Entomologists have now classified what was Stenonema fuscum with Stenonema vicarium. Although Stenonema vicarium live under and around the stones of fast moving riffles, they can also be found under rocks in medium to slow moving riffles prior to emerging. Like all Stenonema, vicarium never hatch in large numbers. Hatching mainly in the evening, but like other Stenonema will hatch sporadically through out the day on cloudy cool days. Males display large black eyes that turn iridescent green to blueish green when exposed to light.

   Mature nymph species identification - S. vicarium, Tails rigid, and held apart, threadlike gills on abdominal segment 7, abdominal segments 1 - 6 gills truncate at apex, lateral spines on abdominal segments 3 - or 4 - 9, brown stripe on the posterior margin of sternites 3 - or 4 - 8, sternite 9 with entire posterior half dark brown, or with a pair of large, brown sublateral spots. Modified to include what was fuscum from - Burks - The Mayflies, or Ephemeroptera, of Illinois - 1909 reprinted 1953.