Unifying framework of vortex interactions from air to water and in between

We explore how organisms from jellyfish to fruit flies harness vortex interactions to boost locomotion. While previous studies focus on bulk fluids, we examine vortex re-energization at fluid interfaces, using water-walking insects as a case study. These insects employ an alternating tripod gait, where hind legs re-energize vortices shed by middle legs, enhancing efficiency. We show how leg positioning either re-energizes or dissipates these vortices. Using dimensionless analysis, we compare this phenomenon across organisms in air, water, and at fluid interfaces, offering a universal framework for understanding energy recapture from vortices.