White-nose syndrome (WNS) has spread to endangered gray bats, the U.S. Fish and Wildlife Service confirmed Tuesday, marking the seventh species under attack from the disease. Gray bats cram large colonies into just a few caves, so WNS — which has a 100 percent mortality rate at some sites — could kill them off relatively quickly.

Biologists found the infected gray bats during two trips to Bellamy Cave in Montgomery County, Tenn., in February and March. Tipped off by a white fuzz on the bats' snouts, wings and tails, they collected specimens for testing at the University of Georgia and the National Wildlife Health Center in Madison, Wis. Both labs have now confirmed their fears: WNS is attacking gray bats, which are the disease's second already-endangered victims (it also affects endangered Indiana bats).

"The documented spread of WNS on gray bats is devastating news," Paul McKenzie of the FWS says in a press release. "This species was well on the road to recovery, and confirmation of the disease is great cause for concern. Because gray bats hibernate together in colonies that number in the hundreds of thousands, WNS could expand exponentially across the range of the species."

WNS has invaded 19 states and four Canadian provinces since it emerged from a single New York cave in 2006 (see map below), killing roughly 6 million bats along the way. It remains mysterious, although last year scientists finally found its cause: a recently discovered fungus named Geomyces destructans. And earlier this year, a study showed G. destructans is an invasive species from Europe. While it mainly spreads from bat to bat, experts think people may inadvertently help it move around when spores stick to the shoes or other equipment of hikers and spelunkers.

Click map to enlarge. (Image: U.S. Fish and Wildlife Service)

It's still unclear how exactly WNS kills, but infected bats show a variety of symptoms. White fuzz tends to grow on their faces, wings and tails, and many exhibit strange behavior such as waking up from hibernation too early and flying outside their cave, even though it's still winter and little food is available. Many of these bats apparently starve to death, since necropsies later show their stomachs are empty.

The gray bat was listed as an endangered species in 1976, largely because such big colonies live in so few caves, making it vulnerable to human disturbances. The species occupies a limited range in limestone-karst areas of the U.S. Southeast, and usually lives in caves year-round. Conservation efforts have helped it recover in recent years, namely by restricting human access to key hibernating and roosting sites, according to the FWS. But while there's no evidence yet that WNS is killing gray bats, the fact that it's infecting them is "cause for concern," the agency reports.

"We are not sure what this diagnosis is going to mean for gray bats and the spread of WNS," FWS white-nose syndrome coordinator Jeremy Coleman says in a statement. "Increased vigilance and improved diagnostic procedures may mean that we have identified the very early stages of infection in a new species. It is also possible that gray bats have been exposed for a few years, but do not succumb to the infection. Individual bat species appear to respond differently to WNS, and only research and time will reveal where gray bats fit on the spectrum."

Aside from their ecological importance, gray bats play an important economic role, too. Since they eat an array of different insects, they help control bug populations that damage crops or spread diseases — saving money and reducing the need for chemical pesticides. "Bats provide tremendous value to the U.S. economy as natural pest control for American farms and forests every year," says FWS director Dan Ashe. "Research and management of this disease remains a priority for the Service, and we will continue to work closely with our partners to understand the spread of this deadly disease and minimize its impacts to affected bat species."

This week's news is just the latest in an especially bad year for American bats. After the FWS raised its estimated death toll in January from 1 million to 6 million bats killed, it went on to announce several more setbacks. In March it revealed that WNS has reached Alabama for the first time, and that it has infiltrated Acadia and Great Smoky Mountains national parks. And in April, the agency reported evidence of WNS in Missouri — marking its first confirmed appearance west of the Mississippi River.

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MNN tease photo of bat: Shutterstock

Russell McLendon ( @russmclendon ) writes about humans and other wildlife.

Killer fungus hits endangered gray bats
After killing 6 million bats from six other species, white-nose syndrome is now attacking one of North America's most vulnerable varieties.