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Lateral view of a Female Hexagenia limbata (Ephemeridae) (Hex) Mayfly Dun from the Namekagon River in Wisconsin
Hex Mayflies
Hexagenia limbata

The famous nocturnal Hex hatch of the Midwest (and a few other lucky locations) stirs to the surface mythically large brown trout that only touch streamers for the rest of the year.

27" brown trout, my largest ever. It was the sub-dominant fish in its pool. After this, I hooked the bigger one, but I couldn't land it.
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Lateral view of a Male Rhithrogena hageni (Heptageniidae) (Western Black Quill) Mayfly Spinner from the Ruby River in Montana
Although 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 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.
Troutnut
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Bellevue, WA

Posts: 2758
Troutnut on Jul 22, 2019July 22nd, 2019, 8:11 pm EDT
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
Millcreek
Healdsburg, CA

Posts: 344
Millcreek on Jul 23, 2019July 23rd, 2019, 10:34 am EDT
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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