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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.

Dorsal view of a Neoleptophlebia (Leptophlebiidae) Mayfly Nymph from the Yakima River in Washington
Some characteristics from the microscope images for the tentative species id: The postero-lateral projections are found only on segment 9, not segment 8. Based on the key in Jacobus et al. (2014), it appears to key to Neoleptophlebia adoptiva or Neoleptophlebia heteronea, same as this specimen with pretty different abdominal markings. However, distinguishing between those calls for comparing the lengths of the second and third segment of the labial palp, and this one (like the other one) only seems to have two segments. So I'm stuck on them both. It's likely that the fact that they're immature nymphs stymies identification in some important way.
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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Red Quill Spinners

Like most common names,"Red Quill Spinner" can refer to more than one taxon. They're previewed below, along with 16 specimens. For more detail click through to the scientific names.

Mayfly Species Ephemerella subvaria

These are often called Red Quill Spinners.
The Hendrickson hatch is almost synonymous with fly fishing in America. It has been romanticized by our finest writers, enshrined on an untouchable pedestal next to Theodore Gordon, bamboo, and the Beaverkill.

The fame is well-deserved. Ephemerella subvaria is a prolific species which drives trout to gorge themselves. Its subtleties demand the best of us as anglers, and meeting the challenge pays off handsomely in bent graphite and screaming reels.
Lateral view of a Female Ephemerella subvaria (Ephemerellidae) (Hendrickson) Mayfly Dun from the Beaverkill River in New York
I collected this female Hendrickson dun and a male in the pool on the Beaverkill where the popular Hendrickson pattern was first created. She is descended from mayfly royalty.
Ruler view of a Female Ephemerella subvaria (Ephemerellidae) (Hendrickson) Mayfly Spinner from the Bois Brule River in Wisconsin The smallest ruler marks are 1/16".
This one's a bit bedraggled because it was rainy and I had a hard time keeping anything dry, including the container I was putting mayflies in. I was practically juggling up there balanced on a rock trying to catch mayflies and trout at the same time.
Ephemerella subvaria (Ephemerellidae) (Hendrickson) Mayfly Nymph from unknown in Wisconsin
This is another unusual brown Ephemerella nymph. The "fan-tail" which defines the Ephemerella genus is particularly evident on this specimen.

Mayfly Species Ephemerella invaria

These are sometimes called Red Quill Spinners.
This species, the primary "Sulphur" hatch, stirs many feelings in the angler. There is nostalgia for days when everything clicked and large, selective trout were brought to hand. There is the bewildering memory of towering clouds of spinners which promise great fishing and then vanish back into the aspens as night falls. There is frustration from the maddening selectivity with which trout approach the emerging duns--a vexing challenge that, for some of us, is the source of our excitement when Sulphur time rolls around.

Ephemerella invaria is one of the two species frequently known as Sulphurs (the other is Ephemerella dorothea). There used to be a third, Ephemerella rotunda, but entomologists recently discovered that invaria and rotunda are a single species with an incredible range of individual variation. This variation and the similarity to the also variable dorothea make telling them apart exceptionally tricky.

As the combination of two already prolific species, this has become the most abundant of all mayfly species in Eastern and Midwestern trout streams.
Lateral view of a Male Ephemerella invaria (Ephemerellidae) (Sulphur) Mayfly Dun from Penn's Creek in Pennsylvania
Lateral view of a Male Ephemerella invaria (Ephemerellidae) (Sulphur) Mayfly Spinner from the Teal River in Wisconsin
Dorsal view of a Ephemerella invaria (Ephemerellidae) (Sulphur) Mayfly Nymph from the Beaverkill River in New York
This small Ephemerella invaria nymph was at least a month away from emergence.

