These Worms Build Towers of Poop That Seem to Defy Gravity. Physicists Now Know How

Not all poop piles look alike. One stubborn worm builds towers.

Most animals let gravity take care of the final stage of digestion. Their feces fall downward, piling into the familiar coiled mounds that inspired the poop emoji. Lugworms do something stranger.

From inside their underground burrows, these marine worms push a thick stream of sand-rich waste upward. The material bends and buckles into remarkably tidy coils, producing miniature towers that can cover intertidal beaches at low tide.

Now, in a study, physicists have discovered the physics behind this unusual pooping process. They found that despite the different result, this anti-gravity poop obeys the same hidden laws that shape ordinary animal droppings.

Charles Darwin was fascinated by worm poop

In his 1881 book The Formation of Vegetable Mould Through the Action of Worms, Charles Darwin carefully documented the castings left behind by worms. Some formed familiar spiral heaps, while others resembled narrow towers built from stacked coils. 

Darwin described what he saw and he realized it was pretty weird. But he didn’t have the tools needed to explain the mechanics behind those shapes.

This mystery resurfaced recently when the study authors noticed coiled piles of sand on a beach near Roscoff, France. The structures were produced by lugworms (Arenicola marina), marine worms that spend their lives inside U-shaped burrows beneath the sand.

Unlike most animals, which release feces downward, lugworms expel a thick stream of soft, sand-rich waste upward through an opening in the seabed. 

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“Most animals defecate downward. As their feces coil, the pile grows higher, and the fall height decreases, making each successive coil smaller. This creates the characteristic pointy mound—precisely the shape of the poo emoji. Lugworms, however, defy gravity by extruding their feces upward,” Daniel Bonn, one of the study authors and a physicist, told Gizmodo.

The result is a striking tower made from nearly identical coils stacked on top of one another.

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This unusual behavior offered researchers a natural experiment. If ordinary feces form under gravity, what happens when the same process occurs in the opposite direction?

Turning worm poop into a physics experiment

The researchers began by photographing 40 fresh castings made by the blow lugworm, Arenicola marina, at Roscoff. The fecal strands measured between about two and six millimeters across. Their coils had radii ranging from roughly eight to 25 millimeters.

The team then collected fresh material and tested how it responded to deformation. The feces behaved as a soft, elastic-dominated material. It could hold its shape and resist bending, but it also had a measurable viscous component. That combination allowed the strands to buckle like flexible ropes rather than simply spreading like a liquid.

Next came the practical part.

The researchers mixed chickpea flour and water to create a material with properties resembling the lugworm castings. When they pushed it upward through small openings, it spontaneously produced the same uniform, tower-like coils.

They repeated the experiment with softened spaghetti and rice noodles. Once again, the materials bent into coils whose sizes could be predicted from their stiffness, density and diameter.

The worms weren’t doing anything special. Basic mechanics did most of the work.

So then why does this poop look different?

For most animals, gravity assists the process. As feces accumulate, the growing pile rises closer to the animal. As the distance between the source and the top of the pile steadily decreases, each successive loop becomes slightly smaller than the previous one. 

This naturally produces the cone-shaped mound familiar from farms, forests, and even smartphone keyboards. However, lugworms operate in a different mechanical regime. Since they extrude material upward from below the surface, the geometry changes. 

The coiling process is no longer controlled by a shrinking fall height. Instead, the coil size remains largely constant, creating a cylindrical tower composed of nearly identical loops. In the lugworms’ case, the size of those loops was determined primarily by the properties of the material itself rather than by the height of the growing structure.

The researchers found that factors such as the material’s elasticity, density, and diameter largely determined the final structure. Surprisingly, the worm’s own muscular control and extrusion rate didn’t seem to matter that much. In other words, the worms are not carefully engineering these elegant towers. The towers emerge naturally from the interaction between soft matter and gravity.

New pasta inspiration?

Lugworms don’t work like toothpaste tubes. They control the position of their bodies and the rate at which they expel waste.

According to the researchers, the study provides a mechanical framework for understanding how coiled structures form when soft materials are extruded. While the work focused on lugworms and a small number of model materials, the underlying principles could apply much more broadly.

Many industrial products, including pasta, noodles, confectionery, polymers, and printable materials, are manufactured through extrusion processes similar to those examined in the study. 

Since many manufactured products are made by squeezing soft materials through nozzles, the findings could help explain why unwanted coils form during production—or how those same coiling patterns might be used to create useful structures.

The researchers now plan to investigate whether similar mechanical rules govern other biological and engineered systems that produce coiled forms. 

As for the lugworm towers, perhaps, they deserve their own emoji—one inspired not by gravity-shaped mounds, but by poop that grows upward.

The study is published in the journal Nature Communications.