External Anatomy

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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.
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Adult insects develop as a composite of fused
segments with specific body part associations
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The first body region is the head. Insect heads
can be highly variable, but most possess eyes,
antennae and mouthparts.
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Antennae are used by insects as major sensory
devices, especially for smell, and can be
adaptive for the insect in many ways.
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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.
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The middle body region is called the thorax and
is composed of three fused segments. All legs
and wings are located on the thorax.
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Legs
Like the mouthparts and antennae, insect legs are
quite variable in form and function and reflect
the insect's lifestyle.
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The last body region is called the abdomen. It
is composed of many segments connected by
flexible sections allowing it great movement.
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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.
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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.
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Digestive System
midgut
foregut
hindgut
Digestive sys
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.
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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.
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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.
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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.
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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.
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Without Metamorphosis
Without meta
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.
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Incomplete Metamorphosis Example (Or
Hemimetabolous)
egg 1st 2nd
3rd 4th
5th adult
instar instar instar
instar instar
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Incomplete Metamorphosis Example
egg 1st 2nd 3rd
4th 5th
shortwing normal wing
instar instar instar
instar instar
adult adult
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Complete Life Cycle Example (Or Holometabolous)
egg 1st 2nd
3rd
pupa adult
instar instar
instar
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Complete Life Cycle Example
egg 1st 2nd
3rd
pupa adult
instar instar
instar
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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

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Collembola (springtails)
no wings as adults, caudal appendage designed for
jumping (furcula colliphore) adults may molt
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Thysanura (silverfish, firebrats)
no wings as adults, 2-3 caudal appendages (two
cerci and sometimes central telson) adults may
continue to molt
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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

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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
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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
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Phasmatodea (Walking sticks)
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Orthoptera (Crickets, Grasshoppers)
front wings leathery, hind wings folded like a
fan, chewing mouthparts, two cerci - usually short
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Mantodea (praying mantis)
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Blattodea (cockroaches)
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Dermaptera (earwigs)
front wings short, leathery hind wings double
folded abdominal cerci forceps-like chewing
mouthparts
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Plecoptera (stoneflies)
front wings narrow hind wings folded fanlike
aquatic nymphs (naiads) with abdominal gills
abdominal cerci straight, moderately long
chewing mouthparts
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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
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Orders of Insects (incomplete metamorphosis
contd)

• Hemiptera - true bugs bug-like insects
• Thysanoptera - thrips
• Psocoptera - barklice, booklice
• Phthiraptera - biting sucking lice

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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
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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
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Hemiptera (s.o. Sternorrhyncha) (buglike insects
psyllids, whiteflies, aphids, mealybugs, scales)
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Thysanoptera (thrips)
small front and hind wings bladelike with hair
fringe, often absent mouthparts modified rasping
sucking antennae short
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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
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Phthiraptera (Mallophaga) (biting lice)
very flat, small no wings chewing mouthparts
external parasites of birds and mammals
Chicken biting louse
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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

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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
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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
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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
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Diptera (flies, midges, mosquitoes)
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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
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Lepidoptera (butterflies, moths, caterpillars)
Hypopta agavis
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Siphonaptera (fleas)
wingless, extoparasitic adults laterally
compressed jumping hind legs larvae have
chewing mouthparts and resemble midge larvae
Cat flea adult and larva
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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
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Coleoptera (beetles weevils)
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Coleoptera (beetles weevils)
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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
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Hymemoptera (bees, wasps, sawflies)
Aphid wasp parasitizing aphid
Ichneumonid wasp attacking wood-boring larva
Acrobat ants
Yellowjacket wasp
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Hymemoptera (bees, wasps, sawflies)