"Vampire bats are amazingly well-equipped to live on a diet of blood and only blood - something no other mammal in the world does. Its teeth are so razor-sharp that the bird or mammal it feeds on usually does not even feel the tiny bite it inflicts. The bat's saliva contains a chemical that keeps the blood flowing, and its tongue is grooved - the bat uses it almost like a straw. As soon as the bat feeds, it urinates. Its body retains the nourishing part of the blood but gets rid of the water, so that it does not have to fly away carrying an extra load of weight. Diphylla ecaudata is one of three species of vampire bats, all of which are found only in the New World tropics. Only one specimen of a vampire bat has ever been found in the United States, in Texas in 1967, and it probably had wandered some 700 km north from its breeding population.."

Links:
Mammal Species of the World
Click here for The American Society of Mammalogists species account