Female Ephemerella excrucians (Pale Morning Dun) Mayfly Spinner Pictures

I wish I had been able to get a male spinner for a positive ID. I wasn't able to collect any, unfortunately. The keys I have to the adult genera of the Ephemerellidae require one.

I've placed several specimens collected from a similar emergence on nearby rivers into the species Attenella attenuata, because they look exactly like the picture of that species in some books, most recently Ted Fauceglia's Mayflies. They are handy midday and early evening emergers in northwest Wisconsin at a time when not much else is on the water. But I'm not convinced that the identification is correct.

For one thing, although I tried sampling several times in stretches where the duns were emerging, the only mature Ephemerellid nymphs I found keyed out to Ephemerella inermis, which is now Ephemerella excrucians. These adults fit the general description for that widely variable species. I never found any Attenella nymphs.

I suspect they are the same species referred to in nearby parts of Wisconsin as "Kinni Sulphurs" and "Booger Sulphurs." As best I can tell from looking up those names, they seem to have been identified as Ephemerella inermis but there is a local belief that they are Ephemerella needhami, even though their color does not at all fit the description for that species.

Ah, to have a male spinner under the microscope...