Bat-killing fungus expands across Minnesota

White-nose syndrome has now killed bats in six counties in Minnesota, up from two last year, and probably has spread to virtually everywhere in Minnesota where bats spend their winters. The Minnesota Department of Natural Resources confirmed the ...

A northern long-eared bat that was captured with a net as part of a research project in the Superior National Forest in July 2015. (file / News Tribune)


White-nose syndrome has now killed bats in six counties in Minnesota, up from two last year, and probably has spread to virtually everywhere in Minnesota where bats spend their winters.

The Minnesota Department of Natural Resources confirmed the expansion of the fatal disease on Thursday.

The News Tribune first reported two weeks ago that the disease is being blamed for a more than 70 percent decline in bats at the Soudan Underground Mine during this winter's annual survey of the state's largest bat wintering area, called a hibernaculum, where white-nose syndrome was first confirmed in 2013.

The disease is causing thousands of bats to leave the idled iron ore mine in the heart of winter when they should be hibernating. The bats are dropping to the ground, dead from starvation or freezing to death.


Nearly 3,000 dead bats were found in just two weeks outside the mine in northern St. Louis County, DNR officials noted Thursday. Many more are believed to have died farther away.

The DNR said the disease has recently been confirmed in Becker, Dakota, Fillmore, Goodhue and Washington counties. The disease is also present in at least four other counties - Lake, Pine, Hennepin and Ramsey - but hasn't yet been confirmed as killing bats there yet, said Ed Quinn, DNR Parks and Trails Division resource management supervisor.

"While some locations are still testing negative, the results of recent surveys lead us to conclude that WNS is likely to be present anywhere bats hibernate in Minnesota," Quinn said.

Officials said the disease is spreading and killing bats at about the rate as expected considering how devastating the disease has been in eastern states. At Mystery Cave in Fillmore County, no decrease in bats was seen this year. But experts expect to see a big decline next year because so many bats there have been seen with the disease.

In southeastern Minnesota, the bat population at Brightsdale Tunnel was down 39 percent from the most recent count and the count at Bat River Cave decreased 31 percent.

"Four of Minnesota's bat species hibernate, and four species migrate," Quinn noted. "WNS will have a substantial effect on Minnesota's hibernating bat population. Neighboring states have reported declines of 70 to 95 percent in specific locations, as we recorded this year at Soudan Mine."

White-nose syndrome is named for the fuzzy white growth of fungus observed on the faces of infected bats. Infected bats show unusual behavior, such as flying during the day in summer or leaving caves during their usual winter hibernation, when no bugs are present for them to eat. A wildlife veterinarian at the University of Wisconsin confirmed the disease kills bats by causing their bodies to overheat, burning energy too quickly and at a time - in winter - when no insects are present to replace the lost calories and when it's far too cold for the mammals to survive outside.

The disease is known to spread from bat-to-bat but also is believed to be spread by people who carry the disease on shoes or clothing as they tour different caves and mines. Despite that transmission possibility, however, the DNR continues to offer tours of both the Soudan Underground Mine and Mystery Cave, where the DNR will continue to follow recommended national decontamination protocols. The DNR urges owners of private caves to take similar visitor precautions.


The disease was confirmed last Thursday in Texas, now the 31st state to confirm the fungus. It's also in five Canadian provinces.

It was first discovered in New York in 2007 and has killed millions of bats, generally wiping out between 90 and 100 percent of bat populations in each area it spreads.

"We may possibly see that in some of our hibernating sites," said Gerda Nordquist, a DNR bat expert.

Scientists are working on fungicides to stop the disease and are studying why a few bats have returned to some infected areas and appear to be surviving. Bat experts said Thursday, however, that it's too early to say if any bat recovery is taking place where the disease has hit.

Bats can live for 30 years but reproduce slowly, with generally one pup per year, so it will take decades to rebuild the populations, if they rebuild at all.

Bats are considered important for ecosystems because they eat so many insects and some species pollinate fruits and flowers. One Minnesota bat impacted by white-nose syndrome, the northern long eared bat, was given federal Endangered Species Act protection in 2015.

White nose syndrome is not known to impact any other species except bats.


John Myers reports on the outdoors, natural resources and the environment for the Duluth News Tribune. You can reach him at
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