World’s largest cave system battling deadly bat disease

Aug 10, 2021 | News

By Sille Veilmark

The rocky chamber in the world’s biggest cave system, Mammoth Cave, is dimly lit. The echoing chatter from 107 mouths dies out as the flock approaches a slim man with red beard. He is wearing a stiff park ranger hat, and the glue in his hiking shoes are not holding the sole together completely anymore. The air is cold, dry, and tastes slightly of stone. Visitors over the years have burned their names in the flat cave ceiling with torches, in a font that looks like a typewriter.

“I’ve met people who, when I told them bats are dying, would think, ‘Great. I hate bats. They are disgusting,’” park guide Ethan Mefford, 26, says in a loud, clear voice, and the murmurs die out completely.

“Bats are a natural pest control, bats pollinate fruit, but most noteworthy, the Brazilian free-tailed bat that lives in Southwest U.S. is the only animal on earth that is equipped to pollinate the agave cactus,” Mefford says.

“Oh!” a few men respond.

“Very important,” Mefford emphasizes, and the adults in the group laugh out loud.

(The agave cactus is used for making tequila.)


Mammoth Cave National Park is situated in south central Kentucky, and includes the largest cave system in the world with 82,63 square miles. People began exploring the caves 5,000 years ago and in the 1830s the first tourism of the caves began.

The park was established in 1941 to preserve the cave systems that have more than 405 miles of passageways. The park continues to attract visitors. Annual visitor numbers are slowly increasing, and last year 587,853 visitors took a cave tour. In a year, more than 2 million visitors come to the park itself.

But Mammoth Cave National Park is only one out of many parks that are dealing with a fungal disease that have caused more than 7 million hibernating bats to die throughout northeastern America since 2005.

The disease is impacting the bats in such a way that the Northern Long-Eared Bat, which had been the most common in the park, now has decreased by 99 percent. The fungus was originally transported from Europe probably by humans (either directly or by accidentally moving bats). To prevent the disease for spreading further, Mammoth Cave National Park has installed biosecurity stations at the exit of the tours for the many visitors to clean off fungus that they might get on their shoes.


Earlier that day the group of 107 visitors begin their two-hour Historic Tour at the price of $14 for adults, $9 for kids, down a slope between naked tree trunks and sun beams. It’s the last tour of the day, and they halt in front of a massive cave entrance. The group snakes through a lowered pavement, and Mefford climbs an elevated wood bed in front of them to speak.

“I always ask where you are from, who have travelled the farthest to get here. Where are you from?” Mefford shouts to the group.

“Mississippi,” a lady replies.

“First time in Kentucky? First time to Mammoth Cave at least?” Mefford asks.

It’s her first time.

“Welcome,” he replies and continues to a young boy.

“Where you from?”

“Florida,” the boy answers.

“Florida?” Mefford repeats surprised. “Welcome to the United States!”

The group laughs out loud.

“Anybody else?”

The list is long. Wisconsin, New York City, Ontario, Mexico City. But before entering the cave, there are a few formalities that Mefford has to get out of the way. He pulls out a tiny plastic card from his front pocket of his shirt and holds it up. It contains protection rules and regulations.

“Can you read that OK, Albuquerque?” he says.

The group laughs again.

“Just bear with me guys, it’s common sense.” He emphasizes the word “sense” as he pronounces it. Then he reads out loud about uneven trails, not touching the rocks – and what to do if they encounter bats.

“If you see a bat, what are you gonna do, Junior Ranger?” Mefford directs his question to the 10-year-old boy, Reed McCown, who stands out in a blue-green hunters suit, a small brown ranger hat and a golden badge saying, “Mammoth Cave National Park”

“Um, don’t touch it?” Reed says vaguely.

“Exactly, absolutely nothing, leave it alone. If you do come in a contact with a bat, let me know pronto. White-nose syndrome can cause bats to exhibit erratic behavior, and worst they can carry rabies. So, now that I’ve got you all concerned, does anyone have questions?”


The fungal disease White-nose syndrome (WNS) has caused the deaths of more than 7 million hibernating bats across the north-eastern U.S. since it was introduced from Europe. In the fall of 2005, it was discovered in a cave in Howe Cavern in New York, and in 2013 it arrived at Mammoth Cave National Park.

Mammoth Cave National Park is home to 13 species of bats. Three of them are listed under the Endangered Species Act. The Indiana and Gray bats are Endangered, and the Northern Long-Eared bat is Threatened.

The tourist tours of Mammoth Cave do not go through any bigger hibernation sites of any of the four species that have shown a significant decline in population to white-nose syndrome, and the possibility for visitors to encounter a sick bat would therefore be rare.

The species in Mammoth Cave National Park that have shown decline are the Northern Long-Eared Bat, Little Brown Bat, the Indiana Bat and the Tri-Color Bat.

