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Adult longhorned beetles vary greatly in shape, size, and color. In general they are cylindrical and rather long-bodied. Some tropical species are among the world's largest beetles, reaching 15 cm (6 in) or more in length. But most species measure 8 to 50 mm (0.33 to 2.00 in) long. Some species of lorghorned beetles are dull brown, while others have bright colors or intricate patterns on their wing covers. The beetle's prominent antennae are at least two-thirds as long as the body, and in some species the antennae are longer than the body. Males have longer antennae than females. Some species of longhorned beetles are slow-moving, while others can run quickly or are strong fliers. Depending on the species, adults may be observed feeding on flower parts, leaves, or bark.
Females lay eggs in bark crevices or in soil near roots. Newly hatched larvae immediately begin to excavate into the plant they feed on. Some species feed only on dead or decaying wood, while others bore into roots or beneath bark of living trees and shrubs. Larvae are pale-colored, often creamy white, and wormlike. The larvae of large species can grow to several inches in length. Their small round head and cylindrical form distinguishes them from flatheaded borers (larvae of metallic wood borers), which have an enlarged and flattened thorax that is wider than the rest of the body. In some countries, roundheaded borers are eaten by humans as a delicacy.
Like all beetles, longhorned beetles have complete metamorphosis. Larvae commonly pupate in a chamber they construct under bark. Most species require one to three years to complete one generation, although some can develop from egg to adult in as little as two or three months. Mature larvae of a few species can remain inactive in wood for many years. There are records of longhorned beetles emerging from wood beams or furniture in houses after remaining dormant for more than two decades.
Some species of longhorned beetles are pests of forest, shade, or fruit trees and certain shrubs. The roundheaded appletree borer, for example, infests apple trees. Protecting trees from injury and otherwise providing plants with proper care usually will prevent damage by longhorned beetles. Most longhorned beetles attack only injured or weakened woody plants. Longhorned beetles help to decompose dead and dying trees, thereby making nutrients and sunlight available for new plant growth.
Longhorned beetles have many natural enemies, especially parasitic wasps and the larvae of certain other beetles. Many birds feed on adults and woodpeckers are fond of the larvae. Lizards sometimes lie in wait and capture adults when the beetles land on bark to mate or lay eggs.
The brilliantly colored red milkweed beetle is frequently seen on milkweed plants in North America. The California prionus is the largest North American beetle, reaching 6 cm (2.3 in) in length. The huge adults have a spiny neck and can fly. Their larvae bore in the roots and stumps of many species of hardwood and conifer trees. Brightly colored adults of many species of longhorned beetles are a favorite among insect collectors, probably exceeded in popularity only by butterflies and large moths. Partly because of their relatively slow rate of reproduction, the survival of some species of longhorned beetles is endangered. For example, the valley elderberry longhorned beetle is threatened with extinction in California. Development and farming along riverbanks have destroyed much of this beetle's natural habitat.
Scientific classification: Longhorned beetles are in the family Cerambycidae, order Coleoptera. The roundheaded appletree borer is Saperda candida; the red milkweed beetle is Tetraopes tetrophthalmus; the California prionus is Prionus californicus; the valley elderberry longhorned beetle is Desmocerus californicus.