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Blue-winged Olives
Baetis

Tiny Baetis mayflies are perhaps the most commonly encountered and imitated by anglers on all American trout streams due to their great abundance, widespread distribution, and trout-friendly emergence habits.

Mayfly Species Acentrella insignificans (Tiny Blue-Winged Olive)

This species shares its distribution with the much more common Acentrella turbida over much of it's range. In the West, it overshadows turbida in some locales. It can be differentiated from turbida by the presence of hind wings and from most other baetids by its hind wings having two longitudinal veins and a lack of costal projection. It was previously classified as Baetis insignificans.

Specimens of the Mayfly Species Acentrella insignificans

1 Male Dun
Male Acentrella insignificans (Tiny Blue-Winged Olive) Mayfly Dun
This specimen emerged indoors from nymphs I had collected, then partly molted into a spinner but got stuck along the way. I've included a couple pictures showing some of the spinner colors. It got a bit waterlogged after emerging, so the wings aren't in perfect shape, but it still represents one of two Baetids that were emerging and drawing trout to rise on the Yakima. Based on body size and shape, it is most likely the same species as this nymph.
1 Nymph
Male Acentrella insignificans (Tiny Blue-Winged Olive) Mayfly Nymph
Another nymph probably of the same species as this one emerged and was photographed as a dun and partly-molted spinner.

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