The fungal disease known as white nose syndrome is spreading fast and has brought half of Minnesota's bat species to the brink of extinction within the state.

The fungus, which has been spreading westward and was found in Minnesota less than a decade ago, has since wiped out 90 to 94 percent of the bats that hibernate in state-monitored caves and abandoned mines, the Department of Natural Resources (DNR) said Thursday in releasing results from its periodic bat survey.

The DNR has counted bats in a handful of locations each spring since long before the presence of white nose syndrome was confirmed in 2015.

The deep recesses and winding tunnels of places such as Mystery Cave in southeastern Minnesota that sheltered thousands of northern long-eared, big brown and little brown bats only a few years ago are now hauntingly empty, said Gerda Norquist, DNR mammalogist.

"In the old days we would count over 700 bats in just a portion of the cave," Norquist said. "You walk down a path now and you don't see anything."

Biologists counted just 40 bats this spring in Mystery Cave.

It was just as bad in the Soudan Underground Mine in northeastern Minnesota, where the disease has cut the population by 90 percent, and in crevices and shallow caves along the Mississippi River.

The fungus, which produces a white, powdery substance, was discovered in New York in 2007 and has since spread to 33 states and killed millions of bats. It's only known to harm hibernating bats and doesn't pose a threat to humans, pets, livestock or bats that migrate during winter.

Highly contagious and almost always fatal, the fungus attacks bats at their weakest. Even in normal circumstances, the animals barely survive winter. They need to shut down their bodies almost completely to survive six-month stretches without mosquitoes and other sources of food.

"They slow their heart rate, drop their body temperature and basically shut off their immune system," Norquist said. "That's what gives the advantage to the fungus."

The fungus can sprout on the tips of bats' wings or across their faces and annoys them while they try to sleep. They wake up periodically to try to groom themselves, much like a dog or a cat. But the amount of energy spent on that alone is often enough to cause starvation. Sometimes they die right in the cave, other times they fly off in a doomed search for flying insects to eat in the dead of winter.

Little help is on the horizon. Researchers have been experimenting with vaccines and other means of suppressing the growth and spread of the fungus, but no one has discovered a way to apply any of the experiments in the wild.

Biologists say it's too soon to know for sure if the disease has spread to every part of the state, but they know it's getting there.

Minnesota has four bat species that hibernate and four that migrate south for the winter. Some researchers believe the hibernating bats will be completely wiped out in Minnesota within the next few years, while others hold out hope that a handful will survive, Norquist said.

In some Eastern states that have been infected longer than Minnesota, a few bats have been found to live through multiple winters with the fungus. Scientists don't know if that's because they are resistant to it in some way or are just big and fat enough to have the spare energy to fight off the disease.

Whether the Minnesota bats are eradicated or cut to a fraction, the consequences could be far-reaching. The four species at risk are pollinators. They're also voracious mosquito and moth killers that eat their weight in biting insects every night.

DNR officials believe their decline could set off a troubling chain reaction: More moths in the environment will damage crops and vegetable gardens, which will likely increase pesticide use, which can further harm already endangered bee, butterfly and other pollinator populations.

Humans, however, can help by leaving bats alone in the spring to recover, and by building havens such as bat houses where they can heal, Norquist said.

"They need a safe space to allow the mothers to give birth to the next generation and have a place in the summer to forage and build up their fat stores before they go back into the caves for another winter," she said.