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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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Closeup insects by Bnewell from the Touchet River in Washington

Onocosmoecus unicolor (Limnephilidae) (Great Late-Summer Sedge) Caddisfly Adult from the Touchet River in Washington
Male Paraleptophlebia bicornuta (Leptophlebiidae) (Mahogany Dun) Mayfly Dun from the Touchet River in Washington
You wonder sometimes how certain insects get their common names. This one is called the 'mahogany dun' for some unknown reason.

Comments / replies

Entoman
Entoman's profile picture
Northern CA & ID

Posts: 2604
Entoman on Oct 6, 2011October 6th, 2011, 9:09 am EDT
Hi Bob,

You wonder sometimes how certain insects get their common names. This one is called the 'mahogany dun' for some unknown reason.

Yeah, I agree with you that Blue Quill (defined as a dun hackled, peacock quill bodied fly) is a better handle for this specimen. As to why it's stuck with the name Mahogany Dun, I'm afraid it is a victim of lumping as important species of leptophlebiids are mahogany colored. Important baetids go by the name Blue-Winged Olive in spite of having brown bodies for the same unfortunate reason.

Regards,

Kurt
"It's not that I find fishing so important, it's just that I find all other endeavors of Man equally unimportant... And not nearly as much fun!" Robert Traver, Anatomy of a Fisherman

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