Humans have a lot of taboos around certain things other animals frankly relish.

Eating poop is one of those things. The technical name for poop-eating is coprophagy.

And it can refer to eating your own or somebody else's, and it is not all that uncommon in the animal kingdom. Reasons for coprophagy can range from social to nutritional to medicinal. And sometimes it's just plain complicated.

And I know you might be thinking about not watching this video now, but now is not the time to feel smug about your human exceptionalism. Because humans are not excluded from the list of animals that snack on feces from time to time. So here are just a few of the most foul-mouthed members of the animal kingdom. [♪ INTRO] Now to start, we know that poop is just the waste products of an organism’s food.

But not all organisms digest in a particularly efficient way, which means that some nutrients get pooped out that are still perfectly useful, aside from being a little grossed up. Of all the droppings that litter the natural world, bat guano is some of the most nutritious. The bat lifestyle is pretty energy-expensive and their digestive systems are short, so although they eat extremely nutritious foods, they poop out as much as 31% of the nutrients they ingest.

As a result, bat guano has almost twice the protein of a McDonald's hamburger. Human scientists have even commented that if we could figure out how to sterilize bat guano, it would make a great human food. Although, I’m happy to have someone else get in front of me on that particular line… So, it makes sense that another animal might have gotten the bright idea to recycle the rest of that nutrition.

Blind cave-dwelling salamanders in the U. S. midwest live amongst all this guano, and they take full advantage of all those life-giving nutrients the bats are basically leaving on the table. Salamanders in general are usually uncompromising carnivores, but these cave-dwellers have been found to supplement their meat-forward diet with bat guano, since it's pretty comparable to what they already eat, nutrient wise.

For instance, bat guano contains a heck of a lot of protein, which they need to build muscle. And not only is the poop itself crazy nutritious, but the microbial biofilm that grows on bat poo is kind of like adding a nutritional booster to the smoothie. It’s the icing on the cake.

For a lot of the animals that eat feces, it’s more like a side dish. They still eat other things too, and they could get by just fine without turning to that particular course. But for rabbits, feces is so vital to their diet that they can die of malnutrition without their own poop.

Rabbits exhibit a trait called cecotrophy. And that means that in order to get all their nutrient needs covered, they literally have to eat their own droppings. See, the digestive system of a bunny is uniquely weird.

They evolved to eat rough plant material, but their bodies don't make enzymes to break it down. So they're faced with the same evolutionary hurdle as cows. How does one wring every last bit of nutrients from a diet that’s mostly lawn clippings?

The solution they came up with was to develop a special structure called a cecum, a pouch between their small and large intestines, where their food can sit and ferment, allowing bacteria and fungi to do the hard work of breaking into the nutrients locked inside. And at the other end of the system, after it passes through, they produce two kinds of waste matter: regular old fecal pellets, which consist mostly of undigested fiber, get left alone. It’s only the specialized, nutrient-rich feces called cecotropes that they eat, often right out of their own buttholes.

Gross? Sure, but it's the way they've found to get a second shot at receiving nutrients from all that grass. And they really need it, since they will die of malnutrition if they don't regularly eat their cecotropes.

So eating rabbit-poo is not only a good idea, it’s the only idea if you’re a rabbit. For this next animal, eating poop seems like a great strategy for getting some sick gains. But the reality is a bit more complex.

Being a tadpole is challenging. 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. And while feces isn’t really a health food for tadpoles, it turns out that for some animals, it’s a great idea if you want to keep the whole group in tip-top shape.

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. If they learn to eat the feces while it was hot off the presses, everybody wins. Except for the parasites.

They can go take a dump. Thankfully for Fido, we now have plenty of pharmaceutical interventions for parasite infections, so house-dogs can pass on that particular dish. 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. And because all the colony's other females aren’t breeding, they don't make any of the hormones that are usually associated with motherhood.

So how do they know what to do? Some research suggests that the queen makes the caring hormones for the babysitters. And that they ingest those baby-caring hormones when they eat her poop.

During and after pregnancy, the queen experiences fluctuations of the hormone estradiol, a hormone that's been found to stimulate maternal behavior in rodents. These can range from practices like grooming and retrieving pups to nesting and defense behaviors. The pups do a lot of vocalizing, and experiments show that the babysitters pay a whole lot more attention to their whimpers after they have eaten the queen's estradiol-soaked turds.

Although naked mole rats are definitely coprophagous, scientists don't totally agree about whether that’s the reason naked mole rats suddenly experience a hormonal shift, because it's hard to catch them eating the queen's feces, specifically. But there is some evidence that her poop is involved. 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. Thanks to all of you for getting through all of that. And thanks in particular to our supporters on Patreon.

Our community of patrons make it possible for us to dig deep into some subjects that advertisers may turn their noses at… but we think are worth exploring, even if they are, you know, bat guano covered in a layer of bacterial icing. Not only that, but our patrons get access to a whole bunch of perks, from blooper reels – this episode had plenty of those – an exclusive podcast, and a private Discord server just for our patrons. If you want to learn more, head on over to Patreon.com/scishow.

Thanks for watching and learning with us! [♪ OUTRO]