Vampire bats feed solely on the blood of other animals, usually on cattle and horses. However, vampire bats do not suck blood. With their razor-sharp teeth, they make small incisions, usually in a sleeping animal. Then they lap up the blood, roughly one teaspoon, without ever waking up the animal.
While the bat is the only mammal that can fly, the vampire bat always approaches its prey on all fours. It creeps up to its prey and attaches itself to a spot where blood flows closest to the skin. There it feeds for roughly half an hour. A chemical in the saliva of the vampire bat numbs the prey's skin to prevent it from waking up.
Another substance in the saliva, Draculin, prevents the blood of the victim from clotting inside the bat. The vampire bat does not drink enough blood to harm the animal, but its bite has been known to cause infection or disease.
Vampire bats live in colonies located in South and Central America. Their homes are caves in hot and humid environments. A typical colony has about 100 bats, but colonies have been known to have more than 1,000 bats. In one year, a colony of a hundred bats can drink the blood of 25 cows.