Insect Order Plecoptera (Stoneflies)

Family-level ID following Merritt, Cummins, & Berg 5th Edition:
1. Thoracic gill remnants absent
2. Arms of mesosternal Y-ridge approach posterior end of furcal pits
3. Submental gill remnants short, obscure, or absent
4. Male. Note that sternum 9 (the long, dark, last segment) appears to be the 8th if you count from the front in the ventral view, because the first segment is not easily visible ventrally.
5. Male abdominal tergum 10 not divided posteriorly; Paraprocts modified as hooks.
6. Male abdominal tergum 10 simple without notches or other prominent processes. This one was tricky, because at first glance it looks like the hooks arise from tergum 10, but in fact they're coming from the paraprocts underneath. There's a medial groove on tergum 10 that could be seen as a "notch" too, but it seems by "notch" the key is referring to a notch in the margin.
7. Abdominal sternum 8 with a conspicuous lobe and sternum 7 without such a lobe.
This leads to Isoperla.
Among Isoperla species known in Washington, most species are ruled out by different shapes of the vesicle (the rounded posterior bump on sternum 8). Isoperla pinta is ruled out by the lack of a region of stout spinules on tergum 9. The remaining options (without knowing how to properly dissect and image the aedeagus) are Isoperla fulva, Isoperla marmorata, Isoperla tilasqua, and Isoperla gravitans, the latter of which is too large. The other three are all at least slim possibilities, but several described characteristics seem to best match Isoperla fulva, which is also mentioned as the most common western Isoperla.

I found this stonefly on some streamside vegetation. I didn't see any in the air in several hours of fishing.

A few of these larger stoneflies were fluttering around the South Fork on an evening dominated by much smaller species.

This one has been difficult to identify. I can't spot any of the gill remnants characteristic of Perlidae, but the wing venation seems to point in that direction. I tried keying it out as Perlodidae but arrived at Isoperla, every western species of which has significantly smaller bodies than this one.

Edit: See forum comments for a likely correct identification.

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.

This is the smallest stonefly I've ever collected, with a body only 5.5 mm long.

Although not in-focus in my pictures, its first tarsal segment is similar in length to the third, while the second is much shorter. This helps with family-level identification.

Examining this specimen under a microscope shows a membranous lobe on the dorsal base of the cerci, which is the key characteristic in Merritt & Cummins (4th ed.) to place the genus definitively as Malenka.

Following the species key in Jewett Jr's Stoneflies of the Pacific Northwest, the species appears to be Malenka tina. My dissecting microscope seems to show sternite 9 ending in a rounded knob, which distinguishes it from Malenka bifurcata, but the detail is hard to work out.

Also worth noting is that Montana appears to have this species, whereas birfucata is not know there: http://fieldguide.mt.gov/displaySpecies.aspx?family=Nemouridae

The adult stoneflies of this family look surprisingly normal given the strange shape of the nymphs. I tried to identify it beyond family level 15 years after collecting it, based on my photos, which are not ideal. It's difficult even to tell the gender for sure because I don't have a good picture of the terminalia, but the body size suggests it's a male, and the species ranges suggest either Peltoperla arcuata or a male Tallaperla maria. One distinctive feature of the original description of this species is that the antennae are paler for a short distance beyond the first two thick, dark segments. That can be seen on this specimen and on a specimen on BugGuide identified as Tallaperla maria.

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.

The family ID on this one was a little bit tricky. Just going by the size, shape, and color, it looks like Chloroperlidae. However, the second anal vein of the forewing is does not appear to be forked, and the apical maxillary palpal segment is close to the length of the penultimate segment, both of which rule out that family. The position of the cubitoanal crossvein relative to the anal cell in the forewing -- touching it in this case -- indicates Perlidae (and it really doesn't have the "look" of Perlidae at all), but other characteristics, such as the metathorastic sternacostal sutures and lack of gill remnants, point to Perlodidae. That's the right answer. Moving on to Perlodidae, the key characteristics in Merritt & Cummins lead straightforwarly to Isoperla, and the species key in Jewett 1959 (The Stoneflies of the Pacific Northwest) leads to Isoperla fusca.

There is one caveat: That source does suggest a May-July emergence, whereas this one was collected in mid-September.

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.

I caught this female in the vegetation on a trail about 50 feet above the stream. The coloration on its head differs from that of a male I collected recently on a nearby river, and from another female I collected on the same river. But it still keys out confidently to Calineuria, and californica is the only species of that genus in the area.

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.

Several stoneflies of this species were flying around a small stream last night. I tied on a brown drake imitation of about the right size/color to approximate these stones, and was rewarded with a hard-fighting 17-inch brown trout.

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.

A friend brought me this stonefly to photograph. He found it floating on the surface of a trout stream with its wings in a crippled position.

This striking golden stonefly is the first of its species I've had the chance to photograph.

This Skwala nymph still has a couple months left to go before hatching, but it's still a good representative of its species, which was extremely abundant in my sample for a stonefly of this size. It's obvious why the Yakima is known for its Skwala hatch.

I'm not aware of any way to tell the two species of Doroneuria apart as nymphs, so this one is classified to species based on location alone. Doroneuria baumanni is found in the Cascades and in Washington, and the other species is not known here yet.

(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 specimen represents a common find in a late-April sample from the far upper Yakima River. It seems to be the same species as another one I collected previously. Of the species keyed in Szczytko & Stewart 1979, it probably matches Isoperla fusca closest, but there's a good chance it's a species that wasn't in the key. The leg segments have a fringe of fine hairs which is supposed to be absent in Isoperla fusca, and the four dark stripes of the mesonotum and metanotum don't continue as 4 separate stripes on the pronotum as they should in the description of fusca. It's possible fusca is more variable than previously described, or this is a different species not included in that key. It's also worth noting there's definitely no fringe of fine setae on any part of the cerci, just the whorls of little stout ones around segment bases.

This is a difficult one. It keys convincingly to either Calineuria or Doroneuria. There is no mesal longitudinal row of silky hairs on thorax and abdominal dorsum, in either my pictures or anything I can see up close under the microscope. Lacking those hairs should indicate Calineuria. But abdominal sternum 7 has an incomplete posterior setal fringe, which would indicate Doroneuria, although the key says "usually" on that characteristic. For now I'm going with Calineuria, but it's far from certain. Maybe it's a younger Doroneuria and they don't grow that row of hairs until they're older. The markings on the head, especially the shape of the bright spot around the posterior ocelli, match online images of Calineuria californica better than Doroneuria.