Water striders adjust leg movement speed to optimize takeoff velocity for their morphology

Eunjin Yang,Jae Hak Son,Piotr G Jablonski,Sang-Im Lee,Ho-Young Kim

doi:10.1038/ncomms13698

Abstract

Water striders are water-walking insects that can jump upwards from the water surface. Quick jumps allow striders to avoid sudden dangers such as predators' attacks, and therefore their jumping is expected to be shaped by natural selection for optimal performance. Related species with different morphological constraints could require different jumping mechanics to successfully avoid predation. Here we show that jumping striders tune their leg rotation speed to reach the maximum jumping speed that water surface allows. We find that the leg stroke speeds of water strider species with different leg morphologies correspond to mathematically calculated morphology-specific optima that maximize vertical takeoff velocity by fully exploiting the capillary force of water. These results improve the understanding of correlated evolution between morphology and leg movements in small jumping insects, and provide a theoretical basis to develop biomimetic technology in semi-aquatic environments.

Highlights

Water striders are water-walking insects that can jump upwards from the water surface
It is widely known that the superhydrophobic hairy legs of water striders enable them to float only on tarsi[1,2], and that the striders transport the momentum via vortices and capillary waves to propel themselves across the water surface[1,3,4,5]
What are the mechanical characteristics of jumping off the water surface? Vertical and near-vertical jumps are performed in natural habitats in a series of frequent jumps that are triggered by attacks of predators, such as fish and backswimmers, from under the water surface[6,7]

Summary

Introduction

Water striders are water-walking insects that can jump upwards from the water surface. We find that the leg stroke speeds of water strider species with different leg morphologies correspond to mathematically calculated morphology-specific optima that maximize vertical takeoff velocity by fully exploiting the capillary force of water These results improve the understanding of correlated evolution between morphology and leg movements in small jumping insects, and provide a theoretical basis to develop biomimetic technology in semi-aquatic environments. A simple mechanical model of interactions between A. paludum legs and the water surface has been created to aid designing the robot It is still uncertain whether the combinations of species-specific morphology and leg movements observed in water striders maximize the insects’ jumping performance as expected from natural selection for predation avoidance. Despite having different morphological constraints on leg dimensions, species tune their leg rotation speed to optimize the takeoff velocity from the water surface

Methods

Results

Conclusion