As Halloween approaches, it's the bats who should be scared.

A relatively new disease has ravaged populations across the eastern half of North America, but Louisiana could hold the key to keeping species alive.

Bats — of the order Chiroptera, meaning "winged hands" — may conjure images of blood-sucking vampires, but the local varieties are interested in eating only insects, making them vital to their human neighbors.

"The fewer bats we have, the more (pesticide) chemicals go on our crop foods. … (Bats) contribute billions in ecosystem services to the agriculture industry," says Louisiana Fisheries and Wildlife zoologist Beau Gregory.

The plague on bats is a disease known as white nose syndrome. It's caused by the ominously named fungus Pseudogymnoascus destructans, or Pd for short. Bats contract white nose when they come into contact with another bat or surface where Pd is present. It's especially dangerous for  hibernating bats because their immune system is suppressed while they're dormant.

As its name implies, the syndrome causes white fungus to grow on non-hairy parts of bats' bodies, including their noses and wings. Those areas can develop infected lesions.

Yet the bigger problem is the disease wakes up hibernating bats when they should be conserving their energy, says Texas Tech biology professor Richard Stevens, a bat researcher who formerly worked at LSU.

"They're on a pretty tight energy balance … and they just run out of energy and die," he said.

Louisiana's warm climate and lack of rock caves is giving scientists hope that the state's particular ecosystem could shelter species that are dying out elsewhere.

The state's warm climate means insects are active year-round, so bats don't have to hibernate. Also, Pd has an unusual preference for cooler temperature. 

Also, without rock caves, concentrate bat populations elsewhere and allow the mass transmission of disease, Louisiana bats are more likely to roost in trees and other smaller sites, preventing large-scale Pd breakout.

White nose is believed to have originated in New York state around 2006, likely caused by a human traveler introducing Pd from Europe. In the years since, the fungus has raced up and down the Appalachian Mountains and spread around the Great Lakes and the Ozarks.

When white nose breaks out in a bat population, more than 90 percent of individuals have died, federal Fish and Wildlife officials wrote in a June statement. At that time, they were announcing that the disease had penetrated into Alabama. Researchers found infected bats within the Lake Purdy Corkscrew Cave outside Birmingham. For the first time, the southeastern bat species had fallen ill.

While many affected species range widely throughout North America, the southeastern bat is more particular, confining itself to the Gulf and southern Atlantic coasts and the lower portions of the Mississippi and Ohio river basins.

"We are disappointed to find white-nose syndrome in another species, but hopeful that the southeastern bat may fare better than many of its more northern cousins based on how long it took to be diagnosed with the disease," Jeremy Coleman, the national white nose coordinator for the U.S. Fish and Wildlife Service, said in a  written statement.

Louisiana is home to at least a dozen bat species, according to the state Department of Wildlife and Fisheries. Four of those varieties — the big brown bat, tri-colored bat, long-earned northern bat and southeastern bat — have contracted white nose, though none of the cases were reported in Louisiana.

However, the state is surrounded by outbreaks of Pd. White nose is already prevalent in Arkansas, and while the disease has not yet been confirmed in Texas or Mississippi, scientists have found the fungus that causes it.

"We have been vigilant in doing surveillance projects," like swabbing bridges and culverts in northeast Louisiana where bats like to live, said Gregory, the state zoologist.

Leslie Lattimore, director of the Wings of Hope wildlife sanctuary in Livingston, said her organization works with the state and the Centers for Disease Control and Prevention to test bats for illness, including rabies and white nose. The fungal disease is alarming due to its rapid transmission; Lattimore says the status seems to change every day.

"It travels so very, very fast," she said.

Some species may go extinct, Stevens predicts. The northern long-eared bat, which has a wide range that includes north Louisiana, has already been classified as a threatened species due to the white nose epidemic. Alabama officials have said the tri-colored bats — which also live in Louisiana — are disappearing from their state.

Humans have tried to intervene by using anti-fungal agents to kill Pd, but those haven't proven very effective. The best thing people can do is clean their clothes and gear before entering a bat habitat such as a cave to prevent spores from spreading, the experts say.

"I imagine this is just going to play out naturally," Stevens says.

What he means is that eventually the susceptible bats will die off, leaving only the individuals resistant to white nose which can hopefully pass that hardiness on to their offspring. European bats appear immune to the syndrome, evidence that those species have already weathered their epidemic.

However, those species-wide shifts could take hundreds — if not thousands — of years to play out. Until then, there is a hope that Louisiana could be a reservoir where species could hide out without going extinct.

Bats fill an important ecological niche. The world's only flying mammals can consume a whopping 85 percent of their body weight in insects each night, Stevens says. While some bats eat fruit or even blood elsewhere in the world, the varieties across Louisiana are all insectivorous.

In one study, 150 big brown bats were able to scarf down 1.3 million bugs in a year, Stevens says. Some species specialize on moths or beetles, while others, like the southeastern bat, are less picky. Texans have proven that bats are especially helpful in controlling bollworms and other pests that eat their corn and cotton, but they're important to all types of crops.

In fact, the federal government has quantified just how important bats are to the U.S. economy: $74 per acre for the average farmer.

"Insect-eating bats keep agricultural pest populations down, saving farmers at least $3.7 billion per year in lost crop revenue and preventing the need for spraying costly toxic chemicals," the U.S. Fish and Wildlife Service announced in July as it distributed money for states to study white nose.

Louisiana claimed $24,500, to be used to survey bat ecosystems this winter.

Follow Steve Hardy on Twitter, @SteveRHardy.