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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
Baetis

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 Glossosoma (Glossosomatidae) (Little Brown Short-horned Sedge) Caddisfly Larva from the Yakima River in Washington
I caught this tiny larva without a case, but it seems to key pretty clearly to to Glossosomatidae. From there, the lack of sclerites on the mesonotum points to either Glossosoma or Anagapetus. Although it's difficult to see in a 2D image from the microscope, it's pretty clear in the live 3D view that the pronotum is only excised about 1/3 of its length to accommodate the forecoxa, not 2/3, which points to Glossosoma at Couplet 5 of the Key to Genera of Glossosomatidae Larvae.
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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Wwelz
Posts: 2
Wwelz on Jun 26, 2008June 26th, 2008, 2:49 am EDT
I was fishing the Natchaug river a steam in eastern ct on June 23 from five pm till dark. I saw a couple of sulphurs size 18 on the water at six pm. As the evening went on the fish were acting like they were chasing nymphs to the surface sometimes leaping totally out of the water. They were also swirling for something right under the surface. I caught a few fish on a sulphur dry fly but lots of refusals. I never saw a dun emerge after six pm or any sign of any insect emerging. I tried many emerger patterns under the surface with no luck. whats going on here? Behavioral drift?
GONZO
Site Editor
"Bear Swamp," PA

Posts: 1681
GONZO on Jun 26, 2008June 26th, 2008, 6:43 am EDT
Wwelz,

What you describe sounds very much like what happens when a strong caddisfly emergence coincides with a minor emergence of mayflies. Here are the italicized headings Gary LaFontaine uses in the section "Learning to Recognize a Caddisfly Emergence" in Caddisflies:

One, a trout occasionally leaps into the air.
Two, most of the feeding trout are bulging or splashing.
Three. There are no insects on the surface.

Although these signs do not apply to all caddisfly emergences (some do not emerge on the surface), and other activity could also be the cause, it is a good possibility that this is what you witnessed. Unlike many mayfly emergences, adult caddisflies often are not as obvious on the surface or in the air during an emergence. The times when we see large numbers of caddisflies flying about are usually during mating flights. Unless these coincide with an emergence, they typically have little to do with the feeding activity of trout until the females start laying eggs. (There are a few exceptions to this. For example, I often see trout leaping for the tightly clustered adults in black dancer [Mystacides] mating swarms.)

What I usually do when confronted with the situation you describe is to hold a pocket nymph seine at the surface in a strong line of drift. Sometimes emerging caddisflies are captured, but even when they are not, the filmy, transparent shucks left by emerging caddisflies often show up in the net.
Wwelz
Posts: 2
Wwelz on Jun 26, 2008June 26th, 2008, 9:54 am EDT
Thank you - I think you are right . I will try your suggestions

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