Allometry of antipredatory jumping on water by water striders

Current theory for surface tension-dominant jumps on water, created for small and medium size water strider species and used in bio-inspired engineering, predicts that jumping individuals are able to match their downward leg movement speed to their size and morphology such that they maximize the takeoff speed and minimize the takeoff delay without breaking the water surface. Here, we use empirical observations and theoretical modeling to show that large species (heavier than ~80 mg) do not conform to this prediction but switch to using surface-breaking rather than surface tension-dominant jumps in order to achieve jumping performance that appears sufficient for evading attacks from underwater predators. This suggests that natural selection for avoiding predators may break the theoretical scaling relationship between prey size and its jumping performance within one physical mechanism leading to an evolutionary shift to another mechanism of jumping on water.