Water surface swimming dynamics in centipedes

Centipedes use body and limb coordination to navigate diverse terrains. In terrestrial environments, the animals use body travelling wave and limb-stepping waves for locomotion. Less is known about how centipedes navigate fluid environments. Here, we challenged a primarily terrestrial centipede, L. foficatus (N=8, L=2.3±0.3 cm, 14 leg pairs), to locomote in water. On the water surface, centipedes locomoted via body waves propagated in the direction of motion. This was surprising since centipedes that use a direct limb-stepping pattern do not use body undulation in terrestrial environments. In contrast, amphibious centipedes swim using body waves that travel opposite to the direction of motion, folding their limbs towards their body (Yasui et al., Sci. Rep., 2019). When L. foficatus used body undulation on the fluid surface, the centipedes achieved speeds of 0.22±0.03 BL/cyc using body waves with maximum amplitude of 3.9±1.5 cm^-1 and 1.3±0.23 waves along their bodies. Without body undulation, the animal’s displacement was negligible. This suggests that surface swimming in this species is facilitated by 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).