WATER-BEETLE. Any beetle which lives in or upon the water; more specifically. one of the true water-beetles or 'water-tigers' of the family Dytiscithe. They live in the water both as larva> and as adults, although they are prob ably modified terrestrial insects resembling the ground-beetles of the family Carabi&e. The pupa is terrestrial. They are elliptical convex insects with the hind legs formed for swimming. The wing-cases fit perfectly to the body except at the tip, so as to form an air-tight spec above the body proper. This space is the ai?-ehamher, and the beetle rises to the surface of the water, exposing the tip of its body and drawing in a supply of air which will last it for some time, when it goes below the sill-face again. The larva of the true water-beetles are very rapacious, and suck the juices of small, soft aquatic insects. The mandibles are hollow, with a hole near the tip and another at the base, thus being fitted for suction. The water-beetles are more numer ous in temperate and boreal than in tropical regions. About 1800 species are known, of which nearly three hundred inhabit the United States.
Whirligig beetles of the fancily Glyrinithe are small oval forms which swim about on the sur face of the water, usually darting in curious curves, from which habit the popular name is derived. They can dive, carrying with them a small supply of air, but their proper life is on the surface. The two himl pairs of legs are so
modified as to form paddles. The larvae arc aquatic and are elongate with sharp mandibles. They are earnivonms in the larval stage as well as in the adult,. About :300 species are known, of which nearly forty occur in the United States.
The water-beelles of the family Hydrophilithe are sometimes called 'water seavenger-beetles.' The larvae are predaceous and earnivorous, but the adult beetles are, as a rule, vegetable feed ers, though they will prey upon small aquatic animals. They are usually dark-colored, of elliptical shape, and do not swim as readily as do the other water-beetles, nor is the supply of air which may be carried as extensive as with the others. Many species construct egg-coeoons, which are sometimes attached to the body of the boctlo aml sometimes to aquatic plants, and fre quently cmattaehed, floating on the surface of the water. From 20 to 100 eggs are laid in each cocoon. About 1000 species a re known, and of these 150 are found in the United States, and about 90 in England. Other beetles. such as the Amphizoithe and Pelobibbe, live in the water in their early stages. The strangely modified para sitic beetle, Platypsyllus eastoris, found com monly upon the beaver, might also with justice be called a water-beetle. Consult Minn, The Natural history of Aquatic Insects (London, 1895).