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.
The Life Cycle of Beetles
All beetles pass through four stages of development, called metamorphosis. Life begins within eggs laid by the female beetle, usually in a protected place such as beneath a rock, on the underside of a leaf, or inside the bark of a tree. The females in some species lay up to two thousand eggs at once, while in other species a single egg is laid. When the eggs hatch, a small wormlike creature, called a larva or grub, emerges. The larvae of some species are mobile and have legs, while those of other species may be legless and can move about only by wiggling. Those with legs are predatory and move about easily in their quest for food. The legless larvae usually attach themselves to plants and survive by eating the leaves. Beetle larvae have huge appetites and frequently are destructive to crops. Their voracious eating causes them to grow rapidly, forcing them to shed their old skins, which they outgrow, in a process called molting. When the larva reaches full size, it enters the next phase of its metamorphosis by becoming a pupa, sequestering itself in a safe place where it remains for about a month. Its body changes drastically as it evolves toward its adult stage. When the pupa cracks, the adult beetle emerges, its body soft and flexible. Within twenty-four hours, however, the body hardens and the metamorphosed beetle looks and acts like other adult beetles. The integrity of the species is maintained in some types of beetles by the shape of the male sexual organs which allows them to enter only females of that species. Also, the white fringed weevils of Argentina and some other beetles are parthenogenetic, which means that their eggs are not fertilized by a male. This species is exclusively female. Destructive and Beneficial Beetles Many species of beetles are destructive, devouring everything in their paths, ruining crops, devastating forests by attacking the roots of trees, and wreaking general havoc wherever they exist. Japanese beetles were particularly destructive to farm crops in New Jersey during the 1930's. The boll weevil deposits its eggs in vegetables or in the blossoms of cotton plants. The resulting larvae quickly consume the plants in which they are hatched. Some types of beetles eat grain and flour, while the larvae of carpet beetles eat all kinds of fiber. The predatory nature of some species of beetle can help solve ecological problems. St. John's wort, also called Klamath weed, is a rapidly growing plant that annihilates grasses that grow in the places where it takes hold. It also causes animals that eat it to have sore mouths and debilitating skin eruptions. When it was discovered that a leaf beetle the size of a pea would devour this intrusive plant, such beetles were introduced into the affected areas and within a few years had eradicated the plant. Ladybugs contribute to agriculture by eating aphids and other pests from the leaves of plants. In many parts of the Third World, people depend upon the larvae of beetles to add protein to their diets. Many folk remedies, including aphrodisiacs and diuretics, are made from dried beetles. Scarabs and other beetles consume carrion and clear away dead material that is potentially infectious.
Order: Coleoptera (beetles)
Suborders: Polyphaga (rove beetles, scarabs, stag beetles, metallic wood boring beetles, click beetles, fireflies, blister beetles, mealworms, ladybugs, leaf beetles, longhorn beetles, weevils); Adephaga (ground beetles, tiger beetles, predacious diving beetles, whirligig beetles); Archostemata (small, rare group characterized by wings coiled in a spiral)
Geographical location: Every continent except Antarctica
Habitat: Mostly land (forests, deserts), although some live in freshwater and a rare few in salt water
Gestational period: Varies greatly among species
Life span: Many exist for four months to a year; several species of ground beetles in Alaska, protected from subzero temperatures by an ability to produce glycerol that creates an antifreeze in their bodily fluids, survive for up to eight years
Special anatomy: Six legs, three on each side of the thorax; two pairs of wings, two hard, cutaneous wings on top that serve as armor, two more membranous wings underneath used in flying
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