Do Wombats Poop Squares?

Did you know wombats produce perfectly cube-shaped poop — and scientists spent over 200 years trying to figure out how? In this episode, we dig into the surprisingly brilliant biology behind one of nature's strangest quirks. Hit play and find out why square is the smartest shape in the Australian outback.

Written by Zack Margiotta

Transcript: Do Wombats Poop Squares?

Hey there, Curious Minds. I'm your host, Marissa, and welcome to I Wonder, the show where we explore the questions you've been wondering about. If you've got a question of your own, head to iwonderpodcast.com and you might hear it in a future episode.

Today's question comes from Josh in Germany. He heard from a friend in school that a wombat's poop is really square. Other than wanting to know how his friend knows this and why he's looking up types of animal poop, he wonders if it's really true. Well, Josh, to be fair, it does kind of sound like something someone would make up just to see if you believe them, right? And while we can't answer why your friend knows about wombat poop, we can answer the question: is a wombat's poop really square?

In the animal kingdom, we're used to seeing all sorts of shapes, but they usually involve circles, ovals, or just messy piles. Nature loves curves because they're easy to make.

But the common wombat, a sturdy, furry, short-legged marsupial from Australia, decided to break all the rules of geometry. Yes, Josh, wombat droppings are actually shaped like little six-sided cubes. They look less like something from a forest floor and more like a square piece of fudge that no one wants to eat. Now, imagine being one of the first European explorers to land in Australia in the late 1700s. These scientists and sailors were already confused enough. They were seeing bears that lived in trees like koalas, and giant rats that hopped on two legs like kangaroos. But when they started finding neat little stacks of square bricks on top of rocks, they were truly stumped. Some of the first records from explorers like John Price in 1798 described the wombat as a badger-like creature, but the poop was its own scientific mystery. For a long time, people didn't even believe it was natural. There were even old stories and myths that maybe the wombats were shaping the cubes with their little paws after the fact, or that it was just a strange trick of the dry Australian heat. It took over 200 years for scientists to actually sit down and figure out how a round-looking animal with a round-looking exit hole could produce a perfect cube. It's not like they have a square-shaped cookie cutter inside of them. To understand the why, we first have to talk about the why. Evolution usually doesn't do things just for a laugh. There's almost always a survival reason behind it. To understand the cube, you have to understand the wombat social life. Wombats are very solitary creatures, meaning that they enjoy being alone and don't usually hang out in big groups. They live in burrows underground, and they're very protective of their space. But they can't exactly put a keep out sign or send a text message to their neighbors, so they use their scent to mark their territory. Wombats like to leave these scent markers on high ground. They'll climb onto a flat rock, a fallen log, or even the small mound of dirt at the entrance of their burrow to leave a message. If the poop were around, like a rabbit's or a deer's, it would just roll right off the rock and disappear into the grass. But a cube? A cube stays exactly where you put it. By having flat sides, the wombat's wa acts like a little organic brick that stays stacked on top of a prominent landmark. It's basically a smelly line in the sand that tells other wombats, hey, this is my hill. Go find your own. In fact, modern scientists have discovered that these stacks of cubes called latrines are basically the wombat version of a dating app or a social media profile. Wombats have an incredible sense of smell, and they use a special organ in their nose called the bombaronasal organ to read the chemicals in the poop. By sniffing a stack of cubes, a wombat can tell who was there, how healthy they are, if they're looking for a mate, or if they are a recluse who wants to be left alone.

A few years ago, a team of researchers decided to solve the physical mystery of the cube using physics and biology. They discovered that it all comes down to the wombat's intestines, which are incredibly long and about 10 times the length of the wombat itself. To give you an idea of how long this takes, a human usually digests food in about a day or two. A wombat, however, has a super slow metabolism. It can take anywhere from 8 to 14 days for a meal of tough, wiry Australian grass to make its way through a wombat's system. This slows the process, allows the animal to soak up every single drop of water, every bit of nutrition from its food. By the time the waste reaches the last section of the intestine, it's extremely dry and stiff. This is where the magic or the physics happens. Most animals have intestines that stay the same amount of stretchy all the way around, like a standard garden hose. But in the last section of a wombat's gut, the walls aren't uniform. Two sides of the intestine are soft and flexible, while the other two are much stiffer and thicker. As the intestine rhythmically contracts to push the waist along, which it does about 40,000 times during the journey, the stiff parts resist the pressure while the soft parts stretch out. This uneven squeezing flattens the sides of the waist, molding it into a cuboid shape as it moves through. Imagine you were squeezing a tube of dough, but instead of using your whole hand evenly, you use two flat wooden boards to press down. You'd end up with something much flatter and sharper than a circle. By the time the wombat is ready to deposit its message, the cube has been squeezed so dry and packed so tightly that it keeps its shape even after it leaves the body. In fact, a single wombat can produce about 80 to a hundred of these little cubes in a single night. That's a lot of masonry work for one marsupial. It's a perfect example of how nature finds weird, specialized solutions to a very simple problem. How to make sure your message doesn't roll away in the wind.

Beyond the shape, wombats themselves are fascinating little tanks of the animal world. They're built for digging with powerful claws and a pouch that faces backward. If you're a marsupial like a kangaroo, your pouch faces forward, which is great for carrying a joey while you hop. But if you're a wombat and you spend your day digging tunnels, a forward-facing pouch would just fill up with dirt and burrow your baby. Evolution flipped the pouch around so that the joey stays clean and safe while mom is excavating her underground mansion. They also have a reinforced butt made of thick skin, cartilage, bone. If a predator like a dingo tries to follow a wombat into its burrow, the wombat just turns its back and blocks the entrance with its literal shield of a butt. They can even use that tough rear end to crush a predator's head against the roof of the tunnel. So, between the square poop, the armored backside, the wombat might just be the most engineered animal in the outback. It's easy to look at something like square poop and think, it's just a funny quirk of nature. But when we look closer, we see an intersection of biology and physics. It's about communication, territory, and surviving in the harsh environment where you have to make the most of every blade of grass you eat. The wombat didn't set out to be a geometric rebel, it just found the most efficient way to stay put and be heard. So, next time you're playing with building blocks or looking at a square box, just remember that out in the Australian bush, there's a furry little architect making its own blocks every single night. It's a reminder that no matter how much we think we know about the world, there is always something strange, gross, and absolutely brilliant waiting to be discovered.

Thanks again to Josh for such a great question. And remember, if you have a question you're curious about, submit it on our website iWonderPodcast.com, and we might just feature it in our next episode of I Wonder. Until next time, stay curious and keep wondering.