How does a water bird survive a raindrop?

By our employee Ninky Pentema

Water striders, small, slender insects that run at lightning speed across the surface of the water, have a remarkable resistance to the impact of raindrops. This is what American and Turkish scientists write this week With people. They analyzed film images they took with high-speed cameras, and applied all kinds of physics to the forces between a raindrop and an insect.

The possibility of a water skier being hit by a raindrop is high. During a heavy shower, the average person gets a drop of water on their head at least every seven seconds, researchers calculate. A droplet is five to forty times heavier than an insect, and can travel at speeds of up to 30 kilometers per hour. This has a huge impact. Researchers describe it in a plastic way: they write about the “fate” of the insect that “fell” due to the “attack.”

But it seems that the effect is not so bad: every animal happily continues on its way. how is that possible? In the lab, researchers measured the force needed to crush a water bat between two surfaces. Or yes, to hurt, they write. This happens at about one and a half newtons. The force exerted by a falling raindrop on a water strider is less than half that force, partly due to surface deformation. So far no problem.

But what if the water skier ends up underwater? That doesn't matter either, as the video footage showed. First, the water strider is sucked into the hole created by the raindrop's impact. If this hole collapses, the insect can spin around underwater. But this collapse creates an upward flow of water, which the water skier can then toss back. Sometimes it lands safely on the water, sometimes in a second hole, which is formed by the fall of that water jet. Even after that, it could be released again, or end up underwater, depending on its initial location.

The water strider also has no problems underwater. It is then surrounded by a very thin layer of air held together by thin shield bristles. This coat is therefore very water repellent. The air layer helps waterfowl float up and break through the surface of the water while swimming. Overall, survival during the study was 100%, with the exception of crush tests.

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