The body of an adult insect is subdivided into three sections, including a head, a three-segment thorax, and segmented abdomen. Ordinarily, the thorax bears three pairs of legs and a single or double pair of wings. The vision of most adult insects is specialized through two large compound eyes and multiple simple eyes.
Features of an insect’s mouth parts are used in classifying insects into types. Biting mouth parts, called mandibles, such as the mouth parts found in grasshoppers and beetles, are common among insects. Behind the mandibles are located the maxillae, or lower jaw parts, which serve to direct food into the mouth between the jaws. A labrum above and one below are similar to another animal’s upper and lower lips. In an insect with a sucking mouth function, the mandibles, maxillae, labrum, and labium are modified in such a way that they constitute a tube through which liquid such as water, blood, or flower nectar can be drawn. In a butterfly or moth, this coiled drinking tube is called the proboscis because of its resemblance, in miniature, to the trunk of an elephant or a very large nose. Composed chiefly of modified maxillae fitted together, the insect’s proboscis can be flexed and extended to reach nectar deep in a flower. In mosquitoes or aphids, mandibles and maxillae are modified to sharp stylets with which the insect can drill through surfaces like human or vegetable skin membranes to reach juice. In a housefly, the expanding labium forms a spongelike mouth pad that it can use to stamp over the surface of food, sopping up food particles and juices.
Insects, the most numerous creatures on our planet, are also them most adaptable. They require little food because they are small. They easily find shelter and protection in small crevices in trees and surface geological formations. Species of insects can evolve quickly because of their rapid reproduction cycle; they live in every climate, some making their homes in the frozen Arctic regions and many others choosing the humid, warm, and nutrient-rich rain forest environment. An active part of the natural food cycle, insects provide nutrition for animals and devour waste products of other life forms.
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