Image: David Fulmer / Flickr Creative Commons

FARMINGTON, PENNSYLVANIA—In a chamber a few hundred feet underground known as the Stomach, long-time cave guide Lisa Hall is talking about bats. Less than a decade ago, this cave system was home to thousands of them—little brown bats, northern long-eared bats, Indiana bats, and big brown bats. Today, she says, when the staff spot a single individual (almost always a big brown bat, Eptesicus fuscus), they get excited.

This situation is not unique to Laurel Caverns, the enormous cave system sixty miles south of Pittsburgh that I toured with a group of journalists in early October. (In addition to the Stomach, Laurel is home to the Flue, the Dining Room, and the Panini Press.) White-nose syndrome, the fungal scourge that first arrived in Howe Caverns in New York in the winter of 2006-2007, has killed off an astonishing number of bats around the Northeast and elsewhere.

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Winter refuges like caves—ecologists call them hibernacula—have seen devastating decreases to bat populations that sometimes numbered up to 100,000 individuals. Greg Turner, a biologist at the Pennsylvania Game Commission, offered up some examples: One site, the Canoe Creek Mine near Altoona, had over 30,000 bats as of a 2007 hibernation survey. Two years later, it had 155. Another site went from that 30,000-bat level down to six individuals in little more than a year. Across Pennsylvania, the total decline in bats may be over 99 percent since the pre-white-nose era.

Hall said she has done a survey of a different type of hibernaculum, an abandoned bathroom building at an Army Corps of Engineers site, for years. There used to be more than 3,000 bats, but last year, that number was zero.

The little brown bat (Myotis lucifugus), which used to be the most common species in this area, has seen a mortality rate at some sites of 99.9 percent from one year to the next. The Indiana bat (Myotis sodalis), the tricolored bat (Perimyotis subflavus), and the northern long-eared bat (Myotis septentrionalis) aren’t far behind. A few other species, like the big brown bat and the eastern small-footed bat (Myotis leibii), have not been quite as badly decimated, but their numbers have still dropped.

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Down in the Stomach, Hall talks fondly of what it was like when the bats were everywhere. When the pups were born and starting to fly around, she says they could be found hanging out behind the Pepsi machine in the visitor center, helping themselves to its warmth. She has hand-removed bats that were taking a break inside the women’s restroom. They would show up in early September sometimes, before hibernation time, maybe just to scout it out: “Cave’s still here, we’re good. Let’s go eat bugs for a month and come back.” Now, nothing.

A bat on snow in a dehydrated state after waking up during its hibernation. This situation is typical of bats afflicted with white nose syndrome. Photo Courtesy Hal Korber / Pennsylvania Game Commission

White-nose syndrome is caused by a fungus, the appropriately-named Pseudogymnoascus destructans. It likely stowed away on that friend to all invasive species, a human, on its way from Europe or Asia, and the bats in its new home in North America were not equipped to combat it. (European and Asian bats have the fungus too, but do not suffer ill effects.) The fungus covers bats’ skin, resulting in the fuzzy white beard that gives the syndrome its name. It kills through a few mechanisms, most notably its ability to wake bats up while they hibernate.

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A healthy bat will wake up periodically through the winter, but each time it does so it uses a substantial portion of the energy in its fat stores to warm up to standard body temperature. If a bat wakes up every three or four days instead of every fifteen, those fat stores are depleted far too rapidly. With no food available, the bat dies. Bats also appear to suffer from an electrolyte imbalance, and dehydration—biologists have found bats outside of hibernacula in the dead of winter, sitting on the ground and desperately lapping up water from the snow and ice. They even land on icicles, and get frozen to them.

The speed of white-nose fungus’ impacts, and the speed of its spread, shocked everyone who was watching. Robyn Niver, an endangered species biologist at the U.S. Fish and Wildlife Service’s New York Field Office, described going to the bat sites in those early years when it first hit, and her recollections were as dark as a field biologist might ever sound. “It felt… just helpless,” she said. “It was terrible.”

At first, no one knew what was causing the carnage, and that only added to the despair. Once the fungus was identified, there was some hope we might stop its spread, but its march away from New York has been relentless. At latest count, the fungus has been found on bats in 31 states, from Minnesota down to Arkansas and everywhere east of the Mississippi, as well as an as-of-yet unexplained 1,500-mile jump to Washington. Niver says one of the main projects now is to prepare people in other western states for what’s coming, since it seems nearly inevitable.

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That’s not to say that authorities haven’t been trying a host of options to slow or stop the disease’s spread. Most efforts involve trying to reign in the human influence: we are often the ones who enter a cave, carry out some fungal spores, and bring them to another cave where they can decimate another colony. Bat gates that keep people out but let bats in to caves, strict decontamination protocols for cavers, and even just outright banning caving (which Laurel Caverns did for a couple of years in a fruitless attempt to save its bats) have all been tried. There is (still early) work on single-application vaccines, and pilot projects where scientists alter the climate of bat hibernacula to slow fungal growth or make it easier for bats to survive.

The general public can help by just being careful around bats: if you find one in your home, do your best to resist the urge to swing heavy things in its direction. Call animal control organizations that can remove the bats and take them somewhere safe.

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The goal, from here on out, isn’t to regain what was lost in terms of bat populations. “Stabilization,” Turner said. “That’s what we’re aiming for.” In other words, those ninety-plus percent declines are, for the foreseeable future, what we’re stuck with. Niver thinks it is possible that some bat species will go extinct as a result of the fungus.

There’s also a faint chance that the few surviving bats are more capable of handling the infection, and that whatever traits that involves are passed on to future generations. Turner said that in some spots, the winter arousal rates among the few survivors of the most susceptible species have started to creep back up toward the normal 15 days. Some species, like the Virginia big-eared bat and the silver-haired bat, have been confirmed to have the fungus on them but don’t seem to suffer any of the same consequences.

But the most upbeat pronouncement the experts can muster is not encouraging. “I think we’ll continue to have bats, in general,” Niver says. Just different ones, and in far smaller numbers. On our way back up from the depths of the caves, having survived the tight crawl through the Panini Press, our guide, Rick, stops a few times and shines his light into small cracks in the ceiling. “I was trying to find a bat for you.” He shrugs, and trudges back up toward the light.

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Dave Levitan is a journalist, and author of the recent book “Not A Scientist: How politicians mistake, misrepresent, and utterly mangle science.” Find him on Twitter and at his website.