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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Stonefly Genus Hesperoperla (Golden Stones)
The important western genus Hesperoperla currently has only two species. See the species hatch pages for details.
Genus Range
Identification
To determine whether a specimen of Perlidae belongs to Hesperoperla, use the Key to Genera of Perlidae Nymphs.
Specimens of the Stonefly Genus Hesperoperla
1 Male Adult
4 Female Adults
My blurry photo at first makes it look like there might be a distinct notch in the subgenital plate of this specimen, but that's not the case -- just a poor photo. That's important to the ID.
I collected this specimen as a nymph and had it in line to be photographed, but it emerged inside my holding container before I got the chance. However, I was able to get some interesting photos of the very freshly-emerged adult that really demonstrate how strikingly colors can change within a few short hours after emergence. The before-and-after pictures are combined here under a single specimen since they portray the same individual at different times within the same stage.
Based on the identification of another specimen from the same date/site, I'm calling this Hesperoperla pacifica.
Based on the identification of another specimen from the same date/site, I'm calling this Hesperoperla pacifica.
Fly fishermen refer to this stonefly as one of "golden stones".
4 Nymphs
This monster started to feed within a few minutes of sharing the inspection tray with its victims. This nymph is a voracious predator of small invertebrates and has even been noted for feeding on small fish and salmonid alevins. The niche it fills in fast water is equivalent to the Dragonfly nymphs that inhabit slower water.
Hesperoperla pacifica nymphs are easily distinguished from other western perlids by the presence of anal gills (obfuscated by algae in the tray) in combination with an hour glass shaped pale mark on the front of their heads.
Hesperoperla pacifica nymphs are easily distinguished from other western perlids by the presence of anal gills (obfuscated by algae in the tray) in combination with an hour glass shaped pale mark on the front of their heads.
Start a Discussion of Hesperoperla
References
- Schwiebert, Ernest G. 1955. Matching the Hatch. MacMillan Publishing Company.
Stonefly Genus Hesperoperla (Golden Stones)
Taxonomy
Species in Hesperoperla
Hesperoperla pacificaWillowflies
9
73
Species in Hesperoperla: Hesperoperla pacifica
1 species (Hesperoperla hoquei) isn't included.