q) ; ven- anterior portion narrow; epinotum usually with- tral side of head without such long curved hairs tend avid be Sdekie Te wes oe 33 33. Dorsal profile of thorax forming an even (Fig. 10H) or only slightly indented arc (Fig. 10D) ..... 34 Dorsal profile of thorax markedly steplike or sinuate (Fig. 10)» 00 2iaies. octet (oe 35 34. Head with straight and strong striae over its entire front and dorsal surface (Fig. 10N) ; dark brown AMES Ahir stots epic eek ar eee 35. Tetramorium Head covered with weak striae, many connected with cross-striae to give a reticulate appearance (Fig. 100) ; light brown ants, usually with a pair of dark brown suffusions on the abdomen Fc: jere oSaat ink eto eit i (eRe eae 36. Leptothorax 35. Second antennal segment not much longer than third segment; scape extending far above dorsal margin of head (Fig. 10P) .. 30. Aphaenogaster Second antennal segment as long as next two or three combined; scape not as long (Fig. 10M and iQ.) oc ieee Wid cake a Ae ee 36 36. Eyes as large as in Fig. 10M and last three antennal segments enlarged into a club; two types of workers, one with a greatly enlarged head kare i Srpid, = ntae ee phere eee 33. Pheidole Eyes smaller and antennal club not pronounced (Fig. 10Q) ; only one type of worker, with ordi- Maihy-sizeG yea Cent een eens 32. Stenamma — Fig. 11.—Pseudomyrmex queen, front view of head. KEY TO SUBFAMILIES AND GENERA (QUEENS) Fig. 12.—Diagnostic parts of queen ants of the subfamily ‘ : ‘ Ponerinae. A, Amblyopone, front view of head; B, Ponera, side ue Petiole two segmented (Fig. ) oe : view of thorax and petiole; C, Amblyopone, side view of thorax Petiole one segmented (Fig. 12B) .............. 4 and petiole. Fig. 13.—Diagnostic parts of queen ants of the subfamily Dolichoderinae. A, Dolichoderus, side view of thorax and pro- : § ee podeum—p, posterior projection of epinotum; B, Tapinoma, Fig. 14.—Front views of heads of queen ants of the subfamily side view of thorax and epinotum; C, Dorymyrmex, side view of Formicinae. A, Polyergus; B, Camponotus; C, Lasius; D, head—m, maxillary palp. Formica. 2. Compound eye represented by only one facet or absent (subfamily Ecitoninae) .............. 6 Compound eye represented by more than a single eee (ie, WD) ac Shopebagmoodomaasooman 3 3. Head oblong in face view, with large, smooth eyes (Fig. 11); antennae always close together at base, scape little more than half length of head (Fig. 11) ; medium-sized to large ants of wasp- like appearance (subfamily Pseudomyrmecinae) Head shorter, eyes no larger than in Fig. 13; bases of antennae frequently well separated; scape usually longer, frequently longer than head (Fig. 3) (subfamily Myrmecinae) 4, Genital opening small and circular, surrounded by stiff hairs forming a terminal nozzle (Fig. 6C and D) (subfamily Formicinae) ........... 13 Genital opening slitlike or inconspicuous (Fig. 7C) _ 5. Gaster with a distinct constriction between first and second segments; abdomen with a well-devel- oped sting that is frequently retracted and not visible externally (Fig. 7C) (subfamily Ponerin- BIS) 9 9.0580 ae aoc taats a IE a eran RCe a ae a eee 7 Gaster without a constriction between first and second segments (Fig. 8A—D) ; abdomen without a sting (subfamily Dolichoderinae) ......... 10 Subfamily ECITONINAE 6. Tarsal claw toothed (Fig. 17A) ....... 1. Labidus Tarsal claw without a tooth (Fig. 17B) 5:6. C5°0 OLS OORT RR ne 2. Neivamyrmex Subfamily PONERINAE 7. Scale of petiole upright, rectangular (Fig. 12B)..8 Scale of petiole ovoid, rounded (Fig. 12C) ..... 9 11 8. Second segment of abdomen unusually large (Fig. TEE epee ey Atanas a inet ae PL 5. Proceratium Second segment of abdomen of normal size (Fig. Tl oilers ees eae Re eRe eR Meera eae 4. Ponera 9. Mandibles with enlarged teeth (Fig. 124); second segment of abdomen of normal size (Fig. 7H) BRB cb Bae a EOS Ot TaOPT 3. Amblyopone Mandibles without enlarged teeth; second segment of abdomen unusually large (Fig. 7C) HO oo en ee ee eae 6. Sysphincta Subfamily DOLICHODERINAE 10. Epinotum with a flat, dorsal projection extending posteriorly and forming an overhang in lateral walany (ite, BAD) occ oe coodaace 7. Dolichoderus Epinotum without a dorsal projection (Fig. 13B) idle a Padaleneva satAtrarn ever esis Pia ticueraneee a eee 11 11. Maxillary palp with segment 3 as long as segments 4, 5, and 6 combined (Fig. 13C) Pitta des ACER RAG Cn toc OVE emt 8. Dorymyrmex Maxillary palp with segment 3 much shorter than segments 4—6 combined 12. Node of petiole vestigial (Fig. 8A) .. 10. Tapinoma Node of petiole as prominent as in Fig. 8C’ pinta, adeestaetn athens emuraepe a leneaa cs, 9. Iridomyrmex Subfamily FORMICINAE 13. Antenna with 9 segments ..... 11. Brachymyrmex Antenna with) l2'seoments «eects ree see 14 14. Mandibles sickle shaped, their inner margins with minute indentations but no teeth (Fig. 144) Se PteME aaah nee etnies Bel ane genes 16. Pofyergus Mandibles stouter and toothed (Fig. 14B)........ 15 15. Maxillary palp with three or four segments NE eee Spoganeant sana Mane samna 12. Acanthomyops Maxillary palp with five or six segments ....... 