Millions of bats are dying due to a deadly disease sweeping across the United States, their tiny bodies strewn across cave floors.

The northern long-eared bat is one of the bat species that was hardest hit by the white-nose syndrome, a deadly fungal disease. The U.S. Fish and Wildlife Service finalized new regulations on Thursday to protect the species — but some environmentalists say the government should be doing more.

The new regulations list the species as "threatened." Dan Ashe, director of the U.S. Fish and Wildlife Service, says biologists will now be able to do more to protect the caves where the bats hibernate and part of the forest where the bats live in summer.

"And then it allows us to provide protections to maternity trees, so protecting that vulnerable life stage when the bats are having pups and when the pups cannot fly," Ashe says.

Some environmentalists say Ashe's agency should have gone further by adding these animals to the endangered species list — the highest protection allowed by federal law.

"The species, by any sensible measure, clearly deserves endangered status," says Mollie Matteson, a senior scientist at the Center for Biological Diversity in Vermont. "It's dying at rates of 90 to 100 percent."

Vermont is where some of the biggest bat die-offs have occurred. Matteson says these new regulations still allow risky development by wind farms, loggers and oil and gas companies.

"The Fish and Wildlife Service has now basically opened the door for any and all kinds of activity that may affect this bat and its habitat," she says.

Northern long-eared bats were once one of the most common bats found in the country, living in states from North Carolina to Montana and Wyoming. The bats are voracious hunters and play a big role in controlling insects.

The white-nose syndrome was first identified in 2007, earning its name from white fungus found on infected bats' faces. It has since spread to 26 states and is poised to turn up in Nebraska this winter. The spread of the disease isn't expected to stop until it reaches the West Coast.

Ashe thinks these regulations will prompt companies to work more cautiously in forests where northern long-eared bats live, and biologists will monitor how well the new rules are protecting crucial habitat.

"Certainly in the future I could see a potential that its status would change to endangered. So in the meantime, people shouldn't, you know, be relaxing," he says. "We should be working with the wind industry and the oil and gas industry and the utility industry and others to put in place durable protections."

It's unclear just how effective regulations like this will be in saving northern long-eared bats. After all, it's that deadly fungal disease that's pushing them to the brink and scientists still have no way of stopping it.

Copyright NPR 2019.