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Exopterygota (Hemimetabola)

  • Mallophaga - Biting lice
  • Siphunculata - Sucking lice (syn. Anoplura)
  • Hemiptera - True bugs
  • Euphemeroptera - May flies
  • Odonata - Dragonflies
  • Dictyoptera - Cockroaches and Mantids
  • Isoptera - Termites
  • Plecoptera - Stoneflies
  • Grylloblattodea - Rock crawlers
  • Phasmida - Stick and Leaf-insects
  • Orthoptera - Crickets and Grasshoppers
  • Embioptera - Webspinners
  • Zoroptera - (small rare group - no common name)
  • Thysanoptera - Thrips
  • Psocoptera - Book lice
Exopterygota (Hemimetabola) Features:
  • Group includes all insects with wings and those considered to be secondarily apterous (i.e. at some point in evolutionary history winged forms have occured). (B502)
  • Young (usually called nymphs) very similar to parents. (B502)
  • wings appear as pads developing externally on the thorax in the later stages of nyphal life. (B502)
  • Rarely a resting stage or pupa and changes that occur when the nymph becomes an adult are usually termed "partial metamophosis". (B502)
  • Adult stage may change habitat. (B502)

Endopterygota (Holometabola)

  • Diptera - True flies
  • Siphonaptera - Fleas (syn. Aphaniptera)
  • Neuroptera - Lace wings
  • Mecoptera - Scorpionflies
  • Tricoptera - Caddisflies
  • Lepidoptera - Butterflies and Moths
  • Hymenoptera - Wasps, bees and ants
  • Coleoptera - Beetles
  • Dermaptera - Earwigs
Endopterygota (Holometabola) Features:
  • Young (usually called larvae) bear little resemblance to parents. (B502)
  • Change from larva to adult is complex. (B502)
  • a "resting stage" always present; insect does not feed and is apparently quiescent whilst great internal changes occur. (B502)
  • Wings develop internally in the larva and become visible externally during the pupa stage. (B502)
  • The changes from larva to adult are termed "complete metamorphosis. (B502)


  • Thysanura - Silver fish, bristle tails
  • Diplura - Campodeids
  • Protura - Myrientoma
  • Collembola - Spring-tails
  • Wingless insects, primitive structure, virtually no metamorphosis. (B502)

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General Features

  • Body
    • divided into three regions:
      • head
      • thorax
      • abdomen


    • outer protective covering (chitinous cuticle) serves as an exoskeleton for body covering and attachment of muscles. (B503)
    • chitinous cuticle is secreted by hypodermis (layer of single columnar epithelial cells). (B503)
    • chitinous cuticle is covered by the epicuticle (a thin lipoidal surface layer) which is permeable to lipids, but not water. (B503)
    • chitinous cuticle is molted (ecdysis) at intervals for the purposes of growth and metamorphosis; the hypodermis lays a new elastic cuticle under the old one which then splits allowing the insect to emerge. This process divides the life of the individual insect into a series of stages or instars (B503)
    • thick plates of cuticle are connected by much thinner section to allow movement and a degree of expansion (e.g. for egg laying). (B503)
    • muscles are striated and may be capable of extreme movement. (B503)
  • Head:
    • consists of a variable number of fused segments. (B503)
    • one pair of antennae only (rarely no antennae). (B502)
    • one pair of maxillae. (B502)
    • one pair of mandibles. (B502)
    • a labium (formed by the medial fusion of a second pair of maxillae). (B502)
    • a hypopharynx. (B502)
  • Thorax
    • consists of three segments - pro-, meso- and metathorax. (B503)
    • usually three pairs of legs, one on each thoracic segment. (B502)
    • a few insects are legless, and some larvae posses additional leglike appendages (e.g. prolegs) on the abdominal segments. (B502)
  • Abdomen:
    • consists of 11 or fewer segments. (B503)
    • no walking appendages (except in some primitive hexapods). (B502)
    • other appendages (if present) occur at apex and consist of a pair of cerci, an ectoproct, and a pair of paraprocts. (B502)
    • terminal segments of abdomen are modified for copulation or egg-laying. (B503)
    • gonopore (external opening of the reproductive organs) on the posterior portion. (B502)
  • Reproduction:
    • Flagellum of spermatozoa has microtubule arrangement of 9 + 9 + 2. (B502)
  • Respiration:
    • spiracles (external openings) along sides of body connected to ramifying tubes or tracheae. (B502)

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Primary References at the level of this taxa
B502 Kenneth G.V. Smith
Insects and Other Arthropods of Medical Importance
B503 D.J. Borror, C.A. Triplehorn, N.E. Johnson
An Introduction to the Study of Insects - Sixth Edition
B46 G M Urquhart, J Armour, J L Duncan, A M Dunn, F W Jennings
Veterinary Parasitology: Second Edition
B73 Eleanor Lawrence
Henderson's Dictionary of Biological Terms, 11th Edition
B24 E J L Soulsby
Helminths, Arthropods and Protozoa of Domesticated Animals: Seventh Edition
B80 Michael Allaby
Oxford Dictionary of Zoology
B79 Lynn Margulis and Karlene V Schwartz
Five Kingdoms - An Illustrated Guide to the Phyla of Life on Earth, 3rd Edition

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