Beetles

The Coleoptera includes the largest and smallest insects in the world, ranging from the giant, 6.3-in (16-cm) Longhorn beetle (Titanus giganteus) of the Amazon region to the dot-sized, fringed ant beetle (Nanosella fungi) of North America, which reaches only 0.25 mm in length—smaller than a large protozoan.

Beetles are economically important in agriculture, either feeding directly on crops and trees, or preying on other species that harm plant crops. For example, the ground beetles (Carabidae) and the rove beetles (Staphylinidae) feed on caterpillars and other larvae as well as on many soft-bodied insects and insect eggs. Many of the adult and larval forms of the ladybugs or ladybird beetles (Coccinellidae) feed on plant-sucking insects (Homoptera) such as aphids and scale insects, while only a few of the Coccinellidae themselves (e.g., Epilachna) feed on plants.

Many other beetles, however, do feed on plants. Among the most important of these beetles are the leaf beetles (Chrysomelidae) and the weevils and their relatives (Curculionoidea). The larvae of leaf beetles feed on leaves, stems, or roots, while most adults chew on leaves; the larvae of weevils feed on almost every part of plants. For example, larvae and adult forms of bark beetles (Scolytidae) attack tree tissue beneath the bark.

The scarab beetles (Scarabaeidae) are important pests of crops, lawns, and pastures. One of these insects, the dung beetle, was an important religious symbol to ancient Egyptians, who considered its life cycle to be a reflection of the cyclical processes of nature, especially the "rebirth" of the sun each morning. Glazed steatite (soapstone) and other ancient Egyptian ceramic or stone representations of the beetle, called scarabs, were a symbol of the soul and used as talismans.

Many beetles act as scavengers, breaking down organic material such as wood and dead plant and animal matter. The larvae of some beetles, such as the wedge-shaped beetles, are parasitic on wasps, bees, and cockroaches. The European elm bark beetle (Scolytus multistriatus) transmits the fungus that causes Dutch elm disease.

The vast array of forms and colors of Coleoptera ranges from the black, furry Brazilian beetle, with creamy-white and orange spots, to the squat tortoise beetle, the long-snouted Peruvian beetle, the stag beetle with its two threatening "horns," and the whirligig beetle, often found gyrating rapidly on the surface of ponds.

Click beetles (family Elateridae) are named for the sharp noise they make. When turned onto its back, a click beetle will bend its head and the upper part of its body backward, then suddenly straighten. This movement produces a click and propels the beetle into the air. This maneuver is repeated until the beetle lands right side up.

Lightning bugs or fireflies (family Lampyridae) produce light; some species produce flashes, while others produce continuous luminescence. These insect light shows, common in spring and summer, are a mating ritual through which the opposite sexes find each other.

The classification of beetles established by R. A. Crowson in 1955 (The Natural Classification of the Families of Coleoptera), divides the order into four suborders: Archostemata (rarely found beetles), Adephaga (the tiger beetles and various water beetles), Myxophaga (the minute bog beetles and skiff beetles), and Polyphaga (the majority of beetles, such as carrion beetles, scarab beetles, ladybugs, and long-horned beetles). The Polyphaga is the largest suborder, with 18 superfamilies. In all, there are about 135 known families of beetles, of which 120 are found in the Western Hemisphere.