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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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Black Quills

Like most common names,"Black Quill" can refer to more than one taxon. They're previewed below, along with 8 specimens. For more detail click through to the scientific names.

Mayfly Genus Leptophlebia

These are pretty much always called Black Quills.
Leptophlebia mayflies do not generate superhatches, but their medium-large size and other properties make them a relevant part of the early season.

The information below was mostly discovered in Leptophlebia cupida, the most important species, but it is not known to differ in the others.
Lateral view of a Male Leptophlebia cupida (Leptophlebiidae) (Black Quill) Mayfly Dun from the Teal River in Wisconsin
This Leptophlebia cupida dun was extremely cooperative, and it molted into a spinner for me in front of the camera. Here I have a few dun pictures and one spinner picture, and I've put the entire molting sequence in an article.
Lateral view of a Female Leptophlebia cupida (Leptophlebiidae) (Black Quill) Mayfly Spinner from the Namekagon River in Wisconsin
Leptophlebia cupida (Leptophlebiidae) (Black Quill) Mayfly Nymph from the Namekagon River in Wisconsin

Mayfly Species Rhithrogena hageni

These are very rarely called Black Quills.
According to Fred Arbona in Mayflies, the Angler, and the Trout, this is an excellent hatch and one of the most common fast-water mayflies in the West.
Lateral view of a Female Rhithrogena hageni (Heptageniidae) (Western Black Quill) Mayfly Dun from Mystery Creek #249 in Washington
I was surprised by the olive cast on the body of this female Rhithrogena dun, which led me to mistake it for a western green drake (Drunella) in the field. I was pleasantly surprised to get a closer look and find something I hadn't collected yet. Its species ID is based on proximity to male spinner collected on the same trip, as well as physical similarity (size, tergite coloration, dark streaks on the femora) to that specimen.
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.
Dorsal view of a Rhithrogena hageni (Heptageniidae) (Western Black Quill) Mayfly Nymph from the South Fork Snoqualmie River in Washington
This mature nymph was collected in the same riffle as a male spinner, from which I got the identification for both.

Mayfly Species Rhithrogena morrisoni

These are very rarely called Black Quills.
Despite the reputation of Rhithrogena as being the most tenacious of clingers, Rhithrogena morrisoni or Western March Brown has the greatest populations in moderate runs over cobble. It can reach amazing densities in this water type on rivers like the Rogue in Oregon, Lower Yuba In California, and the Henry's Fork in Idaho.

These large flies range between 9mm and 12mm and are the first important hatch of the year. Generally speaking, they have two distinct color phases and hatching periods, with the Coastal states having the lighter version emerging late February through April in lower elevation tailwaters and the darker version in the Rocky mountain states emerging a month or two later. This has led to much confusion as these significant regional differences are seldom pointed out in angling literature.

They offer the western angler some of the finest fishing of the year during moderate precipitation cycles. It's biggest spoiler is high water or early runoff. On many rivers, there is also a fine hatch of a large late Winter stonefly (Skwala spc.) that usually precedes it that helps to get the fish "looking up". It is the West's equivalent of the East's mottle winged Macaffertium vicarium (American March Brown), both in terms of appearance and importance. Primarily due to western fishing seasons of the past that excluded this mayfly's activity, reporting on this species in angling literature is a relatively recent phenomenon. Thus, it lags in tradition compared to the blotchy winged Heptageniidae of the East and Midwest. But given time...
Rhithrogena morrisoni (Heptageniidae) (Western March Brown) Mayfly Nymph from the Lower Yuba River in California
Size - (excluding tails) - 12 mm
Status at time of photo - preserved, but photographed within days of capture.

W. C. Day, Aquatic Insects of California differentiates morrisoni nymphs by submedian pale dots on tergites 8 & 9, which look to be in evidence. This is one of the "super-hatches" on this river that can be prolific March through April.

Entoman

References

Black Quills

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