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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 Genera of Rhyacophilidae Adults

Identification: Key to Genera of Rhyacophilidae Adults

Adapted from Merritt R.W., Cummins, K.W., and Berg, M.B. (2019)
This couplet refers figures (usually designated 'sf') from this source.
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Option 1Option 2
Mesoscutellum without long hairs
Figure from this Rhyacophila adult.
Mesoscutellum with tuft of long, fine hairs
Forewings each less than 20 mm longForewings each more than 20 mm long
WidespreadPacific states
Adults as in sf 10.191
1 Example Specimen
Rhyacophila Himalopsyche
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Couplet 1

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Couplet 1 (You are here)
Leads to Rhyacophila:
  • Mesoscutellum without long hairs
  • Forewings each less than 20 mm long
  • Widespread
  • Adults as in sf 10.191
Leads to Himalopsyche
(Himalopsyche phryganea):
  • Mesoscutellum with tuft of long, fine hairs
  • Forewings each more than 20 mm long
  • Pacific states

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