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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 Ephemerella mucronata (Ephemerellidae) Mayfly Nymph from the Yakima River in Washington
This is an interesting one. Following the keys in Merritt R.W., Cummins, K.W., and Berg, M.B. (2019) and Jacobus et al. (2014), it keys clearly to Ephemerella. Jacobus et al provide a key to species, but some of the characteristics are tricky to interpret without illustrations. If I didn't make any mistakes, this one keys to Ephemerella mucronata, which has not previously been reported any closer to here than Montana and Alberta. The main character seems to fit well: "Abdominal terga with prominent, paired, subparallel, spiculate ridges." Several illustrations or descriptions of this holarctic species from the US and Europe seem to match, including the body length, tarsal claws and denticles, labial palp, and gill shapes. These sources include including Richard Allen's original description of this species in North America under the now-defunct name E. moffatae in Allen RK (1977) and the figures in this description of the species in Italy.
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 Ephemerellidae (Hendricksons, Sulphurs, PMDs, BWOs) Mayfly Dun Pictures

This one was collected in association with a male spinner, but they appear to be different families.

Female Ephemerellidae (Hendricksons, Sulphurs, PMDs, BWOs) Mayfly Dun from the South Fork Stillaguamish River in Washington
Ventral view of a Female Ephemerellidae (Hendricksons, Sulphurs, PMDs, BWOs) Mayfly Dun from the South Fork Stillaguamish River in Washington
Female Ephemerellidae (Hendricksons, Sulphurs, PMDs, BWOs) Mayfly Dun from the South Fork Stillaguamish River in Washington
Dorsal view of a Female Ephemerellidae (Hendricksons, Sulphurs, PMDs, BWOs) Mayfly Dun from the South Fork Stillaguamish River in Washington
Lateral view of a Female Ephemerellidae (Hendricksons, Sulphurs, PMDs, BWOs) Mayfly Dun from the South Fork Stillaguamish River in Washington
Markings are 1/16 inch.

Ruler view of a Female Ephemerellidae (Hendricksons, Sulphurs, PMDs, BWOs) Mayfly Dun from the South Fork Stillaguamish River in Washington The smallest ruler marks are 1/16".

This mayfly was collected from the South Fork Stillaguamish River in Washington on July 1st, 2017 and added to Troutnut.com by Troutnut on July 2nd, 2017.


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Female Ephemerellidae (Hendricksons, Sulphurs, PMDs, BWOs) Mayfly Dun Pictures

Collection details
Location: South Fork Stillaguamish River, Washington
Date: July 1st, 2017
Added to site: July 2nd, 2017
Author: Troutnut
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