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> > Puzzled on this mayfly, not even confident on family

The Specimen

Rhithrogena hageni (Western Black Quill) Mayfly SpinnerRhithrogena hageni (Western Black Quill) Mayfly Spinner View 14 PicturesAlthough I could not find the preserved specimen to examine under my good new microscope, I'm tentatively calling it one Rhithrogena hageni, based on apparent similarity to this specimen, which I was able to positively ID.

The relative angle of the penes (Penes: The paired genital structures of most male insects, which vary widely in form and are one of the main characteristics used for species identification.) is a bit shallower in this specimen, but I photographed another specimen from the same collecting trip (and I think even the same swarm, although I don't recall for sure) as the other one, and it had the shallower angle seen on this specimen. I'm guessing it's just variation within the species.
Collected July 8, 2019 from the Ruby River in Montana
Added to Troutnut.com by on July 18, 2019

The Discussion

TroutnutJuly 23rd, 2019, 12:11 am
Administrator
Bellevue, WA

Posts: 2723
This seems to be some sort of Heptageniid, based on the two tails and five segments on the hind tarsus. Following the key in Merritt & Cummins seems to lead to Rhithrogena, but it doesn't fit a characteristic described in Needham's Biology of Mayflies for that genus: "Tibia of hind leg in both sexes about 1/4 length of femur."
Jason Neuswanger, Ph.D.
Troutnut and salmonid ecologist
MillcreekJuly 23rd, 2019, 2:34 pm
Healdsburg, CA

Posts: 356
For what it's worth, this seems to be Heptageniidae and Rhithrogena based on the wings and penes. Also, if you take a look at Bugguide the photos there don't show the hind tibia being 1/4 the length of the femur.


https://bugguide.net/node/view/50753/bgimage?from=0

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