White-nose syndrome is killing Indiana bats. Colder caves might save the vital bug eaters

·6 min read

Bats get a bad rap. Thanks to the likes of Bram Stoker and visions of vampiric, blood thirsty creatures, the only mammals that can truly fly are unduly denoted as fearsome, sometimes creepy creatures.

But images of Batman, a superhero capable of eliminating a plague of pests might be more accurate.

Bats play a vital role in Indiana’s ecosystem and even its economy, but cave-dwelling species across the state, some of them listed as endangered, are facing unprecedented death rates.

Feeding on beetles, mosquitoes and moths, a bat can eat half its body weight in insects each night providing benefits to Hoosiers out for an evening stroll as well as farmers plagued with pests.

The Indiana Department of Natural Resources estimates bats save the country’s agriculture industry more than $3.7 billion each year by acting as a natural pesticide. Not only do they protect plants, they help propagate them. The 13 documented bats in the state also pollinate plants and spread seeds, helping sustain a diverse ecosystem.

A study performed on one of the most common bats in the state, the big brown bat, found it helped alleviate a corn pest.

“One of the food items they found was the spotted cucumber beetle — the larval form of that is southern root corn worn, which is a huge agriculture pest,” said Scott Johnson, wildlife science supervisor with DNR. “They provide in keeping insect populations in check and that’s really valuable.”

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For the past decade, however, Indiana’s bat population has been facing an existential threat: white-nose syndrome.

Fuzzy fungus

Researchers discovered in 2006 a fungus in New York thriving in cold, damp habitats where bats hibernate over winter. The fungus, Pseudogymnoascus destructans, can grow on the exposed skin of bats — including noses, wings and ears — and damages it. The sometimes-distinct white color on the muzzle gives the disease its name.

The fungus can cause a bat to awake early from hibernation and use excess energy stored in fat. That energy is essential to the bat’s survival in the spring when it needs to use those stores to find food. If it wakes early, however, the bat will then burn through the remaining energy storage too quickly in the spring, leading to its death.

Workers with DNR’s Division of Fish and Wildlife first discovered white-nose syndrome in Indiana in 2011 while conducting routine surveys of winter hibernation sites. The fungus was first documented that winter in six caves throughout Crawford, Monroe and Washington counties. The next winter, 20 caves were harboring the fungus.

It’s difficult to count individual bat populations generally, but hibernating bats are a bit different, Johnson said. Bats can hibernate in clusters, like a carpet of bats in a cave, and surveying 15 or 20 caves will give researchers a pretty good idea of the winter population.

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Since the ‘90s, Indiana state biologists have been surveying caves every other year. In 2009, the survey year before white-nose syndrome was discovered in the state, biologists counted about 220,315 hibernating bats. During its most recent survey, in 2020, that number dropped about 17% due to the disease.

Researchers found white-nose syndrome is widely distributed throughout most of south-central Indiana and the fungus has been reported in most of the state's important hibernation sites.

Researchers noted the disease affects some species more than others.

Tri-colored bats saw the greatest death rate in that time frame, dropping from a population of 1,163 to only about 100. Little brown bat populations declined 89%, big brown bats dropped 47%, and Indiana bats saw the smallest effects dropping 15%.

The state determined the population losses of the the tri-colored, Indiana and little brown bats were enough to list them as endangered.

As seen in these little brown bats, the most commonly observed symptom of white-nose syndrome is the white fungal growth on the muzzle.
As seen in these little brown bats, the most commonly observed symptom of white-nose syndrome is the white fungal growth on the muzzle.

Disturbing hibernation cycles

Brad Westrich, a mammologist with DNR, said a lot of research has gone into why it affects some species more than others and that some just have better immune responses while in hibernation.

“That response means their bodies are working a lot harder, burning energy to fight the pathogen,” Westrich said. “They’re waking up more and burning energy.”

Bats needs those extra stores of energy in the springtime to hunt for food.

“Some bats wake up and fly around inside the cave trying to find food, and other bats are driven outside and eventually starve or succumb to hypothermia,” Westrich said.

The fungus spreads easily from cave to cave when spelunkers track it on their shoes and visit other caves as well as bats moving from one hibernation site to another. For this reason, DNR in 2009 shut down public access to caves, sinkholes, tunnels and abandoned mines on its properties.

The DNR, in 2014 however, began offering limited access to certain caves at Spring Mill State Park and Cave River Valley Natural Area for recreational caving during summer months when bats are not hibernating.

Indiana continues to monitor for white-nose syndrome, and the research is in part funded through the Indiana Nongame Wildlife Fund.

Looking ahead

Recent research published in April shows there might be a “viable strategy for combating” white-nose syndrome.

Surveys of hibernation sites in Pennsylvania found winter counts of some bat species were higher and increased over time in colder locations, suggesting cooling warmer sites may help alleviate declining populations.

Researchers cooled these sites by altering the cave entrances, improving airflow and allowing the caves to cool down.

The U.S. Fish and Wildlife Service published a national plan to address white-nose syndrome in bats in 2011 and is working toward a series of goals to assist states, federal agencies and tribes manage the disease.

The plan, meant to guide local working groups, calls for establishing sufficient lab testing capacity to diagnosis the disease, implement timely reporting to help inform resource management and support white-nose syndrome research. In the most recent update in 2014, FWS completed a disease tracking system and a web-based repository of information for researchers

Being a bat advocate is probably the best thing a person can do to help, Westrich said.

IDNR | Courtesy photoTwo little brown bats have visible fungal growth, a sign that they are infected with white-nose syndrome.
IDNR | Courtesy photoTwo little brown bats have visible fungal growth, a sign that they are infected with white-nose syndrome.

“What does that mean? Not just thinking about bats when Halloween comes around but year-round,” he said. “And if you hear fear mongering or bat myths spreading, catching and correcting them or pointing toward resources to educate them on how we benefit.”

The study looking at big brown bats found that a single colony of 150 in Indiana ate nearly 1.3 million insects each year, potentially disrupting the life cycles of agricultural pests. These are the benefits that would be lost with the bat populations.

Installing bat boxes can help provide emergency shelters for bats that might need them when proper roosts are unavailable. Planting pollinator gardens are also going to help bat populations as they support native insects that help sustain bat populations.

Karl Schneider is an IndyStar environment reporter. You can reach him at karl.schneider@indystar.com. Follow him on Twitter @karlstartswithk

IndyStar's environmental reporting project is made possible through the generous support of the nonprofit Nina Mason Pulliam Charitable Trust.

This article originally appeared on Indianapolis Star: Indiana bats are at risk from white-nose syndrome