Norma Donovan, 93, of Waterville has spent many a summer evening watching bats as they flit across the twilit sky.

But this year, she said, the bats are gone.

At the same time, she’s noticed more mosquitoes and other flying insects coming out at dusk.

“When the bats were in good health, they took care of them,” she said.

Donovan said she has heard that there is a problem with bat populations, but hearing it in the news and witnessing the animals’ absence in the night skies are two different things. She expressed concern for the bats’ future, not only because she likes them, but also because of the important role they play in the ecosystem.

“They’re kind of important,” she said.

She’s no expert, but she knows what she sees.

“I’m 93,” she said, “but I still have most of my buttons.”

Donovan’s observations are spot on, according to wildlife biologists. As she has suspected, bat population numbers are crashing, and there are accompanying concerns about increases in certain insect pests. The culprit is a disease, known as white-nose syndrome, caused by a fungus that invades the bodies of bats while they hibernate.

“The fungus will show up around the muzzle area, but the major damage that is done is a skin infection of the flight membranes,” said Anne Ballmann, a field investigator for the eastern United States looking into the white-nose syndrome problem for the National Wildlife Health Center of the U.S. Geological Survey.

With their wings damaged by the fungus, bats are less able to keep warm, meaning they burn through their fat reserves more quickly in the winter while they hibernate. Even more deadly is the impact on their ability to fly. Some infected bats can’t take wing at all. Others can fly, but not as well, making it much more difficult for them to corner and consume insects. Scientists haven’t quite pinned down all the specific ways the fungus kills bats, but they do know that the animals are dying and the fungus is spreading.

First discovered in Albany, N.Y., in 2007, the fungus has swept across the country, spreading to 25 states and five Canadian provinces in the past seven years. Once the disease takes hold in a state, it spreads quickly.

“In each state (where) it’s been found, it’s being found in more and more counties,” Ballmann said.

THE SPREAD OF THE DISEASE

With no immediate solution on the horizon, Ballmann and her colleagues are urging people to do what they can to slow the spread of the disease. The fungus travels on bats, but it can also hitchhike on humans who visit bat habitats. Ballmann asked that people recognize and respect caves posted as off-limits by federal environmental officials. If hikers do go into a bat habitat, Ballmann recommends that the gear, footwear and clothes they are wearing not be taken into another bat habitat unless stringent decontamination standards are followed.

According to the recommendations, clothing, footwear and equipment used in an area affected by white-nose syndrome should never – under any circumstances – be used in an unaffected state or region.

Decontamination procedures include submerging contaminated gear into water of at least 122 degrees for 20 minutes or using certain commercial cleansers on various types of materials.

In Maine, white-nose syndrome decimated bat populations in Oxford County in 2010 and Hancock County in 2011, according to a map prepared by the U.S. Geological Survey. Cases of the disease were suspected, though not confirmed, in Piscataquis County in 2012.

When the syndrome surfaced in Acadia National Park, Superintendent Sheridan Steele said “losing even a small percentage of Maine’s bats could have a devastating effect” because of the role the animal plays in controlling forest and wetland insects.

“Some places have been completely wiped out,” Ballmann said. “In others, it has knocked the population back, but some bats remain.”

Bruce Connery, the wildlife biologist at Acadia National Park, said the map doesn’t tell the whole story in Maine. Once the disease has been documented in a state, he said, scientists are less likely to investigate and fully document further suspected cases within that state’s borders.

Connery said that Maine’s biologists don’t have a good handle on exactly how many bats were affected and how many remain. No one knows how many bats there were before white-nose syndrome took hold, he said

However, he said, all indications are that bat populations have plummeted in recent years, and not just in the counties in which it has been confirmed. About 70 percent of the bats usually identified during an annual bat capture are little brown bats and northern long-eared bats. This year, he said, there was just one little brown bat and no long-eared ones. Scientists in Acadia are undertaking a new project in which they hope to hitch radio transmitters onto bats and track them to hibernation sites. For the first time, he said, he hopes to learn specific details about bat life cycles. The information could be valuable in helping to establish and protect safe hibernation spots in the future.

“A lot of species, you do this kind of work and it takes multiple years, but I think many people in many states are seeing we don’t have a lot of time,” he said.

