If you stumbled across a small, neat pile of cubes on a rock somewhere in the Australian bush, you'd be forgiven for thinking someone had left them there deliberately. They look almost manufactured: flat sides, sharp corners, roughly the size of a die. But they weren't carved, molded, or cut by anyone. They were produced, overnight, by a wombat.
Wombats hold a genuinely unique distinction in the animal kingdom: they are the only known animal on Earth that produces cube-shaped feces. Not rabbits, not deer, not any of the countless other species that produce distinctively-shaped droppings. Just wombats. And for decades, this strange biological fact sat almost entirely unexplained, a genuine scientific mystery hiding in plain sight across the Australian countryside.
A Distinction Nobody Could Explain
The bare-nosed wombat (Vombatus ursinus) is a stocky, burrowing marsupial native to Australia, most often described as a cross between a small bear, a pig, and a gopher. Wombats are solitary, nocturnal, and famously hard to spot, spending most of their time underground in extensive burrow systems. What they leave behind aboveground, however, is much harder to miss.
The earliest formal scientific record of this phenomenon dates back to 1960, when biologist Eric Guiler noted that wombat droppings had a "characteristic rectangular shape." For decades after that initial observation, the phenomenon remained mostly a curiosity rather than a subject of serious research. Actual scientific investigation into exactly how and why wombats produce cube-shaped scat remained scarce, leaving the scientific community largely in the dark on a question that seems almost too strange to be real.
That changed thanks to an unlikely research collaboration between mechanical engineers at Georgia Institute of Technology in the United States and a wildlife ecologist at the University of Tasmania in Australia — two groups that, on paper, have very little reason to ever cross paths, brought together by one deeply unusual biological mystery.
A Discovery That Started With a Question From an 8-Year-Old
The origin story behind this research is almost as charming as the discovery itself. Georgia Tech mechanical engineering professor David Hu and then-PhD student Patricia Yang had previously published research on the physics of animal urination, finding that most mammals empty their bladders in roughly the same amount of time regardless of body size. While presenting this research at a conference, a scientist in the audience mentioned that his eight-year-old children were fascinated by cube-shaped wombat feces, and asked whether Hu and Yang's mathematical models could explain it.
As Hu later recounted, neither of them had ever heard of such a thing before. Curious, they searched for photos of wombat scat on their phones and were, in their own words, amazed by what they found.
That curiosity led them to Scott Carver, a wildlife ecologist at the University of Tasmania and one of the world's few genuine experts on wombats. Carver studies wombats primarily for conservation purposes, particularly researching the animals' susceptibility to a form of mange that can be fatal to entire populations. As part of that work, Carver periodically receives wombat cadavers from wildlife sanctuaries when animals have been humanely euthanized due to illness.
Ruling Out the Obvious (and Slightly Absurd) Explanation First
Before any real answer could be found, researchers first had to rule out the most obvious, if faintly ridiculous, hypothesis: that wombats simply have a square-shaped anus, physically stamping the feces into a cube shape as it exits the body.
It was Carver's own dissections that definitively debunked this idea. While examining a wombat cadaver, he made a genuinely surprising discovery: the feces was already shaped into distinct cubes while still inside the intestine, well before it reached the end of the digestive tract. Later CT scans of wombat anuses confirmed they were entirely round, not square. Whatever was creating the cube shape, it wasn't happening at the exit point at all, it was happening somewhere further up, inside the gut itself.
This finding reframed the entire investigation. If the cubes were forming internally, the explanation had to lie in the structure of the intestine itself, not in any specialized shape of the sphincter.
Two Kinds of Tissue, Working Against Each Other
With cadaver material supplied by Carver, Hu's team at Georgia Tech began a genuinely inventive phase of research. To understand how the intestine might be shaping the feces, researchers experimented by inflating long balloons inside preserved wombat intestines, carefully measuring how different sections expanded and where the tissue resisted stretching. They also built physical models out of cloth, sewing in deliberately stiffened sections to mimic what they were finding in the real tissue, essentially trying to recreate the cube-forming process by hand before confirming it mathematically.
What they discovered was that the wombat intestine is not uniformly flexible along its length or around its circumference. Looking at any single cross-section of the gut, researchers found the tissue has two distinctly stiffer regions positioned opposite each other, and two distinctly more elastic, stretchier regions positioned opposite each other in between them.
