Physics of sliding on water predicts morphological and behavioral allometry in water striders

Water striders, Gerridae, serve as model organisms to understand locomotion on the water surface, but only a narrow range of body sizes have been studied. The hydrodynamics of their thrust is well understood, but the subsequent sliding dynamics has been less explored. Here we create a theoretical model of sliding and use it to predict the effect of body mass, striding gait (symmetrical or asymmetrical) and wetted leg lengths on the striders’ ability to float and the resistance during sliding. We show that the water strider species with large body size have two alternative solutions: development of long forelegs that support frontal body during symmetrical striding or asymmetrical striding when one midleg extends forward to support the frontal body. The model lays the theoretical grounds for the future comparative analyses of adaptive allometry in locomotion of Gerridae, and for bioinspired water walking devices of a wide size range.