ONALASKA, Wis. — It's best to let sleeping bats lie in winter.

When bats prematurely wake from their hibernation and leave their haunts — as some did after polar vortex conditions gave way to 40 degree temperatures — they may die. But it's not the cold that kills them, it's the extra activity.

So when animal control gets calls about bats in the building, Kathy KasaKaitas rescues them and brings them to the Coulee Region Humane Society in Onalaska. It's the only facility in southwestern Wisconsin permitted to overwinter bats.

"They've already used up their reserved calories, so they'd probably starve to death otherwise," KasaKaitas, the animal control supervisor at the Humane Society, said to the La Crosse Tribune.

On a recent afternoon, there were 42 bats overwintering in the Humane Society's enclosed garage, housed in bat boxes stacked one atop the other.

The bats come from all over La Crosse, including the La Crosse Center, as well as surrounding counties. They stay in KasaKaitas' care until they can be released in the spring, when the bugs return.

KasaKaitas got a permit to rehabilitate bats four years ago, after she noticed an uptick in bat calls during the winter. The bats were fur, skin and bone, and there was little she could do to save them.

"When I saw how many bats had to be euthanized, I wanted to learn how to care for them," KasaKaitas said.

This was especially crucial given that white-nose syndrome, a fungal disease, had appeared in Wisconsin bats at around the same time.

The state is home to eight bat species, four of which are threatened. Bats play a vital role in the ecosystem and the economy. They eat agricultural pests and disease-carrying insects, and their poop is a food source for many cave organisms.

Since the arrival of white-nose syndrome in North America from Europe a little more than a decade ago, the condition has spread to 33 states and seven Canadian provinces and millions of bats have died from the fungal disease.

The fungus grows on the wings, ears and snouts of hibernating bats, coating their bodies with what looks like a white powder. Each time the bat rouses to clean its face, it wastes precious energy. Eventually, the bat starves.

Most of the bats overwintering at the Humane Society are big brown bats or little brown bats. While the species differ by a few centimeters in body length — both tend to be less than three inches long — both can catch and spread white-nose syndrome to other bats.

Bats are a protected species in Wisconsin and it is illegal to kill them. The Department of Natural Resources recommends leaving hibernating bats alone in the winter. If they do wake up, you can call a wildlife animal rehabilitator to remove them from your house.

When bats find their way indoors during the rest of the year, particularly in late summer when baby bats are learning to fly, DNR recommends shooing the bat into a room with an open window or door and letting the bat leave on its own. If that doesn't work, you can trap the bat in a cardboard or plastic box when it lands, and slide a piece of cardboard underneath. Then, set the box outside and let the bat come out on its own.

Homeowners can also install one-way doors that let bats fly out and not back in. However, these doors are not allowed between June 1 and August 15 so that bat mothers are not separated from babies.

Eviction involves installing one-way doors that allow the bats to leave but not re-enter the building. One-way doors can be made of plastic or screening but must not cause harm to the bats.

If you or your pet has been bitten by a bat, or if bat saliva or brain matter comes into contact with your eyes, nose, mouth, or open wound, the Center for Disease Control recommends consulting your doctor or veterinarian and capturing the bat to get it tested for rabies.

KasaKaitas quarantines new bats in closed containers with air holes before she houses them around other bats. She also inspects their wings and snouts with UV light for traces of white fungus, which glows orange under black light.

As another precaution, KasaKaitis wears latex gloves, which can be swapped out, on top of her regular gloves to prevent the spread of disease from bat to bat.

Once the new bats pass inspection, KasaKaitis teaches them to eat mealworms from a dish. Wild bats use their tail membrane to catch and consume insects mid-flight, she said. KasaKaitis hand-feeds them mealworms held between tweezers until they learn to associate the dish at the bottom of the cage with food. As the bats adjust to their new surroundings, their metabolism and activity slow down and they go back to sleep. KasaKaitis' longest-staying residents are so still they look like they're barely breathing.

KasaKaitis keeps the bat boxes supplied with food and water and the cages clean. Otherwise, she lets the bats hang out upside down until spring, when they are released within two miles of where they were found.

An AP Member Exchange shared by the La Crosse Tribune.