The world of insects has been known to man for a long time. Still on the cave paintings (twenty thousand years ago), images of bees were found, and the cultivation of the silkworm in China was carried out five thousand years ago. Even in Ancient Egypt, the sacred symbol of which was the scarab beetle, inscriptions about the invasion of locusts were preserved.
The class of insects is one of the most numerous. If you carefully examine the body of the insect, you can observe a clear division: head, chest, abdomen. A pair of antennae, which are sensory organs, a pair of eyes and an oral apparatus are located on the head. Each of the three segments of the thoracic region is endowed with a pair of legs. The dorsal side of the two segments is provided with one, and sometimes two pairs of wings. The abdomen of any individual representing the class Insects is also divided into segments, which can be from six to twelve.
The hypoderm, which is located immediately below the chitin that covers the body from the outside, is composed of homogeneous cells, some of them are glandular. Chitin, which has the peculiarity not to stretch, replaces the old layer with a new one, that is, the process of molting occurs. This process is very important for insect growth.
The class Insects is distinguished by a complex oral apparatus, consisting of upper and lower jaws, upper and lower lips, as well as the tongue, which is a chitin protrusion of the bottom of the oral cavity.
The mouth apparatus of insects is of several types: it is gnawing in beetles, licking in flies, sucking in butterflies, and stinging-sucking in mosquitoes and fleas.
The respiratory organs are the trachea, they supply tissue with oxygen. Up to ten pairs of respiratory openings are located on the lateral parts of the body of the insect.
Weak development of the circulatory system is associated with a special structure of the respiratory organs. The nervous system, on the contrary, has a high level of development. There are three sections of the "brain" - front, middle and rear.
Creatures representing the class Insects possess well-developed sensory organs. Sensitive hairs present throughout the body serve as the organs of touch, and the antennae and mandibular palps are the organs of smell. As for the hearing organs, certain types of insects, a grasshopper, for example, pick up sounds from a third pair of legs. It is here, on the legs, that the hearing organs are located . The eyes of this class of insects can be simple and complex. When the cloves of the upper wings rub against the thighs of the hind limbs, a sound characteristic of an insect appears.
As a rule, insects bring a lot of problems to humans. They are carriers and pathogens of various diseases. Therefore, scientists have long been studying this class. The science of insects is called entomology. Today it has been singled out as a separate branch of biology, and this industry is developing at an unusually fast pace.
Entomology can be divided into several independent areas: general entomology, medical, forestry, veterinary, agricultural. A separate story with beekeeping and sericulture - they very closely adjoin entomology.
In general, each area of this science has its own specifics. For example, general entomology studies the main structural features of insects, both internal and external, studying their lifestyle, development and reproduction, as well as identifying their relationships with the environment.
Insect pests and pollinating insects fall into the field of attention of agricultural entomology. Scientists in this area are also developing ways to control pests in order to minimize the damage done to agriculture.
The class of insects is huge and diverse. Its representatives live everywhere: soil and plants, air and water, as well as mountains and lowlands, deserts and snow - all this is their usual habitat.