A member of the insect order Coleoptera, which contains the beetles and the weevils and is the largest of the insect orders. The 250,000 known coleopteran species include some of the smallest and largest of the insects: the smallest coleopterans are less than one millimetre (0.04 inch) in length, while the largest (e.g., the rhinoceros beetle Xyloryctes satyrus) can exceed 20 centimetres (8 inches). Beetles can be found in almost all environments except Antarctica and the peaks of the highest mountains. The tropics contain the most diverse beetle fauna, while in temperate zones, the fewer species are represented in greater numbers. The major diagnostic characteristic of the order is a modification of the forewings, or elytra. These may be either rigid or thickened and leathery; they lie protectively over the back and hindwings and meet in a line down the centre of the back. The hindwings are used for flying in most species. This protective modification perhaps allowed early beetles to exploit niches underneath bark, where unprotected wings would be damaged. The body is built on the general insect plan of head, thorax, and abdomen; in coleopterans, however, the last two thoracic segments are joined to the abdomen, and the prothorax stands alone under a protective plate called the pronotum. The legs may be adapted for running, digging, swimming, or jumping. The antennae are normally composed of 11 segments, but their form may vary widely. Depending on the diet, the mandibles may be quite large or nearly absent. Most coleopterans possess a pair of prominent compound eyes.
Source: Encyclopaedia Britannica 2002