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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 Pycnopsyche guttifera (Limnephilidae) (Great Autumn Brown Sedge) Caddisfly Larva from the Yakima River in Washington
This specimen appears to be of the same species as this one collected in the same spot two months earlier. The identification of both is tentative. This one suffered some physical damage before being photographed, too, so the colors aren't totally natural. I was mostly photographing it to test out some new camera setting idea, which worked really well for a couple of closeups.
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 Genus Acentrella (Tiny Blue-Winged Olives)

The only Acentrella species commonly reported to be important to anglers is Acentrella turbida, though Acentrella insignificans is important in some western locales. See the species pages for distribution and timing details. This genus is one of two (including Heterocloeon) that can easily be distinguished from other Baetidae genera by the presence of a conical mesonotal projection. A. turbida lacks hindwings which is useful for distinguishing this species from all others in either genera. A. turbida was previously known by the names of its synonyms Pseudocloeon turbidum in the West and Pseudocloeon carolina in the East.

Where & when

In 46 records from GBIF, adults of this genus have mostly been collected during July (37%), June (33%), August (11%), and May (7%).

In 348 records from GBIF, this genus has been collected at elevations ranging from -66 to 10302 ft, with an average (median) of 1969 ft.

Genus Range

Hatching behavior

Time of day : Early evening; sometimes all day

The nymphs are normally excellent swimmers, but they become much less mobile as they're emerging and dead-drift helplessly to the suface. Considering that they then emerge and fly away quickly, this makes the nymphs the prime stage to match during this emergence.

Spinner behavior

Time of day: Dusk

These species molt into spinners and mate the same day they emerge. The spinner activity usually comes at dusk, or even after dark.

Nymph biology

Current speed: Slow to Medium

Substrate: Rocks, logs, gravel, vegetation

Environmental tolerance: Widely tolerant, but best in cold rivers

Specimens of the Mayfly Genus Acentrella

1 Male Dun
1 Female Dun
1 Male Spinner
3 Female Spinners
1 Nymph

2 Streamside Pictures of Acentrella Mayflies:

Discussions of Acentrella

acentrella nymph
20 replies
Posted by Goose on Nov 3, 2006
Last reply on Sep 3, 2011 by Oldredbarn
Hi Jason! Do you have a picture of the (acentrella-miniature BWO nymph) on the site? I've been fishing them and wanted a better idea of how they look.

Start a Discussion of Acentrella


  • Fauceglia, Ted. 2005. Mayflies . Stackpole Books.

Mayfly Genus Acentrella (Tiny Blue-Winged Olives)

5 species (Acentrella alachua, Acentrella barbarae, Acentrella feropagus, Acentrella lapponica, and Acentrella nadineae) aren't included.
Genus Range
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