Insects from the largest single group of animals in the world. About 700.000 different kinds of insects are known, and more are being discovered every year.
Insects are found almost everywhere on earth. Some live deep in underground caves, and some on the tops of the world`s highest mountaints. There are insects that live on the surface of the ocean, far from land. Some live in hot springs whose water temperature is as hot as 50 degrees Celcius. Many different insects have been found in cold Antarctica. One insect is able to live in vinegar. Another insect lives in salty lakes. Insects can live in a great many different kinds of places. This is one of reasons they have remained on earth for over 300 million years.
Most insects are very small. Only a few kinds grow to more than 1 or 2 inches. Some are so tiny that they can hardly be seen. But the lagest ones are bigger than some mice.
The small size of insects makes it possible for them to escape their enemies by crawling into cracks or other hiding places. Because they are so small, they need very little food and water to live. Thus their small size is a very great advantage.
All adult insects have six legs, three on each side on their bodies. This is the one sure way to tell an insect. Each ensect`s body has three main parts—a head, athorax, and an abdomen. Insects also have one pair of feelers or antennae, on the front of the head. Most insects have one or two pairs of wings.
Look carefully at a spider and count its legs. There are eight of them. Its body has two pairs instead of three. A spider, therefore, is not an insect.
If you can do so, catch a grasshopper and examine it. The grasscopper is a typical insect. See if you find the three sections of the body.
The thorax is next to the head. The wings and the three pairs of legs are attached to it.
The hind part of the insect`s body is the abdomen. It is the biggest part the body. The abdomen is in sections, or segments, that looklike rings attached together. This makes the insect`s body flexible, that is, it can bend and twist easily.
Most insects hatch from tiny eggs. Insect eggs are of many shapes. Some are long and oval; others are round like a ball. Some insects lay only one egg at a time. Others, like termites, lay ten thousand or more in a day. They may lay this large number of eggs several times each year.
Most insects go through several forms as they grow from egg to adult. This method of growth is called metamorphosis. The world “metamorphosis” means “change in shape.”
The young that hatch out of the most insect eggs are called larvae (singular larva). They look like worms and are some times wrongly called worms. The “worm” in mango or tomato is really a larva.
You have certainly seen caterpillars. They are the larvas of moths and butterflies. You may find it hard to think of a crawling caterpillar as the young of butterfly. It does not look at all like the adult. The same thing is true the most insects. Their larvae sometimes have more than three pairs of legs. They have no wings, and their mouths and other parts are quite different from those of the adult.
As soon as larva hatches out of egg, it begins to eat. It eats constantly, bitting and chewing its food with powerful jaws. It grow rapidly, but its outer skin does not grow with it. Instead, the larva molts, or sheds its skin when it becomes too tight. Each time a new and bigger skin grows in place of the old one.
There is no average length of life for adult insects as group. The life of one kind of insect may be very short. Some flies, for example, live for less than a day. During the time they do not eat. They mate, lay their eggs and die. Most adult months and butterflies live for only a few days or weeks.
Some insects live for one summer; some live for several years. Probably the insect with the longest life is the queen of one kind of termite that lives on the tropics. Some scientists think this queen termite may live for as longas 50 years.
Insects make sounds that carry messages to other insects of the same kind. The ears of each kind of insect can pick out the sound intended for it. The sounds are usually mating calls made by the male to attract the female. But with mosquitoes the female makes the sound to attract the male. Sometimes male make sounds to drive off rival males or to frighten away enemies.
Insects do not have voices, as we do. Most insect calls are made by the rubbing of one part of the insect`s body against another.
Insects protect themselves from their enemies in many ways. One of these is by disguising themselves so that they blend into their surroundings. This is called camouflaged. Many caterpillars are camouflaged to look like twigs. Some insects may look like tree bark, leaves or soil. Some harmless insects look horrible or fearful and thus frighten off their enemies.