Water striders are a common sight on ponds, pools and puddles. On clear summer days, these insects appear to walk on water. They do this thanks to a combination of long legs that distribute their weight on the water’s surface and micro-hairs that make these invertebrates extremely water-repellent. But what happens to these water striders when it rains?

It seems logical that a shower of water would capsize tiny swimming insects. In heavy rain, something the size of a water strider can be hit by a drop every seven seconds on average. And each of those drops can have five times the mass of an adult water strider. Daren Watson, assistant professor of mechanical engineering at Florida Polytechnic University, wanted to find out how these insects stay afloat.

Watson set up a rain simulator in the lab. Water dripped from a ceiling-high nozzle into an artificial pool filled with water striders. Watson’s lab-created “rain” fell at the slowest end of the speed range for natural rain. He recorded video of the water striders as they were hit by the drops and later analyzed their reactions in slow motion.

When a raindrop hits the surface of the water, it forms a crater of water. This crater collapses, then rebounds and becomes a jet that falls back into a second crater. Finally, the water flows back in waves to a state of rest. This whole series of very rapid events is a “splash.” A raindrop splash happens far too quickly for a water strider to anticipate and avoid.

“A direct, first splash always pushes them underwater, mainly because (the insects) are so light,” Watson said. During his experiments in the lab, water striders were submerged underwater by the initial impact and cratering, then carried upward as the jet formed. In one case, however, a strider jumped from the top of the jet, landing well away from the splash zone and thus avoiding further wetting.

Most of the water striders in the lab fell back into the second crater when the jet collapsed. If a water strider landed near the crater floor, it was pulled back under the water’s surface. Submerged water striders were always able to move back to the surface thanks to their buoyancy adaptation and ability to swim underwater.

The extremely water-repellent microhairs that cover their bodies help water striders surface. These hairs trap an air bubble, called a plastron, around a water strider’s body to create additional buoyancy. Water striders also use their plastron to breathe while underwater, much like a scuba diver’s air tank. Water striders can also swim underwater by rotating their long middle legs forward and then paddling them back.

During Watson’s laboratory experiments, he found that repeated falls likely damage a walking insect’s abdominal carapace, suggesting that in heavy rain, the insects may eventually become waterlogged and become trapped beneath the water’s surface. However, a walking insect without an abdominal carapace still has the ability to resurface. Submerged walking insects in the laboratory used their legs to grasp and climb onto floating acrylic squares in their habitat. In the outside world, aquatic plants and floating debris may be important to their survival during heavy rain.

Watson also tested how water striders survive compression forces such as those encountered when struck by falling drops of water. He found that water striders can withstand compression forces more than twice as strong as the forces exerted by drops falling at the highest possible rain speed.

Watson is excited to explore more questions about water striders and physics. For example, he and his team suspect that water striders can be a model for how other lightweight, hydrophobic objects, such as microplastics, behave in aquatic environments. “I really enjoyed this project,” he said. “We were thinking outside the box – what mechanical engineers usually do. This was a fusion of biology, fluid mechanics and physics.” It was also an example of how asking a simple question about a familiar insect can lead to new insights about nature.

Rachel Sargent Mirus is a teaching artist and writer. Opinions expressed by columnists do not necessarily reflect the views of Vermont News & Media.