Bats in New York and Vermont are mysteriously dying off by the thousands, often with a white ring of fungus around their noses, and scientists in hazmat suits are crawling into dank caves to find out why.

“White nose syndrome,” as the killer has been dubbed, is spreading at an alarming rate, with researchers calling it the gravest threat in memory to bats in the U.S.

“This is definitely unprecedented,” said Lori Pruitt, an endangered-species biologist with the U.S. Fish and Wildlife Service in Bloomington, Ind. “The hugest concern at this point is that we do not know what it is.”

A significant loss of bats is chilling in itself to wildlife experts. But —like the mysterious mass die-offs around the country of bees that pollinate all sorts of vital fruits and vegetables — the bat deaths could have economic implications. Bats feed on insects that can damage dozens of crops, including wheat and apples.

“Without large populations of bats, there would certainly be an impact on agriculture,” said Barbara French of Bat Conservation International of Austin, Texas.

Found by Tracy Taylor.