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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Some characteristics from the microscope images for the tentative species id: The postero-lateral projections are found only on segment 9, not segment 8. Based on the key in Jacobus et al. (2014), it appears to key to Neoleptophlebia adoptiva or Neoleptophlebia heteronea, same as this specimen with pretty different abdominal markings. However, distinguishing between those calls for comparing the lengths of the second and third segment of the labial palp, and this one (like the other one) only seems to have two segments. So I'm stuck on them both. It's likely that the fact that they're immature nymphs stymies identification in some important way.
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Black and Olive Duns
Like most common names,"Black and Olive Dun" can refer to more than one taxon. They're previewed below, along with 2 specimens. For more detail click through to the scientific names.
Mayfly Species Leptophlebia johnsoni
These are sometimes called Black and Olive Duns.
Mayfly Species Hexagenia atrocaudata
These are very rarely called Black and Olive Duns.
This species is slightly smaller than Hexagenia limbata and it occurs later in the year. It is only mentioned in passing by a few authors, but it can be locally important.
I found this lone Hexagenia atrocaudata dun fluttering by herself on the surface of a small, still stretch of river one evening as I paddled home from fishing for smallmouths in the warm August weather.
I found this spinner and a few of his friends bobbing above the river amidst a snowstorm hatch of white Ephoron flies.
See 1 more specimen...
References
- Jacobus, L. M., Wiersema, N.A., and Webb, J.M. 2014. Identification of Far Northern and Western North American Mayfly Larvae (Insecta: Ephemeroptera), North of Mexico; Version 2. Joint Aquatic Science meeting, Portland, OR. Unpublished workshop manual. 1-176.