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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.

Ventral view of a Hydropsyche (Hydropsychidae) (Spotted Sedge) Caddisfly Larva from the Yakima River in Washington
With a bit of help from the microscope, this specimen keys clearly and unsurprisingly to Hydropsyche.
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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Lateral view of a Male Eurylophella minimella (Ephemerellidae) (Chocolate Dun) Mayfly Spinner from the Namekagon River in Wisconsin
The genus ID on this specimen is confident but species is very tentative, based on the tentative ID of a seemingly-identical specimen from a nearby river a few days apart.
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"Bear Swamp," PA

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GONZO on May 24, 2009May 24th, 2009, 11:00 am EDT
This spinner is Eurylophella rather than E. invaria. The long 9th abdominal segment of Eurylophella is often the easiest way to avoid confusing the duns and spinners with Ephemerella. The claspers and genitalia of this male are also representative of Eurylophella.

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Wiflyfisher on May 24, 2009May 24th, 2009, 3:05 pm EDT
Lloyd, what the heck is Eurylophella???
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"Bear Swamp," PA

Posts: 1681
GONZO on May 24, 2009May 24th, 2009, 4:18 pm EDT

Eurylophella species comprised the "bicolor" group of Ephemerella until Allen elevated subgenera (like Drunella, Serratella, Attenella, etc.) in 1980. Although widespread and fairly common, they are infrequently mentioned in fly-fishing literature. In streams and rivers, Eurylophella nymphs usually inhabit slow, weedy water, but some are also found in lakes. Most Eastern/Midwestern species seem to emerge sometime in June/July. The dark-winged duns can also be mistaken for other species, like Ephemerella needhami.

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