Humans have a lot of taboos around certain things other animals frankly relish, such as eating poop. The technical name for this is coprophagy, and it can refer to eating your own or somebody else’s. Reasons for coprophagy can range from social to nutritional to medicinal. Surprisingly, humans are not excluded from the list of animals that snack on feces from time to time.
For instance, bat guano is some of the most nutritious droppings that litter the natural world. Blind cave-dwelling salamanders in the U.S. Midwest have been found to supplement their meat-forward diet with bat guano, since it’s comparable to what they already eat, nutrient wise.
Rabbits also exhibit a trait called cecotrophy, which means that in order to get all their nutrient needs covered, they literally have to eat their own droppings. The digestive system of a bunny is uniquely weird, so they have to eat their own cecotropes (specialized, nutrient-rich feces) in order to get a second shot at receiving nutrients from all that grass. Eating rabbit-poo is not only a good idea, it’s the only idea if you’re a rabbit. But it turns out that the workers also have a special relationship with the queen’s poop.It seems that the queen’s droppings contain some kind of chemical signal that helps the workers coordinate their activities.When the queen poops, the workers rush over to eat it, and then disperse to carry out the queen’s bidding.It’s possible that the poop contains some kind of pheromone that helps the workers figure out what the queen wants done.It’s also possible that the workers are eating the poop to get some kind of nutrient that helps them coordinate their activities.Whatever the case, it seems that coprophagy is a way for the workers to get the message from the queen.
For this next animal, eating poop seems like a great strategy for getting some sick gains. However, the reality is a bit more complex. Being a tadpole is challenging, as their digestive systems aren’t fully developed and don’t have enough folds to absorb a ton of nutrients from their food. And tadpoles need to eat constantly to consume enough calories to grow into fully-fledged frogs. So what’s a tadpole to do when it needs a ton of nutrition? Well, they eat a decent amount of their neighbor’s droppings. All that waste is just floating around, and it’s a safe bet that the first guy to eat it didn’t get all the nutrients out of it. However, there’s a big problem with this strategy: tadpole guts, as well as their poop, contain a kind of algae that has its own interests in mind. The algae can only reproduce when it passes through a tadpole gut, so it has a good reason to make itself tasty. And just like eating junk food all day can make a kid turn up their nose at a nutritious meal, tadpoles who eat mostly poop end up preferring the pathogen-laced poo to more nutritious food sources, and they languish as a result.
Researchers studying groups of tadpoles of different species living and feeding together found that smaller tadpole species ate more poop than the larger tadpoles. Plus, the larger tadpoles have more of the pathogen in their digestive tracts, and the algae’s presence seems to attract the smaller tadpoles to their poop – even when a higher quality food is available. The larger guys really only dabbled in coprophagy, where the smaller tadpoles really made a habit of it. Thanks to the work of a tiny pathogen, big tadpoles become successful and the smaller ones become malnourished. All because they got tricked into developing a taste for fecal fast food.
You may have noticed that dogs will sometimes eat poop – their own or some other dog’s, they don’t care. And it turns out they might be doing this for the good of the whole pack. It seems that dogs find excrement much more appetizing when it’s fresh. The likeliest explanation for this has to do with parasite prevention. Because dogs seem to strongly prefer poop that is less than two days old, scientists think these dogs – or, rather, their wolf ancestors – have an interest in the common good that we don’t give them enough credit for. See, dogs are really prone to intestinal parasites. And these parasites spread when their eggs travel out of one host and into another, which happens via egg-infested poo. However, the eggs have to mature into larvae in order to take root in a new host, which can take a few days. Since the eggs themselves can’t survive in a new potential host’s digestive system, it’s totally safe to eat something full of eggs, and doing so even reduces the risk of a parasite outbreak since you end up wiping out the parasites before they even hatch. So it is possible that wolves began hoovering up the fresh droppings around their dens in order to prevent outbreaks of parasites within the pack, and also to protect against becoming a host themselves.
Our next animals seem to eat feces in order to serve the community – for this subterranean rodent, coprophagy might be a means of communicating with their boss. Naked mole rats live in colonies and serve a queen, much like bees and ants do. The queen is the only reproductive member in the colony, but the non-breeding individuals have a ton of parenting responsibilities, like snuggling, and grooming and moving the queen’s children around. But it turns out that the workers also have a special relationship with the queen’s poop. It seems that the queen’s droppings contain some kind of chemical signal that helps the workers coordinate their activities. When the queen poops, the workers rush over to eat it, and then disperse to carry out the queen’s bidding. It’s possible that the poop contains some kind of pheromone that helps the workers figure out what the queen wants done. It’s also possible Nothing like a mother’s love, I guess. Now, everybody settle down for a moment. We humans are complex creatures. And although there’s no evidence that the people of any culture or society has ever regularly eaten number twos like these other animals do, we have been known to dabble in coprophagy. For instance, the feces of a bird called a ptarmigan is considered a culinary delicacy in Greenland. And one Indonesian coffee processing method uses partly-digested beans defecated by wild palm civets. Another rare coffee varietal is processed through an elephant’s gut. In humans, eating our own poop or that of others is, in general, considered cause for concern. However, human history has been long, and we’re a curious species, so there are tales of humans using our own excrement in medicine, and other cultural practices. In traditional Chinese medicine, the use of both fresh and dry poop of humans and lots of other animals, such as birds, water buffalo, and even sperm whales, can be traced back to the 4th century. For instance, a recipe dating to between 300-400 AD from China called “yellow soup” involved concocting a broth out of a healthy person’s feces, which was used to treat digestive issues like diarrhea and food poisoning.
It turns out that the basic idea of using a healthy person’s poop to help a sick person is still being researched. It’s called fecal microbiota transplantation, and it’s an avenue for deriving therapies for gut flora problems, using direct samples from healthy microbiomes. And in 2023, this year, the FDA approved Vowst, a poop-derived medication for recurrent infections of the bacterium Clostridioides difficile, or C.diff.. So, eating poop kinda maybe has a place in modern medicine, too.
From parasite control to supercharged nutrition, it’s clear that there are a lot of evolutionary reasons for eating poop, whether your own or others’. But I, for one, am gonna leave that to the salamanders.
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