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Lateral view of a Male Baetis (Baetidae) (Blue-Winged Olive) Mayfly Dun from Mystery Creek #43 in New York
Blue-winged Olives

Tiny Baetis mayflies are perhaps the most commonly encountered and imitated by anglers on all American trout streams due to their great abundance, widespread distribution, and trout-friendly emergence habits.

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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Posts: 77
Goose on Sep 13, 2006September 13th, 2006, 1:47 am EDT
Jason, first of all, great photos of the caddis larva. Questions: Using Fontaine's emerger patterns, would you tie this fly with a green body, dark throax, and tan or brown antron for the sheath (bubble)? Is the brown case the green sedge is in what we're trying to simulate with the antron bubble? I hope these questions are understandable. Thanks, Goose
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Bellevue, WA

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Troutnut on Sep 13, 2006September 13th, 2006, 5:05 am EDT
Well, the emerger is going to be a pupa rather than a larva, so you would want to imitate something that looks like this specimen.

There's one important feature you can't see in my pictures: just when it's about to emerge, the fly supposedly secretes some air bubbles underneath the outer skin of the pupa to buoy it to the surface. I haven't seen this myself, but I trust LaFontaine's observations. The air bubbles give it a sparkly look, which he started to imitate with the antron bubble.

His rationale was that the structure of the yarn traps little air bubbles in the same way as the actual pupa, so the sparkling would come from the bubbles rather than the yarn itself. This strikes me as a little strange, since I can't get the patterns to trap much air and the sparkling in the yarn itself seems much more prominent.

Since the yarn is really meant to help imitate bubbles trapped under the skin of the body, I think it should be roughly the same color as the body. Trial and error might prove me wrong, but there's no apparent imitative reason to make the colors different.

I would tie the imitation with a brown/tan thorax and wing pads, and a green body and green antron sheath. I haven't fished a really good Rhyacophila emergence so I don't know how well this would work, but those would be my choices based on looking at the insect.

Jason Neuswanger, Ph.D.
Troutnut and salmonid ecologist

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