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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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Artistic view of a Female Ephemera varia (Ephemeridae) (Yellow Drake) Mayfly Dun from Aquarium in New York
This yellow drake dun hatched out of my aquarium over a month before her brethren in the wild are slated to emerge. She seems a bit small, and that might be the reason.
GONZO
Site Editor
"Bear Swamp," PA

Posts: 1681
GONZO on May 21, 2007May 21st, 2007, 6:35 am EDT
This is a fine specimen of one of the prettiest mayflies, Jason. She is small compared to some limestone specimens, but well within range for the species. I've collected varia males as small as 12mm, but many of the limestone females are 19-20mm. I think premature hatching is to be expected in aquaria.

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