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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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Motrout
Motrout's profile picture
Posts: 319
Motrout on Jun 28, 2010June 28th, 2010, 1:06 am EDT
I'm headed up to the Adirondacks tomorrow for a two week trip, and I was planning to spend most of my time on the West Branch of the Ausable. With that said, I got a call from a friend who lives up there last night, telling me the Hex hatch was on on the ponds. This is a fly I've never encountered before, but he said they are really large , something like #6 or #8, so I thought it might be worth checking out. Does anyone know of any good dry fly patterns to imitate them? Also, what time of day do they usually come off?
"I don't know what fly fishing teaches us, but I think it's something we need to know."-John Gierach
http://fishingintheozarks.blogspot.com/

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