1. External Anatomy
Adult insects are known for having three major body regions, six legs, one pair of antennae and usually two pair of wings as adults.

2. Adult insects develop as a composite of fused segments with specific body part associations

3. The first body region is the head. Insect heads can be
highly variable, but most possess eyes, antennae and mouthparts.

4. Antennae are used by insects as major sensory
devices, especially for smell, and can be adaptive for the insect in many ways.

5. Two Examples of Mouthparts
chewing
piercing/sucking
Insect mouthparts are also highly modified for the insect. Chewing, biting, or sucking, are a few examples. Mouthparts of an immature insect may differ from those of the same insect in its adult stage.

6. The middle body region is called the thorax and is composed of three fused segments. All legs and wings are located on the thorax.

7. Legs
Like the mouthparts and antennae, insect legs are quite variable in form and function and reflect the insect's lifestyle.

8. The last body region is called the abdomen
The last body region is called the abdomen. It is composed of many segments connected by flexible sections allowing it great movement.

9. Insects possess an exterior covering called the exoskeleton
Insects possess an exterior covering called the exoskeleton. They do not have internal bones. This segmented "shell" is what gives insects shape and can be very hard in some insects. It is often covered with a waxy layer and may have "hairs" called setae.

10. Internal Anatomy
Inside the insect we find the systems for respiration, circulation, nerves, and digestion, but there is little resemblance to the same systems found in mammals.

11. Digestive System midgut foregut hindgut
The digestive system is a tube that opens at the mouth and empties at the tail end of the insect. It is divided into three parts called the foregut, midgut, and hind gut. In some insects such as the honey bee, the foregut acts as a crop to carry or hold liquids which can be regurgitated later.

12. Circulatory System aortic pumps
Circ system
The circulatory system is not composed of a central heart, veins and arteries which circulate blood cells and transport oxygen. The insect circulatory system is a simple tube down the back which is open at both ends and slowly pulses body fluids and nutrients from the rear of the insect to the head.

13. Nervous System
two lobed brain
Nervous system
nerve bundles (ganglia)
Insects have a less centralized nervous system than humans. The nerve chord runs along the ventral or bottom aspect of an insect. The brain is divided into two main parts. The largest lobes control important areas such as the eyes, antennae, and mouthparts. Other major concentrations of nerve bundles called ganglia occur along the nerve chord and usually control those body functions closest to it.

14. The respiratory system is composed of air sacs and tubes called tracheae. Air enters the tubes through a series of openings called spiracles found along the sides of the body. The largest spiracles are usually found on the thorax where greater musculature from wings and legs require more oxygen. There are no spiracles on the head.

16. Life Cycles
The many diverse orders of insects have three different types of life cycles. These life cycles are called "metamorphosis" because of the changes of shape that the insects undergo during development.

17. Without Metamorphosis
The first type is "without" metamorphosis (or ametabolous) which the wingless primitive orders such as silverfish (Thysanura) and springtails (Collembola) possess. The young resemble adults except for size.

18. Incomplete Metamorphosis Example
(Or Hemimetabolous)
egg st nd rd th th adult
instar instar instar instar instar
Egg Nymphal Adult
Stage Stage Stage

19. Incomplete Metamorphosis Example
egg st nd rd th th shortwing normal wing
instar instar instar instar instar adult adult
Egg Nymphal Adult
Stage Stage Stage

20. Complete Life Cycle Example
(Or Holometabolous)
egg st nd rd pupa adult
instar instar instar
Egg Larval Pupal Adult
Stage Stage Stage Stage

21. Complete Life Cycle Example
egg st nd rd pupa adult
instar instar instar
Egg Larval Pupal Adult
Stage Stage Stage Stage

22. Orders of Insects
(no metamorphosis)
Some consider these groups insect-like and place in different class or subclass.
Adults do not have wings and may molt after becoming mature
Thysanura - silverfish, firebrats
Collembola - springtails

23. Collembola (springtails)
no wings as adults, caudal appendage designed for jumping (furcula & colliphore); adults may molt

24. (silverfish, firebrats)
Thysanura
(silverfish, firebrats)
no wings as adults, 2-3 caudal appendages (two cerci and sometimes central telson); adults may continue to molt

25. (simple metamorphosis)
Orders of Insects
(simple metamorphosis)
Ephemeroptera - mayflies, shadflies
Odonata - dragonflies, damselflies
Phasmatodea – walking sticks
Orthoptera - grasshoppers, crickets
Mantodea – praying mantis
Blattodea - cockroaches
Dermaptera – earwigs
Plecoptera - stoneflies
Isoptera - termites

26. (Mayflies, shadflies, Canadian soldiers)
Ephemeroptera
(Mayflies, shadflies, Canadian soldiers)
front wings large, triangular, held over body at rest; hind wings small or absent; aquatic nymphs with abdominal gills; caudal appendages (2 or 3) long; chewing mouthparts often non-functional in adult

27. (dragonflies and damselflies)
Odonata
(dragonflies and damselflies)
front and hind wings narrow with many cross veins, membranous; aquatic nymphs (naiads) predatory with caudal or rectal gills; antennae bristlelike, no abdominal cerci; chewing mouthparts

