Perhaps you’ve heard that bat feces (also termed ‘bat guano’) can be harmful to humans. Or, maybe you’ve been told to stay away from caves or abandoned mines because of the dangerous accumulations of guano that can be present there.
Is there any truth based on these warnings? Is bat poop dangerous?
Bat poop is dangerous to humans. Old piles of guano can contain spores that are known to cause a condition known as Histoplasmosis. Histoplasmosis is a potentially fatal disease that can be contracted without the victim even knowing it. While human Histoplasmosis infections originating from bat guano are not thought to be very common, there have been documented cases stretching back for decades.
The Bat Guano Threat Level
A very specific kind of fungus grows on old bat guano and presents a serious health risk to humans who come into contact with it.
This fungus is known as Histoplasma capsulatum, and the spores it releases are known to cause a condition known as Histoplasmosis. Histoplasmosis is a potentially fatal disease that can be contracted without the victim even knowing it. While human Histoplasmosis infections originating from bat guano are not thought to be very common, there have been documented cases stretching back for decades.
According to the CDC, the threat of this disease is very real, and the US Department of Health and Human Services has gone so far as to issue public advisories related to avoiding and containing this disease if it is ever encountered.
Rabies and Bat Guano
Many people mistakenly think that the guano deposited by a rabid bat can itself contain rabies, and therefore, it’s possible to contract the rabies disease by coming into contact with fresh bat guano. According to the EPA, this simply is not true.
Not only do very few bats actively carry the rabies virus (only about one percent do, according to a 2011 study from the University of Calgary), but in order to transmit rabies, the rabid bat would have to transfer its saliva or other bodily fluid to a human via a bite or scratch. So, it’s safe to say that bat guano is most certainly not a potential source of rabies infections.
[Fun Fact: It’s a commonly held belief that bat poop releases high amounts of toxic gases like ammonia gas. This isn’t technically true—rather, it’s the urea excreted by the bat in the form of urine that is source of this dangerous emission. Because bat guano and bat urine are often found together, the assumption is that the bat poop is to blame.]
The Unlikely Role of Bat Poop
It’s hard to believe that the feces of an animal can be anything but disgusting and something to be altogether categorized as worthless. However, what if bat droppings actually played an important role in the environmental ecosystem? The truth might be stranger than fiction.
The reality is that there are entire communities of organisms—both microscopic and otherwise—that rely on the ongoing deposition of bat poop. What’s more, bat guano is often used as a key component in many commercial-grade fertilizers.
Fresh vs. Dry, New vs. Old
When bat guano is initially deposited onto the cave floor, it immediately becomes a source of enrichment for numerous scavengers. Fresh, newly placed bat guano is actually a delectable meal for many worms, insects, and funguses. Some of them include:
- Drosophilidae (flies)
- Isopods (a kind of crustacean)
- Pseudoscorpions (a curious little bug that looks like a scorpion, but isn’t)
- Chilopods (Centipedes)
Fresh/moist bat guano is much more appealing to these organisms than old guano, as there are higher concentrations of digested insect organic matter (insectivorous bats dine on moths, mosquitoes, and other flying insects).
As these bat poop-consuming creatures mature and crawl around the cave floor, they become prey for yet other small animals, a cycle that perpetuates the chain of life both within and without the cave or roost. Over time, however, the bat guano begins to change, drying out and becoming a source of enrichment for entirely different categories of creatures.
Old/dry bat guano begins to oxidize and become much more appealing for things like Troglobites and some beetle species. Mites and cockroaches are also known to feast on the aged remnants of bat droppings.
Because many bats eat fruits and nectars as part of their diet, it’s common for plant material (including plant seeds) to make their way through the bat’s digestive system and onto the cave floor. Many of these processed plant seeds are hardy enough to germinate and grow after being ‘pooped out’, giving newfound plant life to the cave—plant life that can be used as food for crickets and other critters.
The Bat Feces FAQ
Let’s shift our focus now to answering some of the most frequently asked questions related to the subject of bat feces.
Q: Are there uses for bat poop?
A: Bat guano is often harvested and used for numerous industrial purposes. These include agricultural fertilizers, soil conditioners, and plant food additives. Historically, bat guano has been used in the manufacturing of gunpowder, as bat guano contains high amounts of an element known as saltpeter (potassium nitrite).
In fact, during the American Civil War, bat guano was harvested throughout the southeastern part of the country so that it could be used to provide ammunition to the Confederate Forces.
Q: What does bat guano smell like?
A: Most bat droppings are comprised of liquified, digested insect bodies. This organic matter in combination with the bat’s digestive enzymes yields guano that smells similar to bird poo, but nothing like dog or cat poo.
Because bat urine is often mixed in with the guano, the smell of the area can definitely resemble ammonia (due to the ammonia gas referenced above).
Q: What does bat feces look like?
A: Fresh bat droppings can range in appearance from pellet-like to mucus-y and runny. It all depends on what the bat had to eat that day. As the guano oxidizes and hardens over time, the accumulated guano can resemble a kind of spongy, matted texture.
Q: What color is bat poop?
A: Fresh bat poop will often be some shade of black, brown, or yellow. As it ages, guano often turns pitch black or dark brown; however, it can appear bright yellow.
Conclusion: Tread Lightly in Bat Roosts
As we have shown, some concentrations of bat guano can be potentially harmful for human beings. Most of the risk lies in the inhalation of fungal spores released by old, large formulations of the bat poop. For the most part, humans aren’t necessarily threatened by the deposition of bat poop in their homes or buildings—not critically, at least.
Most cases of Histoplasmosis—the most common disease associated with contact with bat guano—are contracted from very old, very large guano deposits that were abruptly disturbed, thus releasing the toxic spores into the air.
Even though the threat of bat poop isn’t necessarily significant, it’s still a good rule-of-thumb to not disturb or disrupt the roosting environment of bats. If necessary, contact your local animal control authority to have the problem resolved by professionals who are trained to deal with bats and their poop.