In October, bats are everywhere. Images of them, at least. The mammals typically are hibernating by Halloween, tucked away in caves and deep rock crevices. Summertime is when you will see real bats around, but if you live in the northeast or mid-Atlantic, you have likely seen dramatically less bats foraging in the summer dusk than you would have a decade ago. The reason why is white-nose syndrome, a disease more terrifying than the scariest ghost story.

Little brown bats (Myotis lucifugus). The individual on the bottom left is exhibiting signs of white-nose syndrome. Credit: Michael Schirmacher.

Even if you are unfamiliar with white-nose syndrome, this pattern is likely a familiar one: A disease or pest is brought to North America, intentionally or accidentally. Unchecked without a natural predator or other controls, the population explodes often at the expense of indigenous species. Such is the story of the chestnut blight to the American chestnut, Dutch elm disease to elms, hemlock woolly adelgid to hemlocks, and emerald ash borer to ashes. It is October, the time of year we at the Alliance celebrate bats and their role in our ecosystems. I like to keep the tone of our blog posts light and fun, but with an estimated loss of 90% of all bats in the eastern United States due to the introduced fungus, I must highlight this important, if sobering, disease. 

White-nose syndrome (WNS) is an affliction caused by a cold-loving fungus, Pseudogymnoascus destructans. The fungus resides in cool, damp caves that are important hibernacula for many of bat species. It cannot survive outside of caves and thus does not infect humans or its bat hosts during the summer, but is devastating during winter hibernation.

WNS is visible as a white fuzz that covers a bat’s muzzle and wings, giving the disease its common name. WNS does not kill bats directly, but instead interferes with their hibernation, repeatedly rousing them from their deep torpor. There are no insects for bats to eat during the winter months, so the tiny mammals’ fat reserves are burned through quickly, causing them to starve before spring arrives. The syndrome is very lethal, often killing 70 to 100% of bats hibernating in an affected cave. Many hibernacula that once hosted thousands of bats each winter now lie nearly empty. We see the loss in our summer skies too; populations of many of the formerly most common bat species have declined by over 98%.

WNS first was documented in a cave in Schoharie County, New York in 2006. It spread rapidly, now detected in 33 U.S. states and seven Canadian provinces. The fungus is native to Eurasia, where it infects bats but does not appear to harm them. Bats do not migrate across the Atlantic, so the prevailing theory is that P. destructans traveled to New York on the clothing or gear of spelunkers. The disease spreads from cave to cave in North America by bats and unwitting people; in 2015, it leapt across the midwest and was found in Washington state, likely transported on spelunking gear.

White-nose Syndrome occurrence map by year (last updated 7/2/18). Available on

In an effort to stem the spread of the fungus, most states have closed human access to critical hibernacula and professionals and spelunkers must follow decontamination protocols after visiting caves. Many researchers currently seek a way to combat or cure WNS, but a solution might come too late for certain bat species.  Smaller species that overwinter in caves are particularly vulnerable to extinction, including the little brown bat (Myotis lucifugus), Indiana bat (Myotis sodalis), and northern long-eared bat (Myotis septentrionalis). Bat species likely to persist include the larger-bodied big brown bat (Eptesicus fuscus) because it can hibernate in buildings where the fungus is likely absent, and migratory species like the red bat (Lasiurus borealis) and hoary bat (Lasiurus cinereus).

Little brown bat (Myotis lucifugus) with characteristic white fungus on its wings and muzzle. Credit: Moriarty Marvin, U.S. Fish and Wildlife Service.

Bats have had a rough century. Their populations grow slowly and have a hard time bouncing back from the destruction and degradation of their hibernacula and/or summer roosting habitat. Poor management of our forests has resulted in the loss of critical breeding habitat; standing dead trees (for roosting) and diverse understory plant communities (for foraging) are increasingly rare on the landscape. And now white-nose syndrome has devastated populations to the point where many species are unlikely to endure. However, as in many other realms of conservation, everyone can do their part to help. This month follow along on social media and the Forests for the Bats site to learn about these amazing, important critters and what you can do to support your local bats. Many people hold a lot of misconceptions and fears about bats, but the scariest thing about them is how quickly these critical mammals are disappearing from our landscape.