The term insect is derived from Latin insectum - to cut into, referring to the segmented body of insects. The body of insect is divided in to three parts viz., head thorax and abdomen. Insects belong to the Phylum Arthropoda which is the biggest phylum of Animal kingdom. Insects appeared 350 million years ago, much earlier than human beings who appeared on earth only 150000 years ago. They are initially aquatic and later became terrestrial. There is much variation in shape, size and colour of the insects. Insects are distributed throughout the world from cooler parts to hottest tropics. They live in water, land, air, deserts, high mountains and also seen in crop plants, gardens, libraries, museums, stores etc.,The body of insect is divided in to three parts head, thorax and abdomen which bears one pair of antennae, one pairs of compound eye, one or two pairs of wings or wingless and possesses three pairs of legs in their adult stage. The number of known species of insects is estimated to vary from 700,000 to 1,500,000 which constitute 70 to 90 per cent of known species of animal kingdom.