Already an endangered species, the gray bat has recently become further threatened by a fatal fungal disease. (Kevin Pieper/ASSOCIATED PRESS)

Just in time for Halloween, the world’s first artificial bat cave is expecting the arrival of its first winged visitors. The nearly 80-foot-long concrete chamber was built to protect bats against white nose syndrome, a disease named for a white fungus that infects the skin of the muzzle, ears and wings of hibernating bats.

In the six years since bats with the syndrome were discovered dead or dying in a cave near Albany, N.Y., more than 5 million infected animals from seven species have died, according to the U.S. Fish and Wildlife Service. In the northeastern United States, 85 percent of hibernating bats have died from the disease, which has spread rapidly through Canada and New England, into the Mid-Atlantic and through most of Appalachia.

White nose syndrome is “unlike anything we’ve ever seen,” says Ann Froschauer, a spokeswoman for the Wildlife Service. Scientists have been confounded by the rapid spread of the disease and its mortality rate, which is higher than has ever been observed in wildlife disease, according to Froschauer. This fungus is particularly hard to treat because it invades deeper layers of the skin than most other fungi that attack mammals. Such a novel affliction, Froschauer said, requires novel strategies for blocking it without harming other cave life.

“Natural caves have lots of good fungi, amphibians and reptiles, insects and arthropods and isopods that live inside, so you can’t go in and hose them down with bleach to kill everything in there,” says Froschauer.

In Tennessee, conservationists reason that if they can’t rid the caves of the disease, maybe they can coax the bats out and lure them into a safer haven.

Gina Hancock, state director for the Nature Conservancy in Tennessee, says the idea of building a bat cave seemed “crazy” to her and others at the organization — until scientists and donors gave it their approval.

Construction of the winter cave, or hibernaculum, cost about $300,000. (It was paid for through private donations to the Nature Conservancy.) Buried beneath a hill in north-central Tennessee, about a 90-minute drive from Nashville, the cavern was outfitted with infrared cameras to allow scientists to observe the animals and with air conditioners to help cool it to a bat-attracting temperature of 45 to 48 degrees.

The cave’s ceilings and textured walls offer bats a wide choice of nooks to explore; netting and metal ridges offer other places to roost. The animals will enter through a rectangular opening aboveground and descend through a wide shaft to the main chamber, about twice as long and twice as wide as a large school bus. When the bats are away in the summer, the human caretakers can enter through a doorway built into the side of the hill.

When operational, the cave will host hibernating bats over the winter. After they clear out in the summer, humans will disinfect the room to get rid of any stray spores of the disease. (The fungus does not pose any threat to humans.)

“In a normal cave, you don’t see bat mortality until about three years after you see the fungus in there,” says Cory Holliday, coordinator of the Nature Conservancy’s cave research and protection efforts.

A yearly disinfection has the potential to reset the clock, giving the bats a disease-free roost for the winter. The animals still run the risk of getting the fungus from fellow hibernators, but they won’t get it from the environment itself. Every year will be the first year, from the point of view of a fungus that moves into the cave.

That problematic fungus, Geomyces destructans , thrives in the damp soil of caves. It doesn’t require bats as a host, which means an infected cave remains toxic even if all the resident bats flee or die: The fungus just squats in the soil. The rapid spread of the disease is believed to be attributable, in large part, to spelunkers who have carried it on their shoes from cave to cave.

For the bats of Montgomery County, the artificial cave may be opening just in time to make a difference. A short walk down the hill leads to a small sinkhole overgrown with vines, with a dark, rugged opening at the bottom. The crevice leads to a large cavern inside Bellamy Cave, a winding, mile-long underground tunnel that is home to hundreds of thousands of gray bats, small wooly creatures that change caves according to the season. Bellamy is one of the country’s handful of large hibernacula for gray bats, which are listed on the federal endangered species list.

The bat entrance to the artificial cave was sited to align with the routes of bats headed to hibernate in Bellamy Cave. Between 2011 and 2012, the number of Tennessee counties with infected caves doubled. And early this year, near the end of winter, white nose syndrome showed up in the habitat of gray bats for the first time — in Bellamy Cave. Bats can still enter the cave, but scientists hope they choose the artificial one instead.

Even after the first bats arrive at the new cave, it will take at least three years to see if the artificial cave will make a difference in keeping white nose syndrome at bay.

“Bats are known to adopt abandoned mine shafts and places like that, so we know they’ll go to man-made structures,” says Hancock. “If we see any bats go in this year, that will be our first success.”

Once the first bats move in and deposit guano, others will follow, she says.

The Fish and Wildlife Service, which is exploring a wide variety of ways to treat the disease, will be among the organizations watching. A success could inspire the creation and construction of similar subterranean structures.

“If this works really well, it’s not out of the question that we would build a bunch of bat caves in the future,” Froschauer says. She points out that artificial caves provide not only a safe haven for bats but also a laboratory for bat scientists, including microbiologists working on a way to treat infected animals. The University of Tennessee and Southern Illinois University have both arranged to start doing research at the Montgomery County site.

“Another idea behind this cave was to give researchers a place to come and actually be able to do some things that wouldn’t hurt other things in the cave system,” such as deploying fungicides or other cleaners, says Hancock.

For now, bat lovers must simply watch and wait for the wing-flapping to begin. “We have a lot of square footage,” Holliday says of the cavern. “It could physically fit over 200,000 bats, but we’ll be happy with 10 to 15 thousand.”

Ornes is an independent science writer in Nashville.