Earth Matters: Little brown bats in the barn

  • A little brown bat (Myotis lucifugus) on a gloved hand. SM BISHOP VIA WIKIMEDIA COMMONS

For the Gazette
Published: 8/17/2019 12:02:21 AM

They have been coming every summer for as long as I can remember — probably even longer than we have lived in the neighborhood. I’ve never paid much attention to them. Sometimes I noted with appreciation their war against mosquitos, waged near our back patio. Other times I was annoyed by the debris that built up under their home. But in general, we lived near each other and didn’t get involved.

This spring I began to watch more closely, to see when they returned. On Easter, my husband said, “They’re back!” He beckoned me into the barn, and we peered up at the ceiling. There, in a crack in one beam, was a dark wriggling mass. The bats were back!

A friend had informed me that I could tell the species by the droppings. If the droppings were the size of rice grains, they were likely “little brown bats.” If they were larger, then they were likely “big brown bats.” These were the two most likely species for our barn.

We set up a thin sheet of plywood under the roost. Then I waited. Each morning I checked the plywood for droppings. I quickly found a few and judged these must be little brown bats.

I wanted to see them fly out of the barn at dusk, so I lurked in the dark under the roost one evening. They made little sounds to each other, and I imagined what they might be saying. I was surprised that I could hear them. I knew that the sounds bats use to locate mosquitoes, through echolocation, are not audible to humans. But it turns out that the sounds they use to discuss the night of bug-hunting ahead are definitely audible, although quiet.

That first week, the droppings were not there every morning. I wondered, had they left? Did they have a different roost that they used some nights? Then I noticed the correspondence with the weather. After a cold and rainy night, no droppings. Cold clear night, few droppings. Warm clear night, a banquet of bat droppings appeared on our catch board! It seemed simple: no bugs, no droppings.

Could I help them out by leaving our outside light on? If bugs were attracted to the light, would that offer better hunting for my bats? On the other hand, what if the light disturbed these little creatures of the dark? I tried to alternate nights when the light was on or off and watched to see if that altered the number of droppings, but it seemed to me the spring weather was the main factor in hunting success.

Is an interest in bat droppings dangerous? I looked up information on the internet and was relieved to see this was probably perfectly safe. I was sad to find out that the little brown bat is now endangered, due to a fungus that has been spreading through the caves where they gather to wait out the winter. The fungus causes “white-nose syndrome,” a white fungus growth on the bare skin around their noses. Hibernating bats with white-nose syndrome have been found in caves in North America since 2006. Affected bats do not hibernate well, waking often and even flying around snowy landscapes. Millions of bats have died.

Where did this new disease come from? One clue is that it is present in Europe, although the bat species there seem to be resistant to its effects. I guiltily looked at my well-traveled hiking boots and wondered what fungal spores I might have carried into a vulnerable region. An online map shows the dramatic spread of this disease from its first report in 2006 in Schoharie County, New York, to now covering the East, the Midwest, and even around Seattle and in Texas.

When I learned all this, I wanted to find a way to help my bats. Could I leave food out for them? That seemed unrealistic. We received a flyer for mosquito control pesticide services, and I felt outraged. The bats need insects to eat. I suspect there has been a huge decline in flying insects over my lifetime, witnessed by the massive reduction in bugs that collect on my car windshield. Of course, this observation could be due to changes in roads, farming methods, or even windshield design. Also, there are millions of species of insects and many show “boom and bust” cycles of abundance. However, many experts are concerned. Summing the overall weight (“biomass”) of flying insects in samples taken over 27 years in Germany showed a decline of 75 percent, as recently reported in the scientific journal PLOS One. Surprisingly, this decline in insects was observed in nature reserves.

Simply watching the accumulation of the droppings each morning has brought me to a strong sense of wanting to protect this small group of bats in my barn. Planting native plants that are welcoming to our insects and buying organic foods to support farmers not using insecticides are two ways I can help the bats stay strong as they face the challenge of this new fungus associated with white-nose syndrome. I now look forward to welcoming my summer visitors for many more years.

Mary Harrington is Tippit Professor in the Life Sciences at Smith College. To see where white-nose syndrome is occurring, visit

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