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Disease wiping out Minnesota cave bats

Melissa Boman of the Minnesota DNR gives a presentation on white nose syndrome in Minnesota cave bats at the Lake City Public Library on March 19, 2019. Steve Gardiner / RiverTown Multimedia1 / 4
Bats hibernating in a cave in Vermont in 2008. Photo courtesy of the National Wildlife Health Center2 / 4
A closeup of a scientist examining wing damage caused by white nose syndrome on a little brown bat. Photo courtesy of National Wildlife Health Center3 / 4
A little brown bat displaying the symptoms of white nose syndrome. Photo courtesy of Fort Collins Science Center4 / 4

A disease known as white nose syndrome - WNS - is proving deadly to Minnesota's four species of cave bats.

The disease is caused by a fungus called pseudogymnoascus destructans, and infected bats often have a white fungus growing on their wings and muzzle which gives the disease its name.

"White nose syndrome affects bats because of their unique lifestyle," said Melissa Boman of the Minnesota Department of Natural Resources. "It is caused by a fungus that originated in Europe."

Over time, European bats evolved so that many species there are not affected by WNS, however, the fungus is new in the U.S., so bats here are not immune. The first detection of WHS in the U.S. was in 2006 in Philadelphia. Since then, the disease has spread westward to 32 states and seven Canadian provinces.

Minnesota has eight species of bats. Four of them — little brown bats, Northern long-eared bats, tri-colored bats, and big brown bats — live in caves or mines and are being severely affected by WNS. Four other species — Eastern red bats, silver-haired bats, hoary bats, and evening bats — are migratory and are not being affected by WNS, according to Boman.

"The fungus thrives in cave systems where it is about 50 degrees and no sunlight," Boman said. "When a bat is in hibernation, their immune system is shut down, so the fungus takes advantage of that by infecting the tissues with spores which causes the bat to wake up and display abnormal behavior like flying out of the cave."

This disruption to their normal hibernation cycle "depletes their energy," Boman explained. "They end up starving to death, because there is no food in the winter, and they have to live off their reserves."

WNS usually takes about three years from the time it is detected until it begins killing large numbers of bats, according to Boman. It can cause mortality rates as high as 99 percent in cave bats.

Build bat houses

The DNR is researching ways to prevent these deaths and they have considered spraying cave systems with a fungus inhibitor, using UV light to damage the DNA of the fungus, and using vaccinations, but have not found the best answer yet.

One thing people can do to help is put out bat houses in their yards to help bats that have been displaced from other locations. Boman said the website for Bat Conservation International is a good resource for information about bats and bat houses. The DNR website also has information about bats and WNS.

Boman said that people often think of bats as vermin, but they actually very helpful in an ecosystem. They pollinate many plants, spread seeds, and eat millions of insects daily.

She admitted that bats might not be a good choice for a pet, but added that "not all bats are ugly."

Boman corrected two myths often associated with bats. First, she said a "lot of people think that bats carry rabies, but just like other animals, raccoons or foxes, they can contract rabies, but it's actually less than one percent that have rabies."

Second, "bats are not blind," she said. "People think that because they fly at night, but between their eyes and echolocation, they can actually see very well."

The loss of bats to WNS is important, Boman said, because "they eat a lot of insects, not just mosquitoes, but beetles and other pests. They make a difference in how much pesticides that farmers have to use."

Steve Gardiner

Steve Gardiner taught high school English and journalism for 38 years in Montana and Wyoming.  He started working at the Republican Eagle in May 2018.  He focuses on features and outdoor stories.  

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