THE XERCES SOCIETY FOR INVERTEBRATE CONSERVATION

Aquatic Invertebrates in Pacific Northwest Freshwater Wetlands
An Identification Guide and Educational Resource

The little stout crawlers are fairly tolerant mayflies that are very diverse in the Southwest, but are represented by only two genera in the Northwest. You typically find them in more open valley streams. Until recently, and in many of the general guides, you will only find two genera listed for this family (Tricorythodes and Leptohyphes) and they are typically under the family name of Tricorythidae. A 2000 review of the little stout crawler mayflies by N.A. Wiersema and W. Patrick McCafferty separated the family into 10 genera. The species Tricorythodes minutus has been collected in wetlands in Oregon.

The little stout crawlers are usually cream or light brown in color, and as their name suggests, are relatively small and robust. They don't swim particularly well and tend to undulate in the water in a collecting tray if they are dislodged from the bottom. The key character of the Northwest Leptohyphidae is the large gill attached to abdominal segment 2 that covers the remaining gills. This large or "operculate" gill is typically a triangle shape but is sometimes rounded.