Animals Of Tropical Africa

The group of animals that are most numerous in the world, and accordingly are of great importance in many ways to human beings, are Insects. These are of importance to man, not only because of their great numbers and wide distribution over every part of the world, but also because certain insects are among man's worst enemies, whereas others are among his best friends. Others are of great interest because of their method of living and the definite "nests" or "cities" that they build.

Finally, about two-thirds of the plants upon the earth depend upon insects to pollinate them; without insects most of the plants which are of use to man would cease to exist. Before dealing with insects in particular, it is necessary to know something about them generally. If you examine almost any insect you will see that the body is divided into three distinct parts - the head, the chest or thorax, and the belly or abdomen. On the head can be seen (especially if you use a magnifying glass) the eyes, the mouth-parts, and the two hair-like feelers called the antennae; there may also be two or more smaller attachments arranged in pairs.

The mouth-parts of insects vary greatly according to the kind of food that they eat. Thus certain insects, such as the mosquito, have mouth parts specially designed to pierce the skin and suck the blood of animals; others have biting mouth like the long horned beetles which eat wood; and some, such as butterflies, have long tubes through which they can suck the honey from flowers. From the thorax of the insect arise six jointed legs: and usually two pairs of wings; while from the abdomen there may or may not be a pair of small apparently useless objects attached to the hind end. All attachments to the bodies of insects (i.e., legs, wings, and so on) are called by the general name, apperidages. Between the head and thorax there is a distinct joint, and between the thorax and abdomen the body is very narrow and forms a "waist". The bodies of all insects are further subdivided by lines across them, the parts between these lines being called segments. Most insects have a hard, horny covering outside their real skin; this covering is for protection. Insets do not have lungs to breathe with, but breathe through very fine air pipes or tubes, called trachea, which open through holes in the horny covering, and by repeated branching reach into every part of the body.

A very curious and important characteristics of insects is that they appear first as eggs, which do not hatch out into insects direct, but into worm-like beings called larvae, these larvae in some cases develop into the full-grown insect direct, but in most cases they pass through another third stage of existence on the way; in this third stage, during which the insect is called pupa, it appears to be rolled up dead or asleep; and it is from this pupa stage that the fully developed insect emerges. An insect has, therefore, at least three, and in many cases four, distinct stages in its life history: