Vampire bats evolved from leaf-nosed bats by eating burrowing insects like screw worms, gleaning ticks and/or other blood sucking ectoparasites that burrow into the skin of animals. The bats then making the transition by licking around wounds, soon afterward to just eating blood. Vampire bats are the only known mammals that survive solely on blood and each night, vampire bats drink about half their body weight in blood. Vampire bats need 2 tablespoons of blood each day. They can eat approximately 1.5 times their body weight in the wild. The Common vampire bat cannot go 2 nights without food, otherwise it starves to death. Vampire bats, which weigh between .5 and 1.7 ounces (15 and 50 grams), often feed on animals 10,000 times their size in weight. Vampire bats don't suck animals' blood, they make a small hole with their two very sharp incisor teeth and using their tongues lap up the blood, which doesn't clot (thicken) because of anti-coagulants (anti-thickeners) in the bat's saliva keeps blood from clotting. Draculin, a blood-thinning drug developed from vampire bat saliva, helps prevent strokes and heart attacks in humans! These Vampire bats are so light and agile that they are sometimes able to drink blood from an animal for more than 30 minutes without waking it up. The blood sucking does not hurt the animal. Feeding on the blood of animals like cows, pigs, and horses, the vampire bat locates their prey is a combination of smell, sound, echolocation, and heat.

The Common vampire bat (Desmodus rotundus) uses echolocation, emitting ultra-high frequency sounds and interpret the sounds' echoes to locate prey, objects and for navigation. The reflected sounds, or echos, are picked up by the bats large sensitive ears. Bats and also dolphins are able to use sound to "see". Vampire Bats can tell how far something is by how long it takes the sounds to return to them. Common vampire bats avoid attacking dogs because canines can detect a bat’s high-frequency sounds as they approach!

Vampire Bats are the only true flying mammals and like all mammals give birth to live young and nourish them with milk. They are nocturnal; they are most active at night and sleep during the day hanging upside-down. Hanging upside down also provides bats with roosting space away from predators in safe places on the ceilings of caves, mines, in trees, and buildings. They live in colonies of up to 1000, but usually about 100. Their colonies are quite structured with strong social bonds, grooming each other and recognizing their fellows with voice and smell. In the wild, vampire bats live to about 9 years old, but can reach 20 years in captivity. Vampire bats mate all year round and usually have only one offspring per year. Gestation is 6-8 months in length. There are three species of Vampire bats the White-winged vampire bat (Diaemus youngi), the Hairy-legged vampire bat (Diphylla ecaudata) and the Common vampire bat (Desmodus rotundus found only in the New World tropical and subtropical regions (Central and South America).