White-nose syndrome: Bats hit by killer disease
The descent into the abandoned mine is treacherous. The loose rocks, caked in mud, ice and guano, slip and slide under your feet. At some points the entrance is so tight, the only option is to crawl through the dirt, flat on your belly.
But for this team of scientists, it is a rare chance to assess the damage of a mystery killer that has so far led to the deaths of more than a million bats in North America.
The disease, called white-nose syndrome, came out of nowhere, taking scientists completely by surprise.
It was first found in 2006, in a cave in New York state, near to the site we have just entered.
Now it has now been confirmed in 16 US states, suspected in two others, and has been found in four Canadian provinces.
So worried are scientists, that they have taken the unprecedented step of sealing some bat caves to try to halt the disease.
But at this disused limestone mine, special access has been granted so the team can assess the devastation that white-nose syndrome has left in its wake.
Shining a torch at the ceiling reveals a few small clusters of bats, but a glance down at the floor shows that it is littered with bat bones.
Carl Herzog, a wildlife biologist with the New York State Department of Environmental Conservation, says: "This site was our largest in the state for Indiana bats, approximately 25,000 used to spend the winter here.
"Last year that number was down to 7,000. And today it's difficult to stay."
As a bat is gently loosened from its snug spot in the rocky wall, it is clear that it is suffering from white-nose syndrome.
Its wings are scarred and tatty, and it has smudges of a white substance dotted over its face and feet.
Scientists think that the disease is caused by a newly discovered fungus called Geomyces destructans, which infests the flying mammals while they hibernate. But they are still trying to understand why this is causing such high and widespread mortality.
Dr Herzog explains: "The mechanism that causes the problem is not understood, but the best evidence is that it causes the bats to arouse more often than normal during their hibernation and to stay awake for a longer period of time, thereby burning through their fat reserves that they need to live on over the course of the winter.
"The bats either end up starving, or they fly out of the site in the middle of winter where they die or freeze to death."
In some hibernacula, 90% to 100% of the bats are dying, and scientists say it could bring some species, even those that were once common such as the little brown bat, to the brink of extinction.
Researchers around the United States are now racing against time to get to understand this mysterious disease.
Thomas Kunz, who runs the Bat Lab at the Centre for Ecology and Conservation Biology at Boston University, says: "None of us were prepared for this. I dropped half of the research we were doing just to go and start looking at this."
The first puzzle that scientists are trying to work out is where the fungus came from.
Had it always been present in the US caves but suddenly started to adversely affect the bats? Or had it come from somewhere else?
One possibility, says Professor Kunz, is that the fungus arrived from Europe. Geomyces destructans has been found across the Atlantic - although it does not seem to give bats there the disease.
"Are the bats in Europe resistant to the fungus somehow? Have they evolved resistance over time? Or once the fungus got to the States, did it evolve and mutate into a more virulent form?" he asks.
Researchers are also looking at how the disease spreads.
They believe it can pass between bats, but they also think humans have unwittingly carried the fungus as they have moved from cave to cave.
However, many questions remain. And with treating bats with fungicide or a mass cull an impossibility because of the sheer numbers involved, a solution is a long way off.
Professor Kunz says: "That's pretty dire when you think about it - extinction is for ever. You are not going to be able to bring these bats back."
Researchers are now having to get to grips with what it means to lose so many bats in such a short space of time.
Professor Kunz explains: "Bats eat up to one half to their entire weight in insects every single night.
"Given there are least a million bats that have died from white-nose syndrome, that's a lot of insects not being eaten still flying around."
This, he says, will have a major impact on forests and grassland ecosystems - and on agriculture. A recent study published in the journal Science estimated that the mammals helped to save the US economy between $3bn and $53bn a year by helping to limit pesticide use and reducing crop damage.
With so much at stake, scientists say it is frustrating to have to sit back and watch as the disease continues its seemingly unstoppable march.
And researchers around the world are now on high alert in case it extends its deadly reach.
As we begin the tricky ascent to exit the abandoned mine, leaving the bats behind in the darkness to finish their hibernation, Dr Herzog admits that he is worried about the future.
He explains: "Many talented, knowledgeable people are working on various aspects of this problem, but as this point there really are no promising avenues.
"It's also possible that the bats may figure out how to deal with this on their own, by developing some kind of resistance, be that from an immune system or behavioural changes that will cause them to be less susceptible to the disease.
"At this point that might be the best thing that we have to hope for."