This species is slightly smaller than Hexagenia limbata and it occurs later in the year. It is only mentioned in passing by a few authors, but it can be locally important.
Where & when
Time of year : July and August
I have heard rumors of fishable hatches of this species in both Wisconsin and the Catskills. The duns and spinners have been a common sight for me on several Wisconsin rivers during August, but they have been too sparse to cause good rises.
I have had some luck with an imitation. Last year a very nice smallmouth bass rose to my atrocaudata spinner pattern as subtly as any trout.
Specimens of the Mayfly Species Hexagenia atrocaudata
I found this lone Hexagenia atrocaudata dun fluttering by herself on the surface of a small, still stretch of river one evening as I paddled home from fishing for smallmouths in the warm August weather.