BAT, a flying mammal, with greatly elongated fore limbs espe cially adapted for flight. Bats move about more exclusively by flying than any other group of animals, for, unlike most birds and insects, their limbs and feet are not adapted for walking. There are about 90o species of bats, constituting the order Chir optera (q.v.). Bats are distributed throughout the world, but are most abundant in the tropics and the warmer parts of the tem perate zones; the Malay "flying fox" (Pteropus edulis) measures about a foot in the head and body, and has a wing-spread of 5 ft., while in the smaller forms the head and body may be only about 2 in., and the wing-spread no more than a foot. The colour is generally sombre, but there are exceptions; the fruit-bats are brownish yellow or russet on the under surface; two South Amer ican species are white; Blainville's bat is bright orange In habits bats are social and nocturnal; the insect-eating species feed on the wing; in winter in the temperate regions they migrate to a warmer climate or hibernate. Most bats are insect-eaters, but the tropical "flying foxes" or fox-bats of the Old World live on fruit ; some are blood-suckers, and two feed on small fish. Twelve species are found in Great Britain, among which is the pipistrelle (Pipistrellus pygmaeus), and some 35 species occur in the United States. See FLYING-FOX and VAMPIRE.