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Lateral view of a Female Hexagenia limbata (Ephemeridae) (Hex) Mayfly Dun from the Namekagon River in Wisconsin
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.

Dorsal view of a Neoleptophlebia (Leptophlebiidae) Mayfly Nymph from the Yakima River in Washington
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.
27" brown trout, my largest ever. It was the sub-dominant fish in its pool. After this, I hooked the bigger one, but I couldn't land it.
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Identification: Key to Species of Agnetina Nymphs, Couplet 1

Identification: Key to Species of Agnetina Nymphs, Couplet 1

Adapted from Stark et al (1986)
Option 1Option 2
Apex of tergum 10 dark
Nymphal tergum 10 of Agnetina annulipes.
Nymphal tergum 10 of Agnetina annulipes. Figure source: Stark et al (1986)
Apex of tergum 10 light
Nymphal tergum 10 of Agnetina flavescens.
Nymphal tergum 10 of Agnetina flavescens. Figure source: Stark et al (1986)
Remaining species: Agnetina capitata and Agnetina flavescens
3 Example Specimens
Agnetina annulipes Go to Couplet 2
Adapted from Stark et al (1986)
The current couplet is highlighted with darker colors and a icon, and couplets leading to this point have a icon.
Couplet 1

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Couplet 1 (You are here)
Leads to Agnetina annulipes:
  • Apex of tergum 10 dark
Leads to Couplet 2:
  • Apex of tergum 10 light
Couplet 2
Leads to Agnetina capitata:
  • Arms of light-colored M-shaped line on head directed essentially laterally
  • Dark pigment of tergum 10 continuous
Leads to Agnetina flavescens:
  • Arms of light-colored M-shaped line on head directed posterolaterally
  • Dark pigment of tergum 10 interrupted mesally

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References

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