BIO 385 — Invertebrate Zoology

Invertebrate Diversity
Phylum Arthropoda
Class Insecta

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Insecta Characteristics

Body with three distinct tagmata: head; thorax (with 3 pairs of legs); & abdomen Direct or indirect development: Ametabolous (direct) development = young are identical to adults except for size, gonads; only in primitive wingless insects and entognaths Hemimetabolous (direct) development = nymphs (or naiads if aquatic) generally similar to adults, but wingless; do not undergo complete metamorphosis Holometabolous (indirect) development = larvae very different from adults, require complete metamorphosis via pupal stage Mouthparts external (usually visible) Most with either hemimetabolous or holometabolous development Most have 2 pairs of wings (a few are primitively wingless and some are secondarily wingless) Eyes and other sensory structures well developed Most diverse class; nearly 1 million species described (with at least several million more awaiting discovery!) 33 Orders
Ametabolous Development Springtails, Tomocerus nigritus: adult (left) & nymph (upper right)	Hemimetabolous Development Large Milkweed Bug, Oncopeltus fasciatus: nymphs and adult	Holometabolous Development Cabbage Looper Moth, Trichoplusia ni: larva, pupa, and adult

See also Insect Coloration Page

Class Insecta

Order Archaeognatha

• Jumping bristletails
• Primitively wingless; ametabolous development
• 3 posterior filaments
• Arched (humped) back

Order Zygentoma

• Silverfish & firebrats
• Primitively wingless; ametabolous development
• 3 posterior filaments
• Dorsoventrally flattened
• Silvery scales

Order Ephemeroptera

• Mayflies
• Wings held vertically over back
• Hindwings much smaller than forwings (sometimes absent)
• Back is often held in concave arch
• 2 elongated tail streamers (cerci)
• Naiads are aquatic

Order Odonata

• Dragonflies & damselflies
• Do not fold wings flat over body
• Large mandibles and eyes
• Hemimetabolous: nymphs are aquatic (called naiads)

Order Plecoptera

• Stoneflies
• Wings membranous, with complex venation
• Chewing mouthparts
• Pair of long cerci at end of abdomen
• Naiads are aquatic

Order Embioptera

• Webspinners
• Males have wings; females wingless
• Spin silk from forelimbs to line burrows
• Body cylindrical
• Enlarged, bulging tarsus on forelimb
• Cerci present

Order Phasmatodea

• Stick insects, walking sticks
• Highly elongated bodies with long legs
• Generally resemble sticks or leaves

Order Orthoptera

• Grasshoppers & crickets
• Hind legs elongated for jumping
• Forewings leathery
• Chewing mouthparts (herbivores)
• Males frequently stridulate (produce sound)
• Tympanic membranes (hearing) present

Order Blattodea

• Roaches & Termites
• Dorso-ventrally flattened
• Forewings leathery or wings absent
• Chewing mouthparts (except some termites)
• Pair of cerci at end of abdomen
• Termites specialized for eating cellulose:
  • Eusocial: live in colonies
  • Multiple castes, typically with reproductives, soldiers, workers
  • Alates (new reproductives) have 2 pairs of long membranous wings; all other castes wingless

Order Mantodea

• Mantids
• Large raptorial forelegs
• Triangular heads with large eyes
• Leathery forewings cover hindwings at rest
• Ambush predators

Order Dermaptera

• Earwigs
• Elongated, flattened body
• Enlarged cerci form posterior pincer
• Wings small: hindwings hidden under pad-like forewings

Order Hemiptera

• True Bugs, hoppers, aphids, etc.
• Sucking beak tucked underneath body
• Base of forewings leathery (true bugs) or entire wing membranous

Other Orders of the Exopterygota

• Phthiraptera: lice
  • Wingless, flattened, external parasites

  Thysanoptera: thrips

  • Tiny (≤ 1 mm) plant-feeding insects with wings fringed by hairs

Order Neuroptera

• Lacewings, antlions, owlflies, etc.
• Both pairs of wings similar in size
• Wings heavily veined with many cross-veins
• Relatively soft-bodied and delicate
• Larvae are mostly predators (antlions dig pits to trap ants)

Order Megaloptera

• Alderflies & dobsonflies
• Resemble the neuroptera, but have creased hind wings
• Typically have very large mandibles
• Larvae are aquatic

Order Coleoptera

• Beetles
• Forewings hardened into elytra that cover abdomen & form seam along body midline
• General chewing mouthparts
• Largest order; >350,000 species
• Larvae are often referred to as grubs

Order Trichoptera

• Caddisflies
• Somewhat mothlike
• Wings covered in hairs, held tent-like over body
• Antennae usually very long
• Larvae aquatic, make cases

Order Lepidoptera

• Butterflies & moths
• Wings broad, covered in scales
• Coiled, sucking mouthparts
• Larvae are called caterpillars

Orders Mecoptera* (& Siphonaptera)

• Scorpionflies & hangingflies
• Superficially fly-like, but with 4 long, membranous wings
• Rostrum (snout) elongated
• The Siphonaptera (fleas) are derived from within the Mecoptera
  • Wingless external parasites of mammals and birds
  • Body laterally compressed
  • Extremely long jumping hind legs
  • Proboscis for sucking blood

Order Diptera

• True flies
• Hind wings absent (reduced to club-like halteres)
• Sucking or sponging mouthparts
• Mobile head with large eyes
• Larval types include maggots and aquatic forms

Order Hymenoptera

• Bees, wasps, ants
• Hindwings smaller than and hook to forewing
• Ovipositer modified for piercing, stinging
• Typically have narrow "waist" between thorax and abdomen
• Social behavior, including eusociality, is common (but not universal)