Lateral view of a Female Hexagenia limbata (Ephemeridae) (Hex) Mayfly Dun from the Namekagon River in Wisconsin

Hex Mayflies
Hexagenia limbata

The famous nocturnal Hex hatch of the Midwest (and a few other lucky locations) stirs to the surface mythically large brown trout that only touch streamers for the rest of the year.

The North Fork Couer d'Alene River in Idaho

Stream photos

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Zapada cinctipes (Tiny Winter Black) Stonefly Nymph Zapada cinctipes (Tiny Winter Black) Stonefly Nymph

Dorsal view of a Zapada cinctipes (Nemouridae) (Tiny Winter Black) Stonefly Nymph from the Yakima River in Washington

Nymphs of this species were fairly common in late-winter kick net samples from the upper Yakima River. Although I could not find a key to species of Zapada nymphs, a revision of the Nemouridae family by Baumann (1975) includes the following helpful sentence: "2 cervical gills on each side of midline, 1 arising inside and 1 outside of lateral cervical sclerites, usually single and elongate, sometimes constricted but with 3 or 4 branches arising beyond gill base in Zapada cinctipes." This specimen clearly has the branches and is within the range of that species.

13 Recently Added Photos

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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Stenonema femoratum male spinner

This topic is about the Mayfly Genus Stenonema

Many of America's traditional flies, like the March Brown and the Light and Dark Cahills, originated in the Catskills to imitate the mayflies of this genus. Caucci and Nastasi wrote of them in Hatches II:

"There is a matrimony between Stenonema flies and Catskill rivers that is as synonymous as ham and eggs."

By far the most important species is Stenonema vicarium, variants of which are known to anglers as the March Brown and Gray Fox. Of the others in the "Cahill" group, Stenonema ithaca is the next most important, along with Stenonema modestum and Stenonema pulchellum, which also produce localized fishable hatches. These lesser species together with a few species of Stenacron and the Stenonema femoratum represent the sporadic Light Cahill hatches on evenings in late Spring that often continue throughout the Summer.

Example specimens

9
Male Stenonema terminatum Mayfly Spinner

Male Stenonema terminatum (Heptageniidae) Mayfly Spinner from the Teal River in Wisconsin

6
Female Stenonema modestum (Cream Cahill) Mayfly Spinner

Female Stenonema modestum (Heptageniidae) (Cream Cahill) Mayfly Spinner from the Namekagon River in Wisconsin

Although I couldn't key out this female spinner, I'm fairly comfortable calling her Stenonema modestum based on the markings on the abdomen and their similarity to those on the males of this species. This one probably came from the Namekagon River, although there's a possibility it came from the West Fork of the Chippewa River, because it was found in the truck after fishing those streams on back-to-back days.

12
Male Stenonema modestum (Cream Cahill) Mayfly Spinner

Artistic view of a Male Stenonema modestum (Heptageniidae) (Cream Cahill) Mayfly Spinner from the Teal River in Wisconsin

Jmw975
Guelph, Ontario

Posts: 20

Jmw975 on May 21, 2012May 21st, 2012, 4:53 am EDT

Male Stenonema femoratum collected from the Grand River, Ontario. Note the 3 spots at the hind margins of each of the abdominal segments.

Entoman

Northern CA & ID

Posts: 2604

Entoman on May 21, 2012May 21st, 2012, 8:03 am EDT

Thanks Jeff, for the excellent photo and determination. Readers note that besides the three spots that are clearly seen, spots are also just visible on seg's 3 and 8. The dark transverse dashes are a little harder to make out, but they look to be present as well. The crowded crossveins below the bulla are also indicative of femoratum. This is the last Stenonema species left in what is now the least important genus (to anglers) of the related group. See the genus topic article as well as the family article in the hatch encyclopedia for a brief explanation.

"It's not that I find fishing so important, it's just that I find all other endeavors of Man equally unimportant... And not nearly as much fun!" Robert Traver, Anatomy of a Fisherman

Jmw975
Guelph, Ontario

Posts: 20

Jmw975 on May 21, 2012May 21st, 2012, 10:24 am EDT

Thanks. Did I post this in the right place? I was hoping to have it show up under the species in the aquatic insect encyclopedia.

Here's a lateral shot of another male specimen:

Between the two photos you can clearly see the crowded crossveins in the bulla and the three transverse spots/dashes on the abdominal terga.

A preserved nymph showing the highly distinctive sternal colour pattern:

.

and now I'm going fishin' :)

Jeff

Entoman

Northern CA & ID

Posts: 2604

Entoman on May 21, 2012May 21st, 2012, 10:43 am EDT

Thanks for the ventral! They're hard to find and much easier to work with than descriptions. BTW, you posted in the right place. See PM just sent.

"It's not that I find fishing so important, it's just that I find all other endeavors of Man equally unimportant... And not nearly as much fun!" Robert Traver, Anatomy of a Fisherman