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 dun emerged from a mature nymph on my desk. Unfortunately its wings didn't perfectly dry out.
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Stonefly Family Chloroperlidae (Sallflies)
These stoneflies, the "little yellows" and "little greens," are quite common Summer fauna. They are spread out in a mix between the different genera. The common name for them is Sallfly.
Family Range
Egg-Laying behavior
Time of day: Afternoon and evening
Specimens of the Stonefly Family Chloroperlidae
1 Male Adult
This specimen unfortunately was blown away by the wind mid-way through the photographs, so I wasn't able to preserve it for an ID or get some of the other angles.
6 Female Adults
These stoneflies--abundant during midday--seemed at first to be flying around with plain yellow bodies, but on closer inspection turn out to have striking, fiery red abdomens.
In Baumann's Stoneflies of the Rocky Mountains, this specimen keys to Sweltsa fidelis, but the number of species in that key is fairly small and it might not be accurate.
I didn't key this one out under the microscope, but I just keyed a similar one from Montana and this one matches the macroscopic appearance closely enough that I'm guessing it's the same thing.
These little green stoneflies were the most common bug on a June day fishing the North Fork Couer d'Alene, although the trout never rose more than sporadically to them or anything else.
I collected a few of these throughout the afternoon. The positive ID on the adults allowed me to also put a species ID on the nymphs.
I was not fishing, but happened to be at an unrelated social event on a hill above this tiny creek (which I never even saw) when this stonefly flew by me. I assume it came from there. Some key characteristics are tricky to follow, but process of elimination ultimately led me to Sweltsa borealis. It is reassuringly similar to this specimen posted by Bob Newell years ago. It is also so strikingly similar to this nymph from the same river system that I'm comfortable identifying that nymph from this adult. I was especially pleased with the closeup photo of four mites parasitizing this one.
14 Adults
A large number of photos from the microscope allowed a fairly confident ID on this one, which not coincidentally matches very well a previous specimen of Suwallia pallidula that I collected in Washington.
This specimen was completely green when I collected it from among many others gathered on a midstream rock along with their nymphal shucks early in the morning. There was also a yellow one with them, which I assumed was a different species. Now that I've seen how this one started changing from green to yellow, I have to wonder if they weren't the same species and the yellow one was just older.
Another yellow stonefly from Touchet Corral.
At Touchet Corral.
This is another stonefly that lives its nymphal life in the hyporheic zone, flood plain gravels. In this case, the gravels of a small stream, Roy's Creek, that flows into Flathead Lake at the Univ. of Montana Biological Station.
11 Nymphs
(Edit: I'm putting a species ID on this one based on the great similarity of its markings to those of an adult I collected in 2023 from a tributary of the same river at around the same time of year.)
This one was tricky to identify. The "thick, depressed dark clothing hairs" on the thoracic sterna inside the coxae, which indicate Sweltsa, are fairly sparse and very difficult to see in my photos, although more apparent under the microscope. However, if I decide those hairs are too sparse to be "thick" and follow the key, I end up pretty clearly at Haploperla. However, Haploperla should have the inner margin of the hind wingpads approximately parallel to the body axis, and they're clearly divergent on this specimen. The pronotal fringe hairs should also be longer than they are in this specimen. So following that whole branch of the key was probably wrong, which leads back to this one being Sweltsa. Unfortunately, nymphs have only been described for a small number of Sweltsa species.
I found just a few of these nymphs alongside a much larger number of bland, typical Sweltsa nymphs.
This one was tricky to identify. The "thick, depressed dark clothing hairs" on the thoracic sterna inside the coxae, which indicate Sweltsa, are fairly sparse and very difficult to see in my photos, although more apparent under the microscope. However, if I decide those hairs are too sparse to be "thick" and follow the key, I end up pretty clearly at Haploperla. However, Haploperla should have the inner margin of the hind wingpads approximately parallel to the body axis, and they're clearly divergent on this specimen. The pronotal fringe hairs should also be longer than they are in this specimen. So following that whole branch of the key was probably wrong, which leads back to this one being Sweltsa. Unfortunately, nymphs have only been described for a small number of Sweltsa species.
I found just a few of these nymphs alongside a much larger number of bland, typical Sweltsa nymphs.
This species was fairly abundant in a February sample of the upper Yakima.
This was by far the most abundant stonefly in my sample on May 14th.
This specimen keys out to Suwallia, for which I did not find any nymph species keys. However, I'm placing it in Suwallia pallidula because I caught a few adults in the same spot that closely resembled the abundant nymphs and keyed them out to species. Features I noted under the microscope when keying this specimen to genus included apical hairs of cercal segments that were directed at posterior angles, and the longest apical hairs of distal segments were shorter than their following segment.
This species is uncommonly collected except from wells. It is a hyporheic species living in the river gravels of river floodplains until it is ready to emerge.
The head shape is an important identifier.
The head shape is an important identifier.
2 Streamside Pictures of Chloroperlidae Stoneflies:
Start a Discussion of Chloroperlidae
References
- Swisher, Doug and Carl Richards. 2000. Selective Trout. The Lyons Press.