16 Fig: 15.—Diagnostic parts of queen ants of the subfamily Myr- mecinae. A, Trachymyrmex, tan- gential view of head; B, Lepto- thorax, side view of head; C, Ste- namma, side view of head; D, Pheidole, dorsal view of petiole; E, Leptothorax, dorsal view of petiole; F, Tetramorium, side view of head; G, Pheidole, side view of head. 12 16. Antennal sockets some distance from posterior mar- gin of clypeus (Fig. 14B); clypeus somewhat rectangular, with part of its lateral margins nearly parallel ............-. 15. Camponotus Antennal sockets close to or touching posterior mar- gin of clypeus (Fig. 14C and D) ; clypeus almost diamond shaped, its lateral margins very oblique De Bren ate ooe Ss Mon auc om ro afin oO ae 17 17. Node of petiole low and sloping anteriorly, the whole petiole forming a low triangle (Fig. 9E and: Gin te ee eee or cr-eeeeen 18 Node of petiole upright, the entire petiole forming a high triangle (Fig. 9C and F) ........... 19 18. Scapes of antennae extending beyond the upper margin of the head by about one-third their length or more............ 18. Paratrechina p Fig. 16.—Diagnostic parts of male ants. A, Labidus, front wing; B, Myrmica, front wing; C, Stenamma, front view of head; D, Pseudomyrmex, front view of head; E, Amblyopone, front view of head; F, Pheidole, front view of head; G, Netvamyrmex, ventral view of subgenital plate; H, Labidus, ventral view of subgenital plate; I, Proceratium, lateral view of petiole and base of gaster; J. Solenopsis, antenna; K, Dolichoderus, antenna; L, Myrmecina, head of small specimen; N, Aphaenogaster, side view of head of r mannia, side view of abdomen. front view of mandibles and labrum; M, Aphaenogaster, side view of obust specimen; O, Tapinoma, front view of mandible; P, Was- (All except F, J, K, and N after M. R. Smith, courtesy of the American Midland Naturalist) Scapes of antennae extending beyond the upper margin of the head less than one-third their length; scale of petiole with a broad median im- PINESSION oye -y= 5G sens waite ee sere 17. Prenolepis 19. Clypeus longer, as in Fig. 14D, with a slight mesal crest or angulation for most of its length PE Ses tl cotccrs eueecee yale ).6 ovens 14. Formica Fig. 17.—Tarsal claws of army ants. . Head with dorsolateral projections (Fig. 23) ...22 Head without dorsolateral projections (Fig. 15B) 5 hee is Se cet eu Seo aa eager sh ane 23 Head with long scrobe and several small tubercles (Giga lo Arand 253) eee: 21. Trachymyrmex Head with short scrobe and no tubercles (Fig. DOA, Besctetacloneg het hs ceed tann sett 20. Atta \ \ Fig. 18—The Argentine ant, Iridomyrmex humilis. A, wingless female; B, worker; C, male; D, immature stages: a, eggs; b, young larva; c, full-grown larva; d, pupa, side view; e, pupa, ventral view; f, pupa, dorsal view. All about 12 times natural size. 14 Fig. 19——A common foundation ant, Acanthomyops interjectus. A, queen; B, worker; C, winged queen. B and C, Natural History Survey Circular 39) 23. DO 26. 29. 30. Sil winged natural size. (From _ Illinois Head somewhat heart shaped, as in Fig. 24 ..... 24 Head not heart shaped Mandibles longer, as in Fig. 24A and B 22. Strumigenys Mandibles shorter, as in Fig. 24C and D se sid eee vette ratchet ae shaw ee 23. Smithistruma Antennal scrobe extending to or beyond the pos- terior margin of the eye (Fig. 10E and F).. .26 Antennal scrobe not reaching the posterior margin Ol stew CVO gers rae reuters ioc oe 27 Yellow-orange ants with many deep longitudinal mugae on) the headit-.---n.4- 24. Wasmannia Brown ants with head dull but not markedly TUG OSE .nsigevsuay canker eee eucuere wate 25. Harpagoxenus Epinotum without spines ....:............... 28 Epinotumiswithsspiness (Hips) 3) meer merle 29 Antenna with a distinct two-segmented club (Fig. 10 By eRe yah cic. Steerer ae 27. Solenopsis Antenna without a two-segmented club (Fig. 10A) Bee Rats Ee an Rees 28. Monomorium First segment of petiole either shorter than second or without a dorsal projection (Fig. 107) ....30 First segment of petiole longer than second and with a marked dorsal hump on its posterior half (Bie MLO GSD iG andl fl) premetre te retatsersreiei«) 31 Head with strong longitudinal rugae, much as in Fig. 10, texture somewhat dull . .31. Myrmecina Head with only faint sculpturing, surface shiny 26. Crematogaster Mesal portion of anterior margin of clypeus concave (Fig. 10L); ventral side of head with long curved hairs (Fig. 10K) ... 