FILE: <insect1.htm> Bibliography Bibliography #2 Terminology [Navigate to MAIN MENU ]


For educational purposes only; do not review, quote or abstract:--

A Public Service on the basics of Insect Identification





E. F. Legner, University of California, Riverside


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This key is in a form commonly used in North America. If the statement is true, proceed to the designated couplet, whereas if it is false, go to the "b" portion of the couplet. Numbers in parentheses refer to the previous couplet or couplets read. Details on families may be found in <Principal Groups>. See MORPHOLOGY to learn about insect structure. -- The Class Entognatha is included herein Citations


(For References, please refer to <Biology References> & <General References> [Additional

references may be found at: MELVYL Library]


Navigate directly to: Coleoptera Diptera Hemiptera Lepidoptera Neuroptera


Strepsiptera Hymenoptera (Chalcidoidea Pteromalidae Subfamiliea)



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[A will display all images for both pairs of a couplet]


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1a. Adults have well-developed wings



1b. Adults wingless or with wings vestigial or rudimentary (nymphs, larvae & some adults)



2a (1a). Wings membranous, not hardened or leathery



2b. Front wings hardened or leathery, at least at base (Figs.A-E); hind wings, if present, usually membranous . . . . A



3a (3a). Only 1 pair of wings



3b. Two pairs of wings



4a (3a). Body shaped like a grasshopper; pronotum ( = dorsal plate or sclerite of prothorax) extends back over abdomen and is pointed apically; hind legs enlarged (Figs.A-F) [pygmy grasshoppers ... A ........ Orthoptera <General Characteristics>; <Adults> & [Latest Classification[



4b. Body not shaped like a grasshopper; pronotum not as previous; hind legs not so enlarged.



5a (4b). Antennae with at least 1 segment bearing along lateral process; front wings minute, hind wings like a fan (Figs.A-B); minute insects [male twisted-winged parasitoids) A Strepsiptera <General Characteristics>; <Adults> & <Juveniles> [Latest Classification]



5b. Does not fit previous description exactly


6a (5b). Abdomen with 1-3 thread-like or bristle-like caudal (= tail) filaments; mouthparts vestigia



6b. Abdomen without thread-like or bristle-like caudal filaments; mouthparts almost always developed, mandibulate (= chewing) or for sucking



7a (6a). Antennae long and conspicuous; abdomen terminates in one long style (rarely 2); wings with a single forked vein (Fig.A); halteres (= knobbed modified hind wings) present and usually terminating in a hooklike bristle; minute insects, usually <5 mm in length [male scale insects] ...... A ,,,,,,.. Homoptera <General Characteristics> [Latest Classification]



7b. Antennae short, bristle-like, and inconspicuous; abdomen with 2-3 thread-like caudal filaments; wings with numerous veins and cells; halteres absent; usually >5 mm in length (Fig. A) [mayflies] ...... Ephemeroptera <General Characteristics> [Latest Classification]



8a (6b). Tarsi almost always with 5 segments; mouthparts for sucking; hind wings knob-like, reduced to halteres (Figs.A-E); body lightly sclerotized (= hardened) [flies] ..... A. .Diptera <General Characteristics>; <Juveniles> [Latest Classification]



8b. Tarsi with 2-3-segments; mouthparts variable; hind wings reduced or absent, not haltere-like



9a (8b). Mouthparts mandibulate (Figs.A-E)[psocids] ...... A ... Psocoptera (Corrodentia) <General Characteristics, #2>; <Adults, #2> & <Juveniles, #2> [Latest Classification]



9b. Mouthparts for sucking (Figs.A-C) [some planthoppers & leafhoppers] ......... Homoptera <General Characteristics> [Latest Classification]



10a (3b). Wings mostly or entirely covered with scales (Fig. A); mouthparts usually in the form of a coiled proboscis (Fig.B); antennae with many segments (Figs.C-G) [butterflies & moths] ....... A ..... Lepidoptera <General Characteristics> [Latest Classification]



10b. Wings not covered with scales; mouthparts not a coiled proboscis, antennae variable



11a (10b). Wings long and narrow, veinless or with only 1-2 veins, and fringed with long hairs (Fig.A); tarsi with 1-2 segments, the last segment swollen; minute insects, usually <5 mm in length (Figs.A-D) [thrips] ....... A ........ Thysanoptera <General Characteristics>; <Adults> & <Juveniles> [Latest Classification]



11b. Wings not as previously described , or if wings are somewhat linear, then the tarsi have more than 2 segments



12a (11b). Front wings relatively large and usually triangular; hind wings small and usually rounded, the wings at rest held together above the body; wings usually with many veins and cells; antennae short, bristle-like, and inconspicuous; abdomen with 2-3 thread-like caudal filaments (Fig.A); delicate, soft-bodied insects (Fig.B) [mayflies] ... A ...... Ephemeroptera <General Characteristics> [Latest Classification]



