Vampire Bats
Just like the mythical creature after which these creatures were named, vampire bats drink the blood of other animals in order to survive. While they commonly drink blood from cows, horses, birds, and pigs, they are also known to occasionally bite humans too. Vampire bats are found across South America and while attacks on humans are rare, these creatures are known to carry diseases, specifically rabies. Vampire bat saliva is, however, believed to have some use in medicine, particularly in helping increase blood flow in stroke patients.