Meniscus-climbing insects

Water-walking insects and spiders rely on surface tension for static weight support(1,2) and use a variety of means to propel themselves along the surface(3-8). To pass from the water surface to land, they must contend with the slippery slopes of the menisci that border the water's edge. The ability to climb menisci is a skill exploited by water-walking insects as they seek land in order to lay eggs or avoid predators(4); moreover, it was a necessary adaptation for their ancestors as they evolved from terrestrials to live exclusively on the water surface(3). Many millimetre-scale water-walking insects are unable to climb menisci using their traditional means of propulsion(2,3,9). Through a combined experimental and theoretical study, here we investigate the meniscus-climbing technique that such insects use. By assuming a fixed body posture, they deform the water surface in order to generate capillary forces(10-13): they thus propel themselves laterally without moving their appendages. We develop a theoretical model for this novel mode of propulsion and use it to rationalize the climbers' characteristic body postures and predict climbing trajectories consistent with those reported here and elsewhere(3).