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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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First trout of 2021!

First trout of 2021!

By Troutnut on April 9th, 2021
Friday I drove from the Seattle area out to Yakima, Washington, where a FEMA-run Covid vaccination clinic has so many extra doses and appointments that they're eagerly offering them to people who aren't yet officially eligible. (Washington is one of the last states to open the vaccine to everybody.) I'm looking forward to being able to safely travel on airplanes again and have at least a couple exciting fishing trips planned for this summer.

For now, I just wanted to catch the first fish of the year on my drive home via the Yakima Canyon.



Action on the Yakima was slow, and I'm consistently frustrated there by the difficult access to good spots from the road-side bank. But I did see one single rise, then caught the fish on a nymph.

My first trout of 2021! Not a big one, but a start.


It's a start!

I also collected quite a few nymphs as an excuse to have some fun with the new microscope I got last fall. The highlight was probably finding a specimen of Heptagenia pulla, which isn't known from Washington or neighboring states.

Photos by Troutnut from the Yakima River in Washington

Closeup insects by Troutnut from the Yakima River in Washington

11
Heptagenia pulla Mayfly Nymph
This specimen is interesting because Heptagenia pulla has not been reported from Washington or neighboring states (Saskatchewan is the closest), yet the distinctive key characteristics are clear. Furthermore, it might even be a species not listed on this site—Jacobus et al. (2014) writes, "the northern and western specimens of H. pulla may in fact be a synonym of the Palearctic species H. dalecarlica Bengtsson (Kjaerstad et al. 2012) and the true H. pulla may be restricted to eastern North America." It keys to the genus Heptagenia because the tarsal claw has a single basal tooth, and the gills on segment 7 have fibrils. For the species key in Jacobus et al. (2014): 1. The left mandible is planate, whereas the right mandible is angulate. 2. The labrum is much wider than long. 3. There's a thin light-colored streak lateral to the eye on the head.
12
Isoperla fusca Stonefly Nymph
This specimen keys to Isoperla fusca using the key in Szczytko & Stewart 1979, but some species of Isoperla weren't represented there. It's probably the same species as this one collected a year later. Despite taking many good pictures of both, I'm not sure of the species ID.
9
Female Baetis tricaudatus Mayfly Dun
This dun emerged on my desk from a container of nymphs I was sorting, so I was able to get an ID from the nymphs. I also uploaded photos of a female nymph and a male nymph.
13
Female Baetis tricaudatus Mayfly Nymph
These nymphs were highly abundant in my early April kick net samples from the Yakima Canyon, and one of them emerged into a dun, which I photographed immediately. Similar-looking nymphs but with distinctly brighter color patterns were also abundant. I just photographed one. After extensive views under the microscope, it's clear the bright ones are males and the dull ones are females of the same species. The most likely guess at the species is Baetis tricaudatus, which may be a complex of related species that haven't all been sorted out yet. It isn't a perfect fit to every key characteristic (and I never seem to find a Baetis that matches the expected pronotum color patterns, but that seems to be the closest. The microscope images here were taken with different specimens from the main photos (so I could dissect them while preserving that one intact), but clearly the same species.
14
Male Baetis tricaudatus Mayfly Nymph
This specimen and many like it were found with other specimens I found to be duller-colored females of the same species. I wasn't aware of such a difference between male and female nymphs in Baetids, but all the morphological characteristics I checked in the key were the same, and the color patterns are, too -- just not the brightness.
13
Helicopsyche borealis Caddisfly Pupa
I'm calling this one very tentatively Helicopsyche borealis, with some big caveats that I might be wrong. It seems to key fairly easily to Helicopsychidae, except at the last couplet in Merritt & Cummins (5th ed) it's supposed to have “anal processes short and straight, each with several mesal setae and 2 long apical setae,” whereas this one has VERY short, straight processes with 3 long apical setae and no mesal ones. Additionally, the only species of Helicopsychidae documented in this region is Helicopsyche borealis, which is supposed to emerge much later in the summer.
10
Ephemerella excrucians Mayfly Nymph
9
Ameletus vernalis Mayfly Nymph
I keyed this one out using the Alberta species key from Zloty & Pritchard 1997. Notes from the ID include: 1. Posterior margin of sternites 6-8 without spines 2. Mesal gill extension "well developed" 3. Basil third of caudal filaments pale 4. Anterior surface of front femora mostly pale 5. Dark band on caudal filaments begins around segment 20 6. Final instars early season This one keys out pretty cleanly to Ameletus vernalis except the color pattern on the tergites doesn't match. However, two species known in Washington aren't included in the key. Of those two, Ameletus vancouverensis would be too small (adult body length 9 mm), but Ameletus andersoni (currently documented only from a spring in Cowlitz County) has a wide range of sizes and emergence times that could be compatible with this one. So I can't rule that species out, but Ameletus vernalis seems the most likely.
9
Ephemerella excrucians Mayfly Nymph
5
Pteronarcys californica Stonefly Nymph
This salmonfly nymph is probably not quite fully grown, as it still has a couple months yet to emerge.

References

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