- [Narrator] A single bat can devour 600 mosquitoes, moss, and other pests in a single hour.

So despite their creepy reputation, scientists say it's life without bats that should terrify us.

And it's why Pat Ormsbee shudders at the news that entire bat colonies are now being wiped out.

- We're talking about the very real possibility of extinction of one or more species in a very short time.

- [Narrator] Pat says a wave of death has now killed over 1 million bats along the east coast, and it's now headed for the northwest.

The killer is a mysterious disease that made its first appearance here in Howe Caverns, New York.

- Water's dripping down forming the calcite.

- [Narrator] It was in this cave back in 2006 that two scientists, Paul Rubin and Ben Guenther, came upon rooms filled with dead bats.

They suspected vandals, but it soon became clear that the problem was far bigger than that.

- [Pat] Other reports started coming in of weird bat behavior, bats out in winter.

There were large number of dead bats were being turned in in Albany County, New York.

And when they started going around and looking, then they were going, whoa, something's not right in the bat world, but we don't really know what this is.

- [Narrator] Scientists investigated and found that many of the bats were covered with unusual white blotches.

They'd found the killer and they called it white-nose syndrome.

- There's a lot we don't know about white-nose.

This has come on so quickly, but currently the popular thinking is that white-nose syndrome is caused by a fungus called Geomyces destructans.

This is a cold-loving fungus that basically invades bats.

- [Narrator] The fungus is deadly because it strikes bats where they live, in cold, dark caves where bats winter together, sometimes in colonies of thousands.

- [Pat] And we think it causes them to arouse during wintertime and they basically burn up their fat reserves and starve to death before winter is over and spring comes and they can find bugs to feed on.

- [Narrator] The fungus basically destroys the flesh of the bat's wings, leaving them completely helpless.

Scientists traced white-nose back to Europe, though for some reason European bats aren't affected in the same way.

In the US though, it's now triggered what's considered the largest wildlife die off in living memory.

- This is huge.

I mean, we've never seen this type.

It's just basically wiping out bats, not just, I mean we think of bats as a group, but there are individual species and we now have nine species of bats that have been affected by white-nose with virtually no resistance.

- [Narrator] White-nose is spreading fast.

It's now made it to nine states as far west as Oklahoma, and it's probably only a matter of time before it invades the northwest.

- [Pat] It is now closer to Seattle than it is to the location in New York where it was first discovered.

(tool clanking) (scientists speaking) - [Narrator] Scientists in this field outside of Burns, Oregon are scrambling.

They wanna study Oregon's bats while they're still healthy.

The white decontamination suits are just a precaution, for now.

- Trust me, I work for the government.

I'm here to help.

Really, buddy.

There we go.

- This little insectivorous bat, Myotis evotis is the species we have here and the common name on that is the Western long-eared bat.

This is a healthy bat.

You can tell just the general condition, like with most animals just looking at 'em.

- [Narrator] Western long-ear's are common, but with white-nose, what's common today could be gone tomorrow.

Little brown bats, for example, used to be one of the most widespread bats in the country, but they've been hit so hard by white-nose back east that there's now a push to list them as an endangered species.

- Our big fear is extinction of species, that we literally see our bat species die off in the northwest.

- Bat number 28 has a 40 millimeter forearm, ear 11.

- [Narrator] Another hurdle facing northwest scientists is the effort it takes to study bats.

Bats in the northeast and southwest winter in massive colonies, making die offs from white-nose easier to spot.

While there are some large colonies in places like Oregon Caves National Monument, many northwest bats live scattered throughout the forest, roosting individually in tree bark and small caves.

With that, though, Pat finds a small glimmer of hope.

- I'd like to think that white-nose syndrome, as it gets to the west, our bats tend to roost in smaller groups, more dispersed across the west.

My hope is that it may slow down.

Maybe some of our bat species, we do have some different bat species in the west.

Maybe some of those will be resistant, we don't know.

But the worst case scenario and what we have to plan for is that's not the case.

- You guys kind of stay close.

- [Narrator] The fact that white-nose made its first American appearance at the tourist-friendly Howe Caverns leads many scientists to suspect that people may have accidentally brought the white-nose fungus to the US on their clothing or luggage.

And that people, particularly cavers, might be spreading white-nose to new places today.

- [Matt] This is Lost Cave.

It's always refreshing, especially on a hot summer day, you can get out of the sun and cool off.

- [Narrator] Matt Skeels is with the Oregon High Desert Grotto.

- [Matt] Watch your step.

- [Narrator] A group dedicated to exploring caves of the northwest.

- Well, this wall right here is pretty cool because it's the lava as it cooled and dripped down.

- [Narrator] Almost all caves on federal land in the Eastern US are now closed because of white-nose syndrome.

And Matt fears western caves are next.

- It scares us because caving is something we love and to be shut out of the caves that we spend so much time in is like almost like a death of a certain lifestyle.

- [Narrator] Julie York is with the Forest Service and she admits that talking about cave closures is not popular.

- It's a lot to ask right now.

It definitely is, and I don't know that we're gonna ask that for all caves right now.

We may in the future, we don't know.

It's a lot.

We're trying to grapple with this really difficult issue on a fast track when we're not sure exactly what we're gonna do at this point.

- [Narrator] For now, caves in Oregon remain open with one caveat.

Cavers are being asked to decontaminate.

- This is what we're asking cavers to do between caves, wash your clothes and boots and rinse them, and then apply one of these for 10 minutes and then rinse and then air dry.

- [Narrator] But there are hundreds of caves in Oregon and thousands of cavers from the casual tourist to the advanced explorer.

- You wanna put all your gear into the box before you just put it into your car so the spores don't spread in the vehicle.

- [Narrator] Matt worries that the government may doing something here just to show that it's doing something.

- Personally, with the whole white-nose syndrome thing, I think it's unavoidable that it's coming here.

It's just, it's sad that it has to be this way for the bats, but to us, it just, it seems unavoidable.

- [Pat] This doesn't look bad.

This looks pretty normal.

You can see some little spotting and that is not unusual for our bats to see that.

We'd call that a wing damage.

- [Narrator] Perhaps the toughest pill to swallow when it comes to white-nose is that awareness of the problem doesn't mean it can be stopped.

Even scientists are left to struggle with the sinking feeling that Oregon's bats may not be able to survive what's coming.

- To me, this is a huge loss.

You know, I can cry myself to sleep at night thinking about this.

If we get through this without loss of species, it would be great, but it also might take a little bit of a miracle.