In the animal kingdom beetles form by far the largest major group or order. At least 250,000 kinds are known. They constitute more than a quarter of all kinds of animals. Most of them feed either upon other animals or upon plants, but some eat decaying matter of various kinds as well as a variety of other organic substances.
Many beetles are injurious, either as larvae or adults by being vectors of disease and as pests. Among those which attack farm crops, the wireworm is important. Wireworms are most prevalent in newly ploughed fields and attack the supervening crops especially cereals and roots. Adult and larvae flea beetles cause great damage to turnip crops. The asparagus beetle is a pest to that plant in North America and Europe. The Colorado potato beetle is destructive to potatoes in the eastern half of North America and in the Bordeaux district of France. The Japanese beetle is injurious to the foliage of fruit and other trees and its larvae damage lawns. The larvae of the May or June beetles attack the roots of grasses, potatoes, strawberries etc., and the adults feed on foliage of trees. The boll weevil is a serious problem to cotton crops. The granary weevil and the meal worms attack stored grain, meal and other dried products. The allied apple blossom weevil is very destructive to unopened blossom buds. The palm weevil injures toddy and coconut palms and the pine weevil attacks young conifers. The alfalfa weevil is a serious enemy of clovers and alfalfa.
Many species of beetles are used to control pest of commercial crops. Lady beetles or ladybirds and ground beetles are of particular benefit. The Australian ladybird has been imported to most citrus growing areas of the world to control fluted scale. Another species is used to control mealy bugs. The European ground beetle preys upon the caterpillars of the gypsy moth and the brown-tail moth. Beetles save millions of dollars in crop damage around the world.