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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 Holocentropus (Polycentropodidae) Caddisfly Larva from the Yakima River in Washington
This one seems to tentatively key to Holocentropus, although I can't make out the anal spines in Couplet 7 of the Key to Genera of Polycentropodidae Larvae nor the dark bands in Couplet 4 of the Key to Genera of Polycentropodidae Larvae, making me wonder if I went wrong somewhere in keying it out. I don't see where that could have happened, though. It might also be that it's a very immature larva and doesn't possess all the identifying characteristics in the key yet. If Holocentropus is correct, then Holocentropus flavus and Holocentropus interruptus are the two likely possibilities based on range, but I was not able to find a description of their larvae.
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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March Browns, Cahills, Quill Gordons

This common name refers to only one family. Click its scientific name to learn more.

Mayfly Family Heptageniidae

These are pretty much always called March Browns, Cahills, Quill Gordons.
Known as the "clinger" mayflies to anglers, a few species of this family can be extremely prolific, with a lot more that aren't. These lesser species account for many of the curious mayflies you find that never seem to associate with a major hatch, let alone a fishable one. Not all heptageniid species are so scarce though; there are superhatches too.

Heptageniids can be broken into "groups" of similar genera (based on angling concerns) to help keep track of them. Although many of them are closely related, they are not officially divided in this way by entomologists. Here are the groups:

Stenonema (blotchy wings)


The genus Stenonema, who's Latin name was one of the first etched in the minds of anglers, was for a while largely reclassified into Maccaffertium but has since been reinstated. It includes the March Brown (S. vicarium) and Gray Fox (previously S. fuscum) superhatches.
The Stenonema species are for all practical purposes limited to the East and Midwest.

Former Heptagenia (plain wings)


While Heptagenia has held on to several species, many of its fishable hatches have been moved to the genera Leucrocuta, Nixe, and Ecdyonurus. Some species of Nixe were subsequently moved to Afghanurus. There are many former Heptagenia species across the continent, but few are important to anglers. Of those, more are in the West than in the East.

Epeorus (two-tailed Nymphs, plain wings)


The closely related genera Epeorus and Ironodes are among the only mayflies to have just two tails as nymphs. Good populations can be found in the West, but it's in the East where the mayfly named after the man that brought the dry fly to America can be found, the superhatch Epeorus pleuralis or Quill Gordon.

Rhithrogena (suction cup gills)


The genus Rhithrogena can be identified by the gills of its nymphs. They extend underneath the abdomen in the front and the back. They are very important for early season anglers in the West, but not very often in the East. For western anglers, it's duns are the blotchy winged equivalent of the East's March Brown (Maccaffertium vicarium). Ironically, it is only the Western March Brown that is in the same genus as the English species for which the common name originated.

Cinygmula (horn heads)


The genus Cinygmula is easily distinguished by the nymph's enlarged palpi (mouth parts) that stick out from both sides of their heads like little blunt horns. They rarely produce fishable hatches, and none are of much significance except for a few species, mostly in certain locales of the West.
Lateral view of a Female Stenonema (Heptageniidae) (March Browns and Cahills) Mayfly Dun from the Namekagon River in Wisconsin
Lateral view of a Stenonema ithaca (Heptageniidae) (Light Cahill) Mayfly Nymph from Paradise Creek in Pennsylvania
This specimen seems to be of the same species as a dun I photographed which emerged from another nymph in the same sample.

March Browns, Cahills, Quill Gordons

Scientific Name
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