Beetles are the largest order of both the insect and the animal worlds. Approximately 300,000 species, some 26,000 of which exist in the United States, have been identified. Every year, however, thousands of new species are discovered and classified. Beetles are found on every continent except Antarctica. There is no reason to believe that some of these highly adaptable creatures do not exist on the somewhat temperate Antarctic Peninsula. Although most beetles are land animals, some are aquatic, carrying air bubbles on their legs, which provide them with air when they are submerged. Most aquatic beetles live in freshwater, feeding on small fish and tadpoles, although a small number of beetles live in salt water. Other beetles live largely underground or beneath the bark of trees, while some species go through their life cycle in caves and are blind. The remarkable adaptability of beetles, which date to the Triassic period, has made them one of earth's most enduring species and accounts for their being found in a broad variety of geographical locations and climates.
Physical Characteristics of Beetles
With over 300,000 species of beetles cataloged and classified, the variations within each species are notable. These insects can range in size from very small to quite large. The fungus beetle is smaller than the period at the end of this sentence, never growing beyond one-fiftieth of an inch in length. The Hercules beetle, found in Central American rain forests, is typically six inches long and often exceeds that length. Despite variations in size, each species of beetle shares anatomical characteristics with every other species. All beetles have three main body parts in common: the head, the thorax, and the abdomen. The head usually contains the mouth and the eyes, although some blind cave beetles have no eyes. All beetles have antennae that protrude from the front of the head and are vital to communication. Blind beetles have more fully developed antennae than sighted ones. A beetle's mouth consists of three parts, the frontal mandibles, the maxillae or second jaw in four or five sections, which is jointed and has palpi (segmented appendages) on its outer side, and the labium or lower lip, which resembles the maxillae but has only three sections. In vegetarian beetles, the jaws point down, whereas in predatory beetles, they point forward. The thorax is behind the head and consists of three segments. The first, the prothorax, larger in beetles than in other insects, has one pair of legs on its underside. The second segment has a second pair of legs and the elytra, the cutaneous wing covers found in all beetles. In some species of ground beetles that do not fly, the elytra may be joined as a single, hard piece of cuticle. The third segment bears the third pair of legs and the delicate hind wings used for flying by species that fly. The abdomen, which contains most of the beetle's internal organs, is behind the thorax. It has nine segments, not all of which are visible. In most species the abdomen is covered almost entirely by the second pair of wings, although in a few species, up to half the abdomen is exposed. In most species, a straight line runs along the abdomen where the two elytra meet. Regardless of size or species, all beetles share this basic anatomy. Individual differences, however, characterize various species. Ground beetles that tunnel into the earth have short, strong legs with projections that make them efficient diggers. Predatory beetles have long legs because they must move rapidly to trap their prey.
Thanks for description - Animal life club