A mysterious white fungus has claimed the lives of more than a million bats during the last three years, and it may only get worse. The fungus has been spreading westward across North America, killing over 80 percent of hibernating bats in each infected cave. While researchers have come to better understand this “white nose syndrome” (WNS), it’s still hotly debated where it came from, what can be done to stop it, and how the deaths of so many bats will undoubtedly impact people.
Not So Alien After All
Bats often seem small, fragile, and alien to us, despite having been flying and surviving for over 50 million years. But for a long period scientific thought held that these winged mammals should be placed in the same taxonomic category as primates. In the 1700s, the “father of taxonomy” — Swedish zoologist Carl Linnaeus — grouped bats and primates together because of their many similarities; both, for instance, have a few poorly developed, dependent young that nurse from their mother’s breasts. More recently, it’s been found that some bats have brain features that were thought to be unique to primates. But recent genetic studies bats have put bats into a different group, a widely-encompassing one that includes hoofed mammals, whales, carnivores, hedgehogs, and others (the superorder Laurasiatheria). (This group was created based on genetic similarities, not any uniting anatomical characteristics.)
Regardless of the taxonomic group they’re placed in, bats, which themselves form the order called “Chiroptera” (literally “hand-wing”), come in all shapes and sizes. There are more than 1,100 bat species (accounting for a quarter of all mammalian species), and they can be found all over the world except for the most extreme environments, although most bats live in tropical forests. They can be very furry or furless, have tiny or huge ears, or even be brightly colored. The smallest bat, Kitti’s Hog-nosed Bat, also known as the “bumblebee bat” (Craseonycteris thonglongyai), is also the world’s smallest mammal, weighing in at two grams (that’s less than a penny!). On the other side of the scale, the endangered Greater Flying Fox (Pteropus vampyrus), has an impressive six-foot wingspan. Famously, bats use echolocation to see fine details in total darkness. However, contrary to popular belief, bats aren’t blind at all; many bats actually have great normal vision (in addition to their echolocation).
What Have Bats Done for You?
Bats not only play key roles in cave, farmland, and forest ecosystems, but they also affect many economically valuable crops. Seventy percent of bats worldwide eat insects, including moths and beetles that inflict billions of dollars of damage upon American farms and forests each year, as well as eating those pesky mosquitoes. A single bat can devour hundreds of insects in one night. This amounts to one million bats taking care of 700 tons of insects in a year, which is just one way in which the loss of one million bats is felt so far.
Most of the bats that aren’t insect-eaters eat fruit and nectar instead and are responsible for pollinating many valuable crops, including the agave cactus, which is used to make tequila. Additionally, bats are essential for the seed pollination and dispersal of over 300 tropical and rainforest plant species; they’re necessary for reforestation efforts. Bats are also needed for the pollination of many wild varieties of valuable crops, including bananas, avocados, figs, peaches, cashews, and more. While these crops are now mostly commercially cultured without bats, maintaining the wild plants helps ensure that disease-resistant and hybrid plants may be generated in the future. All in all, the plants that bats pollinate account for hundreds of millions of dollars of economically important products every year, from drinks, foods, and medicines to fuels, dyes, and more.
“White Nose Syndrome”
Many bats that do not have the luxury of living in the tropics must migrate or hibernate to deal with cold winters, which is where the white nose syndrome, or “WNS,” comes in. WNS is a fungal disease that has been ravaging hibernating bat populations in North America since 2006, when it was first documented on bats in a cave in New York. WNS is thought to cause irritation and itchiness, which may cause the hibernating bats to wake up prematurely. The awoken bats quickly use up their small fat reserves and freeze or starve to death, hopelessly looking for food. As the name implies, the white fungus is usually apparent on the fur around an infected bat’s snout. But it doesn’t stop there. WNS develops into white sores on the bat’s wings, deteriorating the vulnerable tissue and making it difficult for the awoken bat to fly.
After massive numbers of dead bats were discovered littering cave floors (WNS kills more than 80 percent of individuals in infected caves), researchers hurriedly worked to find out more about this deadly white fungus. In 2009, scientists discovered that a never before recognized species of filamentous white fungus, Geomyces destructans, was the likely culprit. (Another species belonging to the same genus, G. pannorum, occasionally infects skin or nails in people, though people aren’t susceptible to G. destructans.)
