If you see what look like miniature water striders skating on the surface of a stream or pond, you may have come upon an aggregation of Broad-shouldered Water Striders, a different family of water striders from the ones we commonly see. They are tiny (2-6 mm) and very fast-moving, zipping here and there with the speed of a bullet, staying on top of the surface film, or surface tension, that is created by the attraction of water molecules. Adaptations to this mode of travel include non-wettable hairs at the ends of their legs that don’t disrupt the surface tension, and claws that are located a short distance up the outermost section of their legs rather than at the end of their legs, so as not to break this film.
Broad-shouldered Water Striders are often found in the more protected areas of a stream, where they tend to congregate in large numbers. Members of a common genus, Rhagovelia, are known as “riffle bugs” and are often found below rocks that are in the current. Broad-shouldered Water Striders locate their prey (water fleas, mosquito eggs and larvae, etc.) by detecting surface waves with vibration sensors in their legs. There can be up to six generations a summer (photo shows that they are still mating at the end of October). Broad-shouldered Water Striders spend the winter hibernating as adults, gathering in debris at the edge of the water or beneath undercut banks.