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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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Female Ecdyonurus criddlei (Little Slate-Winged Dun) Mayfly Spinner Pictures

This one was collected close to a male which, based on size and general structure, was likely the same species. Females are supposed to be lighter-colored and with less distinct markings than the males, although the difference in this pair is particularly stark.

Lateral view of a Female Ecdyonurus criddlei (Heptageniidae) (Little Slate-Winged Dun) Mayfly Spinner from the Bitterroot River in Montana
Dorsal view of a Female Ecdyonurus criddlei (Heptageniidae) (Little Slate-Winged Dun) Mayfly Spinner from the Bitterroot River in Montana
Ventral view of a Female Ecdyonurus criddlei (Heptageniidae) (Little Slate-Winged Dun) Mayfly Spinner from the Bitterroot River in Montana
Ruler view of a Female Ecdyonurus criddlei (Heptageniidae) (Little Slate-Winged Dun) Mayfly Spinner from the Bitterroot River in Montana The smallest ruler marks are 1 mm.

This mayfly was collected from the Bitterroot River in Montana on September 6th, 2021 and added to Troutnut.com by Troutnut on September 8th, 2021.


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Female Ecdyonurus criddlei (Little Slate-Winged Dun) Mayfly Spinner Pictures

Collection details
Location: Bitterroot River, Montana
Date: September 6th, 2021
Added to site: September 8th, 2021
Author: Troutnut
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