These versatile bats can roost everywhere from attics to behind peeling tree bark to abandoned mines and caves. Even with their varied habitat, they can’t hide from WNS.


The little brown bat

Myotis lucifugus

Little brown bats (Myotis lucifugus) live in vast swaths of North America having been spotted from sea level to at least 7,500 feet, from coast to coast in the United States and Canada, and as far south as Mississippi all the way up to Alaska. These versatile bats can roost everywhere from attics to behind peeling tree bark to abandoned mines and caves. Even with their varied habitat, they can’t hide from White-nose Syndrome (WNS).

Sadly, little brown bats are one of the three bats most threatened by White-nose Syndrome (WNS), a deadly fungal disease, caused by the fungus Pseudogymnoascus destructans. The fungus is rapidly spreading throughout North America and has killed millions of bats over the past decade. WNS gets its name from the white, fuzzy fungus that grows on bats’ muzzles and wings. The disease causes bats to use more energy and become dehydrated during hibernation, leading to starvation and death. Many winter colonies of little brown bats have declined over 90% because of WNS.

So, what’s so interesting about the little brown bat?

1) Little brown bats are voracious eaters with nearly bottomless appetites. They feast on many insects, such as midges, mayflies, moths, beetles, but especially favor aquatic insects. It’s estimated that a female little brown bat can eat almost half their body weight in a single night while she is nursing her pup!

2) Before WNS, thousands of little brown bats would hibernate in one place together. With bats often huddled together during this time, it’s easy to see how the fungus may have spread so quickly, and continues to infect bats today. Now, most winter roost sites are home to no more than 10 or 100 bats for the winter.  There are now only a handful of places that still have winter colonies with a few thousand little brown bats.  Conservation efforts to protect these remnant colonies are critical.  Research to understand why some winter colonies manage to persist with WNS while most colonies experience such high mortality is also a high priority.

3) When a little brown bat is flying, its heart can beat over 1,000 times per minute. When hibernating in a physiological state called torpor, their metabolic rate slows down so much their heart only beats around 20 times per minute, and they may go over 30 minutes without taking a breath.

4) During hibernation, little brown bats naturally arouse from the energy-saving state called torpor about every 2-3 weeks.  Why bats arouse so often when there isn’t anything to eat is still a scientific mystery since waking up from torpor burns up a lot of energy—and bats must stretch their stored energy (otherwise known as fat) to last the entire winter.  WNS disrupts these natural patterns and causes bats to arouse from torpor too many times with devastating consequences for survival. Unfortunately, it is also very easy to disturb hibernating bats—even a silent visit to a cave during the winter can cause bats to arouse and burn up precious fat.

5) BCI is working to protect little brown bats by further understanding and mitigating WNS, working to increase survival rates, and identifying conservation priorities.

6) Want to help the little brown bat? Here are some easy first steps you can take today.

– Learn more at:

– Support BCI’s efforts by becoming a member.

– Never go into a cave when bats are hibernating.

– Always clean and decontaminate your gear and outerwear before entering a cave, and never bring items from an area with WNS to an area without WNS. Learn more about WNS cleaning protocol for cavers here.