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.
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It's only barely visible in one of my pictures, but I confirmed under the microscope that this one has a prosternal horn and the antennae are mid-way between the eyes and front of the head capsule.
I'm calling this one Pycnopsyche, but it's a bit perplexing. It seems to key definitively to at least Couplet 8 of the Key to Genera of Limnephilidae Larvae. That narrows it down to three genera, and the case seems wrong for the other two. The case looks right for Pycnopsyche, and it fits one of the key characteristics: "Abdominal sternum II without chloride epithelium and abdominal segment IX with only single seta on each side of dorsal sclerite." However, the characteristic "metanotal sa1 sclerites not fused, although often contiguous" does not seem to fit well. Those sclerites sure look fused to me, although I can make out a thin groove in the touching halves in the anterior half under the microscope. Perhaps this is a regional variation.
The only species of Pycnopsyche documented in Washington state is Pycnopsyche guttifera, and the colors and markings around the head of this specimen seem to match very well a specimen of that species from Massachusetts on Bugguide. So I am placing it in that species for now.
Whatever species this is, I photographed another specimen of seemingly the same species from the same spot a couple months later.
I'm calling this one Pycnopsyche, but it's a bit perplexing. It seems to key definitively to at least Couplet 8 of the Key to Genera of Limnephilidae Larvae. That narrows it down to three genera, and the case seems wrong for the other two. The case looks right for Pycnopsyche, and it fits one of the key characteristics: "Abdominal sternum II without chloride epithelium and abdominal segment IX with only single seta on each side of dorsal sclerite." However, the characteristic "metanotal sa1 sclerites not fused, although often contiguous" does not seem to fit well. Those sclerites sure look fused to me, although I can make out a thin groove in the touching halves in the anterior half under the microscope. Perhaps this is a regional variation.
The only species of Pycnopsyche documented in Washington state is Pycnopsyche guttifera, and the colors and markings around the head of this specimen seem to match very well a specimen of that species from Massachusetts on Bugguide. So I am placing it in that species for now.
Whatever species this is, I photographed another specimen of seemingly the same species from the same spot a couple months later.
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Spatsizi
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Posts: 1
Spatsizi on Sep 15, 2006September 15th, 2006, 3:09 pm EDT
Hello Jason - this is a fabulous site. Are you from Ithaca!
Anyway, I've been finding what I think are small mayfly larvae in a stream near here. How small can mayfly larvae get? And do they emerge in singles? The trout and shiners are sipping something fairly regularly.
I have a little 6 1/2 foot 3 weight, and I'm thinking of trying to find a nymph or fly that would be an imitation of these.
Anyway, I've been finding what I think are small mayfly larvae in a stream near here. How small can mayfly larvae get? And do they emerge in singles? The trout and shiners are sipping something fairly regularly.
I have a little 6 1/2 foot 3 weight, and I'm thinking of trying to find a nymph or fly that would be an imitation of these.
Troutnut on Sep 15, 2006September 15th, 2006, 3:22 pm EDT
Hi Spatsizi,
Yeah, I'm in Ithaca! I finished Cornell in January and I'm sticking around for a while before heading to grad school in Alaska next summer.
Mayfly larvae (nymphs, actually) can get just about microscopic, because they may have just hatched from the tiny egg, especially at this time of year. But if you're seeing trout sip something on the surface at this time of year, it's probably not mayfly nymphs, unless they're full-grown nymphs of a tiny mayfly species just about to emerge (2-4mm Tricorythodes mayflies might be around).
Which stream, and have you seen adult insects on the water when the trout are sipping? At this time of year the most likely culprit for that sort of thing would probably be flying ants. It sounds like you might need a dry fly instead of a nymph.
Yeah, I'm in Ithaca! I finished Cornell in January and I'm sticking around for a while before heading to grad school in Alaska next summer.
Mayfly larvae (nymphs, actually) can get just about microscopic, because they may have just hatched from the tiny egg, especially at this time of year. But if you're seeing trout sip something on the surface at this time of year, it's probably not mayfly nymphs, unless they're full-grown nymphs of a tiny mayfly species just about to emerge (2-4mm Tricorythodes mayflies might be around).
Which stream, and have you seen adult insects on the water when the trout are sipping? At this time of year the most likely culprit for that sort of thing would probably be flying ants. It sounds like you might need a dry fly instead of a nymph.
Jason Neuswanger, Ph.D.
Troutnut and salmonid ecologist
Troutnut and salmonid ecologist
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