The Emptying of America’s Bat Caves


For several years we’ve been hearing about the collapse of honey bee colonies in the environment. Less publicized but equally as dangerous is a new pathogen that is killing bats by the thousands — and if steps aren’t taken soon, SoCal bats will be next on the Soon-to-Be-Infected List.

We’re talking specifically about Geomyces destructans – a noxious fungus that attacks bats while they hibernate – which is quickly moving west after first being observed in a New York cave in February 2006. The fungus erodes the living skin of bats as they sleep, causing lesions and coating their muzzle with white fungal spores that gives the disease its name – White-Nose Syndrome (WNS).

Bat populations in the Northeast have already been decimated in what the U.S. Fish and Wildlife Service calls “the worst wildlife crisis in memory.” Now the fungus has been found in caves across the Mississippi and unless important measures are taken, we may soon be seeing this powdery killer in the Golden State.

A little bat background

Navigating by echolocation, these flying mammals are fascinating miracles of evolution. Two kinds of bats live in the U.S. and Canada; the vast majority are insectivores – bug eaters – while the others favor nectar, pollen or fruit. (The infamous vampire bat is only found in Mexico and points south.) 

No matter the type, bats have never been the animal kingdom’s cuddle bunnies, but they perform a crucial function. It’s estimated that insectivorous bats do between $3.7 and $53 billion worth of work every year for the nation’s farmers by keeping pests under control. Much of this money that farmers would have to spend on pesticide to do the work bats already do for free, and without damage to the environment. Let’s not forget that nectar eaters are important pollinators in Southwestern deserts.

The mystery of WNS

Biologists estimate that more than 1 million bats have died in the Northeast alone, representing up to 1,320 metric tons of insects still on the prowl, and a lot of extra mosquito bites. While the disease mostly moves from bat to bat, it’s believed the fungus – which had never been seen in the Americas prior to 2006 – piggybacked its way here on the clothing or gear of a caver who had recently been in Europe. Bats are not known to cross the Atlantic – too big of a leap.

European scientists reported seeing similar fungal growth on their bats dating back to the 1980s. But there is one big difference: European bats are able to cope with the disease – they don’t die, at least not in the numbers seen in the U.S.

So far partial comparisons of the fungal genomes of the American and European versions have indicated they may be identical. Further genetic testing is underway to determine if, as many believe, they are the same fungus.

These preliminary results, coupled with the the massive bat die-off in the Northeast, have caused many observers to fear that American bats are facing a biological invasion they are not equipped to fight. Just like small pox and other Old World diseases of the past that wracked havoc on native populations, the damage from WNS could be lasting and severe.

What can be done?

First and foremost, experts say closing caves from humans will help stop the spread of the fungus.

The U.S. Fish and Wildlife Service maintains a page advising of state and federal cave closures. For caves still open, Fish and Wildlife has published rules on how to decontaminate clothes and other gear before entering and after leaving. But the best thing to do is stay out of caves and mines altogether while the epidemic is in full flight. As writer Mollie Matteson explains in the June 2011 Desert Report:

There is some evidence that bat populations do not mix a great deal between eastern and western regions. This may provide some protection to western bats, which reach their greatest species richness in the desert regions of the Southwest and Southern California. However, scientists still fear that humans could cause a leapfrogging of the disease into the West, through the transport of the white-nose fungus on contaminated caving gear, clothing or other material.

For most people, avoiding dark places full of possibly diseased bats isn’t much of a sacrifice. But even dedicated cavers, faced with the prospect of barren, lifeless caves in the near future, should find it easy to refrain. Bats, says Matteson, are the lynchpins of many cave ecosystems:

 Bats bring nourishment, through their guano and bodies, into sites where full-time cave denizens, such as springtails, millipedes, spiders and many other creatures directly or indirectly depend on the influx of organic matter bats provide. Ultimately, the bat die-off precipitated by White-Nose Syndrome could lead to the unraveling of numerous bat-dependent relationships in both the natural world and in human systems such as agriculture and forestry.

On May 17, 2011 the U.S. Fish and Wildlife Service unveiled a National Plan to combat WNS, but some wildlife advocates, including the Center for Biological Diversity, say the Federal Government has been slow to react to the crisis by failing to close caves in advance of the disease.

Although caves and mines have been closed in the Eastern United States where WNS  has already taken hold, caves and mines across millions of acres of federal lands in the West…remain open.

Yet is it precisely those regions…where the disease has not yet appeared that cave closures are most needed. Because of the transport of the disease by people, it is vital that caves in currently WSN-free areas be protected by a strict cave closure policy.

Light at the end of the tunnel?
As daunting as this all sound, there are rays of hope. First off, the fungus is not all-powerful. It appears to require two things to do its damage: cool, humid caves and hibernating bats. WNS has thrived in the chilly, damp Northeast, but it’s unclear if it will be similarly destructive in hot, dry climates. And even if it does get cold enough in remote desert caves, it’s likely only bats that hibernate will develop WNS from the fungus. A U.S. Geological Survey paper found that:

during hibernation, immune function and metabolism are dramatically down regulated, and possibly even inhibited, with an accompanying drop in body temperature…making the hibernating bat a most accommodating host that provides nutrients, ideal environmental conditions and little or no resistance to an expanding infection.

Hibernators make up 25 of the 45 species of bats found in the U.S. and Canada. Especially hard hit with WNS has been the little brown bat – a good worker that’s capable of eating 600 bugs an hour – that faces extirpation in the Northeast due to WNS.

Remarkably, some hibernating species have demonstrated a resistance to the disease – gray, cave and Southeastern bats have all tested positive for the fungus but not displayed the symptoms of WNS.

Any recovery will be difficult. Bats reproduce slowly, typically one offspring per year. They depend on high rates of adult survival to keep colonies going.

For California, home to a rich mixture of 24 species of hibernating and non-hibernating bats, it appears some species may be safe, but others, including our own little brown bats, could be highly vulnerable.

It seems to us our best defense is to keep up the defense. Stay out of caves. Leave the bats alone.  For populations to recover, enough bats must survive WNS to start new generations that can cope with the fungus, as European bats have learned to do. Let’s hope we’re smart enough for the challenge.

Click here for the Center for Biological Diversity’s animated map of the spread of the fungus that causes White-Nose Syndrome and here for an excellent interview of bat expert Paul Cryan of the U.S. Geological Survey.

You can also join the Center’s For Biological Diversity’s campaign to raise awareness and encourage the closure of more caves to reduce the spread of the disease.

– James Myers