Four species of Minnesota bats may be facing a death sentence now that a lethal fungus that decimated their populations in other states has been discovered at two of their largest hibernating sites here.

The disease that results — white-nose syndrome — has not been detected yet in Minnesota, but the underlying fungus has been discovered on four bats in two locations — Forestville/Mystery Cave State Park and Soudan Underground Mine State Park.

The discovery is an early signal of a disease that has wiped out as many as 90 percent of bats in affected colonies in eastern states, which could deal a huge blow to Minnesota’s agricultural economy.

Bats, which can eat half their body weight in insects each night, save Minnesota farmers an estimated $1.4 billion annually in pest control, officials said. They also play a critical role in pollinating many crops and other plants.

The disease is almost impossible to contain once it takes hold, researchers said Friday at a news conference organized by the Minnesota Department of Natural Resources (DNR).

White-nose syndrome does not pose a threat to humans, pets, livestock or other wildlife, but it is devastating to the four species of bats in Minnesota that hibernate during the winter in caves and abandoned mines.

Three other species that migrate every year are not known to be affected.

First documented in New York in 2007, the disease has spread rapidly across the eastern United States and Canada, and the fungus has been detected as far west as Oklahoma.

Bats with the disease, characterized by white growths on their noses and lesions on their wings, exhibit uncharacteristic behavior during cold winter months, including flying outside during the day and clustering near the entrances of their caves.

Winifred Frick, a bat researcher from the University of California, Santa Cruz, said that, while the disease is little-understood, it causes infected bats to wake up too often in the winter. That depletes their hibernation energy stores, and they starve before spring arrives.

The disease has killed more than 5.7 million bats in eastern North America. In some colonies, or hibernacula, 90 to 100 percent of bats have died.

Hard to stop

State and federal officials said Friday that, though research is underway, there is little they can do to stop the spread of the disease or treat infected bat colonies.

Bats spread the fungus from cave to cave, and they range up to 250 miles.

Once the fungus becomes established in a site, then, just like human fungal diseases, it’s extremely difficult to eliminate.

The only practical precaution for now is to reduce the risk of humans carrying it from cave to cave, said Jeremy Coleman of the U.S. Fish and Wildlife Service.

In Arkansas, caves have been closed to spelunkers. But in Minnesota, the two affected sites are extremely popular tour destinations for state park visitors.

From now on, visitors will be asked to walk across special mats that remove fungus spores from their shoes, and they’ll be warned not to wear the same clothes if they visit other bat caves because standard laundering does not remove the spores, said Ed Quinn, natural resource coordinator for DNR’s Parks and Trails Division.

“We’re hoping to reduce the chances of [it] taking those big leaps caused by human transmission,” Quinn said.

The fungus was found in Minnesota as part of a national study tracking its spread across the country. Gerda Nordquist, a state mammalogist, said the fungus was detected on the wings of four bats at the two sites — three little brown bats and one long-eared bat. A total of 47 bats at five hibernation caves were tested.

Mystery Cave, in southeastern Minnesota, has about 2,300 bats. Soudan Underground Mine, in the northeastern part of the state, has 10,000 to 15,000 bats.

If the pattern established in other states holds true here, the disease is likely to show up within two to three years, officials said. And then the outcome will likely be swift and long term.

Bats are mammals that live up to 30 years and reproduce only once a year, Nordquist said. That means a population could take years to recover, if at all.

In Europe, where the fungus is common, bats have developed immunity — which would be an ideal outcome for American bats, Coleman said. But their numbers could fall so low that it becomes impossible for their populations to recover, and they would, in effect, be extinct, he said.