Susan Gallo, wildlife biologist with Maine Audubon, said the organization has conducted colony surveys over the past two summers, and have solicited population estimates from people who have bats on their properties. Connery said the Audubon survey probably gives a better picture of the bat populations in Maine than the official Geological Survey map.

But the results of the survey are grim. Nearly every survey participant from across the state reported seeing local bat populations not merely reduced, but eliminated.

“Probably 40 reports of colonies that historically had 50 or 100 or even 1,000 bats were all down to zero,” she said. “It was really bad news.”

Gallo said the survey indicated that a few bat colonies seem to have been unaffected so far.

The fungus is also worrisome because it affects bats of different species – eastern pipistrelle, northern long-eared bats and the little brown bat have all been killed, as well as rarer species.

BATS’ PLACE IN THE ECOSYSTEM

Bats are not universally embraced by humans.

Gallo said that when Maine Audubon began advertising its bat colony survey project, it received many calls from people who wanted to know how to get rid of the bats in their homes, garages and barns.

“I was trying to convince them they were lucky,” she said. “It was challenging because it’s not the way they thought.”

Donovan is aware that many people are squeamish when it comes to bats, which feature heavily in vampire legends and Hollywood horror movies.

She still remembers the day she lost her own fear of bats.

“One day, I had the ladies at the house playing cards,” she said. “I lived in an old house at that time, you know, with those living room doors that come out and slide back into the wall. Usually, in the old days, they would be between the sitting room and the parlor and you would pull these doors out. The bats would come out of that space. A lady said I had a bird in my living room. Well, I knew what it was, but if I said ‘bat’ they would have gone crazy. But I went in with my dish towel and was able to catch it. I had never seen a bat up close. It was nice, you know, it had fur on it. I took it into the bathroom and opened the window and pulled the shade down and off it went.”

The card-playing ladies never knew, she said.

While bats are not necessarily beloved, they do perform a vital function for the ecosystem and for humans.

“They’re consuming massive amounts of mosquitoes and moths,” Gallo said. “And the more insects you have, the more vectors you have for diseases. We’re at risk as well.”

Gallo said people still do a very poor job of predicting the consequences of eliminating or adding a species to the environment.

As an example, she pointed to the Midwest, where unusual weather conditions created a bumper crop of black flies that have, in turn, caused 70 percent to 80 percent of loons to abandon their nests.

“Who would have thought that an increase in black flies could have led to a decrease in loons?” she said. “You mess with one thing and who knows what the consequences are.”

Ballmann said she and other biologists are concerned that the lack of bats will result in increased demand for use of insecticides in the agricultural sector.

Jim Dill, pest management specialist for the University of Maine Cooperative Extension, said the impact on the number of crop pests is likely to be minimal.

“We haven’t noticed any increase in insects due to reduced bat populations,” he said. “It’s been in the back of people’s minds, but we haven’t seen it.”

COEXISTING WITH THE FUNGUS?

Scientists across the country are working to figure out how to stop white-nose syndrome in its tracks, but so far, no solution has presented itself. Gallo said she was hopeful that North American bats would develop a resistance to the fungus, as is the case in Europe, where the fungus originated before it was discovered in New York.

Killing the fungus altogether doesn’t seem to be a realistic possibility, Ballmann said.

“It’s probably not practical to say we’re going to be able to wipe the fungus out, because it can survive in the environment with or without bats,” she said.

Instead, biologists are focused on figuring out how to help the bats coexist with the fungus. This might mean spraying bats with a chemical agent that protects them from the fungus, like treating a dog to ward off fleas, or it might be introducing a biological agent that feeds on the fungus, keeping it in check so that it is less likely to overwhelm an entire population of bats.

Connery said that people can help by improving the chances of survival for the bats near their homes.

Because mother bats rear only one bat pup per year, he said, it is extremely important that bats reach maturity, a process that typically begins in late May and can last until the third week of July. People often unwittingly kill the babies by doing major roofing work on structures in which bats have taken refuge before the pups have become independent.

“You’ll scare the females away from their babies, and like any baby, they need milk,” he said.

He also encouraged people to buy well-constructed bat-houses, which are usually sold by conservation organizations. Newly posted houses, he said, might give bats a clean alternative to an infected roosting spot and allow them to escape white-nose syndrome, at least temporarily.

If the bats can hold on long enough for a more permanent solution to be found, they may be able to repopulate their historic ranges and once again flit across the night sky.