Water striders are tiny insects that have a surprising ability to survive impacts with raindrops dozens of times heavier than they are. Slow-motion videos of them getting smashed by water have revealed the tricks they use to avoid getting crushed – including how they can shoot into the air aboard a water jet and somersault off before landing.
As their name suggests, water striders can be found walking across the surfaces of ponds, lakes and rivers around the world. They have long legs covered in microscopic hairs that trap air, helping the insects to float on water.
“I saw them skating around the water one day, and I thought, ‘what do they do when it rains?’” says Andrew Dickerson at the University of Tennessee. Raindrops can weigh more than 40 times as much as adult water striders. “How do they survive? Are they submerged, or are they ejected into the air?” he added.
To investigate, Dickerson and his colleagues put some water striders into a glass aquarium filled with water, bombarded them with droplets and recorded the critters’ reactions with slow-motion videos.
The researchers noticed that, when a raindrop collided with an insect on the water’s surface, the bug initially remained unscathed, as a result of its low density. However, it did get dragged down into the resulting impact crater. The collapse of the crater then shot a jet of water back up above the surface – and the insect went with it.
In a handful of cases, the team witnessed water striders jumping away from the water jet before it fell back to the surface. “It was pretty neat; we saw some backflip off that jet,” says Dickerson.
But if the water striders couldn’t escape the jet of water, they would get sucked back down again. Luckily, their hairy, water-repelling legs allowed them to float and swim back to the surface.
“It’s the equivalent of us getting hit by a car, and they survive it – and undergo this quite acrobatic journey in the process, in some cases,” says Dickerson.