Blue-winged Olives
Baetis
Tiny Baetis mayflies are perhaps the most commonly encountered and imitated by anglers on all American trout streams due to their great abundance, widespread distribution, and trout-friendly emergence habits.
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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 Adults
Identification: Key to Species of Agnetina Adults
Adapted from Stark et al (1986)
| Option 1 | Option 2 |
|---|---|
Femora transversely banded 
| Femora longitudinally banded 
|
Male hemitergal process foot-shaped with long slender ankle and toe 
| Male hemitergal process either with toe blunt or ankle short 
|
Female subgenital plate truncate, dark pigment covers sternum 8 in continuous mesal band 
| Female subgenital plate rounded with areas of basolateral dark pigment 
|
| Remaining species: Agnetina capitata and Agnetina flavescens | |
2 Example Specimens
This stonefly emerged in my aquarium, and unfortunately I severely damaged its wings just trying to catch it. It's still an interesting specimen, especially since I was able to also photograph the nymphal shuck it emerged from. I was surprised by just how light it was shortly after emerging. I photographed it a couple days later when it had darkened considerably; it was a pale, almost pastel yellow at first.
| |
| 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:
- Femora transversely banded
- Male hemitergal process foot-shaped with long slender ankle and toe
- Female subgenital plate truncate, dark pigment covers sternum 8 in continuous mesal band
Leads to Couplet 2:
- Femora longitudinally banded
- Male hemitergal process either with toe blunt or ankle short
- Female subgenital plate rounded with areas of basolateral dark pigment
Couplet 2
Leads to Agnetina capitata:
- Ventral margin of femora dark forming mesal yellow window
- Apical portion of male hemitergal process long and sinuate, toe bluntly rounded
- Dark pirgment areas on female sterna 8 and 9 large quadrangular
Leads to Agnetina flavescens:
- Ventral margin of femora light
- Swollen area of male hemitergal process adjacent to foot obscuring ankle area
- Dark pigment areas of female sterna 8 and 9 not quadrangular
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.