An Elementary Study of Insects | Page 3

it."
--REV. J. G. WOOD.
CHAPTER I
INSECTS
"There is a difference between a grub and a butterfly; yet your butterfly
was a grub."
--SHAKESPEARE.

In undertaking a study of insects it is well first of all to know
something about what they are, their general nature, appearance, habits
and development. The insects comprise the largest group of animals on
the globe. There are about four times as many different kinds of insects
as all other kinds of animals combined. Insects vary greatly in size.
Some are as large as small birds, while others are so small that a
thousand placed in one pile would not equal the size of a pea.
Insects are commonly spoken of as "bugs." This term, however, is
properly used only when referring to the one order of insects which
includes the sap and blood-sucking insects such as the chinch bug,
bed-bug, squash bug, and the like. Then too, there are many so-called
"bugs" which are not insects at all. Spiders, thousand-legs, crawfishes
and even earth-worms are often spoken of as bugs.
What They Are
[Illustration: Side view of grasshopper with wings and legs partly
removed. Note the division of the body into head, thorax, composed of
prothorax, mesothorax and metathorax, and abdomen consisting of
ring-like segments.]
Insects are variously formed, but as a rule the mature ones have three
and only three pairs of legs, one pair of feelers, one pair of large eyes,
and one or two pairs of wings. The body is divided into a head, thorax
and abdomen. The head bears the eyes, feelers and mouth, the thorax
bears the legs and wings, and the abdomen is made up of a number of
segments. The presence of wings at once decides whether or not it is an
insect, for, aside from bats and birds, insects alone have true wings.
These are the distinguishing characters of the full grown insect, but,
like birds, they hatch from eggs and while young do not always look
like their parents. When young they may take on various shapes as
caterpillars, borers, maggots, grubs, hoppers, and the like. Young
insects are often difficult to distinguish from true worms, centipedes,
snails, and such forms, but after one has collected and reared some of
the young and watched them pass through the different stages and
emerge with wings they are much more easily recognized.

Their Principal Characteristics
[Illustration: Face of grasshopper enlarged showing parts; ant., antenna;
eye, compound eye; oc., ocellus or simple eye; cl., clypeus; lbr., labrum
or upper lip; mx. p., maxillary palpus; lb. p., labial palpus; lab., labium
or lower lip.]
Young insects as a rule are soft like caterpillars and maggots, while the
old ones usually have a hard body wall, similar to the beetles and wasps.
The wings are usually thin and transparent though in some cases they
are leathery or hard as in case of beetles or covered with scales as in the
butterflies. The three pairs of legs are jointed and used for running,
climbing, jumping, swimming, digging or grasping. The feelers or
antennae are usually threadlike, clubbed, or resemble a feather and
extend forward or sidewise from the head. The large eyes are
compound, being made up of many great small units which, when
magnified, resemble honey-comb. In some cases two or three small
bead-like eyes may be present besides the two large eyes. The mouth
parts of insects may be formed for chewing, as in the grasshopper, or
for sucking up liquids, as in the mosquito. The mouth of an insect is
built on an entirely different plan from our own. Chewing insects have
an upper and lower lip and between these there are two pairs of
grinding jaws. These jaws are hinged at the side of the face and when
chewing they come together from either side so as to meet in the
middle of the mouth. They therefore work sidewise rather than up and
down. The mouth parts of the sucking insects are drawn out to form a
sucking tube or proboscis as in case of the butterfly or mosquito.
[Illustration: Mouth parts of grasshopper shown in relative position; lbr.,
labrum; md., mandibles; hyp., hypopharynx; max., maxillae; lab.,
labium.]
[Illustration: Leg of grasshopper showing segmentation. The basal
segment c, is the coxa, the next t, the trochanter, the large segment f,
the femur, the long slender one ti, the tibia, and the three jointed tarsus
ta, with claws at the tip.]
The internal organs of insects are similar to those of other animals. The

digestive tube consists of oesophagus, gizzard, or stomach, and
intestines. The nervous system is well developed as shown by the
extreme sensitiveness of insects to touch. The brain is comparatively
small except in the bees and ants. The circulatory system consists
simply of a long tube