Meniscus-climbing insects

Abstract

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^3,4,5,6,7,8. 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 predators⁴; moreover, it was a necessary adaptation for their ancestors as they evolved from terrestrials to live exclusively on the water surface³. 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^10,11,12,13: 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 elsewhere³.