Biology of Insects
Classification
The categorization of insects is actually a contentious issue in many entomological circles. There is disagreement on which order some insects belong in, and where those orders should appear on the family tree. For this reason, it is not uncommon to find differences between the scheme shown below and those from different sources. That is not to say that either of them is right or wrong.
Insects are classified under Kingdom Animalia, Phylum Arthropoda, Subphylum Ateleocerata, and finally Class Hexapoda. There are 31 orders of insects under Class Hexapoda, each of which is briefly described below with distinguishing characteristics, dividing them into their respective groups.
KINGDOM ANIMALIA
Eukaryotic, multicellular, ingestive heterotrophs, cell membranes, usually motile.
Phylum Arthropoda
Animals with metamerism and tagmetization, a jointed exoskeleton, and a ventral nervous system.
Subphylum Atelocerata (=
Uniramia; =Mandibulata)
Head with one pair of antennae and
ususally one pair of mandibles; all appendages uniramous.
Class Hexapoda (or Insecta)
Three pairs of leg; usually two pairs of
wings; body with head, thorax, and abdomen.
Subclass Apterygota
Primitively wingless insects; pregentital
abdominal appendages; ametabolous metamorphosis; indirect sperm transfer.
Order Protura
Minute, with cone-shaped head; antennae, compound eyes,
and ocelli absent; abdomincal appendages on first three segments; inhabit soil and leaf
litter. eg: Proturans.
Order Collembola
Antennae with four to six segments; compound eyes absent;
abdomen with six segments, most with springing appendage on fourth segment; inhabit soil
and leaf litter. eg: Springtails.
Order Diplura
Head with many segmented antennae; compund eyes and
ocelli absent; cerci multisegmented or forcepslike; inhabit soil and leaf
litter. eg: Diplurans.
Order Thysanura
Tapering abdomen; flattened; scaleson body; terminal
cerci; long antennae. eg: Silverfish
Subclass Pterygota
Insects descendent from winged
ancestors. No pregenital abdominal appendages; direct sperm transfer.
Superorder Exopterygota
Paurometabolous (or hemimetabolous)
metamorphosis; wings develop as external wing pads.
Order Ephemeroptera
Elongate, abdomen with two or three tail filaments; two
pairs of membranous wings with many veins; forewings triangular; short bristlelike
antennae. eg: Mayflies.
Order Odonata
Elongate, membranous wings with netlike venation; abdomen long
and slender; compound eyes occupy most of head. eg: Dragonflies, damselflies.
Order Phasmida
Body elongate and sticklike; wings reduced or absent;
some tropical forms are flattened and leaflike. eg: Walking sticks, leaf
insects.
Order Orthoptera
Forewing long, narrow, and leathery; hindwing broad and
membranous; chewing mouthparts. eg: Grasshoppers, crickets, katydids.
Order Mantodea
Prothorax long; prothoracic legs long and armed with
strong spines for grasping prey; predators. eg: Mantids.
Order Blattaria
Body oval and flattened; head concealed from above by a
shieldlike extension of the prothorax. eg: Cockroaches.
Order Isoptera
Workers white and wingless; front and hind wings of
reproductives of equal size; reproductives and some soldiers may be sclerotized; abdomen
broadly joins thorax; social. eg: Termites.
Order Dermatptera
Elongate; chewing mouthparts; threadlike antennae;
abdomen with unsegmented forcepslike cerci. eg: Earwigs.
Order Embioptera
Two segmented cerci, filiform antennae, four similar
sized wings in males; females are wingeless. eg: Webspinners.
Order Plecoptera
Folded wings; simple metamorphosis; don't fly
that much; very inconspicuous, hiding in vegetation, debris, rocks. eg: Stoneflies
Order Zoraptera
Very rare and small insects; chewing mouthparts;
9-segmented antennae. eg: Zorapterans.
Order Psocoptera
Similar to lice, gnawing mouthparts, roof-like
wing position. eg: Barklice.
Order Mallophaga
Wingless ectoparasites; very small;
dorsoventrally flattened; mandibulate mouthparts. eg: Biting lice
Order Anoplura
Wingless ectoparasites; very small;
dorsoventrally flattened; haustellate mouthparts. eg: Sucking lice
Order Hemiptera
Proximal portion of forewing sclerotized, distal portion
membranous; sucking mouthparts arise ventrally on anterior margin of head. eg:
True bugs.
Order Homoptera
Wings entirely membranous; mouthparts arise ventrally on
posterior margin of head. eg: Cicadas, leafhoppers, aphids, white flies, scale
insects.
Order Thysanoptera
Small bodied; sucking mouthparts; wings narrow and
fringed with long setae; plant pests. eg: Thrips.
Superorder Endopterygota
Holometabolous metamorphosis; wings
develop internally during the pupal stage.
Wings membranous; hind wings held rooflike over body at rest. eg: Lacewings, snakeflies,antlions, dobsonflies.
Order Coleoptera
Forewings sclerotized, forming covers over the abdomen;
hindwings membranous; chewing mouthparts; the largest insect order. eg: Beetles.
Order Strepsiptera
Small parasites ranging in size from 0.5-4 mm;
vestigial mouthparts. eg: Twisted-wing parasites.
Order Mecoptera
Slender body with the head prolonged into a
beak; chewing type mouthparts; antennae threadlike about one-half the length of the body.
eg: Scorpionflies.
Order Trichoptera
Mothlike and setae-covered antennae; chewing mouthparts;
wings covered with setae and held rooflike over abdomen at rest; larvae aquatic and often
dwell in cases that they construct. eg: Caddisflies.
Order Lepidoptera
Wings broad and covered with scales; mouthparts formed
into a sucking tube. eg: Moths, butterflies.
Order Diptera
Mesothoracic wings well developed; metathoracic wings
reduced to knoblikes halteres; variously modifed but never chewing mouthparts. eg:
Flies.
Order Siphonaptera
Leterally flattened , sucking mouthparts; jumping legs;
parasites of birds and mammals. eg: Fleas.
Order Hymenoptera
Wings membranous with few veins; well-developed
ovipositor, sometimes modified into a sting; mouthparts modified for biting and lapping;
social and solitary species. eg: Ants, bees, wasps.