1. Department of Mathematics, MIT, Cambridge, Massachusetts 02139, USA

Correspondence to: John W. M. Bush¹ Correspondence and requests for materials should be addressed to J.W.M.B. (Email: bush@math.mit.edu).

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.

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