Childrens Illustrated Encyclopedia

CoCkroaCh

a typical insect, such as the common

cockroach, above, has a body in three

main parts. at the front is the head, which

encloses the brain and bears the antennae,

mouthparts, and eyes. In the middle is the

thorax, where the six legs join. at the rear is

the abdomen, which contains the digestive,

reproductive, and sex organs. The hard,

outer skeleton is made mainly

of a substance called chitin.

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Insects 279-

Segment of

abdomen

Middle leg

Eye

Exoskeleton

Midgut (cuticle)

Ommatidium

Corneal

lens

Leg joint

Heart

Mouthparts

Main nerves

Spiracle

Compound eye

an insect’s eye is made up

of many rod-shaped units called

ommatidia. The eye of a housefly

has about 4,000 ommatidia. each

single ommatidium detects the

amount and color of light

entering the eye, but it cannot

form an image by itself.

Together, all the thousands of

ommatidia in the eye produce

a mosaic-like view of the outside

world made up of light and

dark patches.

Wing

Claw

Crop

Hindgut

Trachea

Sex organs

Rectum

FeedIng

Insects feed on almost anything—wood, blood,

nectar, paper, shoe polish, seaweed, and other

insects. The mouthparts of most insects,

however, are specialized for a particular kind of

food. Some mouthparts are adapted to bite,

others to pierce, suck, sponge, scrape, and probe.

The mouthparts have four main structures. The

mandibles are hard jaws that bite and chew;

the maxillae are secondary jaws; the labrum

and labium are the upper and lower lips.

earTh IS CraWLIng with insects; in fact, they make up the

largest group of animals. There are at least one million

different species, including beetles, butterflies, ants, and bees.

Insects first appeared on earth more than 500 million years

ago and are found in almost every kind of habitat, from cold

mountains to tropical rain forests. although all insects have

six legs and a body covered by a hard exoskeleton (outer

skeleton), they vary enormously in size and shape.

The goliath beetle weighs more than 3.5 oz (100 g);

the tiny fairyfly is almost invisible to the human eye.

Some insects cause problems for humans. Flies spread

diseases, and weevils and locusts eat farm crops.

parasites such as ticks and lice live and feed on

farm animals and sometimes on humans, too. But

insects are a vital part of nature. They pollinate

flowers and other crops and are an important

source of food for many birds, bats, and reptiles.

Certain insects are also very useful to humans—

without bees, for example, there would be no honey. Antenna

(feeler)

Butterfly’s tubular

mouthparts work like

a drinking straw.

Bugs such as aphids

have needlelike,

piercing mouthparts.

Optic nerve

Lens to brain

Facet

Casing is thin and

flexible at leg joint.

Seta (touch-

sensitive hair)

Front leg

Eye

Antenna

Brain

InSIde an InSeCT

The tough exoskeleton,

or cuticle, surrounds and

protects the soft internal

organs. an insect breathes

through tiny air tubes called tracheae,

which form a network inside its body. The

tubes open at holes called spiracles in the

cuticle. Water-dwelling insects such as the grubs

of pond beetles breathe through gills, which are

formed from delicate folds of cuticle.

Malpighian

tubules (kidneys)

help control

water balance.

Thorax

Back leg

Housefly sucks up liquid

food through its padded,

spongelike mouthparts.

Anus

Tubelike

casing of leg

Leg joint

Head

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