Gracefully springing from the water’s surface as if it were a trampoline, water striders snatch and eat prey that fall into the water, such as mosquitoes, larvae and dragonflies. Bugs that can walk on water appear to defy the laws of nature. Scientists have studied these nimble insects to find out the tiniest details of their anatomy, which could help engineers design robots, nonstick coating and boats.
How to Walk on Water
They look like spiders (and a few spiders can walk on water), but when you see a bug skating on the surface of the water, it is likely an insect called Gerridae. These bugs have many nicknames: pond skimmers, Jesus bugs, skaters and more. They are commonly found on the surface of calm or slow-moving water such as ponds, vernal pools and marshes. There are 1,700 species of water striders, according to Nature. Three key factors allow bugs to walk on water: surface tension, weight distribution and their long, hairy legs.
Water striders take advantage of water’s chemical properties, which allow them to skip across a liquid’s surface without sinking. According to the United States Geological Survey, surface tension occurs because water molecules are attracted to each other. At the point where water meets air, the water molecules cling to each other even more than usual and form stronger bonds. In this way, the outer layer of water molecules create a membrane that water striders can use to their advantage.
Surface tension is a good start, but there are only certain kinds of bugs that can walk on water. Water striders’ anatomy perfectly distributes their body weight so they can stay buoyant on the surface. Like all insects, they have six legs. Their legs are long and wide, so their body weight is spread out among the legs without putting too much pressure on the water at any one point, according to ScienceNews for Students.
Water striders use two short front legs to attack and eat prey, while their middle pair of legs act as paddles to push them along the water, and the long back pair provides power, steering and brakes, according to Nature.
Strangely, one of the big reasons these bugs don’t sink is that they have microscopic hairs on their legs. While other lightweight bugs float on the surface, they get wet, and end up stuck in the water. But the hair on water striders’ legs trap tiny air bubbles that allow the bugs to hover on the water’s surface without getting wet, according to Sciencing. When people or other animals swim, water exerts resistance on the moving body, causing fluid drag that slows them down. But on the water’s surface, bugs can move incredibly quickly — the equivalent of a person swimming at speeds of more than 400 miles per hour, according to Nature.
What Can We Learn From Bugs That Can Walk on Water?
These bugs have evolved to thrive in their environment at the water’s surface. We won’t be able to walk on water anytime soon, but according to the National Wildlife Federation, scientists are studying the legs of water striders to learn how to engineer materials that easily repel water and help objects move faster over water. Many inventions have been inspired by Earth’s biodiversity, and water striders could influence the next generation of inventors.
Engineers who design racing yachts, for example, need to overcome the fluid drag that occurs when water flows past the hull of the boat. One way to increase a yacht’s speed, according to The Conversation, is by using hydrofoils — small underwater wings — that lift the yacht to the water’s surface. Just like the water striders’ long, hairy legs, hydrofoils reduce the surface area and the volume of the boat that’s underwater; this reduces drag and allows it to sail faster.
Several research groups around the world have studied water striders to develop various non-stick coatings. For example, scientists in China built an unmanned ship for oil spill cleanup. To build the boat, they engineered a mesh material based on the water striders’ legs, which repel water and reduce drag, according to a paper published in ACS Applied Materials & Interfaces.
Roboticists have also been inspired by water striders, AZO Robotics explains. Replicating the way water striders balance on water surface could help improve the stability, speed and efficiency of robotic boats that are used to monitor the environment.