Bats are the only mammals that can fly, but vampire bats have an even more interesting distinction—they are the only mammals that feed entirely on blood.

These notorious bats sleep during the day in total darkness, suspended upside down from the roofs of caves. They typically gather in colonies of about 100 animals, but sometimes live in groups of 1,000 or more. In one year, a 100-bat colony can drink the blood of 25 cows.

During the darkest part of the night, common vampire bats emerge to hunt. Sleeping cattle and horses are their usual victims, but they have been known to feed on people as well. The bats drink their victim's blood for about 30 minutes. They don't remove enough blood