Vampires are huge in Hollywood these days, thanks largely to media franchises like "Twilight," "True Blood" and "Vampire Diaries." But there's a reason why such bigshot bloodsuckers are rare in real life, even on Halloween: Vampirism is hard work.

 

The main ingredient in blood is water, which means it usually can't provide enough energy for big-bodied hunters. And since most animals keep their blood closely guarded, real-world vampires must rely on stealth and persistence for even the tiniest sip. But while they don't get much love from Team Edward or Team Jacob, life in the shadows is still big business for the following 13 vampires of the animal kingdom. (Text: Russell McLendon)