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 specimen keys to the Epeorus albertae group of species. Of the five species in that group, the two known in Washington state are Epeorus albertae and Epeorus dulciana. Of the two, albertae has been collected in vastly more locations in Washington than dulciana, suggesting it is far more common. On that basis alone I'm tentatively putting this nymph in albertae, with the large caveat that there's no real information to rule out dulciana.
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Identification: Key to Genera of Glossosomatidae Larvae, Couplet 1
Identification: Key to Genera of Glossosomatidae Larvae, Couplet 1
Error: Tried to access a key that isn't live.
Adapted from Merritt R.W., Cummins, K.W., and Berg, M.B. (2019)
This couplet refers figures (usually designated 'sf') from this source.
You will need the source (make sure to get the same edition!) to see them.
This couplet refers figures (usually designated 'sf') from this source.
You will need the source (make sure to get the same edition!) to see them.
| Option 1 | Option 2 |
|---|---|
| Mesonotum with 2 or 3 sclerites (sf 19.156, 19.157, sometimes hard to see) | Mesonotum without sclerites |
| Head with ventromesal margins of genae not thickened | Head with ventromesal margins of genae thickened |
| Posterior median ventral ecdysial line about 1.5 times as long as each anterior divergent branch (sf 19.159, 19.160) | Posterior median ventral ecdysial line about as long as each anterior divergent branch (sf 19.158) |
| Anal opening without dark, sclerotized line on each side | Anal opening with dark, sclerotized line on each side (sf 19.60, 19.164) |
| Remaining genera: Agapetus, Culoptila, Padunia, and Protoptila | Remaining genera: Anagapetus and Glossosoma |
1 Example Specimen
I caught this tiny larva without a case, but it seems to key pretty clearly to to Glossosomatidae. From there, the lack of sclerites on the mesonotum points to either Glossosoma or Anagapetus. Although it's difficult to see in a 2D image from the microscope, it's pretty clear in the live 3D view that the pronotum is only excised about 1/3 of its length to accommodate the forecoxa, not 2/3, which points to Glossosoma at Couplet 5 of the Key to Genera of Glossosomatidae Larvae.
| |
| Go to Couplet 2 | Go to Couplet 5 |
Adapted from Merritt R.W., Cummins, K.W., and Berg, M.B. (2019)
The current couplet is highlighted with darker colors and a icon, and couplets leading to this point have a icon.
Couplet 1 (You are here)
Leads to Couplet 2:
- Mesonotum with 2 or 3 sclerites (sf 19.156, 19.157, sometimes hard to see)
- Head with ventromesal margins of genae not thickened
- Posterior median ventral ecdysial line about 1.5 times as long as each anterior divergent branch (sf 19.159, 19.160)
- Anal opening without dark, sclerotized line on each side
Couplet 2
Leads to Couplet 5:
- Mesonotum without sclerites
- Head with ventromesal margins of genae thickened
- Posterior median ventral ecdysial line about as long as each anterior divergent branch (sf 19.158)
- Anal opening with dark, sclerotized line on each side (sf 19.60, 19.164)
Couplet 5
Leads to Padunia
(Padunia jeanae):
(Padunia jeanae):
- Each tarsal claw apparently trifid, with 3 points subequal in length (sf 19.161)
- Southeast
Padunia
(Padunia jeanae)
(Padunia jeanae)
Leads to Couplet 4:
- Each tarsal claw with normal single point, basal seta and basal process much smaller (sf 19.162, 19.163)
Couplet 4
Leads to Protoptila:
- Basal seta of each tarsal claw long, thin, and arising from side of stout basal process (sf 19.163)
- Case constructed with some relatively large stones (sf 19.167)
- Widespread
Leads to Glossosoma:
- Pronotum excised 1/3rd anterolaterally to accommodate coxae (sf 19.165)
- Dome-like case of stones with transverse ventral strap of finer sand and interchangeable ends (sf 19.38, 19.459a, 19.459b)
- Widespread
Leads to Anagapetus:
- Pronotum excised 2/3rds anterolaterally to accommodate coxae (sf 19.166)
- Case similar to that at left
- West
Anagapetus
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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.