The Class INSECTA is subdivided into orders based on recognizable physical characters. Unfortunately, the division of the multitude of insects into a classified system is not static; changes are always being made even at the rank of order.

Class INSECTA

Subclass APTERYGOTA (wingless insects)

1. Order PROTURA (Gr. protos, (primitive) + oura, tail; alluding to terminal filament on abdomen). 90 species. 0.6 to 1.5 mm.
2. Order THYSANURA (Gr. thysanos, tassel + oura, tail; alluding to terminal filament on abdomen). Bristletails or silverfish. 700 species; worldwide except polar areas; to 30 mm; minor economic importance, some feed on books, paper and clothing.
3. Order COLLEMBOLA (Gr. kolla, glue + embolon, bar, wedge or peg; from the sticky projection ventrally on abdominal segment). Springtails or snow fleas. 2,000 species; worldwide, many cosmopolitan; to 5 mm.; minor agricultural pests; beneficial to forest soils.

Subclass PTERYGOTA (winged insects)

Group Paleoptera (non-folding wings)

1. Order EPHEMEROPTERA (Greek ephemeros, living but a day, short-lived; alluding to brief adult life). Mayflies. 1,500 species worldwide; erect net-veined wings; long tail filaments; small antennae; fish feed on larvae and adults. Slide: Note net-veined wings held vertically.
2. Order ODONATA (Greek odonotos, tooth + gnatha, mouth, alluding to sharply toothed mandibles). Dragonflies, damselflies. 4,500 species worldwide; predaceous; usually found near water; powerful fliers; fish feed on larvae. Slide: Note large eyes, long slender abdomen, elongate net-veined wings held horizontally, and small antennae.

Group Neoptera (folding wings)

Subgroup Hemimetabola (simple metamorphosis)

Isopteroid Insects

1. Order ISOPTERA (Gr. isos, equal + pteron, wing; alluding to similarity of fore and hind wings). Termites, white ants. 1,800 species: temperate and tropical areas; small to medium; chewing mouth parts; wings only present on the reproductive forms; great economic damage to structural wood and tropical plantations. Slide: Note enlarged mandibles of soldier termite.

Plecopteroid Insects

1. Order PLECOPTERA (Gr. plecos, to fold or plaited + pteron, wing; alluding to the wings over-lapping the sides of the body). Stoneflies; salmon flies. 1,500 species; worldwide but largely temperate and polar areas; moderate to large; simple metamorphosis; fish food; some predaceous.
2. Order EMBIOPTERA (Gr. embios, lively; alluding to their extreme agility.) Embiids, webspinners. 200 species; largely tropical and subtropical; small; no economic importance.

Orthopteroid Insects

1. Order ORTHOPTERA (Gr. orthos, straight + pteron, wing; alluding to the straight wings of grasshoppers). Grasshoppers, locusts, katydids, crickets, cockroaches, praying mantids, walking sticks. 30,000 species; worldwide except polar areas; medium to large; chewing mouthparts; some destructive agricultural and forest pests, particularly important in rangelands. Slide: Note the "leathery" forewing and hind legs enlarged for jumping on grasshopper
2. Order DERMAPTERA (Gr. derma, skin + pteron, wing; alluding to leathery texture of the abbreviated front wings (tegmina). Earwigs. 1,100 species; temperate and tropical areas; 6-11 mm.; minor agricultural pests.

Psocopteroid Insects

1. Order PSOCOPTERA (Gr. psokhos, dust) Book lice, bark lice, psocids. 500 species; worldwide; small to minute; some economic damage to libraries and insect collections.
2. Order MALLOPHAGA (Gr. mallos, lock of wool + phagein, to eat; alluding to their feeding on wool and hair). Bird lice; biting lice. 2,700 species; worldwide; small to medium size; medical importance.
3. Order ANOPLURA (Gr. anoplus, unarmed + oura, tail; alluding to rather naked tail). True lice, sucking lice, crab lice. 500 species; worldwide; small; important in medical and livestock entomology.

