Hundreds of thousands of tiny white-nosed bats have died over the past few winters, falling to cave floors across the eastern United States. The killer is White Nose Syndrome, a mysterious disease inflicted by an unusual cold-loving fungus that attacks bats while they are hibernating. Come spring, as few as 5 percent of the bats in heavily infected roosts are still alive. More than 2 million bats have already been killed by the disease. And the prognosis could get worse, as White Nose Sydrome is spreading westward at an alarming rate.