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Lateral view of a Male Baetis (Baetidae) (Blue-Winged Olive) Mayfly Dun from Mystery Creek #43 in New York
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.

Dorsal view of a Neoleptophlebia (Leptophlebiidae) Mayfly Nymph from the Yakima River in Washington
Some characteristics from the microscope images for the tentative species id: The postero-lateral projections are found only on segment 9, not segment 8. Based on the key in Jacobus et al. (2014), it appears to key to Neoleptophlebia adoptiva or Neoleptophlebia heteronea, same as this specimen with pretty different abdominal markings. However, distinguishing between those calls for comparing the lengths of the second and third segment of the labial palp, and this one (like the other one) only seems to have two segments. So I'm stuck on them both. It's likely that the fact that they're immature nymphs stymies identification in some important way.
27" brown trout, my largest ever. It was the sub-dominant fish in its pool. After this, I hooked the bigger one, but I couldn't land it.
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Pdcox has attached these 2 pictures to aid in identification. The message is below.
Pdcox
Kansas city

Posts: 12
Pdcox on Jul 23, 2020July 23rd, 2020, 9:17 am EDT
Underside and topside of a nymph found at 8200' elevation, middle Colorado, small rolling creek. Note the red underbelly
Taxon
Taxon's profile picture
Site Editor
Plano, TX

Posts: 1311
Taxon on Jul 23, 2020July 23rd, 2020, 12:18 pm EDT
Hi Paul-

I believe this mayfly nymph to be of genus Rhithrogena.
Best regards,
Roger Rohrbeck
www.FlyfishingEntomology.com

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