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.

Cedar sweepers line the fertile spring creek headwaters of a famous trout stream.

From the Bois Brule River in Wisconsin

Stream photos

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Neoleptophlebia Mayfly Nymph Neoleptophlebia Mayfly Nymph

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.

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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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Any help with this mayfly?

Canerodder has attached this picture to aid in identification. The message is below.

Canerodder
Posts: 1

Canerodder on May 26, 2009May 26th, 2009, 3:52 pm EDT

Found this guy on a small creek in west Michigan yesterday around 1:30pm....a few ive talked with thought March Brown...but it was very cream colored?

GONZO
Site Editor
"Bear Swamp," PA

Posts: 1681

GONZO on May 26, 2009May 26th, 2009, 5:43 pm EDT

Looks like a female M. vicarium dun (March Brown/Gray Fox) to me.

Konchu

Site Editor
Indiana

Posts: 498

Konchu on May 27, 2009May 27th, 2009, 1:30 am EDT

We've had a lot of March Browns out this spring in Indiana. The light color could be because this one just emerged from the nymph stage. It takes them a bit to darken up.

Wiflyfisher

Wisconsin

Posts: 622

Wiflyfisher on May 27, 2009May 27th, 2009, 5:02 am EDT

We've had a lot of March Browns out this spring in Indiana. The light color could be because this one just emerged from the nymph stage. It takes them a bit to darken up.

Just adding to what Konchu is saying... If you ever put your rod down and pick up a seine and capture some duns as they are emerging from their nymphal case you will probably be "dun shrucked" how much lighter they can be at this time.

I have observed that some duns spend too much time sunning themselves and get sun burned easily, which accounts for the color variations.

John S.
https://WiFlyFisher.com

Martinlf