Self-removal of condensed water on the legs of water striders

TLDR

Condensing water droplets can be self‑removed from water strider legs, a process that has important implications for their locomotion. Droplets first migrate into the leg’s textured hairs and grow, then are suddenly expelled as the hairs elastically deform, ultimately removing the condensed water from the leg. Self‑removal of condensed water protects the strider from losing hydrophobicity and illustrates how hydrophobicity, geometry, and flexibility together maintain water repellency at multiple scales.

Abstract

Significance Condensing water droplets can be self-removed from the legs of water striders in a three-step mechanism. First, droplets migrate inside the texture and grow. Then, drops are suddenly expelled out of the hairs, owing to the elastic deformation of the network of setae by growing drops. Ultimately, condensed drops are expelled from the leg. Self-removal of condensing water prevents a major source of risk for the creature, whose hydrophobicity would reverse if setae were impregnated by water. The design of the legs therefore provides a remarkable example where the conjunction of hydrophobicity, geometry, and flexibility yields water repellency both at large and very small scales.