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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.

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 Caudatella Nymphs, Couplet 4

Identification: Key to Species of Caudatella Nymphs, Couplet 4

Adapted from Jacobus 2010 (2010)
Option 1Option 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 bluntDistinct 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

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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

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