Vortex interactions in Water-walking insects

Microvelia are water walking insects of the order Gerromorpha, which locomote on both water and land. Unlike Gerridae’s rowing gait on water, these insects use an alternating tripod gait on both water and land. Microvelia shed pairs of vortices during the power strokes of their middle legs and hind legs. In the case of microvelia, hind legs stir the vortices shed from the middle legs, enhancing their circulation. However, such energy recapture phenomenon is absent in water locomotion of other water walking insects. Here, we unveil the role of vortex interactions in Microvelia and other insects of the same order. Our observations are based on the data collected via high-speed imaging and particle imaging velocimetry (PIV) techniques. Furthermore, we also built a physical model to study vortex-structure interactions in Microvelia, where we studied the effect of the stroke frequency, the stroke duration, and the time difference between the middle and hind legs’ strokes on the vortex circulation. Our work on understanding the vortex interactions of water walking insects can be used as a guide to design the efficient microscale water walking robots.