29, Pogonomyrmex Mesal portion of anterior margin of clypeus either produced, convex, or bilobed (Fig. 10M-Q) ; ventral side of head without such long curved hairs 32. Posterior border of clypeus with a distinct semicir- cular, deep, sharp depression (Fig. 10/) ; epino- tum with large flange at base of petiole (Fig. 10G) 34. Myrmica Posterior border of clypeus with either a short, shal- low depression (Fig. 10M/), or its margin merg- ing smoothly into rest of head (Fig. 10N) ; epinotum with smaller or inconspicuous flange at base off petioles|(Bigs110@)) eee eee 33 33. Pedicel extending far above dorsal margin of head (Fig. 10P) (Fig: 10)... cde ce gene eee 34 34. Dorsal aspect of second segment of petiole about as wide as long, its sides nearly straight (Fig. 1s) 2) ee Ecos SAM ins Go emoS Ode 3k se 35 Dorsal aspect of second segment of petiole about twice as wide as long, its sides angulate (Fig. ka) 0) eae eines ene SRG oe od oe 36 35. Eyes as large as in Fig: 15B....... 36. Leptothorax Eyes smaller, as in Fig. 15C....... 32. Stenamma 36. In lateral view, long axis of eye nearly parallel to long axis of head (Fig. 15F) .. 35. Tetramorium In lateral view, long axis of eye markedly tangential to long axis of head (Fig. 15G) ... 33. Pheidole KEY TO SUBFAMILIES AND GENERA (MALES) 1. Petiole of two segments Petiole of only one segment 2. Eyes elongate and bean shaped; clypeus not extend- ing close to bases of antennae (Fig. 16D) (sub- family Pseudomyrmecinae) Eyes relatively small, ovoid, or hemiovoid (Fig. 21C [SS he ee eee 30. Aphaenogaster — Pedicel not extending above dorsal margin of head © and #7) ; clypeus extending dorsally almost to or above level of antennal bases (subfamily Myr- AMIE CIIAG) Weer sera lrs a) cyvenela tw eticye aoe tie sce sees 3 23 3. Subgenital plate elongate, with two or three apical teeth (Fig. 16C, E, and F) ; front wing with cell M long, vein Cu; with a sharp bend at cross- vein m-cu, and Cuj, distinct and _ sclerotized (Fig. 16A) (subfamily Ecitoninae) ......... 5 Subgenital plate without apical teeth; front wing, if present, with cell M much shorter or open, vein Cu, with only a slight curve or none at crossvein m-cu, which is sometimes atrophied, and Cu, usually forming only an indistinct apex LOMO (Mig MGB) fa Awihen ctoesmcent nero ae 4 4. A pronounced constriction between first and second gastric segments (Fig. 7C, E, and H) (subfamily PONELINAG) Mercian) Soferd oi bersoews pl mye fe eee 6 No constriction between first and second gastric segments (Fig. 8A and B; Fig. 9B) (subfamilies Dolichoderinae and Formicinae) ........... 10 Subfamily ECITONINAE 5. Tarsal claws with a tooth (Fig. 17A) .. 1. Labidus Tarsal claws simple (Fig. 17B) .. 2. Neivamyrmex Subfamily PONERINAE GRMN NATION GSS tits Siaieitis ateie'e tile seas « 4. Ponera VVATIVG RRM My rips mnteha re sesbstaitis ace sateelntals gots o5 7 7. Metanotum with a dorsal spine (Fig. 167) ...... 8 Metanotum without a spine .................. 9 8. Petiole rectangular or angulate at apex in lateral VICWAEER CPE Sriclon ast ces 5. Proceratium Petiole rounded at apex in lateral view Meee trodes cinta wate. 6. Sysphincta 9. Clypeus with minute teeth (Fig. 162) ME eae ah cipounls tdi ers ¥ weltievaca sie: 3. Amblyopone Clypeus without teeth (Fig. 16F) ...... 4. Ponera Subfamilies DOLICHODERINAE and FORMICINAE 10. Antenna 10-segmented; pale cream colored ants MM nes ise Sheges ncn ticks, oss + 11. Brachymyrmex Anteunaswithmloeseaments eae ae ade e - 11 11. Second segment of funicle longer than body of scape (Rig el ORMS srtctaone np eryyscniates. 4 9. Iridomyrmex Second segment of funicle about the same length as or shorter than body of scape ........... 12 12. Third segment of maxillary palp as long as segments 13. 14. 15. 16. 18. 20. 21. 15 4) ang Oicombined =e eee 8. Dorymyrmex Third segment of maxillary palp much shorter than Seeioeaus 4 3), Gravel (8) Cevaaloyvaeel coo cecaanoce 13 Maxillary palp three or four segmented slic rey Shale ragatede Evens seats 12. Acanthomyops Maxillary palp five or six segmented .......... 14 Body of scape shorter than the combined lengths of the first three funicular segments (Fig. 16K) Peete svt eben hls MEER AS ee 7. Dolichoderus Body of scape as long as or longer than the com- bined lengths of the first three funicular seg- IMEMLES Here aces ores eee ae eee Peet een ie 15 Mandible sickle shaped, without distinct teeth (Fig. LAM, sco. c a ie, we eden seats ied eres fetes 16. Polyergus Mandible somewhat triangular, sometimes with teeth ecient, eee ated Raney gee otros 16 Anterior face of the gaster flat or convex ....... 17 Anterior face of the gaster dished out and concave, forming a shallow cavity into which the petiole fT EStTAeT POSE a. serge ey aewe cece Mae eae eee 19 Body of scape shorter than combined lengths of first four funicular segments; body length 2-3 mm RP citar eet ace Mane BMP 9. Iridomyrmex Body of scape much longer than combined lengths of first four funicular segments; body length Sa Ohana Peete ees a cake 5 ee ae 18 Antennae inserted at a distance from the posterior margin of the clypeus........ 15. Camponotus Antennae inserted close to the posterior margin ofsthiercly peusime sere eee 14. Formica Body of scape shorter than the first four funicular segments combined ........... 17. Prenolepis Body of scape longer than the first four funicular Keane Comalyinel so osccuneusosoruvaecve 20 Petiole upright and high.............. 13. Lasius Petiole inclined forward and lower ............ 