As digested material — essentially a soft, semi-liquid slurry at this stage — moves through this section of the intestine, the stiff regions resist stretching and expanding, while the stretchier regions between them give way more easily. Over the course of the intestine's final stretch, this repeated, uneven resistance gradually presses the material into shape: four relatively flat sides where the stiff sections held firm, and four defined corners where the stretchier sections allowed just enough give to form an edge rather than a smooth curve.
David Hu described the process using a memorable comparison: the stiffer sections behave "like a stiff rubber band," contracting faster than the surrounding softer tissue. It isn't a single dramatic squeeze that produces the cube. It's a slow, repeated, almost rhythmic process. According to Hu, the material experiences roughly 40,000 individual contractions as it travels the length of the intestine, with each one very subtle on its own, but the cube's corners becoming more and more defined as that number accumulates.
Why Wombat Poop Is So Dry — And Why That Matters
There's a second ingredient that turns out to be just as important as the intestine's shape: how dry the material actually is by the time it's shaped.
Wombats have remarkably long intestines for their body size, roughly ten meters in total, an enormous length packed into a relatively compact animal. That extended length gives their digestive system far more time and surface area to extract water from food than most other mammals. Wombat feces ends up containing only around 60 to 65 percent water, compared to roughly 75 to 80 percent in human feces, and even higher water content in many other herbivores.
This dryness matters enormously for the cube shape to actually hold. A more liquid, water-heavy material would simply slump back into a rounder shape after being molded, the same way wet sand won't hold a sharp edge the way dry, compacted sand can. Because wombat waste is unusually dry and dense by the time it reaches the shaping section of the gut, it's firm enough to genuinely hold the flat sides and sharp corners the intestine presses into it, rather than losing that shape immediately afterward.
Researchers have even noted that this relationship works as a rough indicator of a wombat's hydration and digestive health: in captive wombats with easier access to water, droppings tend to be noticeably less cube-like and less well-defined than those of wild wombats extracting every possible drop of moisture from a naturally dry diet.
Why Bother Making Cubes At All?
Understanding how the cube forms only answers half the mystery. The more interesting question, evolutionarily speaking, is why a wombat would benefit from producing cube-shaped droppings in the first place.
The leading theory ties directly back to wombat behavior. Wombats are solitary, deeply territorial animals that rely heavily on scent to communicate with each other, marking their home ranges and signaling their presence to potential rivals or mates. Rather than depositing droppings randomly, wombats will often carry their feces to prominent, elevated locations, placing them deliberately on top of rocks, logs, or small mounds where they'll be easily noticed by other wombats.
A round, cylindrical dropping placed on top of a rock or log would be far more likely to simply roll off, undermining its usefulness as a stable, visible marker. A cube-shaped dropping, by contrast, sits securely in place. Researchers believe this is the underlying evolutionary reason behind the whole unusual system: cube-shaped feces stay exactly where a wombat puts them, functioning as a durable, unmistakable territorial signpost.
A Genuinely Useful Piece of Weird Science
This research didn't just satisfy idle curiosity, it was recognized as genuinely valuable scientific work. In 2019, the research team was awarded an Ig Nobel Prize, an annual award presented at Harvard University specifically honoring real, peer-reviewed research that, in the words of the prize itself, first makes people laugh, and then makes them think.
Far from being dismissed as trivial, the researchers involved have pointed out that understanding how tissue stiffness shapes material passing through it could have applications well beyond wombats. Patricia Yang has noted that similar changes in tissue stiffness occur in human colons affected by colon cancer, meaning this seemingly silly research into wombat digestion could eventually contribute to a better understanding of how certain diseases physically alter tissue behavior in the human body.
The Takeaway
Wombats remain the only known animal on Earth capable of producing genuinely cube-shaped feces, a distinction that sat almost entirely unexplained for over half a century until a chance conversation, a curious eight-year-old, and an unusual research partnership finally cracked the mystery. The answer turned out to involve an unusually long, unusually dry digestive system, and a section of intestine that behaves less like a uniform tube and more like a shape-press, alternating between stiff and stretchy tissue to squeeze a round, unremarkable lump of waste into a small, geometrically precise cube, entirely by accident of evolution, and entirely for the very practical purpose of making sure it stays exactly where it's put.
Sources
- Wombats have buns of steel—and they poop in cubes. Here's why. — National Geographic
- How Do Wombats Poop Cubes? Scientists Get to the Bottom of the Mystery — Science, AAAS
- Wombats Poop Cubes, and Scientists Finally Got to the Bottom of It — Smithsonian Magazine
- Did Scientists Discover Why Wombat Poop Is Square? — Snopes
- Studying Wombats' Cubic Poop — Georgia Tech School of Biological Sciences
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