(54d) Interfacial Locomotion By Living Active Matter and Physical Analogs

In the case of locomotion on land and water, different surfaces create different challenges for organisms to move from one surface to the next due to changes in surface deformation, surface roughness, or the addition of fluid motion. Microvelia water striders are semiaquatic insects that locomote on the surface of low flow streams using an alternating tripod gait. In nature, these insects can be found on land and water, and can move at similar top speeds on both surfaces. In this talk, we will discuss how adult Microvelia use the alternating tripod gait to locomote on both solid and fluid surfaces. Furthermore, we will show how hydrodynamic drag, the vortical wakes produced by the legs and capillary forces play a role during interfacial locomotion. We found that when Microvelia transit across the water surface, they produce a pair of counter-rotating vortices during each leg stroke, similar than those previously described on rowing water striders (Gerridae). Remarkably, when Microvelia step into the wake created by their middle leg, their back leg seems to capture it. We discuss how wake recapture can enhance locomotive propulsion in Microvelia water striders. Through particle image velocimetry, we obtain the fluid momentum used for propulsion as well as dimple depth to determine the forces of water walking. We then build a mechanical model to understand the fluid motion at the water surface at different leg and fluid speeds. Using a 2-D physical model, we will then compare the drag and capillary forces at play for the alternating tripod gait. This research can lead to new bio-inspired designs of micro-bots with the capacity to walk on both water and land effectively.