Water surface swimming dynamics via continuous contact in lightweight centipedes

Locomotion at the water surface is ubiquitous across scales (Bush and Hu, Annu. Rev. Fluid Mech., 2006). Previous studies on locomotors at the interface focused on propulsion emerging from limb-surface interactions. Less is known about how animals locomote via body-surface interactions, particularly with many limbs. Here, we discovered that a centipede, L. forficatus (N=8, L=2.3±0.3 cm, 14 leg-pairs), uses body-surface interactions to locomote at the water surface via direct waves of body curvature. Schlieren wave reconstruction of the water surface shows L. forficatus continuously emits water waves, relies on constant self-deformation for locomotion, and inertial forces are dominated by surface wave drag. Inspired by hispid flagella in microorganisms in viscous fluid, we posit forward motion using direct waves is achieved by modulation of the centipede’s ratio of local normal to tangential forces (drag anisotropy, less than one) due to its morphology. Thus, we modeled this centipede’s locomotion using surface wave RFT with experimentally resolved drag force relations of a centipede segment (slender body, extended limbs). Surface wave RFT predictions capture the animal’s swimming performance and shows the locomotor strategy facilitates high performance without introducing undesirable limb-body collisions, and potentially simplifying the animal’s neuromechanical control.