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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 Male Ameletus vernalis (Ameletidae) (Brown Dun) Mayfly Nymph from the Icicle River in Washington
Keying this one out using Zloty & Pritchard 1997:
-No ganglionic markings on sternites 2–8
-Posterior margins of sternits 6–8 without numerous spines
-Mesal gill extension well developed (I really don't like the "well developed" language when it's subjective, but in this case the other option doesn't lead anywhere productive)
-Tails pale in basal 1/3
-Larger species (13–16 mm) — this one is just shy of 12 mm, but closer to 13 than to <10
-Spring emergence
This all points to Ameletus vernalis.
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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Caddisfly Species Nyctiophylax affinis (Dinky Light Summer Sedges)

Where & when

Time of year : Early summer

Altitude: Lakes and streams

This widespread species is most common in the Midwest.

In 81 records from GBIF, adults of this species have mostly been collected during June (33%), July (26%), August (19%), May (14%), and September (7%).

In 39 records from GBIF, this species has been collected at elevations ranging from 328 to 7201 ft, with an average (median) of 2887 ft.

Species Range

Specimens of the Caddisfly Species Nyctiophylax affinis

1 Adult

Start a Discussion of Nyctiophylax affinis


  • LaFontaine, Gary. 1981. Caddisflies. The Lyons Press.
  • Morse, JC. 1972. The genus Nyctiophylax in North America. Journal of the Kansas Entomological Society 42(2): 172-181.

Caddisfly Species Nyctiophylax affinis (Dinky Light Summer Sedges)

Species Range
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