vampire bat any of three species of blood-eating bats, family Desmodontidae, native to the New World tropics. Named after the bloodsucking human spirits of folklore, vampire bats are shy, tailless, brown bats that run swiftly and can leap with considerable agility. They are about 6-9 cm (2 1/3-3 1/2 inches) long and weigh about 15-50 g (1/2-1 1/2 ounces). The three species are the common (Desmodus rotundus), white-winged (Diaemus youngi), and hairy-legged (Diphylla ecaudata) vampire bats.