Beetle

I

Introduction

Beetle, insect belonging to the order Coleoptera, the largest group of animals on Earth. Beetles represent more than a third of all known insect species, and a fourth of all animal species. Scientists have identified about 350,000 species of beetles, but experts estimate that for every known species there are several more species that have not yet been discovered and named. Some experts estimate that there could be more than 8 million species of beetles worldwide. When asked whether his study of nature had provided any insights into the mind of the Creator, British scientist J. B. S. Haldane reportedly responded that God must have “an inordinate fondness for beetles.”

Beetles have evolved over 230 million years to form one of the most successful groups of insects. They have widely diverse shapes, sizes, and colors and they live in almost all parts of the world except the oceans, Arctic regions, and Antarctica. Beetles are especially successful in tropical habitats, but they can also be found in frigid mountainous habitats as well as in some of the hottest, driest deserts.

II

Characteristics of Beetles

Coleoptera, the scientific name of the beetle order, comes from the Greek words coleos (“sheath”) and pteron (“wing”). The term refers to the characteristic feature of beetles—hardened front wings that form a protective sheath over the hind pair of flying wings. While most beetles can fly, many are clumsy fliers, and some have lost the ability to fly and live primarily on the ground.

Most beetle species live on land, but some spend part or all of their lives in water. Others tunnel underground, in wood, or in the carcasses of animals. Some beetles live in the nests of ants and termites, forming a mutually beneficial relationship. The nest protects the beetles from predators, and the ants or termites receive house-cleaning services as the beetles consume the waste products of the colony.

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The beetle diet varies widely. Many beetles feed on plants, and each species usually prefers a particular plant species. Beetles feed on various parts of a plant, anything from the roots to the flowers. Many beetles are scavengers and eat dead plant or animal matter. Others are predatory, preying on insects, snails, or other small invertebrates.

About 100 species of beetles are considered some of the most destructive of all insect pests, due to their widespread distribution and varied feeding habits. Worldwide each year beetles cause millions of dollars in damage to plant products, such as food crops or timber, by feeding on them or by transmitting fungi and other agents of disease. One of the best-known beetle pests is the Colorado potato beetle. It became a pest in the middle of the 19th century, when settlers introduced potatoes into the beetle’s native range. Farmers find it difficult to control potato beetle infestations because the insects quickly develop resistance to insecticides. Another common pest in gardens and on a wide variety of crops is the Japanese beetle. Accidentally imported from Japan to the United States in 1916, the Japanese beetle feeds on over 400 species of broad-leaved plants. The beetle eats the tissue between the veins of leaves, giving the attacked leaves a lacelike appearance before they wither and die. Another well-known destructive beetle is the boll weevil, which spread into Texas from Central America in 1892. Boll weevils destroy cotton crops in the United States and elsewhere.

Many other types of beetles are beneficial to humans. Farmers release certain beetles in their fields to control insect pests. For example, ladybird beetles feed upon aphids and other small sucking insects that injure food crops, and ground beetles feed on crop-damaging potato beetles and caterpillars that destroy trees and shrubs.

III

Bodies of Beetles

Among the beetles are found some of the largest, as well as some of the smallest, of all insects. The largest beetle is the massive giant longhorned beetle (Titanus giganteus) of northern South America. Adults can grow 18 cm (7 in) or more in length. One of the smallest beetles is the North American feather-winged beetle (Nanosella fungi), which is less than 0.5 mm (0.02 in) in length. Most beetles range from 1 to 3 cm (0.4 to 1.2 in) in length.

As in other insects, the body of the adult beetle has three main parts—the head, which holds an insect’s primary sense organs and feeding structures; the thorax, which is the attachment site for the legs and wings; and the abdomen, which contains the organs for digestion and reproduction. A hard outer covering protects the internal organs.

A

Body Covering

The beetle's cuticle, or body covering, provides a tough, waterproof sheath that protects the soft inner organs and provides a rigid framework for the attachment of muscles. Harder and thicker than that of most other insects, the beetle’s cuticle is composed mainly of chitin, a strong, flexible compound. The cuticle restricts movement, and some beetles have difficulty righting themselves when turned upside down on a smooth surface. An exception is the click beetle, named for the clicking noise the beetle makes when it springs into the air to right itself.

The cuticle is commonly shiny brown or black, often with intricate texture patterns, but it may be brightly colored, or have colored spots, stripes, or other color patterns. Cuticle color in beetles derives from natural pigments in the animal tissue, which provide the many earth tones exhibited by beetles. In some species, minute surface structures refract light of various wavelengths, producing bright metallic or iridescent shades.

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