Hemipteroid Insects

1. Order THYSANOPTERA (Gr. thysanos, tassel + pteron, wing; alluding to the marginal fringe of hairs on wings). Thrips. 3,200 species; worldwide but largely temperate and tropical areas; mostly minute; many diverse habits, including agricultural and forest pests; vectors of disease. Some are pests of developing cones on forest trees.
2. Order HEMIPTERA (Gr. hemi, half + pteron, wing); alluding to partly thickened, partly membranous forewings). True bugs. World wide; small to large; base of forewing "leathery", tips membranous; wings held flat over the abdomen; beak-like mouth parts arising from front of head; feed by sucking juices of plants or animals; many diverse habits including agricultural and forest pests, vectors of disease and predators. Slide: Note that the forewing have a leathery base and membranous tips, and that they are held flat over the abdomen.
3. Order HOMOPTERA (Gr. homo, the same, similar + pteron, wing; alluding to the similarity of texture throughout wings). Aphids, scale insects, leafhoppers, spittlebugs, cicadas. Including true bugs, over 60,000 species worldwide; minute to large; beak-like mouth parts arising from back of head; feed by sucking sap from plants; many agricultural and forest pests; vectors of disease. Slide: Note the membranous wings held "roof-like" over the body. Slide: The wingless form of an aphid. Slide: Scale insect; female resides beneath a hard scale or "cottony" substance for protection. They remain fixed to the host plant by their sucking mouth parts (non-motile). Males are winged, young are mobile.

Hololometabola (Complex metamorphosis)

Coleopteroid Insects

1. Order COLEOPTERA (Gr. coleos, sheath + pteron, wing; alluding to stiff sheath-like forewings or elytra). Beetles and weevils. 280,000 species world-wide; small to large; chewing mouthparts; large and diverse order containing defoliators, wood and cambium feeders, predators and others. Slide: Note the hard, heavy protective forewings that cover the membranous hindwings of this June beetle. Slide: Note that the weevil in this picture has hard protective forewings and mouthparts located at the end of a long "snout" (weevils are sometimes called "snout beetles").
2. Order STREPSIPTERA (Gr. strepsis, a twisting + pteron, wing; alluding to twisted forewings of dried male specimens). Twisted wing insects, stylops. 300 species; world-wide; small; non-economic.

Neuropteroid Insects

1. Order NEUROPTERA (Gr. neuron, nerve + pteron, wing; alluding to the elaborate veining resembling a nerve net in the wings). Lacewings, ant lions, snakeflies, dobsonflies, alderflies and others. 2,700 species world-wide; minute to large; some are important predators of aphids and other soft-bodied insects; larvae of dobsonflies are predaceous on aquatic insects.
2. Order MECOPTERA (Gr. mecos, length + pteron, wing; alluding to the long wings). Scorpion flies. 350 species world-side; small to large; some predators.
3. Order HYMENOPTERA (Gr. hymen, a membrane + pteron, wing; alluding to the naked, membranous wings). Ants, bees, wasps, sawflies, woodwasps, gallwasps, ichneumons, bracondis, chalcids. 103,000 species world-wide; small to medium; membranous wings with reduced veins and small hind wings; ovipositor or "sting" well-developed in females; many diverse habits; beneficial and destructive (sawflies are defoliators; woodwasps bore into wood; many families are parasites on pest insects), chewing mouthparts except bees which have chewing-lapping type. Slide: Note the long ovipositor of this woodwasp.
4. Order DIPTERA (Gr. di, twice + pteron, wing; alluding to the single pair of wings). Flies, gnats, mosquitoes, midges, punkies. 85,000 species world-wide; minute to medium size; many are parasites and predators: some are destructive forest pests (gall midges, cone midges) and vectors of disease. Slide: Note single pair of wings, reduced venation, and large eyes.
5. Order SIPHONAPTERA (Gr. siphon, a tube + aptera, wingless; alluding to sucking habit and absence of wings). Fleas, chigoes, 1,100 species; mostly tropical; minute; important in medical entomology.
6. TRICHOPTERA (Gr. trichos; hair + pteron, wing; alluding to hairy covering on the wings). Caddisflies, water moths. 3,600 species; world-wide; small to large; predators of aquatic insects.
7. LEPIDOPTERA (Gr. lepis, scale + pteron, wing; alluding to a scaly wings). Moths, butterflies, skippers. 125,000 species world-wide; small to large; mostly defoliators but many diverse habits including cone and seed insects, wood borers, agricultural pests and others. Butterfly: Note wings held vertically and covered with scales and knobbed antennae. Moth: Note wings held horizontally and covered with scales and antennae not knobbed.

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