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 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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Identification: Key to Species of Agnetina Adults, Couplet 1
Identification: Key to Species of Agnetina Adults, Couplet 1
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
- 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.