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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.

Lateral view of a Clostoeca disjuncta (Limnephilidae) (Northern Caddisfly) Caddisfly Larva from the Yakima River in Washington
This one was surprisingly straightforward to identify. The lack of a sclerite at the base of the lateral hump narrows the field quite a bit, and the other options followed fairly obvious characteristics to Clostoeca, which only has one species, Clostoeca disjuncta.
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.
Troutnut is a project started in 2003 by salmonid ecologist Jason "Troutnut" Neuswanger to help anglers and fly tyers unabashedly embrace the entomological side of the sport. Learn more about Troutnut or support the project for an enhanced experience here.

Dark Hendricksons

Like most common names,"Dark Hendrickson" can refer to more than one taxon. They're previewed below, along with 12 specimens. For more detail click through to the scientific names.

Mayfly Species Ephemerella subvaria

These are often called Dark Hendricksons.
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 needhami

These are sometimes called Dark Hendricksons.
This small and slightly noteworthy mayfly appears during the finest hours of the year. Ernest Schwiebert describes an Ephemerella needhami day in Matching the Hatch:

"It was a wonderul morning, with a sky of indescribable blue and big, clean-looking cumulus clouds, and the water was sparkling and alive. You have seen the water with that lively look; you have also seen it dead and uninviting in a way that dampens the enthusiasm the moment you wade out into the current."


I have not fished a needhami emergence, but the exquisite nymphs show up often (though never abundantly) in my samples.
Lateral view of a Male Ephemerella needhami (Ephemerellidae) (Little Dark Hendrickson) Mayfly Dun from the West Branch of the Delaware River in New York
See the comments for an interesting discussion of the identification of this dun.
Dorsal view of a Ephemerella needhami (Ephemerellidae) (Little Dark Hendrickson) Mayfly Nymph from the Bois Brule River in Wisconsin
I photographed three strange striped Ephemerella nymphs from the same trip on the same river: this one, a brown one, and a very very striped one. I have tentatively put them all in Ephemerella needhami for now.

Mayfly Species Leptophlebia cupida

These are very rarely called Dark Hendricksons.
Most anglers encounter these large mayflies every Spring in the East and Midwest. They are omnipresent in small portions, providing filler action in the days or hours between the prolific hatches of the early season Ephemerella flies.

See the main Leptophlebia page for details about their nymphs, hatching, and egg-laying behavior. This is by far the most important species of that genus.
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 Teloganopsis deficiens

These are very rarely called Dark Hendricksons.
Anglers in western Wisconsin, where these little flies hatch in good numbers on summer rivers, have termed them "Darth Vaders" because of the very dark color of their wings.

Until recently, this species was known as Serratella deficiens.
Dorsal view of a Teloganopsis deficiens (Ephemerellidae) (Little Black Quill) Mayfly Nymph from the Bois Brule River in Wisconsin
This nymph has tiny, barely detectable tubercles on its abdominal segments, and I could not find the maxillary palpi. I tentatively guessed that it is Serratella deficiens back when that was a thing; the species is now known as Teloganopsis deficiens. One of the key characteristics, tarsal claws with a subapical denticle being larger than the preceding denticles, seems to be visible in some of the pictures.

Mayfly Species Ephemerella excrucians

These are very rarely called Dark Hendricksons.
For trout (if not anglers), this single species is arguably the most important mayfly in North America. In terms of sheer numbers, breadth of distribution and hatch duration, it has a good argument.

Ephemerella excrucians or Pale Morning Dun usually follows its larger sibling Ephemerella dorothea infrequens with which it shares the same common name. What it often lacks in size by comparison is made up for with it's duration, often lasting for months with intermittent peaks. This close relationship with infrequens has led many anglers to confuse Pale Morning Dun biology with that of the multivoltine Baetidae species, having disparate broods that decrease in size as the season advances. Sharing the same common name has not helped to alleviate this misconception.

Until recently, Ephemerella excrucians was considered primarily an upper MidWestern species of some regional importance commonly called Little Red Quill among other names. Recent work by entomologists determined that it is actually the same species as the important Western Pale Morning Dun (prev.Ephemerella inermis), and the lake dwelling Sulphur Dun of the Yellowstone area, (prev.Ephemerella lacustris). Since all three are considered variations of the same species, they have been combined into excrucians, being the original name for the type species reported as far back as the Civil War. Angler speculation had simmered for some time that the stillwater loving Ephemerella lacustris was much more widespread, inhabiting more water types then previously thought and could account for many large sulfurish ephemerellids found in still to very slow water locations throughout the West. With the revisions, this discussion is now moot.

Ephemerella excrucians variability in appearance, habitat preferences, and wide geographical distribution are cause for angler confusion with the changes in classification. They can be pale yellow 18's on a large Oregon river, creamy orange 14's on western lakes and feeder streams, large olive green on CA spring creeks as well as tiny sulfur ones in many Western watersheds. Then there's the little Red Quill on small streams in Wisconsin. Yet, all are the same species.
Lateral view of a Female Ephemerella excrucians (Ephemerellidae) (Pale Morning Dun) Mayfly Spinner from the Bois Brule River in Wisconsin
Dorsal view of a Ephemerella excrucians (Ephemerellidae) (Pale Morning Dun) Mayfly Nymph from the Bois Brule River in Wisconsin
I spent a while with a microscope to fairly positively identify this specimen as Ephemerella excrucians.

References

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