Mayfly Species Epeorus pleuralis

These are sometimes called Red Quill Spinners.
This is the first really good dry-fly opportunity of the season for most Eastern anglers. They are large mayflies and they have good points of vulnerability both underwater and on the surface.
Lateral view of a Male Epeorus pleuralis (Heptageniidae) (Quill Gordon) Mayfly Dun from Dresserville Creek in New York
I kept this specimen after photographing it and it molted into a spinner in perfect condition, which I photographed here.
Lateral view of a Male Epeorus pleuralis (Heptageniidae) (Quill Gordon) Mayfly Spinner from Mongaup Creek in New York
I spent most of the day looking for Epeorus pluralis duns or spinners without any luck on the major Catskill rivers. Finally in the evening I arrived at a small stream somebody had recommended, and when I got out of the car I was happy to find that I had parked in the middle of a cloud of male spinners.
Dorsal view of a Epeorus pleuralis (Heptageniidae) (Quill Gordon) Mayfly Nymph from Mongaup Creek in New York
This Epeorus pluralis dun is recently deceased in these photos. I decided not to photograph several lively, less mature nymphs. This one was ready to hatch, as indicated by the black wing pads. I believe it had not been dead long enough to lose its natural coloration.

Mayfly Species Epeorus longimanus

These are very rarely called Red Quill Spinners.
Epeorus longimanus and Epeorus albertae are the two most common Epeorus species in the West.
Lateral view of a Male Epeorus longimanus (Heptageniidae) (Slate Brown Dun) Mayfly Dun from Mystery Creek #295 in Washington
Identification of this one was as follows. Body 9 mm, wing 11 mm.
Both Epeorus albertae and Epeorus dulciana should have a conspicuously darkened humeral crossvein in the forewing. This one doesn't.
The foretarsal claws are dissimilar (one sharp, one blunt), which also rules out the Epeorus albertae group.
The dark macula on the forefemora rules out Epeorus deceptivus, which is also supposed to be a little bit smaller.
Both Epeorus grandis and Epeorus permagnus should be much, much larger.
Of the species known to be present in Washington, this leaves only Epeorus longimanus, which is exactly the right size. The key to male spinners in Traver (1935) describes distinctive markings that are visible (although more faintly) in this dun: “Black posterior margins of tergites do not extend laterally to pleural fold, but an oblique black line form this margin cuts across poster-lateral triangle to pleural fold.”
Female Epeorus longimanus (Heptageniidae) (Slate Brown Dun) Mayfly Spinner from the Touchet River in Washington
Epeorus longimanus (Heptageniidae) (Slate Brown Dun) Mayfly Nymph from the Vermillion River in Montana

Mayfly Species Cinygmula ramaleyi

These are very rarely called Red Quill Spinners.
This can be the first mayfly of the season on high mountain streams in the western states, but emerges later in the season in Alaska. It is the most important species of Cinygmula for anglers.
Lateral view of a Female Cinygmula ramaleyi (Heptageniidae) (Small Western Gordon Quill) Mayfly Dun from Nome Creek in Alaska
This dun is almost certainly of the same species as this nymph, as it hatched in my cooler from a nearly identical nymph.
Male Cinygmula ramaleyi (Heptageniidae) (Small Western Gordon Quill) Mayfly Spinner from the Touchet River in Washington
Adults were collected from the North Fork of the Touchet River at Touchet Corral, 21 Sept. One photo is the swarm of males over the stream about 3 PM, air temp about 66 degree.
Cinygmula ramaleyi (Heptageniidae) (Small Western Gordon Quill) Mayfly Nymph from Nome Creek in Alaska
This nymph is almost definitely the same species as this dun, which hatched from a nearly identical nymph from the same collection.

Mayfly Species Rhithrogena undulata

These are very rarely called Red Quill Spinners.
This is one of the two most common species of Rhithrogena.
Male Rhithrogena undulata (Heptageniidae) (Small Western Red Quill) Mayfly Spinner from the Madison River in Montana
This male was collected at the same time as this female and is likely the same species.

It keys pretty clearly to Rhithrogena undulata using the key in Traver 1935, although the size is larger than expected for that species in that source.

References

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