Insects are numerous usually small arthropod animals of the class Insecta, having an adult stage characterized by three pairs of legs and a body segmented into head, thorax, and abdomen and usually having two pairs of wings. Insects include the flies, crickets, mosquitoes, beetles, butterflies, and bees. Like other arthropods, an insect has a hard other covering, or exoskeleton, a segmented body, and jointed legs. Adult insects typically have wings and are the only flying invertebrates. The body of the typical adult insect is divided into three distinct parts, the head, thorax, and abdomen. The exoskeleton is composed of a horny substance called chitin. There are about 900,000 known insect species, three times as many as all other animal species together, and thousands of new ones are described each year. They are commonly grouped in 27 to 32 orders, depending upon the classification used. The largest order near the poles and pervade every habitat except the sea (Coleoptera) Insects are found throughout the world except near the poles and pervade every habitat except the sea (although there is one marine species of water strider). Fossile records indicate that many species extist today in much the same form as they did 200 million years ago. Here small attempt is made to give brief account on insects. This book can be referred by college students of various university in the country.
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