Bats

They'd flown north from Central and South America, appearing one day in the southern wetlands of the U.S. like ominous ink stains in the twilight sky. With each sunset, more appeared, first hundreds then thousands. Massing into a great black cloud of terror, the vampire bats were beating their wings in time with the panicked heartbeats in the towns below. No one knew how to stop them as they fell onto their prey like dark, deadly shadows. But someone had to find a way. Because somewhere in the night, they had become a threat to more than wild animals and livestock. Somewhere in the night madness took hold as these vampire bats developed a taste for human blood. And the feasting had only just begun.