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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 Grammotaulius betteni (Limnephilidae) (Northern Caddisfly) Caddisfly Larva from the Yakima River in Washington
This is a striking caddis larva with an interesting color pattern on the head. Here are some characteristics I was able to see under the microscope, but could not easily expose for a picture:
- The prosternal horn is present.
- The mandible is clearly toothed, not formed into a uniform scraper blade.
- The seems to be only 2 major setae on the ventral edge of the hind femur.
- Chloride epithelia seem to be absent from the dorsal side of any abdominal segments.
Based on these characteristics and the ones more easily visible from the pictures, this seems to be Grammotaulius. The key's description of the case is spot-on: "Case cylindrical, made of longitudinally arranged sedge or similar leaves," as is the description of the markings on the head, "Dorsum of head light brownish yellow with numerous discrete, small, dark spots." The spot pattern on the head is a very good match to figure 19.312 of Merritt R.W., Cummins, K.W., and Berg, M.B. (2019). The species ID is based on Grammotaulius betteni being the only species of this genus known in Washington state.
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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Brown Quill Spinners

Like most common names,"Brown Quill Spinner" can refer to more than one taxon. They're previewed below, along with 5 specimens. For more detail click through to the scientific names.

Mayfly Species Siphlonurus alternatus

These are sometimes called Brown Quill Spinners.
This species occasionally produces important spinner falls. Its spinners may join the swarms of Siphlonurus quebecensis or Siphlonurus rapidus, amplifying the importance of all three species.
Lateral view of a Female Siphlonurus alternatus (Siphlonuridae) (Gray Drake) Mayfly Spinner from the Gallatin River in Montana
I'm tentatively classifying this one as Siphlonurus alternatus, because it seems to fit that species best in the old keys in Needham's Biology of Mayflies, but I'm hesitant because I can't find documentation that southwest Montana or the surrounding area is within the species' range, although they are widely distributed throughout eastern North American and western Canada.
Dorsal view of a Siphlonurus alternatus (Siphlonuridae) (Gray Drake) Mayfly Nymph from the Namekagon River in Wisconsin

Mayfly Species Siphlonurus quebecensis

These are sometimes called Brown Quill Spinners.
This is the Siphlonurus species I have encountered most frequently on Eastern trout waters. I often find its spinners swarming in a mix with Siphlonurus alternatus, and I have read that Siphlonurus rapidus may join these groups as well.
Female Siphlonurus quebecensis (Siphlonuridae) (Gray Drake) Mayfly Dun from unknown in Wisconsin
This one hatched in my house after I brought some nymphs home to photograph.
Lateral view of a Male Siphlonurus quebecensis (Siphlonuridae) (Gray Drake) Mayfly Spinner from the Namekagon River in Wisconsin
Siphlonurus mayfly nymph. These mayflies are known as strong swimmers that maneuver like minnows across the stream bottom

Artistic view of a Siphlonurus quebecensis (Siphlonuridae) (Gray Drake) Mayfly Nymph from the Delaware River in New York

References

Brown Quill Spinners

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