Surface swimming dynamics of centipedes

Terrestrial multi-legged animals such as centipedes navigate diverse environments by generating limb-stepping waves and traveling body waves. However, less is known about how these animals navigate fluid environments. Here, we challenged Lithobius foficatus (N=8, 14 leg pairs) to locomote on water. In addition, we used a Schlieren method to reconstruct and observe waves generated by the centipedes. When kept afloat by surface tension, the animals swam successfully; any instances of submersion resulted in the animal sinking without generating motion. Surprisingly, unlike on solid terrain, centipedes propelled via waves of horizontal plane body curvature propagating in the direction of motion. Using body undulation, the centipedes achieved speeds of 0.22±0.03 body lengths per gait cycle using body waves with an amplitude of 3.9±1.5 cm^-1 and 1.3±0.23 waves along their bodies. When the centipedes moved their limbs but did not use body undulation, they achieved negligible displacement. This suggests that surface swimming in this species is facilitated by the propagation of body waves, not limb flexion. We posit these direct body waves enable the animal to swim by varying the animal’s drag anisotropy (ratio of local perpendicular to parallel forces).