The Vampire Bat has three species all native to the Americas. Although the bats have provided inspiration to many excellent horrific cinemas and novels, the real Vampire Bat will make you feel disappointed. For one thing, most of them won't suck humans' blood like they do in novels. Although their food source is blood, most of them prefer the blood of horses or water buffaloes rather than humans. Also, the bats lick, not suck the blood from their hosts, because chemical ingredients in their spittle prevent blood in the bite wound from clotting.
In fact, many scientists have tried to use cure apoplexy. However, you can't think of the bats as harmless because other various kinds of diseases can be transmitted during the direct contact of blood from a different host.