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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 Grammotaulius betteni (Limnephilidae) (Northern Caddisfly) Caddisfly Larva from the Yakima River in Washington
This is a striking caddis larva with an interesting color pattern on the head. Here are some characteristics I was able to see under the microscope, but could not easily expose for a picture:
- The prosternal horn is present.
- The mandible is clearly toothed, not formed into a uniform scraper blade.
- The seems to be only 2 major setae on the ventral edge of the hind femur.
- Chloride epithelia seem to be absent from the dorsal side of any abdominal segments.
Based on these characteristics and the ones more easily visible from the pictures, this seems to be Grammotaulius. The key's description of the case is spot-on: "Case cylindrical, made of longitudinally arranged sedge or similar leaves," as is the description of the markings on the head, "Dorsum of head light brownish yellow with numerous discrete, small, dark spots." The spot pattern on the head is a very good match to figure 19.312 of Merritt R.W., Cummins, K.W., and Berg, M.B. (2019). The species ID is based on Grammotaulius betteni being the only species of this genus known in Washington state.
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 3

Identification: Key to Species of Caudatella Nymphs, Couplet 3

Adapted from Jacobus 2010 (2010)
Option 1Option 2
Cerci approximately two thirds length of median filamentCerci less than one-half length of median filament
Abdominal sterna with solid color, never with longitudinal stripes or other such markingsAbdominal sterna almost always with three dark, longitudinal markings
Remaining species: Caudatella columbiella and Caudatella heterocaudata
Caudatella jacobi Go to Couplet 4
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
Couplet 3

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Couplet 3 (You are here)
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
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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