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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 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.
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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Stonefly Species Pteronarcys dorsata (Salmonflies)

This is the largest common eastern stonefly. It's quite abundant in places, but not to the extent of its western counterparts, and since most of its activity is at night it is generally less important. Nevertheless, nymph imitations produce some very large trout, and lucky or very locally knowledgable anglers may find good fishing to the egg-laying adults.

Where & when

Time of year : Late April through late June

In 27 records from GBIF, adults of this species have been collected during May (41%), April (26%), July (15%), March (11%), and June (7%).

Species Range

Hatching behavior

Time of day : Overnight; some dawn/dusk overflow

Egg-Laying behavior

Time of day: Overnight; some dawn/dusk overflow

Habitat: Riffles

I have watched Pteronarcys dorsata adults gather at treetop level above the riffles a hundred yards upstream from a slow stretch of water that held a tremendous swarm of Hexagenia limbata spinners thirty minutes later. I never saw more than one or two on the water, and the egg-laying supposedly happens well after dark.

Specimens of the Stonefly Species Pteronarcys dorsata

3 Nymphs

1 Streamside Picture of Pteronarcys dorsata Stoneflies:

1 Video of Pteronarcys dorsata Stoneflies:


Discussions of Pteronarcys dorsata

7 replies
Posted by Max29 on Jan 29, 2008
Last reply on Jan 29, 2008 by Taxon
Are stoneflies and salmonflies the same thing or are they just related because here in the mid west we have the stonfly hatch and if they are related the stonfly could be called the salmonfly and the salmonfly hatch is only in the west because I have trouble because I want to become a better insect identifier when it comes to fishing because i went to other sites that so a stonefly is a stonefly and a salmonfly is a salmon fly but yet you say stonefly nymph but in parenteseses you have american salmonfly so is there really no such thing as a salmonfly but it is rather called a stonefly.

Start a Discussion of Pteronarcys dorsata


Stonefly Species Pteronarcys dorsata (Salmonflies)

Species Range
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