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Artistic view of a Male Pteronarcys californica (Pteronarcyidae) (Giant Salmonfly) Stonefly Adult from the Gallatin River in Montana
Salmonflies
Pteronarcys californica

The giant Salmonflies of the Western mountains are legendary for their proclivity to elicit consistent dry-fly action and ferocious strikes.

Dorsal view of a Ephemerella mucronata (Ephemerellidae) Mayfly Nymph from the Yakima River in Washington
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.
27" brown trout, my largest ever. It was the sub-dominant fish in its pool. After this, I hooked the bigger one, but I couldn't land it.
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Sweltsa borealis (Boreal Sallfly) Stonefly Nymph Pictures

(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.

Sweltsa borealis (Chloroperlidae) (Boreal Sallfly) Stonefly Nymph from the South Fork Snoqualmie River in Washington
Ventral view of a Sweltsa borealis (Chloroperlidae) (Boreal Sallfly) Stonefly Nymph from the South Fork Snoqualmie River in Washington
Sweltsa borealis (Chloroperlidae) (Boreal Sallfly) Stonefly Nymph from the South Fork Snoqualmie River in Washington
Sweltsa borealis (Chloroperlidae) (Boreal Sallfly) Stonefly Nymph from the South Fork Snoqualmie River in Washington
Sweltsa borealis (Chloroperlidae) (Boreal Sallfly) Stonefly Nymph from the South Fork Snoqualmie River in Washington
Sweltsa borealis (Chloroperlidae) (Boreal Sallfly) Stonefly Nymph from the South Fork Snoqualmie River in Washington
Sweltsa borealis (Chloroperlidae) (Boreal Sallfly) Stonefly Nymph from the South Fork Snoqualmie River in Washington
This super-enhanced false color image shows the length of the hairs around the cercal segments, and important key characteristic, better than the natural-color version does.

Sweltsa borealis (Chloroperlidae) (Boreal Sallfly) Stonefly Nymph from the South Fork Snoqualmie River in Washington
Sweltsa borealis (Chloroperlidae) (Boreal Sallfly) Stonefly Nymph from the South Fork Snoqualmie River in Washington
Dorsal view of a Sweltsa borealis (Chloroperlidae) (Boreal Sallfly) Stonefly Nymph from the South Fork Snoqualmie River in Washington
Ruler view of a Sweltsa borealis (Chloroperlidae) (Boreal Sallfly) Stonefly Nymph from the South Fork Snoqualmie River in Washington The smallest ruler marks are 1 mm.
Sweltsa borealis (Chloroperlidae) (Boreal Sallfly) Stonefly Nymph from the South Fork Snoqualmie River in Washington
The dark hairs indicative of Sweltsa were not very easily visible in the main camera pictures of this specimen, but they they show up more easily under the microscope.

Sweltsa borealis (Chloroperlidae) (Boreal Sallfly) Stonefly Nymph from the South Fork Snoqualmie River in Washington

This stonefly was collected from the South Fork Snoqualmie River in Washington on May 14th, 2022 and added to Troutnut.com by Troutnut on May 16th, 2022.


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Sweltsa borealis (Boreal Sallfly) Stonefly Nymph Pictures

Collection details
Location: South Fork Snoqualmie River, Washington
Date: May 14th, 2022
Added to site: May 16th, 2022
Author: Troutnut
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