Female Pictetiella expansa Stonefly AdultView 12 PicturesBased on photos, this specimen seems to key out (using Merritt & Cummins 4th Edition) to Pictetiella expansa, but some of the characteristics aren't 100 % clear. However, that species is listed as occurring near Puget Sound and the head markings are similar to (albeit not a perfect match for) those of a male from Colorado in the scientific literature here: https://www.researchgate.net/figure/Head-and-pronotum (Pronotum: The top of the insect prothorax.)-dorsal (Dorsal: Top.)-Pictetiella-expansa-Boulder-Co-Colorado-North-Fork-Middle_fig1_315373449
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Nymph: The juvenile, underwater stages of mayflies, stoneflies, dragonflies, and damselflies and other aquatic insects whose juvenile stages are covered by hard exoskeletons. The word can also refer to the fishing flies which imitate these creatures, in which case it is used as a blanket term for flies imitating any underwater stage of an invertebrate (except for crayfish and leeches).