28. Phasmatodea
(Walking sticks)

29. (Crickets, Grasshoppers)
Orthoptera
(Crickets, Grasshoppers)
front wings leathery, hind wings folded like a fan, chewing mouthparts, two cerci - usually short

30. Mantodea
(praying mantis)

31. Blattodea
(cockroaches)

32. Dermaptera
(earwigs)
front wings short, leathery; hind wings double folded; abdominal cerci forceps-like; chewing mouthparts

33. Plecoptera (stoneflies)
front wings narrow; hind wings folded fanlike; aquatic nymphs (naiads) with abdominal gills; abdominal cerci straight, moderately long; chewing mouthparts

34. Isoptera
(termites)
social insects, winged reproductives with both wings same size and membranous; straight or curved antennae consists of beadlike segments; abdomen broadly joined to thorax; no cerci; chewing mouthparts

35. (incomplete metamorphosis cont’d)
Orders of Insects
(incomplete metamorphosis cont’d)
Hemiptera - true bugs & bug-like insects
Thysanoptera - thrips
Psocoptera - barklice, booklice
Phthiraptera - biting & sucking lice

36. Hemiptera (s.o. Heteroptera)
(true bugs; 23K spp.)
front wings half leathery & half membranous; hind wings membranous; usually long antennae; sucking mouthparts arise from front of head

37. Hemiptera (s.o. Auchenorrhyncha)
(buglike insects: cicadas, leaf, plant & tree hoppers)
front wings same texture throughout, leathery or membranous (wings often absent); long or bristlelike antennae; sucking mouthparts arise from back of head or between front legs

38. Hemiptera (s.o. Sternorrhyncha)
(buglike insects: psyllids, whiteflies, aphids, mealybugs, & scales)

39. Thysanoptera (thrips)
small; front and hind wings bladelike with hair fringe, often absent; mouthparts modified rasping sucking; antennae short

40. (psocids, booklice, barklice)
Psocoptera
(psocids, booklice, barklice)
front wings with reduced venation; hind wings reduced or absent; wings often absent; distinctive frontal bulge on head; long antennae; chewing mouthparts; booklice are extremely flattened

41. Phthiraptera (Mallophaga)
(biting lice)
very flat, small; no wings; chewing mouthparts; external parasites of birds and mammals
Chicken biting louse

42. (complete metamorphosis)
Orders of Insects
(complete metamorphosis)
Tricoptera - caddisflies
Neuroptera - dobsonfly, lacewings
Diptera - gnats, mosquitoes, flies
Lepidoptera - butterflies & moths
Siphonaptera - fleas
Coleoptera – beetles
Hymenoptera - sawflies , bees, wasps

43. Trichoptera (caddisflies)
mothlike adults but no scales on wings; front wings narrow, often covered with hairs. short, leathery; hind wings double folded; abdominal cerci forceps-like; chewing mouthparts

44. (dobsonfly, lacewings, antlions)
Neuroptera
(dobsonfly, lacewings, antlions)
two pair wings with numerous veins, elongate larvae with elongate mandibles, larvae & adults usually predatory
Eggs
Green lacewing adult
Larva
Cocoon

45. (flies, midges, mosquitoes)
Diptera
(flies, midges, mosquitoes)
front wings membranous; hind wings reduced to small balance organ - haltere; mouthparts piercing-sucking or sponging sucking; larvae wireworm shaped or maggots with chewing or rasping mouthparts
Mosquito
House fly
Moth fly

46. (flies, midges, mosquitoes)
Diptera
(flies, midges, mosquitoes)

47. (butterflies, moths, caterpillars)
Lepidoptera
(butterflies, moths, caterpillars)
[front and hind wings generally covered with scales; adult mouthparts a sucking tube, larvae have chewing mouthparts and prolegs on abdomen]
Cranberry girdler moth
Luna moth
Red admiral butterfly

48. (butterflies, moths, caterpillars)
Lepidoptera
(butterflies, moths, caterpillars)
Hypopta agavis

49. Siphonaptera
(fleas)
[wingless, extoparasitic adults; laterally compressed; jumping hind legs; larvae have chewing mouthparts and resemble midge larvae]
Cat flea adult and larva

50. Coleoptera (beetles & weevils)
[front wings shelllike, usually covering abdomen; hind wings membranous, folded under forewings; antennae variable, but evident; chewing mouthparts; larvae variously shaped - elongate, grublike, etc.]
Ground beetle
Passalid beetle
Ground beetle larva

51. Coleoptera
(beetles & weevils)

52. Coleoptera
(beetles & weevils)

53. Hymemoptera (bees, wasps, sawflies)
[front wings large, hind wings smaller, both membraneous; chewing mouthparts; some with stings - modified ovipositors; larvae caterpillar-like, sawflies; or maggot-like]
Redheaded pine sawfly adult, larvae, & pupae

54. Hymemoptera (bees, wasps, sawflies) Aphid wasp parasitizing aphid
Ichneumonid wasp attacking wood-boring larva
Yellowjacket wasp
Acrobat ants

55. Hymemoptera
(bees, wasps, sawflies)