AsianScientist (Dec. 21, 2016) – Water striders are able to calibrate their speed so as to jump as fast as possible without breaking the surface tension. These findings, by researchers in South Korea and Poland, have been published in Nature Communications.
Using slow motion video recordings of jumping insects, a team of researchers led by Professor Kim Ho-Young from Seoul National University made detailed descriptions of leg movements of nearly vertical jumps of water striders. Based on these data, they built a mathematical model to explain jumping mechanics, predicted the jump-speed maximizing behavior of several water strider species with a range of body sizes and leg morphologies, and verified the predictions with the actual data.
The study reveals that jumping water striders behaved as if they ‘knew’ when the water surface may be broken. Normally, the midlegs and hindlegs of the water striders provide the main support without breaking the surface layer of water. Small dimples are visible under each leg because the water surface is pushed against the body weight.
When water striders jump upwards, they push downward on the water surface and the dimples quickly become deeper. As long as the dimples are not broken, the legs are supported on the water surface and push the body upwards making the quick jump possible. But, if the legs move too fast and too deep, then the dimple is broken and therefore the support on the water surface is lost. This makes the jumps slower, and the escape from predators less effective.
Using their mathematical model, the researchers calculated for a the range of insect body sizes and leg morphologies the critical leg speed beyond which the dimple is predicted to break. The actual leg movements of these species of different body weights and morphologies were just below this critical threshold. Hence, the insects move their legs fast, but just not too fast, in order to maximize the jump speeds.
The article can be found at: Yang et al. (2016) Water Striders Adjust Leg Movement Speed to Optimize Takeoff Velocity for Their Morphology.
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Source: Seoul National University; Photo: Marko Kivelä/CC/Flickr.
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