12b. Not as previously described



13a (12b). Tarsi with 5 segments



13b. Tarsi with 4 or less segments



14a (13a). Front wings obviously hairy; mouthparts usually very much reduced except for the palps; antennae usually as long as body or longer; somewhat soft-bodied insects (Figs.A-F) [caddis flies .... A ...... Trichoptera <General Characteristics>; <Adults> & <Juveniles> [Latest Classification]



14b. Front wings not hairy, at the most with microscopic hairs; mandibles well developed; antennae shorter than body



15a (14b). Body quite hard, wasplike insects; clypeus not elongated; the abdomen often constricted at base, 1st abdominal segment fused to thorax; fore wings distinctly larger than hind wings and with fewer veins; front wings with 20 or less cells (Figs.A-F)[sawflies, bees and wasps] ....... A ........ Hymenoptera <General Characteristics> [Latest Classification]



15b. Body soft, not wasplike, the abdomen not constricted at base; hind wings about the same size as front wings and usually with about as many veins; front wings frequently with more than 20 cells



16a (15b). Costal area of front wings (= area just behind anterior margin) nearly always with numerous cross veins per pair of longitudinal veins (Fig.A), or if not (Fig.B) then hind wings shorter than front wings; mouthparts not prolonged ventrally into a beak (Figs.C-G) [lacewings, dobsonflies, antlions] ... A ........ Neuroptera <General Characateristics> [Latest Classification]



16b. Costal area of front wings with not more than 2-3 cross veins per pair of longitudinal veins (Fig.A); mouthparts prolonged ventrally to form a beak-like process (Figs.B-D [scorpionflies].......... Mecoptera <General Characteristics>; <Adults> & <Juveniles> [Latest Classification]


17a (13b). Hind wings as long as front wings and of the same shape or wider at base, the wings at rest held above the body or extended out (never held flat over abdomen); wings with many veins and cells; antennae short, bristle-like, and inconspicuous; abdomen long and slender (Figs.A-B); tarsi with 3 segments; length 20-85 mm [dragonflies, damselflies) A .... Odonata <General Characteristics>; <Adults> & <Juveniles> [Latest Classification]



17b. Not as previously described



18a (17b). Mouthparts for sucking



18b. Mouthparts mandibulate (= chewing)



19a (18a). Beak arises from front part of head (Figs.A-E) [gnat bugs..Hemiptera /Heteroptera ...... A



19b. Beak arises from hind part of head (Fig.A) [cicadas, some hoppers, aphids, some psyllids and whiteflies] ...... Homoptera <General Characteristics> [Latest Classification]



20a (18b). Tarsi with 4 segments; front and hind wings similar in size, shape and venation (Figs.A-E) cerci tiny or absent [termites] ..... A ...... Isoptera <General Characteristics> [Latest Classification]



20b. Tarsi with 3 or less segments; hind wings usually shorter than front wings; cerci either present or absent



21a (20b). Hind wings with anal area nearly always enlarged and forming a lobe, which is \ folded like a fan at rest; venation varying from normal to very dense, the front wings usually with several cross veins between Cu-1 and M and between Cu-1 and Cu-2 (Fig. A); cerci present and often fairly long; mostly 10 mm or more in length; nymphs aquatic, and adults usually near water (Figs.A-F) [stoneflies] .... A ...... Plecoptera <General Characteristics>; <Adults> & <Juveniles> [Latest Classification]



21b. Hind wings without an enlarged anal area and not folded at rest; venation normal or reduced, with no extra cross veins; short cerci present or absent; mostly 10 mm in length or less; nymphs not aquatic and adults not regularly near water


22a (21b). Tarsi with 3 segments, basal segment of front tarsi enlarged A ....(Figs.A-B) [webspinners] ...... Embioptera <General Characteristics> [Latest Classification]



22b. Tarsi with 2-3 segments, basal segment of front tarsi not enlarged



23a (22b). Cerci present; tarsi with 2 segments; wing venation reduced (Figs.A-D); moniliform (= bead-like) antennae with 9 segments ..... A ........ Zoraptera <General Characteristics> [Latest Classification]



23b. Cerci absent; tarsi with 2-3 segments; wing venation not much reduced (Figs.A-D) ;antennae not moniliform, usually long and hairlike, with 13 or more segments ...... Psocoptera (= Corrodentia)



24a (2b). Mouthparts for sucking, beak elongated and usually segmented (Figs.A-B)...... A



