True Bugs, Pacific Northwest
Broad shouldered bugs are predaceous and feed on small arthropods and mosquito eggs on the water surface. They live on the surface of the water or on the adjacent shore line.
Some species of Broad Shouldered Bugs are gregarious and can be found near the riffles of small streams. Other species are found in quieter parts of streams and ponds. Riffle bugs look like small, wingless water striders, just a bit stockier.
They have a broad thorax and long legs. They are dark brown or black, often with silvery markings.