Vampire bats feed exclusively on the blood of living animals and are thus the only true parasites among mammals. There are three species ranging from Argentina to N Mexico. The bat uses its razor-sharp incisors to make a neat incision, usually without waking the victim, then laps the blood with its tongue. Its saliva contains an anticoagulant that causes the wound to seep for several hours.
Vampire bats parasitize a variety of animals, chiefly mammals.
Although the quantity of blood they take is insufficent to harm a large animal, they are dangerous to livestock and humans because they transmit serious diseases such as rabies and Chagas's disease. Vampire bats live in caves, tree hollows, and houses. Members of another bat family, the Megadermatidae, of the Old World tropics, are known as false vampire bats. They are exclusively carnivorous but do not feed on blood. The generic name Vampyrus belongs to a large, fruit-eating bat of Central and South America that was once mistakenly believed to suck blood.