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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

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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DayTripper's profile picture
Northern MI

Posts: 70
DayTripper on Jul 2, 2009July 2nd, 2009, 1:13 am EDT

Found this female dun on the East Branch of the Delaware the first weekend in June. It was ~30mm long. I'm pretty sure it's a female distinctus dun, but was hoping someone could confirm. Thanks.
Site Editor
"Bear Swamp," PA

Posts: 1681
GONZO on Jul 2, 2009July 2nd, 2009, 4:41 am EDT

This is Ephemera varia. A 30mm size estimate is well above what is typical for either E. varia or A. distinctus, though the size range for varia is underestimated in books like Hatches and Mayflies. They give 13-16mm as the range for both species, but the varia females that I've collected from the Yellow Breeches run between 17-20mm.
DayTripper's profile picture
Northern MI

Posts: 70
DayTripper on Jul 2, 2009July 2nd, 2009, 5:12 am EDT
Thanks Gonzo, I really appreciate it. I knew it had to be one of the two (distinctus or varia), but as you mentioned, the large size didn't fit what my reference books had listed. I know looking at coloration is a no-no when identifying bugs, but the coloration seemed more of a match to the distinctus color plate in Hatches, so I ran with it. Thanks, again.

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