Water Striders: Walking on Water
Water striders are small insects that are adapted for life on top of still water, using surface tension to their advantage so they can “walk on water.”
Water acts different at the surface. Water molecules are attracted to each other and like to stay together, especially on the surface where there is only air above. The attraction between water molecules creates tension and a very delicate membrane. Water striders walk on this membrane.
Water striders are about a half-inch long with a thin body and three sets of legs. The water strider's secret is its legs. The legs have tiny hairs that repel water and capture air. By repelling water, the tiny water striders stand on the water’s surface and the captured airs allows them to float and move easily.
Water striders can be seen on the surface of calm or slow-moving water throughout the continental U.S. They prefer ponds, vernal pools, and marshes.
The water strider's shorter front legs are used for catching and holding onto food. Water striders eat insects and larvae on the surface of water, such as mosquitoes and fallen dragonflies.
How do they walk on water?
The first thing you notice about water striders is their rapid skipping across the water surface. Most insects of a water strider’s weight would quickly sink and drown. How do they stay on the surface?
Water strider legs are covered in thousands of microscopic hairs scored with tiny groves.
The water skipper’s legs are so buoyant they can support fifteen times the insect’s weight without sinking. Even in a rainstorm, or in waves, the strider stays afloat.
If a water strider’s legs go underwater, it’s very difficult for them to push to the surface.
Their legs are more buoyant than even ducks’ feathers.
What else do their legs do?
The strider’s legs do more than repel water; they’re also configured to allow efficient and rapid movement across the surface.
As with all insects, the water strider has three pairs of legs. The front legs are much shorter, and allow the strider to quickly grab prey on the surface. The middle legs act as paddles. The back legs are the longest and provide additional power, and also enable the strider to steer and “brake.”
The buoyancy and paddling legs allows striders to be fast. Very, very fast.
Unfortunately for the water strider, these extraordinary capabilities don’t extend to land. Their legs are almost useless on hard surfaces.
That speed is essential for the strider’s most important task: snatching prey off the water’s surface. While striders don’t bite people, they are highly efficient predators. A water strider rapidly grabs a small insect with its front legs, then uses its mouthparts to pierce the prey’s body and suck out its juices.
Many strider species have wings of varying lengths, depending on habitat conditions. Species frequenting calm waters typically have large wings. Species that live in swift waters have short ones, as long wings could be easily damaged.
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