“Compared to pre-white-nose syndrome on an 1997-2009 average, the numbers in 2017 showed a decrease of 99 percent for the Northern Long-Eared Bat, 90 percent for the Little Brown Bat, 80 percent for Indiana and 75 percent for Tri-Color,” says Dr. Rick Toomey, cave resource management specialist.

Every two years, he and monitoring teams have systematically been counting several of the bat species that hibernate in the caves.

The fungus called Pseudogymnoascus destructans wakes up the bats in the middle of their winter hibernation more than usual. Bats generally arouse occasionally, maybe every 10 days during the hibernation period to drink, eat, defecate, or even mate.

To wake up they have to restart their metabolism, which means they raise their body temperature and burn through all of the calories, they had intended to save for spring. With the disease, the bats wake up every second day, and they can freeze to death or die from starvation or dehydration.

The decreasing of bats is bad news for American agriculture as well as the ecosystem. Bats are a natural pest control. An estimate from a report in Science Magazine in 2011 pegs the value of bats to the agricultural industry as roughly $22.9 billion per year in pesticides because of their insect consumption.

Worst case scenario is that the Tri-Color, Northern Long-Ear and Indiana bat will go extinct, Toomey said. He says a more realistic scenario is that none will go extinct, but they cease to be ecologically meaningful.

“Northern Long-Ear haven’t gone extinct in the park, but previously they were the most common bat on the park in the summer. They ate large numbers of insects. Now they are incredibly rare on the park, so now they eat few of the insects on the park. In many ways they are meaningless from an ecologically standpoint,” he says.

And to humans this means that farmers have to defend their crops with a larger amount of pesticides on their land, which means more pesticides in drinking water.


“How much of what we saw was natural versus mining?” Reed’s father Shane McCown, 40, asks Mefford at the first stop of the tour. He is referring to the part of the cave they have just walked through. In front of him is wooden pipes stacked on cave stones and worn wooden boxes.

Mefford answers that the walls and the ceiling are all natural.

“When modern tourism began, they excavated the floor to make it comfortable standing height. They also had another intention for the dirt,” he speaks clearly and intensely.

“Pioneers and home settlers noticed it’s pretty dry down here, meaning that any kinds of nutrient and useful minerals left behind in the cave dirt, haven’t been washed away. In experiments they would scoop up some dirt, build a campfire and sprinkle that dry cave dirt over that open flame. What they got was a spark! A crackle! The soil was rich in nitrogen…”

Ten-year-old Reed McCown leans against his father as he whispers:

“It’s gunpowder.”

“They would mix it into something called saltpeter. What do we use saltpeter for?” Mefford asks.

“Gunpowder,” the crowd murmurs, and Mefford agrees.

“But about 12 or 13 years after the Mammoth Cave was re-discovered by these pioneer families, the prize of saltpeter skyrocketed. Something changed on the east coast, what was it?”

It’s quiet in the immense hall.

“WAR!” Mefford yells so it echoes. The group laughs, and a few kids look to their parents nervously.


What Mefford didn’t include in his story is how nitrogen got there in the first place. Bats have been part of Mammoth Cave’s fauna since pre-historic times, in fact, Mammoth Cave was formerly one of the largest bat hibernacula in the world.

In the past, colonies of perhaps 9–13 million bats hibernated in the cave. They played a critical role in the food web of the cave by contributing nutrient to the ecosystem because of guano: the accumulated excrement of bats. Guano has exceptionally high content of nitrogen, and the bats turned out to play the most important role in the gunpowder industry of Mammoth Cave.

But human activity like saltpeter mining for the British-American war in 1812 and the beginning of tourism afterwards, disturbed the bats and made the cave unsuitable for bat roosts, and they left. But to the trained eye, spots are still visible in the ceiling of Mammoth Cave from where clusters of bats would hibernate.

“After so many years with so many bats, you see little pockets of where they were exhaling and where their Co2 has made marks,” says Katie Gorman, the bat monitoring intern at Mammoth Cave.

A few times a week, Gorman walks the same trails as the pioneers did when they excavated the floors in Mammoth Cave. As a part of her morning ritual she counts the bats hibernating and checks if they have developed signs of white-nose syndrome.

What looks like a brown spot on the cave wall close to the trail turns out to be a small Tri-Colored bat, and it is hanging low enough for Gorman to check it for white-nose symptoms. Visible signs of disease show the fungus as fluffy white fur growing on the bats’ muzzles, like the nose, wings and tail. She lights it with her headlight in short moments at a time, to disturb it the least in its sleep. It doesn’t have any symptoms.

Gorman crawls her way back across a few boulders. As she reaches the waterfall at the exit, she counts 18 bats from her notes. It’s average right now, but four years ago monitors like her would have counted 160-180 on this tour.


