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I believe this is E. invaria because it's a little bigger (about 7 mm) and earlier than E. dorotheas that have started appearing on this stream.
I believe this is E. dorothea because of the small size- about 5 mm.
Cedar waxwings were having a field day picking these off as they flew up from the stream.
Large size (maybe 3/4" or more), brownish body. Eyes and genitalia match the description of Hexagenia imagoes by Edmunds in Mayflies of North and Central America. Except for one dun with a yellowish body w/brown markings and yellowish veined wings, all specimens seen (a couple dozen or so) were spinners with brownish bodies.
Best guess on the ID, please correct if I've miss identified it
Mayflies or shadflies are insects belonging to the order Ephemeroptera (from the Greek εφήμερος, ephemeros = "short-lived" (literally "lasting a day" "daily" or "day-long"), and πτερόν, pteron = "wing", referring to the brief lifespan of adults). They have been placed into an ancient group of insects termed the Palaeoptera, which also contains dragonflies and damselflies. They are aquatic insects whose immature stage (called "naiad" or, colloquially, "nymph") usually lasts one year in fresh water. The adults...