The class Insects is the largest and most diverse group of animals, numbering more than 1 million species.
Insects are the most highly organized arthropods; they have the most advanced nervous system and sense organs. Insects have mastered all habitats and are found everywhere (with the exception of the seas and oceans).
The body of insects consists of three sections – head, chest and abdomen:
* on the head there is one pair of antennae, one pair of compound eyes;
* on the chest – three pairs of legs and two pairs of wings (in most insects);
* there are no legs on the abdomen.
On the head are the eyes, one pair of antennae and mouth organs (which are modified limbs).
The eyes of insects are complex faceted, and some also have simple eyes.
In cockroaches and beetles, mouth organs are gnawing type. In other insects, they change depending on the food consumed. A bee has mouth organs of a gnawing-licking (gnawing-sucking) type, a mosquito and a bug – a piercing-sucking, a butterfly – a sucking, a fly – a licking (filtering) type.
The structure of the antennae in insects is very diverse.
On the chest there are three pairs of legs and two pairs of wings (in most insects).
The characteristics of the wings are an important systematic feature (their structure, the number and characteristics of the wings determine the belonging of insects to orders).
Most insects have running legs (like, for example, a cockroach), they serve only for walking and running, but their structure can change depending on the lifestyle. In grasshoppers, locusts, fleas, the last pair of legs is very long and powerful (jumping legs). The bear’s front pair of legs is powerful, flat and short (digging legs). In the swimming beetle and the water bug, the back pair of legs is covered with long hairs that form a wide surface – a kind of paddle (swimming legs). In the praying mantis, the front legs are armed with spines that help this predator to hold on to prey (grasping legs).