Tubular worms often wriggle their flexible bodies, and many individuals entwine with each other to form ball-like clumps.This mass moves around, changing its shape depending on the situation, like a single living thing.Until now, there have been studies that dealt with such movements on flat ground, but the mechanism of movement in the uneven natural world was unclear.

　Therefore, the research group attempted to elucidate the mechanism by which masses of sludge worms move under an uneven ground environment through behavioral observation experiments, mathematical modeling, and simulations.

　First, many steel array cases were made, one group had stakes on the floor, the other group had nothing, and each case was filled with sludge worms.As a result, the mass moved back and forth between the two chambers of the case, moving faster in the group with stakes.Movement within the case was such that the hemispherical mass first became elongated, and when an individual got entangled in a stake, the mass was drawn there.

　As a result, the research group first found that an individual in the mass turned its head to the outside of the mass, and other individuals entwined one after another with that individual, the mass formed a protrusion, and then the protrusion reached the stake. Then, one after another, other individuals were attracted and entangled in the stake, and they thought that the whole mass was attracted.This behavioral observation result could be reproduced by simulation.

　In addition to understanding how groups of animals move around in a complex, bumpy natural world, the results of this research are expected to lead to the realization of new engineering systems in which many "soft" robots cooperate and exhibit their functions in a phantasmagoric manner.

Paper information:[Frontiers in Neurorobotics] Elongating, Entwining, and Dragging: Mechanism for adaptive locomotion of tubificine worm blobs in a confined environment