Exceptional amphibious locomotive capabilities of tiny water walkers*

Unlike larger animals, small insects such as Microvelia exhibit exceptional water walking abilities by leveraging surface tension. Strikingly, not only are Microvelia able to walk on water, but they can also walk on land with comparable speeds. Microvelia achieve this feat through the alternating tripod gait, commonly found in terrestrial insects such as ants. To understand their outstanding amphibious locomoting capabilities, we use high-speed imaging to study the biomechanics of these organisms on both land and water. Using DeepLabCut, we track the leg tarsi and joints to calculate their speed, acceleration, stroke frequency, and stroke amplitude on water and different terrains. Further, we used Particle Image Velocimetry (PIV) to visualize and quantify the dynamics of vortices generated from the power strokes of the middle and hind legs. Interestingly, the spatio-temporal dynamics of their legs result in the phenomenon of “vortex recapture” wherein the hind legs capture the vortices generated by the middle legs, thereby re-energizing them. We investigate the role of vortex recapture on the interfacial locomotion of these organisms by correlating the vortex circulation and their kinematics. This work not only advances the current knowledge of interfacial locomotion of small water walkers, but also has a potential in influencing designs of amphibious robots.