Deadly Bat Fungus Discovered at Bracken Cave, Home to 20 Million Bats

A deadly fungus that’s wreaked havoc on bat populations across North America has been identified at Bracken Cave north of San Antonio, the world’s largest known bat colony.

Scientists with Bat Conservation International (BCI) on Wednesday announced the discovery of the fungus, Pseudogymnoascus destructans, which has been spreading across the United States since the mid-2000s after its first detection in upstate New York. BCI manages the Bracken Cave preserve after it was safeguarded from development by conservationists and local leaders.

The fungus causes white-nose syndrome when white, fuzzy threads of fungus spread across the bat’s body and become visible on its muzzle and wings. The fungus causes the bats to wake up from their hibernation state, known as torpor. That depletes the fat reserves that help them survive through the winter, and many don’t make it.

Also on Wednesday, the Texas Parks and Wildlife Department announced the fungus has been found in 11 new counties in Texas this year, for a total of 22 known sites in 16 counties. Liberty County marks the fungus’ first known arrival in East Texas, and Frio and Victoria counties are now the edges of its southern spread in the U.S.

Despite the discovery of the fungus that causes the syndrome, scientists have not yet found evidence of the white-nose syndrome disease in Texas.

The fungus has been known to devastate bats that hibernate through the winter. However, the Mexican free-tailed bats that reside at the Bracken Cave are migratory, and even those that overwinter there tend to leave the cave to hunt on warm nights. This tendency likely means the bats will not be as vulnerable to

white-nose syndrome as hibernating bats, according to the conservation group.

“If we’re ever allowed a moment of cautious optimism, it might be with Mexican free-tailed bats,” said Winifred Frick, BCI’s chief scientist.

A maternal roosting colony for mother bats and their young, Bracken Cave is one of the world’s most important bat conservation sites. As many as 20 million Mexican free-tailed bats spend their summers in the cave after their winter migration from Mexico.

The bats are a symbol of Central Texas and the namesake of one of San Antonio’s most prominent breweries. As voracious insect-eaters, their pest control value has been estimated at between $121,000 and $1.75 million per year to South Texas farmers.

Since its detection in the Texas Panhandle, the fungus has been steadily moving south. Last year, Texas Parks and Wildlife officials announced they had found it at Old Tunnel State Park in Kendall County, at the time the southernmost location in the U.S. where the fungus had been observed.

Fran Hutchins, Bracken Cave’s director and a caver who was part of the group that discovered the fungus in the Panhandle in 2017, said BCI has been monitoring Bracken Cave for the fungus’ arrival for a decade. Skin swabs taken from bats at the cave in February ended up testing positive.

Hutchins said its discovery will not affect the ability for people to visit Bracken Cave’s and watch millions of bats emerge in a swirling vortex that’s become known as a “batnado.”

“There’s no risk of any of our visitors picking up the fungus and spreading it,” he said. “There’s no access to the cave.”

This year, scientists found the fungus on 13 Mexican free-tailed bats, four tricolored bats, and 43 cave myotis in Texas, according to TPWD.

Of these, tricolored bats and cave myotis are hibernating bats. The fungus has already “decimated” populations of tricolored bats in other states, Frick said. She said she’s also worried about its potential effect on cave myotis, whose range stretches from the Southwestern U.S. into Mexico and Central America.

“This is the first time that the fungus has really come in contact with those [cave myotis] populations,” she said.

In vulnerable bats, white-nose syndrome tends to show up in the years after the fungus first appears. Scientists with TPWD, BCI, and other groups are testing different methods of treatment to see whether they can reduce the fungus’ effect after its arrival, she said.

“Texas is a place where we really want to sort of keep on top of it and be proactive and comprehensive in our response,” Frick said. “It may play out differently here. It’s too soon to know for sure.”