21 Mandible with many microscopic teeth (Fig. 160) See Ee rath win ge Mon) sage eset Neg 10. Tapinoma Mandible with larger and fewer teeth (Fig. 16C) Bs, dena hoon acorns eg Re eb Se 18. Paratrechina Subfamily PSEUDOMYRMECINAE Ep, OkM\y GAS SONOS . ona sannevess 19. Pseudomyrmex Subfamily MYRMECINAE 73. Dee Antenna 10 segmented ......... 35. Tetramorium Antenna with more than 10 segments .......... 24 Head and body with many erect long hairs (Fig. Fig. 20.—Winged female of the large black carpenter ant, Camponotus penn- syluanicus, (From USDA) 25. 26. Dif 28. 29: 30. 31. 32. 33: 3h Fig. 21—Worker of the crazy ant, Prenolepis longicornis. 10K) ; clypeus shallow, its apical margin concave (Ge, NOV) cosnchoaccoesc 29. Pogonomyrmex Head and body with a few erect hairs, but these are never long or numerous; clypeus deeper and somewhat convex (Fig. 10M) ............. 25 Antenna lilvorl)2!secmented rier ens reir 26 Antennae! Sisepiientec eee etter tere 29 Petiole attached high on anterior face of gaster; segments of funicle appearing somewhat bead- Like yeecetnatehe ord OA areata 26. Crematogaster Petiole attached low on anterior face of gaster; seg- ments of funicle not at all beadlike ......... 27 First funicular segment enlarged, often globose, scape very short (Fig. 16/)...... 27. Solenopsis First funicular segment not markedly enlarged, scape longer, as in Fig. 16K .............. 28 Antennal scrobes well developed (Fig. 10£) fe Sao en ene ene 25. Harpagoxenus Antennal scrobes weakly developed or absent 4 easton ho is eecatchees aasestyee a PNG 36. Leptothorax Mandibles vestigial, reduced to short fleshy stubs (Gait, GO Seonoucaboon bus onc 31. Myrmecina Mandibles developed and sclerotized, although Sometimes small ear yenrstk iret rine rere 30 Abdomen in lateral view with a pair of elongate processes (the parameres of the genitalia) pro- truding from the posterior tip (Fig. 16P) 24. Wasmannia Abdomen with only short protruding processes, which are blunt at the tip, or no visible pro- truding structures Scape very long, at least as long as the first eight funicular segments combined .............. 32 Scape shorter, not as long as the first eight funicular SGUNSNS pecs onneoso do obondocoeeoc mognar 33 Front wing with cell R; short and wide (Fig. 22B) SEES rere on eee ere 21. Trachymyrmex Front wing with cell Ry long and narrow (Fig. 224) 20. Atta Stigma of forewing weakly developed or missing (males too poorly known to permit further iden- tification without other castes). . 22. Strumigenys 23. Smithistruma Stigma of forewing well developed, as in Fig. 16B, butisometumes) palesee reenter teeta tia 34 Head flattened and either shallowly elliptic (Fig. 16M) or almost rectangular in lateral view (Fig. (After Wheeler) IGN) Sade8 oe ee eee eee Head much more rounded 35. Base of clypeus ending in a marked semicircular depression (Fig. 10J) .......... 34. Myrmica Base of clypeus ending in a shallow triangular im- pression, or no depression evident .......... 36 36. Body of scape very short, at most as long as the first and second funicular segments combined Jags AME eas ghedd hithedo ae er 37 Body of scape longer than the first and second funi- cular segments combined ................. 38 37. Funicle threadlike, the same thickness for its entire length; ocelli on a high protuberance (Fig. 16F) SOIR Re eae a creer cienc, Gro cenis cepa bo. < 33. Pheidole Funicle with last four segments much thicker than first few segments; ocelli not on a protuberance 28. Monomorium 38. Ocelli small, separated from each other by twice the diameter of one of them (Fig. 16C’) ; epinotum concave in lateral view........ 32. Stenamma Ocelli large, separated from each other by only the diameter of one of them, somewhat as in Fig. 16Z; epinotum convex in lateral view irsiageage se eee tegeee eecs 36. Leptothorax SYNOPSES OF GENERA Subfamily ECITONINAE These ants are the native American army ants, differ- ing in many characters from the army ants of the Old World. The New World species occur chiefly in the tropics, where the workers may form long foraging col- umns. Their food is mostly other insects and small ground-dwelling animals, but they may kill fairly large animals. The nest is a temporary bivouac built around the queen and brood. Only two genera occur in or near Illinois. 1. Labidus Jurine No species have been recorded from Illinois, but L. coecum (Latreille) is known from Louisiana, Oklahoma, and Texas and may eventually be found in Illinois. The workers range from 3 to 10 mm long, the larger ones with slightly enlarged heads. 