As Halloween approaches, tales of monsters and creepy crawlies abound. Among the most fearsome in places like Mexico and Puerto Rico is the legendary beast known as the chupacabras. 

But the real fiend is not the hairless, fanged animal purported to attack and drink the blood of livestock; it's a tiny, eight-legged creature that turns a healthy, wild animal into a chupacabras, says University of Michigan biologist Barry OConnor.