The basic Grouping of the insect is:
Species present in the Arthropod phylum have three legs (except Nymphalidae family) and do not have the internal skeleton system. Exoskeleton armour like shell protects their inner soft body. The body of the skeleton is divided into three segments. The head segment contains the mouth, eyes, and antennae. The thorax segment contains legs and wings are just behind the head. The last segment is the abdomen.
One more example:
The head segment contains the eye, mouth, and antennae. This segment controls the main nervous system.
Insects have two compound eyes. Eyes occupy the substantial area of the head. Besides compound eyes some insects have three simple eyes called ocelli on the top of their head. The eyes are independent to each other. Insects that mostly rely on their sight have big and complex eyes and the insects that live underground to not have eyes at all or have a very small one.
Almost all the specie of the insects has a variation in their mouths. The shape of the mouth depends on the mouths function. Some insects do not eat with the help of their mouth because they don’t have a functional mouth. Instead they have a tube like mouth which helps them to suck honey or some liquid deep from their container. Some insects use their mouth for biting purpose. Basically insect’s mouth consists of three pair of limbs. They are mandibles, maxillas, and labium.
Insects can smell, taste and detect the sound and air movements around with the help of Antennae. It has a different look from other parts of the body. Some insects use their antennae to navigate and some use them for identifying foods. Though an antenna is small hair like structure it has number of segments which is important for classifying animals.
Insect use their thorax as the locomotion organ. It consists of three segments. The first part contains a pair of legs and the next two parts contains pair of wings.
Different species use their leg for different purpose. Habitually insects have six legs. The legs are segmented and are of different shapes. Cockroaches have strong legs which help them to run faster. Grasshoppers have large and muscular hind legs to jump longer distance. Some insects use their legs to catch their prey while other uses their legs to taste the food. Beside these the insects use their legs for digging and swimming.
Among all the group of animals only four groups have wings. One among them is the insect. Most of the insects have two pair of wings while some are wingless and some have one pair of wings. Some insects have four wings, but all the four wings are not used for flight. The forewings are as guard to protect the hind wings and the abdomen.
The largest part of the insect is the abdomen. It is an important organ and is so soft. The abdomen segment consists of the digestive system and the reproduction system. It is used to store fat.
Insects breathe through Trachea. It is a small tube like structure inside the body. Air enters through the spiracles to the tube on the side of the body.
Haemolymph is the liquid that fill the body cavity. It acts as the blood to the insects. Like human blood it does not circulate in a close veins. It does not carry oxygen instead it just flushes through the internal organs providing them the essential nourishments.
Like other animals in the world insects also have their food through the mouth that enter the mid-gut and passes to the rest of the intestines. The food nourishment takes place here.
You can also know more on insects by seeing the Types of Insects section