24b. Mouthparts mandibulate



25a (24a). Beak arises from front of head (Fig.A); basal portion of fore wing usually thickened and leathery, but membranous at tip, the tips overlapping at rest (Fig.B) A [true bugs] ..... Hemiptera / Heteroptera <General Characteristics> [Latest Classification]



25b. Beak arises from hind part of head, often appearing to begin at base of front legs; front wings of uniform texture throughout, the tips not, or only slightly, overlapping at rest [leafhoppers & some psyllids] ....... Homoptera <General Characteristics> [Latest Classification]



26a (24b). Abdominal cerci like forceps (Fig.A); front wings short, leaving most of abdomen exposed; tarsi with 3 segments (Fig.A) [earwigs] ..... A ........ Dermaptera <General Characteristics>; <Adults> & <Juveniles> [Latest Classification]



26b. Abdominal cerci not like forceps, or if cerci appear as such, then front wings cover most of abdomen; tarsi variable



27a (26b). Front wings entirely leathery and without veins and usually meet in a straight line down middle of back; antennae generally with 11 or fewer segments and have diverse shapes (Figs.A-I); hind wings narrow, usually longer than front wings when unfolded, and with few veins (Figs.J-O) [beetles] .... A ...... Coleoptera <General Characteristics> [Latest Classification]



27b. Front wings with veins and either held like a roof over abdomen or overlapping over abdomen when at rest; antennae generally with >12 segments; hind wings broad, usually shorter than front wings, and with many veins (Fig.A), usually folded like a fan at rest [crickets, grasshoppers, cockroaches and preying mantids]....... Orthoptera <General Characteristics>; <Adults> & <Juveniles> [Latest Classification]



28a (1b). Body usually insect-like, with segmented legs and usually segmented antennae



28b. Body generally worm-like, body regions (except possibly head) not well differentiated, and segmented thoracic legs absent; antennae present or absent



29a (28a). Front wings present but rudimentary; hind wings absent or represented by halteres;tarsi almost always with 5 segments [some flies] ......... Diptera <General Characteristics>; <Juveniles> [Latest Classification]



29b. Wings entirely absent or with 4 rudimentary wings and no halteres; tarsi variable



30a (29b). Antennae absent; length 1.5 mm or less (Fig.A); usually occur in soil or leaf litter. A ....... Protura (in Class Entognatha)



30b. Antennae usually present (sometimes small); size and habitat variable..........



31a (30b). Ectoparasites of birds, mammals, or honey bees and usually found on the host; body somewhat leathery and usually flattened dorsoventrally or laterally



31b. Free-living (not ectoparasitic), terrestrial or aquatic



32a (31a). Tarsi with 5 segments; antennae short and usually concealed in grooves on head; mouthparts for sucking



32b. Tarsi with fewer than 5 segments; antennae and mouthparts variable



33a (32a). Body flattened laterally; usually jumping insects, with rather long legs (Fig.A) A [fleas] ...... Siphonaptera <General Characteristics> [Latest Classification]



33b. Body flattened dorsoventrally; not jumping insects, legs usually short (Fig.A) [louse flies, bat flies & bee lice]......... Diptera <General Characteristics>; <Juveniles> [Latest Classification]



34a (32b). Antennae decidedly longer than head; tarsi 3-segmented (Fig.A) [bed bugs and A bat bugs] ....... Hemiptera / Heteroptera <General Characteristics> [Latest Classification]



34b. Antennae not longer than head; tarsi with 1 segment



35a (34b). Head as wide as or wider than prothorax; mouthparts mandibulate; parasites of birds (with 2 tarsal claws) and mammals (with 1 small tarsal claw) (Figs.A-D) A [chewing lice] .... Mallophaga <General Characteristics> [Latest Classification]



35b. Head usually more narrow than prothorax; mouthparts haustellate (= for sucking); parasites of mammals with 1 large tarsal claw (Figs.A-B) [sucking lice] Phthiraptera (= Anoplura) <General Characteristics> [Latest Classification]



36a (31b). Mouthparts for sucking, with a conical or elongated beak enclosing stylets



36b. Mouthparts mandibulate (sometimes hidden in head), not beaklike


37a (36a). Tarsi with 5 segments; maxillary or labial palps ( = segmented processes) present



37b. Tarsi with 4 or fewer segments; palps small or absent



38a (37a). Body covered with scales; beak usually in the form of a coiled tube; antennae long and with many segments [wingless moths] .......... Lepidoptera <General Characteristics> [Latest Classification]



38b. Body not covered with scales; beak not coiled; antennae variable, but often short, with 3 or less segments [wingless flies] ............ Diptera <General Characteristics>; <Juveniles> [Latest Classification]



