By Judy Semroc, Conservation Outreach Specialist
Most of us have seen the small insects that appear to “walk” on the water, whether it be on a creek, stream, river, pond, lake, or wetland/marshy area. While they typically prefer calm water, these insects can also be found making erratic movements as they move upstream. Often, they are noticeable due to the small, round shadows cast beneath them by the dimples their feet make on the water’s surface.
These small (½- to ¾-inch body length) insects belong to the family Gerridae and are classified in the Hemiptera, or true bug, group of insects. This means they have six legs and their mouthparts consist of a hollow, straw-like piercing tube that is used to extract the body fluids from their prey.
Our most common species in Northeast Ohio is Gerris remigis, which has a brownish-black overall coloration with a silvery or whitish stripe running along each side of the body.
The key to water striders’ ability to “skate” on the water’s surface lies in the anatomy of their long, thin, and widely spread legs. The water-repellent hairs found on the middle and hind leg pairs not only enable the insect to “walk” on the water’s surface, but also allow the body to stay dry. The buoyancy created by these leg hairs and associated grooves can support 15 times the strider’s weight without the insect’s sinking. This is especially important in heavy rain or increased wave action. For humans to “walk on water” like striders, their feet would have to be over 7 kilometers (approximately 4.3 miles) long! The middle legs also act as paddles, and the hind legs are used for steering and braking. The paddling feature of the legs enables striders to move very quickly, at speeds of 100 body lengths per second, as reported by National Geographic. To match this speed, a 6-foot tall human would have to swim at more than 400 mph! The shorter front legs are used to catch and hold prey found on the water’s surface. Interestingly, water striders’ legs are quite useless on land.
Water strider females typically lay eggs on aquatic vegetation or rocks. Upon hatching, striders undergo incomplete metamorphosis. During the immature nymph stages (five instar stages), they look like small adults.
FEEDING & PREDATION
Water striders can eat living or dead insects, and even each other when food is scarce. Since they live on the water, they can easily predate land insects that may fall into the water, struggle, and then create ripples that attract the striders. They are aggressive predators of mosquito larvae, often grabbing them by their breathing “snorkel,” which pokes through the water’s surface and allows the larvae to breathe.
Water are prey for many birds. However, they are not a main food source for fish, which seems to find striders distasteful and possibly hard to see from below the water’s surface.
WINGS & FLYING
Depending on habitat types and conditions, many species of water striders have wings of varying lengths. Those that live primarily on calm water have larger qings than those living on swiftly moving water, as longer wings could be more easily damaged in rapidly mocing water. Interstingly, wing sizes change from brood to brood through polymorphism. This mechanism allows water sliders to better adapt to habitat and environmental water changes, allowing the next generation to move to a more suitable habitat.
Now that you know a little more about the fascinating world of water striders, take a walk to an area with a variety of aquatic habitats and check them out!\