When observing small worms under a microscope, one might observe something very surprising: the worms appear to make a sweeping motion to clean their own environment. Physicists at the University of Amsterdam, Georgia Tech and Sorbonne Université/CNRS have now discovered the reason for this unexpected behavior.

When centimeter-long aquatic worms, such as T. tubifex or Lumbriculus variegatus, are placed in a Petri dish filled with sub-millimeter-sized sand particles, something surprising happens. Over time, the worms begin to spontaneously clean up their surroundings. They sweep particles into compact clusters, gradually reshaping and organizing their environment.

In a study that was published in Physical Review X this week, a team of researchers show that this remarkable sweeping behavior does not require a brain, or any kind of complex interaction between the worms and the particles. Instead, it emerges from the natural undulating motion and flexibility that the worms possess.