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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.

Dorsal view of a Epeorus albertae (Heptageniidae) (Pink Lady) Mayfly Nymph from the East Fork Issaquah Creek in Washington
This specimen keys to the Epeorus albertae group of species. Of the five species in that group, the two known in Washington state are Epeorus albertae and Epeorus dulciana. Of the two, albertae has been collected in vastly more locations in Washington than dulciana, suggesting it is far more common. On that basis alone I'm tentatively putting this nymph in albertae, with the large caveat that there's no real information to rule out dulciana.
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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Mayfly Species Stenonema pulchellum (Light Cahills)

Where & when

Time of year : Mid-June to mid-September, peaking sometime after mid-July

This species is locally abundant.

In 1 records from GBIF, adults of this species have been collected during July (100%).

Species Range

Hatching behavior

Unlike species which hatch earlier in the year, Maccaffertium pulchellum does not migrate to the calm shallows to emerge. It comfortably hatches in the middle of the stream.

Nymph biology

Substrate: Gravel and submerged wood

Physical description

Most physical descriptions on Troutnut are direct or slightly edited quotes from the original scientific sources describing or updating the species, although there may be errors in copying them to this website. Such descriptions aren't always definitive, because species often turn out to be more variable than the original describers observed. In some cases, only a single specimen was described! However, they are useful starting points.

Male Spinner

Body length: 6-7 mm
Wing length: 7-8 mm

A species of Stenonema pulchellum group; dark spiracular dots present; scutellum broadly white; tails darker at joinings.

Eyes of living insect pearly white. Ocelli reddish, blackish at base; bases of antennae fuscous, tips pale. Vertex dark red-brown. Thoracic notum brownish black, with no reddish tinges; scutellum broadly white, not merely white-tipped, as in S. rubrum (now a synonym of Stenonema modestum). Pleura pale, with yellowish brown and occasional pink tinges; a pinkish area anterior to wing roots. Central area of mesosternum brown. Fore legs pale yellowish; femur with median and apical darker bands; tips of tibia and tarsal joinings fuscous; basal tarsal joint fully one-half the length of the second. Middle and hind legs whitish, markings as on fore leg, but paler; median femoral band sometimes obsolescent. Wings hyaline; a pale brown (not reddish) stain in stigmatic area of fore wing. Costa, subcosta and radius yellow, especially in basal two-thirds; all other veins reddish brown; cross veins somewhat heavier than longitudinals, which are quite fine. Cross veins more numerous that in rubrum(now a synonym of Stenonema modestum). Veins in hind wing, behind costa, hyaline.

Abdominal segments 1-7 white, hyaline; posterior margins of tergites faintly darker; dark spiracular dots present, on segments 3-7. Segments 8-10 opaque; tergites dark ruddy, sternites paler. Genitalia of the Stenonema pulchellum type (see fig. 91, rubrum); penes not as sharply L-shaped as in rubromaculatum (now Stenonema modestum). Tails whitish; joinings narrowly fuscous, in the basal alternately wide and narrow.

The blacker thorax, with its lack of reddish shading, the white scutellum and purer white abdomen distinguish this species from the allied rubrum (now Stenonema modestum). The presence of spiracular dots separates it from Stenonema terminatum and placitum (now a synonym of Stenonema terminatum). The smaller size, smaller eye, darker thorax and lack of red stigmatic stain distinguishes it from rubromaculatum.

Start a Discussion of Stenonema pulchellum


Mayfly Species Stenonema pulchellum (Light Cahills)

Species Range
Common Name
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