2. Neivamyrmex Borgmeier The southern and southwestern species, N. nigrescens (Cresson) , has been found sporadically in extreme south- mil H HNL ern Illinois, where it may be an occasional pest in swim- ming pools and basements. In this species the workers are 3-6 mm long and dark blackish red, the larger ones with slightly swollen heads. Several other species occur to the south and west of Illinois. Subfamily PONERINAE The ants comprising this subfamily are seldom found without a deliberate search of rotten logs or beneath leaves and stones on the forest floor. They both forage for small prey and nest in these situations. The nests are small, rarely containing more than 50 workers, and each nest may contain several queens. The workers and queens are reddish or reddish brown, range from 2 to 6 mm in length, and have a sting. Of the 12 or more genera known from North Ameri- ca, the 4 more northern ones have been taken in Illinois. None of the Illinois species is economic. Only rarely are any of them found in the garden or home. 3. Amblyopone Erichson The sole Illinois species, A. pallipes Haldeman, (for- merly placed in the genus Stigmatomma Roger) is the only one known from North America. It is readily recognized in the worker and queen castes by the elongate mandibles (Fig. 7F). Although widely distributed in Illinois, it is a rare species. 4. Ponera Latreille This is the commonest ponerine ant genus in Illinois, where two of the seven North American species occur. The genus is unusual because some colonies produce wingless, workerlike males. 5. Proceratium Roger Of the three North American species, only P. croceum Roger has been found in Illinois. It is a rare species whose nests are usually found in wood attacked by red rot. 6. Sysphincta Roger Of the two North American species, only the wide- spread §. pergandei Emery has been found in Illinois. It is moderately rare. Subfamily DOLICHODERINAE These ants have no sting and the workers are all alike, with no larger soldier caste. Four of the six North American genera occur in Illinois; all of them are small, brownish or blackish ants, the workers ranging from 2.0 to 4.5 mm. Colonies usually contain several hundred individuals. All Illinois species forage in files. 7. Dolichoderus Lund Two of the four U.S. species occur in Illinois. Their nest, made in the soil, is not craterlike and has a con- cealed opening. They are not economic and are seldom seen outside woodlands or forest edges. Dolichoderus is often found tending aphids. 8. Dorymyrmex Mayr The sole North American species, D. pyramicus, has so far been collected in Illinois only in undisturbed 17 Fig. 22.—Wings of leaf-cutting ants. A, Atta sexdens Lin- naeus; B, Trachymyrmex cornetzi Forel. (After Weber, courtesy of Science) sandy areas. The nest is usually in the open and crater- like, but occasionally is constructed under stones. 9. Iridomyrmex Mayr Two species occur in Illinois, the introduced species, I. humilis (Mayr), (the Argentine ant) (Fig. 18) and the native J. pruinosus (Roger). In both, the workers are small, ranging from 2 to 3 mm long. Both species nest in soil or under stones or boards. The workers for- age in narrow columns, often tend aphids, and eat a wide variety of vegetable and animal foods. The Argentine ant is a domestic pest, entering houses and eating all types of sweets, meats, and vegetables. When crushed, the ants have a stale, greasy or musty odor. Key To Species OF IRIDOMYRMEX WORKERS Scape extending beyond top of head by only half the length of first funicular segment. Seldom in houses bod GPR ia) hehe Cake poe gi Sic aber reper emare pruinosus Scape extending beyond top of head by the full length of first funicular segment. Frequently in houses RETO cs: Rote er ee cee humilis 10. Tapinoma Foerster Only the native species, T. sessile (Say), occurs in Illinois. It is a small ant, the worker ranging from 2.0 to 3.5 mm, and it is dark blackish brown. It nests in a great variety of sheltered places inside the house and outdoors, often with several thousand workers in a single nest. The species is practically omnivorous. Common in dwellings, it will eat almost any human food and con- taminates foods with “Tapinoma odor,” a smell some- what like butyric acid that has earned this species the name of odorous house ant. Subfamily FORMICINAE Ants of this subfamily range from nearly the smallest to the largest of Illinois ants. The queens and workers have no sting but are characterized by the curious circle of hairs around the anal opening. 18 Fig. 23—Workers of leaf-cutting ants. A, Atta cephalotes Linnaeus; B, Trachymyrmex arizonensis Wheeler. (After Weber, courtesy of Science) 11. Brachymyrmex Mayr The sole U.S. and Illinois species, B. depilis Emery, has minute workers 1.5-2.0 mm long that forage in the leaf litter of woods and meadows. ‘These ants nest under stones or in the soil and are seldom seen without deliberate search. 12. Acanthomyops Mayr “Of the nine U.S. species, only three are recorded from Illinois. The workers are 3.0-4.5 mm long and a medium shade of reddish brown. Normally these ants forage in leaf litter or underground, where they tend aphids and mealybugs, and are seldom seen except by a person digging in the garden. During the winter, however, entire colonies (including both workers and winged forms) frequently move to house foundations. If there is a break in the foundation, a colony of both workers and winged forms (Fig. 19) may move into the basement and take up residence under a loose brick or board. They do not raid through the house, but many persons find their company disconcerting. If the colony is disturbed, the ants emit a strong, citronellalike odor. When soil temperatures rise in spring, the ants will de- part along the path by which they entered. This winter habit has earned them the name of foundation ants. Formerly these ants were classified in the genus Lasius. 