(from Triplehorn and Johnson, 2005)
Insects are in the kingdom "Animalia", the phylum "Arthropoda", and the class "Hexapoda". Members of Hexapoda can be recognized the combination of the following characteristics: (1) three distinct body regions-head, thorax, and abdomen; (2) a single pair of antennae (rarely antennae lacking); (3) one pair of mandibles; (4) one pair of maxillae; (5) having a hypopharynx; (6) having a labium; (7) three pairs of legs, each pair arising from each of the thoracic segments (a few lack legs); (8) having a gonopore (or rarely 2 gonopores) on the posterior part of the abdomen; and (9) no locomotor appendages on the abdomen of the adult (except in primitive hexapods) and any abdominal appendages, if present found at the aex of the abdomen and consisting of a pair of cerci, an epiproct, and a pair of paraprocts.
Triplehorn and Johnson (2005) recognize 31 orders of hexapods including the enotomognathus (meaning their mouthparts are mostly withdrawn into the head) orders Protura, Collembola, and Diplura (1-3). The "true insects" begin with Microcoryphia (4) and the winged insects begin with Ephemeroptera (6). A list of hexapod orders is given below. Click on the order name to go to a page with photos and information about the orders.
5. Thysanura-silverfish, firebrats
7. Odonata-dragonflies and damselflies
8. Orthoptera-grasshoppers and crickets
9. Phasmatodea-walkingsticks and timemas
10. Grylloblattaria-rock crawlers
19. Hemiptera-bugs, cicadas, hoppers, psllids, whitefiles, aphids, and scale insects
24. Neuroptera-alderflies, dobsonflies, fishflies, snakeflies, lacewings, antlions, and owlflies
25. Hymenoptera-sawflies, ichneumonids, chalcidoids, ants, wasps, and bees
27. Lepidoptera-butterflies and moths
30. Strepsiptera-twisted-wing parasites