G. destructans grows best in the conditions where the bats hibernate. For example, the little brown bat (Myotis lucifugus), which is smaller than a thumb, hibernates in caves around 40 to 45 degrees Fahrenheit with 90 percent humidity, an ideal setting for the fungus, according to laboratory tests. Additionally, bats may have a suppressed immune system during hibernation. Together, these factors have made the fungus a powerful pathogen against hibernating bats.
To make matters worse, bats reproduce very slowly for their size. Most female bats don’t reproduce until they’re over two years old, and then only have one or two young a year. They’re also fairly long-lived, with some bats living over 37 years old. They’re just not well equipped to bounce back from a rapid, significant decline in numbers.
As of the 2009-2010 winter, WNS has been confirmed or highly suspected in over a dozen US states, mostly in the northeastern part of the country, as well as multiple Canadian provinces. WNS has possibly spread as far west as Oklahoma. Of the 45 bat species in the U.S. and Canada, about half hibernate, six of which have been found to have WNS: big brown bat (Eptesicus fuscus), little brown bat, eastern small-footed bat (Myotis leibii), Indiana bat (M. sodalist), northern long-eared bat (M. septentrionalis), and tri-colored bat (Perimyotis subflavus). The Indiana bat was endangered before WNS arrived, and other endangered bats are thought to be in immediate danger of catching this fatal infection. Because nearly all of the bats in Canada and the northern U.S. hibernate, if WNS continues to infect and kill hibernating bats, it may wipe out virtually all of the bats in these areas.
If WNS keeps spreading, it could reach hibernating bat populations in California. Both the big brown bat and little brown bat, as well as several other hibernating bat species, reside in California. About 18 bat species in total call the Santa Barbara/Ventura/San Luis Obispo area home.
Where Did WNS Come From?
Although it’s clear that WNS is spreading quickly, what’s unclear is the origins of WNS. Since Geomyces destructans was identified on North American bats, it’s also been found on some European bats. However, the European bats do not seem to be disrupted from the fungus and are not dying from it. It’s suspected that WNS was inadvertently transmitted from Europe to North America by people (since bats don’t perform trans-Atlantic flights), possibly carried on shoes or clothes.
If this is the case, this will be one more instance of people spreading a devastating disease to vulnerable organisms; the list already potentially includes the chytrid fungus, which is devastating global amphibian populations, and colony collapse disorder seen in honeybee populations, among more clear-cut cases, such as the American chestnut blight. Clearly many organisms are not prepared for the rapid, global transportation we constantly use today.
Alternatively, some researchers hypothesize that G. destructans was already present in North America, but recently mutated to become a lethal strain. Much remains to be understood about WNS, with little time to waste.
Fighting the Fungus
Researchers are currently testing different antifungal agents to see which work most effectively, and are best tolerated by the bats. Although now most researchers believe that G. destructans is the primary cause of WNS and not just a symptom, if it is only a symptom such antifungal treatments may not be so effective. Even if the agents do work, treating millions of bats with antifungal agents may be very difficult logistically.
Now more than ever, these little winged mammals need our support. To help out local bats, put up a bat home to give them a place to roost. If bats are roosting in an unwanted area, read this article for how to properly and safely remove the bats. Contrary to popular belief, most bats do not actually have rabies, though, just as with any wild animal, bats should still be treated with caution and respect.
With WNS spreading across the country and claiming more bats along the way, it’s important to realize that these animals are not only essential for the ecosystems they belong to, but also for many crops and products we’re dependent upon, and for eliminating pests like mosquitoes. The world would be an unimaginably different place without bats.
For more on bats and white nose syndrome, see Merlin D. Tuttle’s book America’s Neighborhood Bats, David Quammen’s article “Bat Crash” in the December 2010 issue of National Geographic, the Fort Collins Science Center website on “White-Nose Syndrome Threatens the Survival of Hibernating Bats in North America,” the National Wildlife Health Center’s website on “White-Nose Syndrome (WNS),” or Wikipedia’s articles on “White nose syndrome” or on the fungus genus “Geomyces. For information on local bats, see Shannon Switzer’s article in The Santa Barbara Independent titled “Don’t Be Bat-Freaked on Halloween,” the California Department of Fish and Game’s website on “Watchable Wildlife: Bats,” or Falcon Services’ website on common “California bat species.”
Biology Bytes author Teisha Rowland is a science writer, blogger at All Things Stem Cell, and graduate student in molecular, cellular, and developmental biology at UCSB, where she studies stem cells. Send any ideas for future columns to her at firstname.lastname@example.org.