Beetles constitute the largest order not only of insects but also of the entire animal kingdom. Scientific descriptions of about one million different species of animals have been published. This figure includes about 700,000 insect species, of which approximately 300,000 are beetles.

The name Coleoptera is derived from the Greek words koleon, meaning "sheath," and pteron, meaning "wing." It refers to the beetle's characteristic hardened front wings that meet along the middle line of the back and form a protective sheath over the hind wings. Beetles are the only insects that fly principally with the hing pair of wings.

Bettles have a nearly worldwide distribution and may be found in a variety of habitats. Almost any organic material may serve as food for some groups of beetles. Many are plant feeders, and others prey on insects, snails, or other small invertebrates. A number are scavengers, feeding on dead or decaying plant or animal matter.

Families of Beetles

More than 100 different families of beetles are known. Some of the larger and more important families and their principal characteristics are shown below.

Carabidae (Ground Beetles) About 20,000 species. Ground beetles are small to moderately large in size. They have long legs, rounded bulging eyes, and sharp mandibles that are directed forward. Both larvae and adults feed extensively on dead or decaying organic material, but most are also predatory. Commonly, ground beetles are black, brown, or metallic in coloring, and the elytra are frequently marked with a regular linear pattern. They are found in or on the ground, especially in gravel near streams and rivers, as well as in decaying wood. In many species an evil-smelling fluid is secreted from the hind end of the body, probably as a defensive mechanism.

Cerambycidae (Long-Horned Beetles) Almost 15,000 species. Long-horned beetles derive their name from their antennae, which may be several times the length of the body. The life cycles of some long-horned beetles extend over several years. As a result, the adult beetles may not emerge until after a tree has been processed for lumber and the lumber used in construction.

Chrysomelidae (Leaf Beetles) Over 25,000 species. Leaf beetles bear a superficial resemblance to ladybird beetles, but can be distinguished by an extra joint in the tarsus and by the fact that they feed on plants. Leaf beetles are often brightly marked, sometimes with metallic colors and sometimes with stripes running lengthwise.

Cicindelidae (Tiger Beetles) About 1,300 species. Most tiger beetles measure from three-fourths to one inch long. They are frequently brilliantly colored in metallic blue, green, or red, especially on the underside. The upper side is frequently sandy-colored and patterned with bold markings. Tiger beetles are most commonly seen in sandy areas, especially when the weather is hot and sunny. They run rapidly, and they have long sharp mandibles, which they will use to protect themselves. The larvae of tiger beetles live in tunnels that may extend several feet in the ground.

Coccinellidae (Ladybird Beetles) About 3,800 species. Ladybird beetles are predatory, with most feeding on slow-moving prey, such as scales and aphids. Generally, ladybird beetles are broad, rounded insects, ranging from one tenth to one half of an inch long. The elytra are often red or orange with black spots, and the antennae are generally somewhat clubbed. The tarsi are adapted for life on the leaves of plants. The larvae often pupate on the host plants of their prey, hanging head downward.

Curculionidae (Weevils) About 40,000 species. Weevils can be readily distinguished by the long snout projecting from the front of the head. In some species this snout may extend to three times the length of the rest of the body, and it is generally longer in females than in males. Unlike most insect snouts, those of the weevils bear biting mouthparts similar to those of other beetles. The antennae of weevils are usually elbowed -- that is, they extend outwards from the head and then forward. The antennae are also clubbed at the end. The majority of weevils are a dull black or brown.

Dermestidae (Hide Beetles) About 600 species. Hide beetles are usually relatively small, and they frequently have a mottled appearance. The antennae are short and clubbed and may be retracted into grooves in the body. The extremely hairy larvae are reddish-brown to black in color. They are found in animal carcasses in an advanced stage of decomposition, or, in some species, in larders; under carpets; or in woolen clothing, furs, or skins, where they may cause serious damage. As adults, hide beetles feed at flowers.

Dytiscidae (Predatory Diving Beetles) About 2,100 species. Diving beetles are aquatic both as larvae and adults. The adults have a smoothly rounded, streamlined body, varying in size from small to a length of almost two inches. They are black or dark brown, sometimes with a linear color pattern. The larvae of diving beetles prey on tadpoles, small fish, and other insects. They capture their prey on with their long mandibles, which are sickle-like in shape and perforated. When the mandibles are inserted into a victim, digestive fluids are injected into the prey through channels in the mandibles. As the tissues of the prey liquefy, they are sucked back through the same channels, digestion already having occurred outside of the beetle's body.

Elateridae (Click Beetles) About 7,000 species. When placed on its back, a click beetle jumps into the air to right itself. As it does so, it makes a clicking noise, from which it derives its name. Most species measure from one fourth of an inch to one half of an inch long and may be brown, black, or metallic green. Their antennae are usually sawlike. The elytra are grooved and usually have a hingelike structure at the front, which is a feature of the click mechanism.

Gyrinidae (Whirligig Beetles) About 400 species. Whirligig beetles are usually seen in groups, and they are generally noticed because of their incessant gyrations on the surface of water at the margins of rivers and lakes. They are oval-shaped and flattened in form. They have two pairs of eyes, one of which is adapted for vision above the water's surface and the other for underwater vision.

Lampyridae (Glowworm Beetles) About 1,100 species. Most members of this family are soft-skinned and loosely articulated. However, the females of some species are quite unlike the males in that they remain permanently grublike and have luminous organs in the abdomen. Such beetles are commonly known as glowworms. In some species wings and luminous organs occur in both sexes. These species are known as fireflies. In some species the eggs, larvae, and pupae are all luminous. Most of the larvae feed on snails.

Lucanidae (Stag Beetles) In many species of stag beetle the males have oddly enlarged jaws that look somewhat like the horns of a male deer. In some cases, these "horns" are nearly as long as the body. Adult stag beetles eat sap and honeydew.

Scarabeidae (Scarabs) Almost 15,000 species. Scarabs are thick-set beetles, ranging from very small to the goliath beetle, which may be several inches long. Nearly all scarabs are recognized by the end section of the antennae, which have a fan-like appearance. This modification of the antennae is associated with an exceptionally well developed sense of smell.

Silphidae (Burying Beetles) About 600 species. Burying beetles lay their eggs on the carcasses of small animals, which are then buried. Some species live in ants' nests, and still others are eyelss and live in caves. In most species a swelling or knob occurs at the tip of each antenna.

Tenebrionidae (Darkling Beetles) More than 10,000 species. Members of this family range in size from about one-half inch to one or two inches are are usually brown or black in color. Many species have projecting spines along the body. Two relatively distinctive features are found in darkling beetles: there are only four sections to the hind tarsi, while the two front pairs each have five, and the hind margin of the eye is frequently invaded by a ridge extending along the side of the head.

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The Robinson Library
Science.--Zoology.--Invertebrates.--Phylum Arthropoda..--Class Insecta (Insects).--Order Coleoptera (Beetles).

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