White-nose syndrome has killed at least 6 million bats in North America, according to the U.S. Fish and Wildlife Service. It attacks them as they hibernate in caves and abandoned mines during winter, creeping across their bodies and causing skin lesions that lead to death. In a pattern that eventually could play out in Texas, the disease emerges two to three years after the first small amounts of fungus are detected.

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“This is devastating news for Texas, and a serious blow for our western bat species,” said Mike Daulton, executive director of Bat Conservation International, a Texas nonprofit group that is working with the state.

The fungus was found in six counties from samples collected by biologists. Some samples were taken from cave myotis bats, a species that often shares caves with the most popular bat in Texas, the Mexican free-tailed bat. The latter famously roosts under the Ann W. Richards Congress Avenue Bridge in Austin and in a huge colony in the Bracken Cave near San Antonio.

Mexican free-tailed bats don’t hibernate for long periods and probably won’t be harmed by the disease, which takes months to destroy skin and wings. But they fly over long ranges and have the potential to carry the fungus as far south as Honduras. Cave myotis bats are found as far west as Arizona.

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“One of the big concerns we have is if it gets into Mex free-tailed populations, it can become a vector for spreading the disease through a large region,” said Jonah Evans, a mammalogist for the Texas Parks and Wildlife Department. “Now that we’re seeing it in western species like the cave myotis . . . there is more potential that it will spread in the West.”

The bat-killing fungus has inched toward Texas for months. It was previously found in Arkansas, Oklahoma and Nebraska. It has reached as far as Washington state, probably carried by a human who visited Europe, where a similar fungus is present but does not cause the mortality witnessed in the United States.

The lower death toll abroad is because the fungus has been present in Europe, Russia and China for a much longer time, allowing bats there to adapt, said Jeremy Coleman, director of the Fish and Wildlife Service’s white-nose response.

In the United States, white-nose syndrome affects different species in different ways, killing about 100 percent of little brown bats in some areas but killing larger bats in much smaller proportions. Still, the disease’s westward spread is a major concern because officials aren’t certain which species can survive. Bats’ value to U.S. farmers has been estimated at $3 billion annually. Without them, insects would be free to ravage crops and trees.

Bats eat insects by the metric ton each night, with a pregnant female capable of devouring nearly a hundred moths and other pests. In a single summer, a colony of 150 little brown bats can eat enough adult cucumber beetles to prevent the laying of eggs that result in 33 million rootworm larvae, according to a study cited by Bat Conservation International.

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The fungus’s leap to Washington state from Oklahoma, the farthest the fungus had traveled West as of last year, baffled those who study it. “Every single avenue we look at seems far-fetched,” Greg Falxa, a wildlife biologist for the Washington Department of Fish and Wildlife, said at the time. “Who knows how it got here? Everything is speculation right now. We’re starting surveillance in that area.”

Some scientists thought the fungus could still be contained, but Katie Gillies, director of the Imperiled Species Program at Bat Conservation International, was not one of them. “We’ve got 15 western species that have the potential to be infected,” she said last year. “Containment is not going to be possible.”