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.
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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.
- 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.
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Arthropod Class Collembola (Springtails)
Collembola are actually a subclass of a class called Entognatha. They are the most common of the only six-legged arthropods (Hexapods) that aren't insects. Many Collembolans are terrestrial, but some live on the surface of their water, and they can be a supplemental food source for trout, especially young-of-the-year trout.
They rarely grow longer than 6mm or occur in trout streams in such numbers that an imitation with a fly is warranted, but they are interesting creatures.
They rarely grow longer than 6mm or occur in trout streams in such numbers that an imitation with a fly is warranted, but they are interesting creatures.
1 Streamside Picture of Springtails:
This is Troutnut.com's first picture of a springtail, a type of six-legged, non-insect arthropod. It's riding on the surface film under the mayfly's left tail.
In this picture: Arthropod Class Collembola (Springtail) and Mayfly Genus Cinygmula (Dark Red Quill).
Start a Discussion of Collembola
References
- Merritt R.W., Cummins, K.W., and Berg, M.B. 2019. An Introduction to the Aquatic Insects of North America (Fifth Edition). Kendall/Hunt Publishing Company.
Arthropod Class Collembola (Springtails)
Taxonomy
8 orders (Entomobryidae, Hypogastruridae, Isotomidae, Mackenziellidae, Neelidae, Onchyiuridae, Onychiuridae, and Sminthuridae) aren't included.