13. Lasius Fabricius The seven Illinois species, all native, are among its commonest field and garden ants. In most of them the workers are dark brown, ranging in size from 2 to 4 mm. They actively search for food above ground and may enter houses and eat a variety of sweats and meats. They make large nests in soil or under covering objects, each nest containing up to 10,000 workers. Two cornfield ants, L. alienus Foerster and L. neont- ger Emery, are often found tending aphids on corn and other plants. JL. neoniger is known to spread the virus causing barley yellow dwarf by its aphid-tending ac- tivities. 14. Formica Linnaeus The dozen Illinois species of this genus, all natives, are the most commonly observed of our entire ant fauna. The workers are brownish black, sometimes with the head red, and range in length from 2.5 to6.0 mm. They forage actively, often in the open, and are called side- walk ants. These ants nest in soil. Some species construct a nest entirely below the soil surface with an obscure entrance. Others build large mounds over the nest, and each may contain 100,000 workers. They are scavengers, predators on other insects, and nectar feeders. In Illinois they enter houses only sporadically and singly, and hence are of no economic importance. If one disturbs them in the wild, however, they bite readily and inflict a painful wound. Some species are “cuckoo” ants; that is, a young queen uses a colony of another species to start her own colony, first killing off the queen of the host species. This results in temporary colonies of mixed workers. 15. Camponotus Mayr The ants of this genus are the carpenter ants (Fig. 20). Eight native species occur in Illinois, including our largest ants. Depending on the species, the workers may be all black, reddish brown, or tan and range in length from 3 to 13 mm in the same nest. The larger workers have heads disproportionately larger than those of smaller individuals; these large, big-headed workers are called majors, the small ones minors. They tend aphids, forage in columns, and are general scavengers. Most species of Camponotus nest in dead wood. In the wild they use logs, stumps, and the wood of standing dead trees. They also nest in timbers of houses, railings, and poles, excavating tunnels by chewing out the softer wood between the harder annual rings of beams, siding, and other structures, weakening the wood and frequently causing extensive damage. The species most frequently encountered in buildings is C. pennsyluanicus DeGeer, a large black species with long grayish or yellowish hair on its upper surface. 16. Polyergus Latreille These ants are the slave-making ants. Two native species occur in Illinois; the workers of both are reddish brown and 6-8 mm long. The nest is 100-120 cm deep in the soil and has an obscure opening. The workers are out of the nest only when scouting or raiding; they do no foraging. On a raid the Polyergus workers attack a Formica nest and carry pupae of Formica workers back to the Polyergus nest. When these pupae develop and emerge as adult workers, they adopt their new “household” and do the foraging for the entire nest. A Polyergus nest, therefore, contains the Formica “slave” workers that come and go freely and the Polyergus workers that spend most of their time inside the nest. 17. Prenolepis Mayr The single native North American species, P. imparis (Say), occurs commonly throughout Illinois. The workers are dark brown and 2-4 mm in length. These aphid tenders and general scavengers forage in thin columns and build their inconspicuous nests in the ground. They are frequent pests in houses and green- houses, eating a variety of domestic foods and sometimes gnawing the tips of flower buds and the shoots of plants for their juices. They take honey from weakened bee- hives. 18. Paratrechina Mutschoulsky The genus is represented in Illinois by three species, including two native species resembling Prenolepis im- paris in general appearance and an introduced species, Paratrechina longicornis. This latter is also small and dark but has very long, slender legs and a peculiar rolling gait when running, earning the species the common name of crazy ant (Fig. 21). All of these species nest in the ground and may be general nuisances in the house, eating a variety of foods. Subfamily PSEUDOMYRMECINAE 19. Pseudomyrmex Lund The five or six native American species occur south of Illinois chiefly in the Gulf states and into the tropics. The workers are 4-10 mm in length, mostly yellow or brown, and wasplike in appearance. Some nest in hollow thorns on acacia trees; if the tree is disturbed, the workers dash out and inflict painful bites and stings. Subfamily MYRMECINAE This is a large and diverse subfamily that is especially abundant in the tropics. The Illinois fauna is quite small compared with that of the entire world. 