Common vampire bats are 3 to 3.5 inches long, with short reddish-orange or brown fur and small or no tails. They have short, blunt muzzles and pointed ears. The upper incisor teeth with which they pierce prey are razor-sharp. They have long, pointed wings and segmented thumbs on their forelimbs.
Because the first joint of their thumbs is extremely long, vampire bats are able to hop along the ground using their forelimbs. Using their strong thumbs to launch themselves 3 feet or more into the air, they are the only type of bat able to attain flight from the ground. During the day they hang from cave ceilings in total darkness in colonies of around 100 to 1,000 individuals, and at night they come out to feed.
Vampire bats are the only mammals that feed on blood and nothing else. Heat sensors on their faces alert them to prey. They normally target sleeping cows, horses and other animals but occasionally take the blood of humans. They usually land near their prey, crawl towards it, make a small incision with their teeth and lap up the blood. An anticoagulant in their saliva prevents the blood from clotting. The amount of blood they take does not endanger the animal, but sometimes vampire bats carry rabies and other diseases. Vampire bats feed for about 30 minutes, and in that time, the amount of blood they consume can double their body weight.