It evolved to drink blood from a variety of Central and South American wildlife, but as growing farms and cities shrank that food supply, it started targeting the intruders instead. Today it feeds mainly on cattle, horses and other livestock, as well as humans, a diet that likely helped it avoid extinction. Its bite alone isn't dangerous, but it can spread rabies, which poses a public-health threat across much of its habitat. This year, for example, four children died in Peru after vampire bats sparked a rabies outbreak among the local Awajun tribe.
Watch the video below for a look at how vampire bats sneak up on their hosts: