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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.

Identification: Key to Species of Caudatella Nymphs, Couplet 2

Adapted from Jacobus 2010 (2010)
Option 1Option 2
Paired medial spines on abdominal terga long and curved (at least on middle segments), some almost hook likePaired medial spines on abdominal terga relatively straight, none longer than respective segment
Remaining species:
Caudatella columbiella
Caudatella heterocaudata
Caudatella jacobi
1 Example Specimen
Caudatella hystrix  Mayfly Nymph
This is a widely distributed species in western Montana but never abundant. Note the length of the middle tail, a key to the identification of this genus.
Caudatella hystrix Go to Couplet 3
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.
Maxillary palp vestigial; tarsal claw with two prominent rows of denticles
Maxillary palp with three distinct segments; tarsal claw with only one distinct row of denticles
Couplet 2
Couplet 2

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Paired medial spines on abdominal terga long and curved (at least on middle segments), some almost hook like
Paired medial spines on abdominal terga relatively straight, none longer than respective segment
Couplet 3
Cerci approximately two thirds length of median filament
Abdominal sterna with solid color, never with longitudinal stripes or other such markings
Cerci less than one-half length of median filament
Abdominal sterna almost always with three dark, longitudinal markings
Couplet 4
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
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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