20. Atta Fabricius This and the following genus belong to a New World tribe called the leaf-cutting ants. The reddish-brown workers cut off pieces of leaves, carry them into the nest, work them into a pulpy mass, and seed them with fungus spores. The ants feed only on the fungus produced by these underground gardens. A mature colony contains thousands of individuals, including a large-headed soldier caste and several sizes of workers. The ants forage in columns; a column of returning workers is a curious sight, each ant carrying a piece of leaf nearly as large as itself. This leaf-carrying habit has earned these ants the name of parasol ants. The leaf-cutting ants are almost entirely tropical, with two genera extending northward into the south- central states. The genus Atta occurs north to central Louisiana. 19 21. Trachymyrmex Forel This small genus is represented in Illinois only by T. septentrionalis (McCook), the northern leaf-cutting ant. It occurs only in sandy soil and makes relatively small nests, each having only a few hundred workers. 22. Strumigenys F. Smith This and the following genus belong to a worldwide, distinctive tribe of minute ants whose workers and queens have long, pointed heads. The workers are dark reddish brown and range in size from 1.5 to 2.5 mm. They oc- cur only in wooded areas, making small nests in rotten wood and foraging in leaf mold. They feed on spring- tails and other minute organisms. The sole North Ameri- can species of this genus, S. lowisianae Roger, occurs in Illinois (Fig. 24A and B). 23. Smithistruma Brown Several species of this genus occur in Illinois wood- lands. In general habits and appearance they resemble Strumigenys, but have shorter mandibles (Fig. 24C and D; Fig. 25). 24. Wasmannia Forel This genus is represented in North America and Illi- nois only by W. auropunctata (Roger), an introduced tropical species that occurs this far north only in houses or greenhouses. The dark workers are minute, only 1.5— 1.8 mm, but sting severely, earning them the name little fire ants. They nest in soil and under cover, often with several queens and several thousand workers in a nest. They feed on honeydew, minute insects, and a wide variety of domestic foods. 25. Harpagoxenus Forel Of the two North American species only H. ameri- canus (Emery) is known from Illinois. The reddish- Fig. 24.—Front views of heads of workers. A, B, Strumigenys louisianae Roger, showing variation; C, Smithistruma angulata Smith; D, Smithistruma pergandei Emery. Inset are details of the mandibles. (After M. R. Smith) 20 Fig. 25—Worker of Strumigenys ohioensis Kennedy and Schramm, showing the soft, white, funguslike growths that occur on the petiole in many species of this genus. Actual size, 2mm. (After Kennedy and Schramm) brown workers are fairly large, ranging in length from 3.0 to 3.5 mm, and forage in leaf mold, under bark, and on low vegetation. ‘This species does not make a nest of its own. Instead, it takes over nests of the genus Leptothorax. The Leptothorax queen is killed, and the Leptothorax workers then assist in raising the brood of the Harpagoxenus queen. This genus does not normally inhabit gardens or houses. 26. Crematogaster Lund Several native species of this genus are extremely common in Illinois. The workers (Fig. 26) usually have red heads and black abdomens, and range in size from 2.5 to 4.0 mm. They are easily recognized by the broad head and wide, heart-shaped gaster. These ants nest under stones or other objects on the grourid, in dead stumps or logs, and sometimes in posts and rafters, but never in the ground. The colonies may contain several thousand workers. They are general foragers and abun- dant both in the garden and house, feeding on a variety of domestic foods. In the garden they are often found tending aphids. When disturbed, they bite and sting painfully. 27. Solenopsis Westwood The only Illinois species of this genus is the native S. molesta (Say). The workers are dark brown and minute, ranging from 1.3 to 1.8 mm. The nests are usually deep in the ground and each may have several Fig. 26—Worker of Crematogaster lineolata (Say). A, side view; B, dorsal view of petiole and gaster. thousand workers. These are among the commonest of garden and household ants, feeding on a variety of domestic foods and often eating garden seeds. To this genus also belong the fire ants, several species of which occur south of Illinois. These ants are chiefly agricultural, and when disturbed, bite and sting pain- fully. 28. Monomorium Mayr The two Illinois species of this genus, the native M. minimum (Buckley) and the introduced Pharaoh’s ant, M. pharaonis (Linnaeus) (Fig. 27), are among our tiniest ants, the workers ranging from 1.2 to 2.0 mm. Both species nest in the soil or in buildings and are frequently abundant in houses, where they eat a variety of domestic food. Pharaoh’s ant is especially fond of fats. The introduced species, M. destructor (Jerdon), occurs to the south of Illinois and may eventually be found in the state. It also is a domestic pest that causes trouble by removing insulation from electric cables and cutting holes in fabrics and rubber goods; it also inflicts a pain- ful sting. Key to SpEcIES oF MONOMORIUM WORKERS 1. Segments of the antennal club successively increas- ing simleng thes aise tose sae destructor First two segments of the antennal club about the same size, the terminal segment larger ...... 