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.
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.
Mayfly Species Iswaeon rubrolaterale (Little Olives)
Species Range
Physical description
Most physical descriptions on Troutnut are direct or slightly edited quotes from the original scientific sources describing or updating the species, although there may be errors in copying them to this website. Such descriptions aren't always definitive, because species often turn out to be more variable than the original describers observed. In some cases, only a single specimen was described! However, they are useful starting points.
Male Spinner
Wing length: 4 mm
Abdominal tergites 2-6 of male imago pale yellowish white; large lateral maroon patches on each.
Turbinate eyes of moderate size, almost circular; reddish brown in dried specimen. Head and thorax deep blackish; pleural membranes paler brown. Legs pale yellowish white; fore femur with smoky tinges. Wings hyaline, venation pale. Abdominal tergites 2-6 pale yellowish white; very distinct large lateral maroon or wine-colored patches on each; sternites pale, each with a small brown dot near the center, on the mid-ventral line. Tergites 7-10 sepia brown; lateral patches visible in certain lights; sternites paler brown, with mid-ventral dark dots. Tails and forceps pale.
The prominent wine-colored lateral patches on the tergites distinguish this species from all others thus far described.
Start a Discussion of Iswaeon rubrolaterale
References
- Needham, James G., Jay R. Traver, and Yin-Chi Hsu. 1935. The Biology of Mayflies. Comstock Publishing Company, Inc.
Mayfly Species Iswaeon rubrolaterale (Little Olives)
Species Range
Common Name
Resources
- NatureServe
- Integrated Taxonomic Information System
- Global Biodiversity Information Facility
- Described by McDunnough (1931)