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The Specimen

Onocosmoecus unicolor (Great Late-Summer Sedge) Caddisfly AdultOnocosmoecus unicolor (Great Late-Summer Sedge) Caddisfly Adult View 15 PicturesI first just assumed this was Dicosmoecus based on anglers' conventional wisdom since it's a large orange "October caddis," but Creno set me straight. I should have keyed it out. After another look under the microscope, it lacks an anepisternal wart on the mesopleuron (Mesopleuron: The side of the insect mesothorax, and the part to which the fore wings are attached in mayflies.), which rules out Dicosmoecus. The midtibiae have 2 apical (Apical: Close to the apex; tip or end.) spurs and 1 pre-apical (Apical: Close to the apex; tip or end.) spur, and from there the color pattern of the wing points to Onocosmoecus. The location then narrows the species to unicolor.
Collected September 17, 2020 from the Yakima River in Washington
Added to by on September 19, 2020

The Discussion

CrenoSeptember 19th, 2020, 1:19 pm
Grants Pass, OR

Posts: 305
Onocosmoecus unicolor?
TroutnutSeptember 19th, 2020, 2:19 pm
Bellevue, WA

Posts: 2737
Didn't mean one thing and write another -- you caught me assuming the genus based on angler-entomology instead of keying it out. Oops! After closer inspection under the microscope, of course you're right.
Jason Neuswanger, Ph.D.
Troutnut and salmonid ecologist
CrenoSeptember 20th, 2020, 11:19 am
Grants Pass, OR

Posts: 305
Interesting that the western angling lit has Dicosmoecus as orange. Within the Dicosmoecinae only Onocosmoecus is orange, the rest are dark greys to blacks when alive and, like Onocosmoecus, often faded to browns when pinned. Amphicosmoecus could be considered orangish on some speciemens but the wings are typically more grey/brown with a reddish tint, and finely speckled. Onocosmoecus unicolor is one of those very widespread species that further study will likely reveal are comprised of several species. But not to worry, it probably won't happen soon :-) I forgot to mention - thanks for the great pics.

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