Artistic view of a Male Pteronarcys californica (Pteronarcyidae) (Giant Salmonfly) Stonefly Adult from the Gallatin River in Montana

Salmonflies
Pteronarcys californica

The giant Salmonflies of the Western mountains are legendary for their proclivity to elicit consistent dry-fly action and ferocious strikes.

Turquoise view of Upper Titcomb Lake

From Titcomb Basin in Wyoming

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Tricorythodes (Trico) Mayfly Nymph Tricorythodes (Trico) Mayfly Nymph

Dorsal view of a Tricorythodes (Leptohyphidae) (Trico) Mayfly Nymph from Mystery Creek #308 in Washington

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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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2 tails or 3

This topic is about the Mayfly Species Stenonema vicarium

In the East and Midwest this is one of the most important hatches of the Spring. They are large flies which emerge sporadically, making for long days of good fishing.

This species contains the two classic Eastern hatches formerly known as Stenonema vicarium and Stenonema fuscum, the "March Brown" and "Gray Fox." Entomologists have discovered that these mayflies belong to the same species, but they still display differences in appearance which the trout notice easily. Anglers should be prepared to imitate both types.

Example specimens

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Male Stenonema vicarium (March Brown) Mayfly Spinner

Artistic view of a Male Stenonema vicarium (Heptageniidae) (March Brown) Mayfly Spinner from the Teal River in Wisconsin

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Male Stenonema vicarium (March Brown) Mayfly Dun

Artistic view of a Male Stenonema vicarium (Heptageniidae) (March Brown) Mayfly Dun from the Namekagon River in Wisconsin

I collected this mayfly on the same trip as a female of the same species. After these photos it molted into a spinner. This is the form of Stenonema vicarium which anglers call the "Gray Fox."

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Female Stenonema vicarium (March Brown) Mayfly Spinner

Lateral view of a Female Stenonema vicarium (Heptageniidae) (March Brown) Mayfly Spinner from the Namekagon River in Wisconsin

I collected this mayfly on the same trip as a male of the same species. They are Maccaffertium vicarium mayflies of the type formerly known as Stenonema fuscom, the "Gray Fox."

Snagy
Posts: 1

Snagy on Feb 5, 2010February 5th, 2010, 3:32 pm EST

I notice that while the dun, nymph, and spinner photos on the page are all listed as March Brown (maccaffertium vicarium). While the coloration patterns all seem to follow other March Browns I have seen, I notice that the winged flies pictures all have 2 tails, but the nymphs in the photos have 3. I was under the impression this species was a 2 tailed mayfly. Is the nymph mislabelled?

Taxon

Site Editor
Plano, TX

Posts: 1311

Taxon on Feb 6, 2010February 6th, 2010, 4:01 am EST

Snagy-

Good observation. Maccaffertium vicarium belongs to family Heptageniidae (Flatheaded Mayflies). Heptageniids have three tails as a nymph, and two tails in their winged stages, except for two genera, Epeorus and Ironodes, which have two tails, both as nymphs, and in their winged stages.

Best regards,
Roger Rohrbeck
www.FlyfishingEntomology.com