Gerridae (water striders) in the order Hemiptera (true bugs)
Water striders have water-repellant hairs on the hind and middle legs that allow these nimble insects to skate on the surface of the water. Velvety hairs on their bodies allow them to stay dry though they spend all their time on water.
There are several species of water striders in North America. The most common and conspicuous one in our area is the large water strider (Aquarius remigis, also called Gerris remigis). It has an elongated body and is dark brown or blackish on the top and bottom, with a whitish or silvery stripe along each side. The legs are long and thin and are generally spread far apart; the hind and middle pairs of legs are used for skating across the water surface. Adults usually lack wings.
Sometimes the first thing you notice are the small round shadows they create on the substrate beneath them, caused by the small dimples their feet make on the surface film of the water.
Water striders in the genus Gerris are smaller, less than ½ inch long.
Similar species: Although also called “water spiders,” water striders are true bugs (related to squash and assassin bugs, aphids, and cicadas), and therefore have 6 (not 8) legs and mouthparts modified into a single piercing hollow straw.
Adult length (not counting legs): ½ to ¾ inch (A. remigis).
These fascinating, harmless insects can be found in nearly any aquatic habitat, including ponds, lakes, swamps, ditches, creeks, streams, and rivers. They generally prefer places where the water is calm, but you can also see them jerking their way upstream, against a current. When it is not mating season, they commonly collect in large numbers. They quickly scatter to individual shelters when alarmed.
Like other true bugs, water striders have mouthparts modified into a hollow straw, with which they pierce and suck nutrients from their food. As predators they eat other insects, alive or dead. Since they live on the surface, they often eat land insects and spiders that accidentally fall into the water and struggle helplessly on the surface. Water striders detect their ripples. Sometimes several striders surround the unfortunate insect, sharing the meal. They also eat mosquito larvae.
Water striders lay eggs on rocks or aquatic vegetation. Upon hatching, they undergo incomplete metamorphosis, where the series of immature nymph stages pretty much resemble the adults, only smaller. The final molt produces an adult that is sexually mature (capable of reproduction). Other insects that undergo incomplete metamorphosis are grasshoppers and box elder bugs.
Usually, when we think of the psychological effect nature has on us, we focus on strikingly beautiful or noble qualities. But there’s something to be said for the quirky and bizarre. These common insects “walk on water” — and “amazement” has value for us, too.
Water striders are predators that specialize in eating land insects trapped on the water’s surface. But many birds feed on water striders, returning the nutrients gained from land insects back to land ecosystems. Apparently, fish find water striders distasteful and rarely eat them.
Missouri’s streams, lakes, and other aquatic habitats hold thousands of kinds of invertebrates — worms, freshwater mussels, snails, crayfish, insects, and other animals without backbones. These creatures are vital links in the aquatic food chain, and their presence and numbers tell us a lot about water quality.