39a (37b). Mouthparts in the form of a cone located basally on ventral side of head; palps present but short; body elongated, usually <5 mm in length; antennae about as long as head and prothorax combined, not bristle-like, and 4-9 segmented; tarsi 1-2 segments, often without claws (Fig.A) [thrips ....... A ....... Thysanoptera <General Characteristics>; <Adults> & <Juveniles> [Latest Classification]



39b. Mouthparts as an elongated segmented beak; palps absent; other characters variable



40a (39b). Beak arises from front part of head; antennae with 4-5 segments and not bristle-like; tarsi usually with 3 segments; abdomen without cornicles (= dorsal tubular structures on posterior abdomen ) [true bugs]. ... A. Hemiptera / Heteroptera <General Characteristics> [Latest Classification]



40b. Beak arises from rear of head; antennae either with >5 segments (and tarsi with 2 segments) or bristle-like (and tarsi with 3 segments); abdomen often with a pair of cornicles (Fig.A) [aphids, hoppers, etc.]...... Homoptera <General Characteristics> [Latest Classification]



41a (36b). Abdomen very constricted at base; antennae often elbowed; tarsi with 5 segments; bodies hard, ant-like [ants & wingless wasps ........ Hymenoptera <General Characteristics> [Latest Classification]



41b. Abdomen not very constricted at base; antennae not elbowed; tarsi variable



42a (41b). Abdomen with 3 long thread-like caudal filaments and with style-like appendages on some abdominal segments (Fig.A); mouthparts mandibulate, but often somewhat A retracted into head; body almost always covered with scales; terrestrial [bristletails]



42b. Abdomen with only 2 thread-like caudal filaments or none; if with 3 [mayfly nymphs] then aquatic; other characters variable



43a (42a). Compound eyes large and usually contiguous; body somewhat cylindrical, with thorax arched; ocelli present; middle and hind coxae often with styli; abdominal styli (= bristlelike processes) on segments 2-9 (Fig.A) .... A ......Class: Insecta; Subclass Monocondylia: Order: Arachaeognatha...... Microcoryphia



43b. Compound eyes small and widely separated or absent; body somewhat flattened dorsoventrally, thorax not arched; ocelli present or absent; middle and hind coxae without styli; abdominal segments 1-6 (sometimes 7) without styli (Fig.A) [silverfish] ... Thysanura <General Characteristics>; <Adults> & <Juveniles> [Latest Classification]



44a (42b). Aquatic insects, often with tracheal gills (= protruding externally at spiracles)



44b. Terrestrial insects, without tracheal gills



45a (44a). Nymphs; compound eyes and usually wing pads present



45b. Larvae; compound eyes and wing pads absent



46a (45a). Prehensile labium (= lower lip), folded under head at rest, and when extended much longer than head (Figs.A-G) [dragonfly and damselfly nymphs] ...... A ........ Odonata <General Characteristics>; <Adults> & <Juveniles> [Latest Classification]



46b. Labium normal, not as previously described



47a (46b). Having 3 caudal filaments; tarsi with 1 claw; gills located on lateral margins of abdominal terga (= dorsal plates or sclerites) and usually leaflike or plate-like A ... (Figs.A-C) [mayfly nymphs]......... Ephemeroptera <General Characteristics> [Latest Classification]



47b. With 2 caudal filaments; tarsi with 2 claws; gills mostly present, somewhat fingerlike, usually located on underside of thorax (Figs.A-D) [stonefly nymphs].......... Plecoptera <General Characteristics>; <Adults> & <Juveniles> [Latest Classification]



48a (45b). Having 5 pairs of prolegs (= fleshy abdominal legs) on ventral side of abdomen, the prolegs with tiny hooks (crochets) [aquatic caterpillars) ............ Lepidoptera <General Characteristics> [Latest Classification]



48b. Abdominal segments without prolegs or with only one terminal pair



49a (48b). Mouthparts with 2 slender and elongated structures, longer than head; antennae long and slender, or least 1/3rd as long as body; tarsi with 1 claw (Fig.A); live in freshwater sponges [Sisyridae larvae] ... A ................ Neuroptera <General Characateristics> [Latest Classification]



49b. Mouthparts, and usually also antennae, short and not as described previously



50a (49b). Tarsi with 2 claws; abdomen with long slender lateral processes and a long slender terminal process (Figs A & B) [Sialidae] or with slender lateral processes and a pair of hooklike structures apically (Fig. C.) [Corydalidae, fishfly and alderfly larvae ...... A ........ Neuroptera <General Characateristics> [Latest Classification]



50b. Tarsi with 1-2 claws; if with 2, then abdomen not as described previously



Key continues with <insect2.htm>





Illustrations were simplified, corrected and/or updated to suit the present key.

However, please refer to cited authors for greater detail.