beetle, common name for insects of the order Coleoptera, which, with more than 300,000 described species, is the largest of the insect orders. Beetles have chewing mouthparts and well-developed antennae. They are characterized by a front pair of hard, opaque, waterproof wings called elytra, which usually meet in a straight line down the middle of the back. The elytra cover the rear pair of membranous flight wings, protecting them and the body from mechanical damage and desiccation. Beetles are poor flyers compared with many other insects, but they are well adapted for surviving rigorous conditions. They are found everywhere except in oceans and near the poles, and they occupy nearly every kind of habitat. Most are terrestrial, but some are underground tunnelers and some live in water. These water beetles are often confused with water bugs, but the latter all have sucking mouthparts. Beetles range in size from under 1⁄32 in. (1 mm) to over 6 in. (15 cm) long; tropical species are the largest. Most are dull, but members of several beetle families are brilliantly colored, some with a metallic or iridescent sheen. The majority of beetles are plant eaters, but there are also many predators and scavengers and a few parasites. Many beetles are highly destructive pests of crops and gardens (e.g., Japanese beetle , potato beetle , boll weevil ), but others are beneficial predators of harmful insects (e.g., ladybird beetles ). The largest of the many beetle families is the scarab beetle family, with over 20,000 species; among these are the dung beetles, which are invaluable scavengers. Weevils are plant-eating beetles with mouthparts elongated into snouts bearing jaws at their ends. The fireflies are luminescent beetles. Blister beetles , including the so-called Spanish fly, produce irritating secretions. Beetles are classified in the phylum Arthropoda , class Insecta, order Coleoptera.
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