2 2a Clearanedcishwyellowaneeeerenn eee pharaonis Shining? black® «soars cuaie terre cege ees minimum 29. Pogonomyrmex Mayr The ants of this genus are the native agricultural ants famous throughout the Great Plains. None has so far been taken in Illinois, but they are known not far to the west. The workers are chiefly reddish brown and large, ranging from 4.5 to 12.0 mm in length. They nest in the ground, constructing a mound of gravel some- times 45 cm in diameter and clearing all vegetation around it to a distance of about 1 meter. When dis- turbed, the workers have a potent sting. These ants feed chiefly on seeds supplemented by general scaveng- ing. 30. Aphaenogaster Mayr This large native genus is represented in Illinois by about six species. The workers are very slender and long legged, are usually reddish brown, and vary in size from 3.2 to 7.0mm. They forage in leaf litter above the ground and in low vegetation, feeding on a variety of foods. They nest in rotten wood, under stones, and in the soil, often making a slightly elevated area on the soil where they have deposited particles from the nest excavation. Each nest may have up to 3,500 workers and several queens. These ants are frequently abundant in the garden; only rarely does one get into the house. If they locate a nest in a lawn, they may be a persistent nuisance for some time and will frequently inflict painful bites when disturbed. Otherwise, they are not pests. 31. Myrmecina Curtis The two North American species, both native, occur in Illinois. The workers are reddish brown and range in size from 2.5 to 4.5 mm. They construct small nests in rotten wood or leaf litter, primarily in woodlands. They are only rarely found in homes. 32. Stenamma Westwood The three Illinois species of this genus are all natives, similar in size and general appearance to those of the preceding genus. They make their nests chiefly in leaf mold and are restricted to woodland situations. 33. Pheidole Westwood This is primarily a southern genus, having over 40 North American species of which only 2 have been found in Illinois. The workers are dark brown and range in size from 2.5 to 4.5 mm. ‘The nest is made under stones or in soil, commonly with openings between cracks in sidewalks. Each nest may contain several hundred workers. The small workers have normal-sized heads, the larger workers greatly enlarged heads with massive mandibles, and these differences are correlated with their food habits. They naturally feed primarily on small plant seeds that are brought into the nest by the smaller workers and then cracked into fragments by the large- headed workers. Around homes these ants nest commonly in the garden and frequently enter the house, where they feed on a variety of domestic foods. 34. Myrmica Latreille Of the 11 native American species, 4 occur in IIlinois. The workers are reddish brown and range in length from 3.5 to 6.0 mm. They build nests in the soil, each nest usually containing only 50-100 workers and one queen. The workers forage in litter and low-level vegetation. Although they usually occur in woodlands, they may at times be common in lawns. 35. Tetramorium Mayr Only a single native species of this genus occurs in Illinois, T. caespitum (Linnaeus) , the pavement ant. The workers are almost black, 2.5-3.5 mm long. The nests are made in soil, often under stones, boards, or sidewalks. In the house the workers eat a variety of domestic foods; 21 Fig. 27.—Pharaoh’s ant, Monomorium pharaonis. A, queen after losing her wings; B, worker. Natural size of queen, 4 mm; of worker, 2 mm. (From USDA) in the garden they may steal seeds and girdle the stems of garden crops. 36. Leptothorax Mayr This abundant North American genus is represented in Illinois by three native species. ‘The workers are usually pale yellow, generally with a dusky spot on each side of the gaster, and range in size from 1.5 to 3.5 mm. They nest in a variety of places, including under rotten wood, under bark, in acorns, and under stones, each nest containing at most a few hundred workers. hey are general scavengers, foraging in ground litter and low vegetation. Although their nests may frequently be found in the garden, they very seldom enter the house. SELECTED REFERENCES Back, E. A. 1946. House ants. U.S. Department of Agriculture Leaflet 147. 8 p. Brown, Wiu1AM L., Jr. 1948. A preliminary generic revision of the higher Dacetini (Hymenoptera: Formicidae). Ameri- can Entomological Society Transactions 74:101-129. Buren, WILLIAM F. 1944. A list of Iowa ants. 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