people who have
studied insects most and know them best, we must include among the true
insects only such air-breathing animals as have six legs, no more, and
have the body divided into three parts--head, thorax, and abdomen. These
parts are clearly shown in Fig. 136, which represents the ant, a true
insect. All insects do not show the divisions of the body so clearly as
this figure shows them, but on careful examination you can usually make
them out. The head bears one pair of feelers, and these in many insects
serve also as organs of smell and sometimes of hearing. Less prominent
feelers are to be found in the region of the mouth. These serve as
organs of taste.

[Illustration: FIG. 137. PARTS OF AN INSECT]

[Illustration: FIG. 138. COMPOUND EYE OF DRAGON FLY]

The eyes of insects are especially noticeable. Close examination shows
them to be made up of a thousand or more simple eyes. Such an eye is
called a _compound eye_. An enlarged view of one of these is shown in
Fig. 138.

Attached to the thorax are the legs and also the wings, if the insect
has wings. The rear portion is the abdomen, and this, like the other
parts, is composed of parts known as segments. The insect breathes
through openings in the abdomen and thorax called _spiracles_ (see Fig.
137).

An examination of spiders, mites, and ticks shows eight legs; therefore
these do not belong to the true insects, nor do the thousand-legged
worms and their relatives.

[Illustration: FIG. 139. THE HOUSE FLY
_a_, egg; _b_, larva, or maggot; _c_, pupa; _d_, adult male. (All
enlarged)]

The chief classes of insects are as follows: the flies, with two wings
only; the bees, wasps, and ants, with four delicate wings; the beetles,
with four wings--two hard, horny ones covering the two more delicate
ones. When the beetle is at rest its two hard wings meet in a straight
line down the back. This peculiarity distinguishes it from the true bug,
which has four wings. The two outer wings are partly horny, and in
folding lap over each other. Butterflies and moths are much alike in
appearance but differ in habit. The butterfly works by day and the moth
by night. Note the knob on the end of the butterfly's feeler (Fig. 143).
The moth has no such knob.

It is important to know how insects take their food, for by knowing this
we are often able to destroy insect pests. Some are provided with mouth
parts for chewing their food; others have a long tube with which they
pierc