ladybird beetle or ladybug, member of a cosmopolitan beetle family with over 4,000 species, including 350 species in the United States. Ladybird beetles are mostly under 1⁄4 in. (6 mm) long and are nearly hemispherical in shape, with very short legs. They are usually red or yellow with black spots, or black with red or yellow spots, the common species differing only in the number of spots. They have a bitter taste, and their bright coloration is thought to serve as a warning to predators.
The name is believed to date from the Middle Ages, when these beneficial beetles were dedicated to the Virgin. Nearly all ladybird beetles, both larvae and adults, are predators on destructive, plant-eating insects. The eggs are laid on plants infested with aphids or scale insects, on which the larvae feed until they pupate in the remains of the last larval skin. The adults gather in large numbers in the fall, prior to winter hibernation, and are often collected at that time by farmers for use in pest control. The first outstanding demonstration of pest control by use of natural enemies occurred in the United States in 1889, when Australian ladybird beetles (Rhodolia cardinalis) were imported to wipe out the cottony-cushion scale, an insect that had accidentally been imported from Australia to California and there became a threat to citrus orchards.
The Mexican bean beetle (Epilachna varivestis), which has spread through E North America, and the squash beetle (E. borealis) are the only North American ladybird beetles considered destructive. They are yellowish with black spots; adults and larvae feed on plants. The Asian, or harlequin, ladybird beetle (Harmonia axyridis), native to E Asia, is a voracious predator that has been widely introduced elsewhere to control pests. In the fall it seeks shelter inside buildings, becoming a household nuisance, and in some areas where it has been introduced its success also has led to the decline of native ladybird species.
Ladybird beetles are classified in the phylum Arthropoda, class Insecta, order Coleoptera, family Coccinellidae.
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