Animals
Why is wombat poop cube-shaped?
The short answer
Because their intestines are not uniformly stiff. Research published in Soft Matter found regions of the wombat's gut are twice as thick and four times as stiff as neighbouring regions, so contractions mould corners into the faeces over the final stretch of intestine.
Wombats are the only animal known to produce cubic faeces, and they produce a lot of them — up to around a hundred cubes a day, often deposited on rocks and logs as territorial markers. A cube, usefully, does not roll off.
The mechanism sat unexplained for years. A team including Scott Carver and David Hu dissected wombat intestines and ran tensile tests, and found the answer was not in the exit but in the last stretch of gut. The cross-section has regions of markedly different thickness and stiffness, so as the intestine contracts, the stiff and stretchy parts squeeze at different rates and press corners into the contents.
The cubes form in roughly the final 17 percent of the intestine, over several days, as the gut pulls out water. The researchers noted a practical spin-off: it suggests a way to manufacture soft materials into shapes without moulds or cutting.
Sources
- Intestines of non-uniform stiffness mold the corners of wombat fecesSoft Matter (Royal Society of Chemistry)
- Wombats Poop Cubes, and Scientists Finally Got to the Bottom of ItSmithsonian Magazine