Scientists solve 100-year-old mystery of lugworm’s strange poop towers that seem to defy gravity — the answer lies in ropes, cables and physics

For centuries, the strange spiral towers left behind by lugworms on Europe’s sandy tidal flats have puzzled observers. Now, physicists say they have finally worked out how the marine worms build these unusual structures — and the answer has little to do with intelligence or deliberate construction.

The secret lies in physics.

Researchers studying the lugworm Arenicola marina found that its soft faecal castings behave much like a flexible rope. As the worm continuously pushes the material out of its burrow, the mucus-coated strand bends and coils under the influence of gravity, elasticity and the speed of extrusion. The result is a narrow, spiral-shaped tower that can rise several centimetres above the surrounding sand.


The findings were published in Nature Communications in a study titled “Coiling of lugworm feces reveals universal mechanics for the shape of poo”.

How does the lugworm build its strange towers?

The lugworm spends most of its life beneath sandy beaches, where it burrows through sediment while feeding on organic matter. It swallows sand along the way and later expels the undigested material at the surface as soft, cylindrical faecal castings.

But instead of scattering the waste across the beach, the worm continuously extrudes it from a fixed point above its burrow.

As the fresh material emerges, it does not simply fall into a heap. The strand bends, curls and coils onto itself. Layer after layer gradually produces the distinctive spiral towers seen on tidal flats.

Researchers combined observations from French tidal flats with laboratory experiments, measurements of the material’s physical properties and mathematical modelling to understand why the structures remain stable.

The physics behind the worm’s poop

The scientists found that the mucus-covered casting acts similarly to a flexible rope slowly falling onto a surface.

Gravity pulls the freshly extruded material downward, while its elasticity allows it to bend and form loops. The speed at which the worm pushes out the material also influences the resulting pattern.

Because the casting is soft enough to bend but sufficiently stiff to support additional layers, each new coil can settle onto the previous one without causing the entire structure to collapse.

The researchers found that the radius of the coils could be described using equations developed to explain the coiling of elastic ropes.

That means the elaborate-looking towers are not the result of complex behaviour by the worm. Their shape emerges naturally from the physical properties of the material and the way it is extruded.

Charles Darwin was fascinated by worm castings

The unusual structures have attracted scientific attention for more than a century. Charles Darwin himself described worm castings and was fascinated by the structures produced by earthworms.

What remained unclear was why the fragile-looking formations could maintain their shape rather than spreading into shapeless piles.

The new research provides an explanation: the spiral is essentially a physical consequence of how a soft, elastic strand behaves when it is continuously deposited from above.

Could worm poop help engineers?

Although the research began with an unusual question about marine worms, its implications extend beyond biology.

The same principles are relevant to materials that are extruded and deposited in manufacturing. Understanding how soft materials bend, coil and remain stable could help researchers working with polymers, food products, industrial fibres and other extruded materials.

The study also offers a broader lesson about nature. Complex-looking structures do not always require complex behaviour. Sometimes, simple biological processes combined with basic laws of physics can produce surprisingly intricate results.

Every time tides wash away a lugworm’s tower, the process begins again. The worm returns to its burrow, processes more sediment and starts extruding another soft strand — allowing gravity, elasticity and motion to do the architectural work.