There is good news from Vermont this Christmas for the little brown bat, a threatened species that’s hanging on to existence “by a tiny little fingernail,” said a state conservationist who’s watched them die by the millions in the Northeast from a mysterious disease.

Scientists who visited more than a dozen sites where the bats nest in the western part of the state found thriving colonies that appear to be resistant to white-nose syndrome, a disease caused by an aggressive fungus.

Pennsylvania biologists are also monitoring about 2,000 bats that appear to be healthy in an abandoned coal mine in Luzerne County in the state’s northeast, the Associated Press reported. The little brown bat seemed hardest hit in that state, where reports said the population dropped by more than 90 percent.

“It’s just a ray of hope that there are bats that have survived over three years of white-nose syndrome, and we want to know how they survived, or if they will continue to survive, and if this is enough bats to . . . recover a population,” said Scott Darling, a biologist for the Vermont Fish and Wildlife Department.

State officials asked residents during the summer to identify bat colonies and followed up with site visits. To their surprise, they found colonies in houses, barns and bat houses — like birdhouses but bigger — on the edge of fields.

“They need to be further evaluated to see if they’re exposed or carrying any of the disease,” Darling said. After the recent carnage, biologists were thankful that “there were survivors here at all. We’ve observed two trends, and one is that many or most of the little brown bat colonies are gone. There were hundreds, and now they’re gone.”

Over the past five years, little brown bats, and several other species, have died by the millions during their annual winter hibernation. A survey conducted at 42 sites last year and published in Bat Research News found that the little brown bat population fell from nearly 385,000 before the disease struck to 30,000, a decline of more than 90 percent. The northern bat’s numbers fell from about 1,700 to about 30, a 98 percent drop.

A separate study in April said the loss of so many insect-eating bats could force farmers to pay tens of millions of dollars more for pesticides to protect crops. The U.S. Fish and Wildlife Service has offered $9 million in grants since 2008 to study white-nose syndrome in a bid to arrest it.

The recent discovery raised hopes that bats in the Northeast and mid-Atlantic regions where the disease is established have somehow developed an immunity to Geomyces destructans, the fungus linked to the disease, according to a study published last week in the journal Nature.

“They’re surviving in places where the fungus has been present, and present for the last five winters,” said Mollie Matteson, a conservation advocate for the Center for Biological Diversity in Richmond, Vt. “I’m cautiously hopeful that eventually these animals can be recovered.

“I don’t want people to get the sense that this crisis is done,” Matteson said. “It’s good news in the sense that bats haven’t entirely fallen off the cliff yet. They’re still hanging on by a tiny little fingernail.”

Conservationists and biologists saw no such glimmer of hope as recently as fall, weeks before the hibernation. A June study published in Bat Research News said the little brown bat “has the potential to become extinct in the northeast in only 7-30 years” and that “a similar fate may await Indiana, northern long-eared, and tri-colored bats.”

In 2009, biologists said at least 1 million bats had dropped dead over three years. Mylea Bayless, a conservation biologist for Bat Conservation International in Austin, said in October that the problem has “absolutely gotten worse since then.”

“Easily, the number of states and sites where it’s been found has doubled,” she said. “It’s probably far more than a million, or likely millions” of dead bats.

White-nose syndrome, so called because the powdery fungus covers the noses and faces of bats, was first detected at Howes Cave near Albany, N.Y., five years ago. Biologists have described Geomyces destructans as athlete’s foot on steroids, burning holes in the membrane that allows bats to flap their wings.

The absence of bats carries costs for agriculture. A single colony of 150 bats in Indiana ate about 1.3 million insect pests that prey on crops in a single year, according to a study, “Economic Importance of Bats in Agriculture,” published in the journal Science.

Using various models, the study’s authors — Justin G. Boyles, Paul M. Cryan, Gary F. Mccracken and Thomas H. Kunz — estimated that up to 1,320 metric tons of insects were not eaten because of the disappearance of a million bats. Using various models, the researchers calculated the bats’ worth to farmers at about $3.7 billion or more per year.