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 an interesting one. Following the keys in Merritt R.W., Cummins, K.W., and Berg, M.B. (2019) and Jacobus et al. (2014), it keys clearly to Ephemerella. Jacobus et al provide a key to species, but some of the characteristics are tricky to interpret without illustrations. If I didn't make any mistakes, this one keys to Ephemerella mucronata, which has not previously been reported any closer to here than Montana and Alberta. The main character seems to fit well: "Abdominal terga with prominent, paired, subparallel, spiculate ridges." Several illustrations or descriptions of this holarctic species from the US and Europe seem to match, including the body length, tarsal claws and denticles, labial palp, and gill shapes. These sources include including Richard Allen's original description of this species in North America under the now-defunct name E. moffatae in Allen RK (1977) and the figures in this description of the species in Italy.
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Identification: Key to Species of Agnetina Nymphs, Couplet 1
Identification: Key to Species of Agnetina Nymphs, Couplet 1
Adapted from Stark et al (1986)
| Option 1 | Option 2 |
|---|---|
Apex of tergum 10 dark 
| Apex of tergum 10 light 
|
| Remaining species: Agnetina capitata and Agnetina flavescens | |
3 Example Specimens
I took a few closeup pictures of this stonely with my old camera and a microscope.
| |
| Agnetina annulipes | Go to Couplet 2 |
Adapted from Stark et al (1986)
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 Agnetina annulipes:
- Apex of tergum 10 dark
Leads to Couplet 2:
- Apex of tergum 10 light
Couplet 2
Leads to Agnetina capitata:
- Arms of light-colored M-shaped line on head directed essentially laterally
- Dark pigment of tergum 10 continuous
Leads to Agnetina flavescens:
- Arms of light-colored M-shaped line on head directed posterolaterally
- Dark pigment of tergum 10 interrupted mesally
Start a Discussion of this Couplet
References
- Jacobus, L. M., Wiersema, N.A., and Webb, J.M. 2014. Identification of Far Northern and Western North American Mayfly Larvae (Insecta: Ephemeroptera), North of Mexico; Version 2. Joint Aquatic Science meeting, Portland, OR. Unpublished workshop manual. 1-176.
- 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.
- Stark, B.P. 1986. The Nearctic Species of Agnetina (Plecoptera: Perlidae). Journal of the Kansas Entomological Society 59(3): 437-445.