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North Hills Monthly

Disease, Habitat Destruction Decimating Pennsylvania’s Bat Population

Oct 31, 2017 05:18PM ● By Vanessa Orr

Two big browns in an observation bat box

There are many misperceptions about bats; one of the most common being that this “mouse with wings” is a rodent, or that they pose a danger to humans. The fact is, bats are an extremely important part of the food chain and without them, agriculture—and in turn, other animals and even humans—will suffer.

This is especially important to note in light of the fact that the most common bat species in Pennsylvania, the Little Brown Bat, has died off in record numbers. While a fungus called white-nose syndrome has decimated its numbers, bats are also being affected by loss of habitat and an increase in wind turbines.

“White-nose syndrome is an invasive fungus from Europe that disrupts bats’ hibernation process,” explained Terry Lobdell, a citizen scientist who has been involved in bat conservation for the past 17 years. “The fungus grows on a bat’s skin, especially around the nose and mouth, and irritates the animal during hibernation. If it is roused too many times, it will burn off too many calories and starve to death.”

According to Lobdell, white nose syndrome has killed off 99 percent of the Little Brown Bat population in Pennsylvania, which is a catastrophic blow, considering that this species used to make up 96 percent of the bat population in the state. The disease also affects Big Brown Bats, the second most common species, though not to the same extent because they tend to hibernate in drier areas where the fungus doesn’t grow. “It’s hard to tell exactly how many Big Brown Bats have been lost because they are hard to monitor; they change roosts about every three to five days,” said Lobdell. “But in Crawford County where I live, people keeping count believe that we’re looking at losses of around 10 to 25 percent.”

Why are bats important?

People who get the heebie-jeebies just thinking about bats may not realize how important these animals are to the environment. Not only do the 1,300 bat species around the world consume a vast amount of insects, but they also pollinate many plants that produce fruit for both animal and human consumption. Because bats eat so many insects, it also reduces the amount of pesticides entering the ecosystem.

“A female bat nursing a pup will eat its body weight in insects in one night,” said Lobdell, adding that Little Brown Bats only have one offspring a year, and big browns have two pups annually. “I read an article about an organic pecan farmer in Georgia who didn’t use pesticides and regularly lost one-third of his crop to Hickory shuckworms. He put 11 bat houses in his orchard, and they completely eliminated these pests.”  In the U.S. alone, scientists estimate that bats are worth more than $3.7 billion a year in reduced crop damage and pesticide use. 

“Bats in Pennsylvania also eat Emerald Ash Borers, the pest that’s killing all of our ash trees,” added Lobdell. 

Pennsylvania has nine species of bats, three of which are migratory. While some species roost in trees, both Little Brown Bats and Big Brown Bats are known to get in people’s houses, which can sometimes lead to bat/people confrontations.

“Unfortunately, as we’ve lost most of the old-growth forest, bats have begun roosting in manmade structures because they are attracted to heat,” said Lobdell. “They need high temperatures to raise their pups, especially in June and July, so they look for places like chimneys or attics that hold their temperature during the night.”

Bat mortality has also risen as a result of the increase in wind turbines, as both birds and migratory bats tend to fly along ridge tops where they can be more effectively carried by the wind. While birds tend to strike the blades, bats die as a result of the rapid decrease in air pressure around the turbines, which causes bleeding in their lungs.

“Biologists are working on ways to make wind turbines more wildlife friendly,” said Lobdell, adding that people need to educate themselves about the hazards facing bats in order to help restore the population.

What can you do?

According to Lobdell, the good news is that the 1 percent of Little Brown Bats that are left tend to be resistant to white-nose syndrome, and some have been found to have naturally occurring bacteria in their skin that inhibits the growth of the fungus. Tests have begun in Missouri to inoculate other bats with that bacteria, but results are not yet in.

In the meantime, those who want to help the bat population can build or buy bat houses to replace the loss of habitat. “Bats like full sun, and they like the houses to be mounted on buildings or poles; not on trees,” said Lobdell. “It may take from one to three years for bats to begin using them, but each year, their use will increase.

“Once they get used to a bat house, they will prefer it to your home,” he added. “They are instinctively drawn to small crevices because they feel safe from predators, so it’s smart to keep your house sealed and to give them this option.”

Even with help, it’s going to take the bat population a long time to recover. “Even if the disease stopped killing bats today, it would take 200 years for the population to see numbers like it had before 2006,” said Lobdell. “They will probably come back, but it will be very slowly.”

To learn more about bats and how you can help, visit or