Bats: Every Gardeners Best Friend, Part 1

Reader Contribution by Erik Thiel
1 / 3
2 / 3
3 / 3


Please. Try not to scream.

And poop.

This is a well-known combination to many organic gardeners. It’s also more commonly known as bat guano.

Bats have been feared as early as Dracula first came out on the big screen in 1931, incorporating a fear into the minds of the audience for blood-sucking creatures of the night. A few decades later, Stephen King paints a picture of bats in his book Cujo, where a bat transmits rabies to a family’s dog which then turns on its own family.

As more information is collected about bats, the better scientists understand the important role they play, both within cave ecosystems, forests, and entire food systems. Whether it is local and organic or global and industrial, bats are good. If a man’s best friend is a dog then a gardener’s best friend must be the bats. Someone needs to rewrite the script.

Organic Fertilizer

Bat guano, coming from the Peruvian word “huano” which means excrement, has been used since 200 B.C. as an organic fertilizer. And it has been exploited and profited from, like many other resources. Bat populations have been decreasing all around the world due to factors such as inappropriate bat guano mining, habitat loss due to development, and the spread of White Nose Syndrome (WNS). As a result, organizations such as the Bat Conservation International (BCI) is working to educate people about what they can do to protect bats and their habitats.

Although bat guano works great as an organic fertilizer, it also serves a larger purpose within cave ecosystems. “It’s the primary energy driver for cave ecosystems,” according to Dave Waldien, director of global programs at BCI. “Inappropriate guano mining is very bad for the cave ecosystem, then the bats themselves.” If the production of guano mining continues while all the bats are there, it can kill them in large numbers, drive the bats further into the cave, or force the bats to abandon the cave, according to Waldien. Guano mining has been done illegally since at least the 1850s, when Americans loaded guano deposits from the caves on Isla de Mona, Puerto Rico, according to the Journal of Cave and Karst Studies. Isla de Mona is an island surrounded by large cave systems. It was first legally mined in 1877 and in less than 100 years, 7 of the 8 cave systems were depleted. The last commercial guano mining on this island finished in 1927.

And this is only one example.

“The challenges are often the communities,” said Waldien. “While some countries have very strong laws as written, they’re often not implemented. To use the Philippines as an example, there are laws against guano mining without permits yet most of the guano mining goes on without permits.” Sometimes laws do not exist. And other times local communities may make the decision to mine guano for immediate financial needs rather than think in terms of long-term sustainability, according to Waldien. “In many of the tropical systems, cave disturbances that come from inappropriate guano mining has potentially driven bats out of these caves so what should of been a renewable resource has become a mine-it-out-and-you’re-done scenario.”

Although guano mining has stopped from most locations in the United States, mining it in a sustainable manner is “something that can be done,” according to Waldien. “And if done right, it doesn’t have to negatively impact bats.” With an increase in public awareness and proper harvesting techniques, bat guano will remain a renewable resource for organic farmers, despite any past guano mining exploits.

“Most of the sites that are mined for guano are sites that have Brazilian free-tail bats ‘cause they form really, really huge summer colonies,” said Katie Gillies, U.S. imperiled species coordinator at BCI. “Consequently, they create a lot of guano.”

Currently, there are between 120 and 150 million Brazilian free-tailed bats estimated globally and the population is stable, according to the Virgin River Habitat Conservation and Recovery Program (VRHCRP). While guano mining is not a threat to this species of bats, it does increase the chances of creating a disturbance to roost sites, which are the bats primary threat next to pesticides.

Roosting refers to where bats live. It could be where they hibernate – if they do – or where females raise their pup. Thousands of bats die each year due to disturbances during hibernation, causing them to wake up and burn their energy reserves, according to the Bureau of Land Management (BLM).

Pesticides then pose the next greatest threat, where the biggest issue “would be in reducing the insect supply for the bats to eat,” said Christina Kocer, northeast WNS coordinator at the U.S. Fish and Wildlife Service.

Bats are also beneficial to food systems in more ways than just their poop. They are an organic alternative to pesticides and insecticides. For example, the bats at Bracken Cave can eat 250 tons of insects each night, according to the BLM. Many of those insects can be crop pests, such as different beetles, leafhoppers, and moths. That means as bat populations decrease, the use of pesticides increase. As do the insects eating crops. But not all bats eat insects. Some of them eat fruit and seeds, cross-pollinating flowers at the same time they eat.

“You can’t have organic farming without bats,” said Gillies. Or farming. “Recent studies have shown that bats provide an average of 23 billion dollars a year in ecosystem services through pest control,” said Gillies. “I mean, that’s more than the farm bill.”While inappropriate bat guano mining and disturbances to roost sites may affect bat populations, neither of these factors have anything to do with the 5.7 million dead bats in North America within the past 8 years. These deaths are attributable to WNS.

WNS is a fungus that affects hibernating bats, much like disturbing them would do. It first appeared in the United States in 2006-07 in a cave in New York and has since been confirmed in 22 states and 5 Canadian provinces, according to“The fungus is found on bats in Europe but it doesn’t cause mass mortalities,” said Gillies. “And looking at the molecular signature of this fungus [scientists] can see it’s been present on the landscape in Europe for many, many thousands of years.”

WNS does not affect humans although humans can spread the fungus, making it important to not visit caves where bats are hibernating or where WNS is present. “Don’t go underground in a site that doesn’t have white nose if you were recently in a site that has white nose,” said Gillies. “And always decontaminate your gear in between sites. That’s the best thing we can do.” Because WNS is new to the United States, the current lack of funding leaves organizations unable to do much to stop the spread. “There’s a lot of information that you have to gather just to have base line data on what to do next,” said Gillies. “We’re finally at the stage where we have enough base line data but the biggest problem is that we don’t have enough research funding to find ways to stop it.”

If bat guano is mined from a site infected with WNS and spread near a site that is not affected, it can potentially spread the spores, although mining bat guano is not a contributing factor to WNS. “Unless the guano is processed to a manner that kills the fungus that causes WNS, it’s not a good idea to take the guano and spread it around,” said Waldien.

Most of the guano comes from the Philippines, Indonesia, Madagascar, and central and South America and it is not affected by WNS, according to Kocer.

Need Help? Call 1-800-234-3368