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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This specimen keys to the Epeorus albertae group of species. Of the five species in that group, the two known in Washington state are Epeorus albertae and Epeorus dulciana. Of the two, albertae has been collected in vastly more locations in Washington than dulciana, suggesting it is far more common. On that basis alone I'm tentatively putting this nymph in albertae, with the large caveat that there's no real information to rule out dulciana.
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Identification: Key to Species of Caudatella Nymphs, Couplet 4
Identification: Key to Species of Caudatella Nymphs, Couplet 4
Adapted from Jacobus 2010 (2010)
| Option 1 | Option 2 |
|---|---|
| Cerci approximately one-third length of median filament (about the length of the abdomen) | Cerci approximately one-sixth length of median filament (about half the length of the abdomen) |
| Distinct pair of medial spines present only on abdominal terga 2–9, with the spine tips blunt | Distinct pair of medial spines present on abdominal terga 1–9, with the spine tips sharp |
| Caudatella heterocaudata | Caudatella columbiella |
Adapted from Jacobus 2010 (2010)
The current couplet is highlighted with darker colors and a icon, and couplets leading to this point have a icon.
Leads to Caudatella edmundsi:
- Maxillary palp vestigial; tarsal claw with two prominent rows of denticles
Leads to Couplet 2:
- Maxillary palp with three distinct segments; tarsal claw with only one distinct row of denticles
Couplet 2
Leads to Caudatella hystrix:
- Paired medial spines on abdominal terga long and curved (at least on middle segments), some almost hook like
Leads to Couplet 3:
- Paired medial spines on abdominal terga relatively straight, none longer than respective segment
Couplet 3
Leads to Caudatella jacobi:
- Cerci approximately two thirds length of median filament
- Abdominal sterna with solid color, never with longitudinal stripes or other such markings
Leads to Couplet 4:
- Cerci less than one-half length of median filament
- Abdominal sterna almost always with three dark, longitudinal markings
Couplet 4
Couplet 4 (You are here)
Leads to Caudatella heterocaudata:
- Cerci approximately one-third length of median filament (about the length of the abdomen)
- Distinct pair of medial spines present only on abdominal terga 2–9, with the spine tips blunt
Leads to Caudatella columbiella:
- Cerci approximately one-sixth length of median filament (about half the length of the abdomen)
- Distinct pair of medial spines present on abdominal terga 1–9, with the spine tips sharp
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References
- Jacobus, Luke M. 2010. Taxonomic Review of the Caudatella heterocaudata (McDunnough) and C. hystrix (Traver) Complexes (Insecta: Ephemeroptera: Ephemerellidae). Psyche: A Journal of Entomology 2010: 1-5.