Bats caught in the gauzy, almost invisible mist nets stretched across the rocky mouth of Barton Cave last week may provide clues to the mysterious plague that has killed hundreds of thousands of the mammals in the Northeast and New England during the winter.

The popular spelunking cave, just off State Route 40 near Uniontown, Fayette County, is one of three bat hibernation sites in the state where biologists have found what appears to be a white fungus dubbed "white nose syndrome" on the snouts, arms and ears of some bats. The fungus has been present on many of the bats that have died over the winter in New York, Vermont, Connecticut and Massachusetts.

Although there have been no reports of bat die-offs in Pennsylvania, and the fungus found on bats at the three hibernaculums has not been positively identified as white nose syndrome, wildlife biologists at the state Game Commission and the Department of Conservation and Natural Resources are extremely concerned about its potential to decimate bat populations.

Aura Stauffer, a wildlife biologist and the state Department of Conservation and Natural Resources' resident bat expert, said the department has decided to close Barton Cave to cavers for the year as a precaution because it doesn't want them to carry the fungus to other caves. Normally the cave would open at the end of May.

"In February we went into the cave and found a white fungus and then went back in recently and found more," said Ms. Stauffer, who helped Game Commission and Bucknell University biologists rig the mist nets outside the mouth of Barton Cave, and take blood samples and place identification bands on the captured bats.

"We suspect we have the fungus but can't confirm it yet," she said, "because the lab results aren't back and the bats there aren't exhibiting any of the weird behavior they did in other states," where bats left caves too early and starved to death. "All our bats that show signs of the fungus are otherwise healthy."

Fungus that may be white nose syndrome has also been found on some bats in the big hibernaculum in an old mine at Canoe Creek State Park, Blair County, where 25,000 bats overwinter, and in the New Angola Tunnel, Luzerne County.

"We've been looking for it and we've found some suspect cases, taken some samples, but we're still awaiting final results from the lab to confirm what we've found," said Jerry Feaser, spokesman for the Game Commission, the lead state agency in the investigation. "More importantly, we haven't found any of the bat die-offs."

Loyalhanna Grotto, a caving organization based in Indiana, Pa., has posted a Web page alert asking its members and all outdoors enthusiasts to report any suspected cases of white nose syndrome to the organization.

Late last year, up to 11,000 bats died in four Albany, N.Y.-area caves -- more than half of all the bats in those caves. The white fungus was present on bats in those caves and has been confirmed at more than 15 other caves and mines in New York and New England that contained approximately 500,000 hibernating bats. Up to 90 percent of the bats in some caves have died.

According to a U.S. Fish and Wildlife Service Web site, little brown bats are sustaining the largest number of deaths, but long-eared, eastern pipistrelle, small-footed and the Indiana bat, a federally endangered species, are also affected. One of the Indiana bat's largest known hibernating populations is in the Canoe Creek mine.

Pennsylvania has more than 1,000 caves that could harbor wintering bats.

Ms. Stauffer said biologists don't know if the fungus is a cause of the deaths, a symptom, or a secondary infection. The actual cause may be fungal, viral, bacterial or something else.

"Something is waking the hibernating bats up early in the year and they are coming out in the daytime and flopping on the ground where they're starving to death," she said. "They're waking up when it's too cold and there's no insects to eat."

Because bats feed heavily on insects, the decimation of bat populations could remove an important control on insects like mosquitoes that are pests for humans. On a typical summer night one bat will consume 25 percent of his body weight while eating up to 1,000 insects an hour.

"That's a reason why we're worried," Ms. Stauffer said. "If we lose that part of the ecosystem, you better go out and buy some bug spray."