vampire bat

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Any of several bats of the subfamily Desmodontinae, found in subtropical and tropical regions of the Americas, that bite mammals and birds to feed on their blood and that often carry diseases such as rabies.
• noun Any of various other bats, as those of the family Megadermatidae, erroneously believed to feed on blood.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A small flying mammal (bat) of South America which uses its teeth to nick larger animals while they are asleep, allowing it to surreptitiously lap a blood meal.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun any of various tropical American bats of the family Desmodontidae that bite mammals and birds to feed on their blood