Jesse Weber | 09.02.2017

White-nose syndrome has plagued bats in the Eastern U.S. for more than 10 years and caused millions to die. Now it's been found in the Pacific Northwest, and the survival of these valuable species is in jeopardy.

Though some think of them as scary and repulsive, bats really do not deserve this reputation. They do not attack people unprovoked, and the only reason they often swoop near people's heads is to eat the flying insects, like mosquitos, that buzz around us. Bats are actually very valuable to people because they are a natural form of pest control.

One bat can consume 8,000 insects in a single night.

They eat not only mosquitos but also pests that may threaten food crops. Certain bat species also drink nectar, and in the process they help pollinate plants and disperse seeds. These operations quite literally fly by night and go unseen by most of us, but scientists have estimated that bats may save humans more than $3 billion dollars annually in the U.S., the cost of performing equivalent pest control services with our own methods.

That is why bats deserve protection, and right now, they need it.

In 2006, a bat from a cave in New York was found with strange white fuzz on its face, and biologists soon noticed that bats from that region were dying during the winter at higher rates than normal. The culprit was later identified as a certain fungus (Pseudogymnoascus destructans) that grows on and under the skin of bats. Though it can occur anywhere on the body, it is most often seen as white growth on the face and snout, hence the name White-nose Syndrome. The fungus can be passed from bat to bat, and it has spread rapidly outward from New York. In only a decade, WNS has killed an estimated 6 million bats in the U.S. and Canada.

Much is still unknown about where this disease came from or exactly how it operates, but what we do know is that the fungus spreads rapidly and it can be deadly, sometimes alarmingly so. Bats in the Eastern U.S. tend to hibernate in colonies, and in more than one case 100% of bats in a particular colony have died over winter from WNS. The fungus does not appear to kill bats outright, but it irritates them so much that they cannot properly rest during hibernation. Instead, they awaken frequently and fly around. This burns energy stored in their bodies' essential fat reserves, which they simply cannot survive the winter without.

The fungus only harms bats, but it can be transported on other animals or people.

Spores can remain viable for a long time and travel on fur, clothing, shoes or other gear before it rubs off on rocks or plants and subsequently be transmitted to bats by contact. Therefore, people traveling between caves may contribute to the epidemic. Many eastern states have closed all public caves in an effort to curb the spread.

Until recently, WNS had not been found outside of eastern North America. In March of 2016 that suddenly changed. In Washington, about 30 miles east of Seattle, cavers found a bat that couldn't fly. It had tell-tale signs of the fungus growing on one wing. Biologists immediately intensified sampling in the region and found more cases of infection. How the fungus got there is not known, but it is possible that a caver who visited an infected cave in the East and later entered a cave in Washington transported it on his or her belongings.

As of yet, only a handful of cases of WNS have been confirmed in Washington. A decade of devastation in the East gives us obvious reason to worry that it might spread out of control on this side of the country as well, but the outlook is uncertain. The fungus appears to affect each species of bat differently, and some eastern species can apparently carry the fungus without suffering the deadly symptoms of WNS, and even among bats with the disease, mortality is not always 100%.

Bat behavior seems to also have a role in the effects of WNS. Bats that hibernate in large groups seem to be at greater risk, presumably because one infected bat can more easily spread the fungus to other bats when they roost in close quarters. Biologists who study bats know that eastern species tend to overwinter in large groups more commonly than western species, who seem to prefer smaller, more dispersed caves and crevices where they live alone or with just a few other bats. This may be a source of hope for lower mortality among bats in the West, but so much is still unknown that nothing can be predicted with confidence. The safest strategy is to do all we can to help prevent spread of WNS by following a few simple but important precautions as you explore in caves or near any likely bat habitat.

1. Do not disturb bats

If you come across a bat, no matter where or what time of year, do not bother it in any way. Keep a reasonable distance and do not make unnecessary movement or noise. You can't always tell when a bat has the fungus. It may appear normal but still be infected. If it is, causing any stress will use up valuable energy and hinder its immune system's ability to fight the disease. Even bats that aren't already infected may be more likely to get the fungus if they are stressed or if they alter their normal behavior.

2. Stay out of hibernacula during the winter

A hibernaculum is any place where bats hibernate for the winter. This is usually in caves, old mines, old barns, rock crevices, and tree holes, but in the West they can also overwinter among rocks of talus slopes, the roots of trees, and other seemingly unlikely places. To the best extent you can, stay out of places where bats might be hibernating, because winter is when they are especially vulnerable to the disease and when they should be resting up to survive the winter.

3. Honor all cave closures

To date, no emergency closures have been implemented in the PNW, but this is a measure that has been taken elsewhere. Existing regulations close some caves in winter, and these seasonal closures remain in effect. If additional closures are deemed necessary, be sure to honor these for the good of the bats

4. Decontaminate clothing and gear

Whenever you visit a cave, climbing area, or anywhere you are in close contact with bat habitat, wash clothing and gear thoroughly and do not move between distant sites until you have done so. This may reduce the risk of transporting the fungus. Full decontamination protocol can be found here.

  • Change into fresh clothes before entering your vehicle to leave.
  • Scrub all exposed skin with soap and water.
  • Wash clothes, boots, and other soft goods with soap and hot water for at least 20 minutes.
  • For gear that cannot be washed, clean with alcohol wipes.
  • Do not bring dogs into caves. They can transport the fungus and otherwise damage cave environments.

5. Report sightings of groups of bats

Distribution of bats across the country is still not entirely understood, and there may be many colonies still unknown to biologists. If you find any habitat that appears to be home to more than just a few bats, report this to your state wildlife agency. This information will help map populations, which is especially important because WNS seems to spread most quickly among bats that roost in large groups. The state of Washington has an online report form here.

6. Report unusual bat behavior

Even without an expert eye, certain bat behavior is easy to identify as unusual, and it may be a sign that bats are suffering from WNS. In general, bats should not be flying around outside or at the mouth of a cave during the cold months of the year. At any time of year, if you see a bat roosting in sunlight, flying outside during the day, or having difficulty flying at all, this is behavior you should report to your state wildlife agency.

7. Improve bat habitat around your home

In addition to WNS, bats face other threats like nighttime light pollution, pesticide poisoning, and habitat loss. You can help bat populations, and reduce insect populations, by improving habitat in your own yard. Here are some easy ways, and more can be found from Washington Dept of Fish and Wildlife here.

  • Reduce outdoor lighting.
  • Keep old and dead trees when possible and safe.
  • Build a bat house on your property.


Feature image by Ann Froschauer/USFWS. Published without modification under Creative Commons 2.0 Attribution 2.0 Generic license.


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