"It's unprecedented in North American wildlife, at least in recorded history," Tom Kunz, a bat biologist at Boston University, told CBS News Science and Technology Correspondent Daniel Sieberg.
Biologists are struggling to understand a fungus called white nose syndrome that has killed more than a million bats over just three winters.
The fungus grows on the faces of bats while they're hibernating. It seems to irritate the bats, upsetting their natural hibernation rhythms. They become more active and burn up critical body fat.
"And they're starving," said Kunz. "They have no other source of food."
In some cases, bats fly out into the freezing cold in a fruitless search for food.
"There have been losses of up to 95 to 100 percent in some caves and mines," Kunz said.
It started in just four caves in upstate New York in 2006, spread in 2007 to three states and last winter exploded to a total of nine.
This winter, it's expected to march further south and west threatening other bat species and the nation's largest colonies.
The past two winters, we've witnessed the profound impact tragic for the million bats killed so far, potentially devastating for America's farms and forests.
Think of bats as nature's pesticide. Just one little brown bat is capable of eating up to a thousand insects every night.
"Those million bats would've eaten each summer about 694 tons of insects," Kunz said.
"Really?" Sieberg asked.
"And so, those insects are?"
"They're out here now."
Surviving insects could do heavy damage to forests and woodlands. Other bat favorites, like moths and beetles, attack cotton and corn, potentially forcing farmers to use much more pesticide.
The best hope, still years away, would be a vaccine or fungicide.
"Words don't really provide the nature of how one feels, except by saying it's a very depressing condition," said Kunz. "These bats are not likely to recover in my lifetime."
They've been surviving for 50 million years, but an entire species of bats may be wiped out in less than a decade.
On the Net:
Cave Biota, a Web documentary about bats: http://cavebiota.com/
Boston University's Tom Kunz: http://www.bu.edu/cecb/BATS/
U.S. Fish & Wildlife Service on White-Nose Syndrome: http://www.fws.gov/northeast/white_nose.html
By CBS News Science and Technology Correspondent Daniel Sieberg