Up along a staircase with a waterfall on the right, the 107 visitors exit the big mouth of the natural entrance of Mammoth Cave. An unexpected heat hits them on the upper steps. The temperature of the cave is 54 degrees Fahrenheit. From there, two 5-foot metal stations with black mats and a foamy detergent await their passage. They go through one by one, and a girl in a pink jogging suit starts whimpering.

“Oh, my feet got wet!” she complains to her mother.

Junior Ranger Reed McCown’s little sister, Lauren McCown, 6, finds it amusing. She runs through the cleaning stations over and over again with a stuffed deer in her arms.

The park experiences more visitors when the kids are out of school, and as spring break began the week before, families like the McCowns are the majority. They are on a national park-crawl, trying to visit as many national parks as they can, before Reed turns 18. This one was within driving distance from Johnson City, Tennessee, where they live and is number 14 on the list. Visiting many national parks Shane and his wife Allison has started to notice something:

“We went to Yosemite probably eight or 10 years ago, and we took the tour of the cave they had there, but they don’t even let people in there now because of the white-nose syndrome. It’s very prevalent,” Shane McCown says.

Significant evidence indicates that humans can have transmitted the fungus from one cave to another, and in order prevent the disease from spreading, Mammoth Cave has cleaning stations for the visitors’ shoes as they exit the tours. But Shane McCown is not concerned about simple tourism tours are causing a spread.

“It’s really about cross-contamination. If you were in one park and packed up your caving-stuff and went to another park, that’s how it could spread,”

“But I’m thankful that they have these measures in place,” Allison McCown, 41, says.

“Yeah, I mean, it’s totally possible, that it could happen,” Shane says to his wife.

“Well, it did. That’s what started it all to begin with,” she replies.


The white-nose fungus was widespread in Europe before it arrived in New York and is believed to be transported either by a caver or a tourist that had been in an infected cave in Europe.

Mammoth Cave National Park is only one of many parks dealing with WNS in the eastern United States, but the fungus has just made a new, big jump that resembles the Europe-New York jump:

“One of the most recent caves is Mount Rainier in Washington. That is a very unfortunate, but very interesting jump. This is also human no matter what. An eastern bat didn’t happen to fly to Washington,” Toomey says.

Fungus spores have been found on visitors’ footwear, which is why there are cleaning stations at the exit of the Historic Tour.

But transporting the fungus is not easy. If it was, the movement of how the disease occurs should be different: WNS should make bigger jumps to places where a lot of people visit caves.

The reason to this is, that in reality, the fungus is easily killed. Heat, ultraviolet light from the surface, bleach, alcohol, and many cleaning products would take out WNS. Even non-hibernating bats can be exposed to WNS and carry the fungus without getting it, because for the fungus to grow, a body temperature needs to be below 70 Fahrenheit. To make matters worse for the bats, during hibernation most of their immune system is shut off.

“As I tell visitors: you can’t get white-nose syndrome. Well, it’s possible, however, the fact that you have a body temperature below 70, probably means you’ve got bigger problems than whether WNS will grow on your skin,” Toomey says.

One of the real issues cave scientists across the nation are facing, is how to get rid of white-nose syndrome.  This is complex for several reasons, however, one is because the fungus is a disease that works very differently than a virus. For example, bats do not acquire immunity when they survive WNS.

“If you catch chickenpox, your body develops immunity to chickenpox in general. You won’t catch it again. Fungi don’t work that way. It doesn’t give immunity once you have it. WNS is more like athletes’ foot: You get it, treat it and six months later you got it again,” Toomey says.

At the moment there are people looking for genes in the fungus to develop a bat vaccine as well as there are people looking at ways to use probiotics’ on bats to fight it. The latest news is that some have worked in lab, and a few are now being tested in the field.

“The issue, I see, is how does it scale? How do you treat hundreds of thousands of bats in a particular? How do you sustain year after years?” Toomey asks.


The area has emptied out and it’s 10 minutes until closing time. Ten to six. Ethan Mefford is the last to leave the cave entrance. A silence fills the air where there before was human voices and nature starts coming alive. Mefford works at three tours a day, on average, and major tours like the Historic Tour sell out at 110 visitors. Two hungry deer approaches while he climbs the slope toward the parking lot.

“Sometimes, if you say: ‘the bats are dying’ sometimes people will say: ‘great’. That’s why I make the joke about the agave cactus. I am trying to get their attention by directing them towards positive things that bats do, like pollinate fruit, and help us have tequila…” Ethan Mefford laughs, “and avocados and other fruit, that people really like.”

He has worked in the park for eight years as park guide, graduated with a linguistics degree from Western Kentucky University. As he reaches the top of the slope a sole bird is jumping through the sunny grass.

“It’s a robin,” Mefford says.

“So, Batman should be nearby.”

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