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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.

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.
Troutnut is a project started in 2003 by salmonid ecologist Jason "Troutnut" Neuswanger to help anglers and fly tyers unabashedly embrace the entomological side of the sport. Learn more about Troutnut or support the project for an enhanced experience here.

Mayfly Species Acentrella turbida (Tiny Blue-Winged Olives)

Although these mayflies are tiny, in places their numbers compensate for their small size and make for excellent hatches.

Rick Hafele and Dave Hughes in Western Mayfly Hatches rate turbida as one of the three most "key" western species of Baetidae, alongside Baetis tricaudatus and Diphetor hageni. In the West, turbida is more variable in size and appearance than its eastern iteration, in keeping with the large and varied regions it inhabits. It can run as small as 3.5 mm and as large as 5 mm, the larger sizes tending to be more brownish. It is often confused with the smaller broods of Diphetor hageni, but its conical mesonotal projection, lack of hind-wings, exaggerated turbinate eyes (hence its name) and stockier build help to differentiate it.

They are often found on the water with a mix of other Baetidae mayflies, making for very challenging fishing.

Taxonomic History

Acentrella turbida was previously known as Pseudocloeon carolina in the East and Pseudocloeon turbidum in the West. Combining these putative species made this one of the most widely distributed mayflies in North America.

Where & when

Time of year : May through October

In Hatches II, Cauci and Nastasi report excellent hatches of this species on Pennsylvania spring creeks, with broods in May, August, and October. They are probably important on similar waters across the country.

Ted Fauceglia's Mayflies mentions Eastern broods of Acentrella hatching from late June to early July and again in September and October, plus a possible earlier brood in late May. Schwiebert mentions in "Nymphs" they can provide excellent fishing in the Fall out West.

Seasonal emergence timing varies from water to water, and these flies may possibly be found at any time of the season depending on locale.

In 18 records from GBIF, adults of this species have been collected during June (39%), July (28%), April (11%), August (11%), May (6%), and March (6%).

In 24 records from GBIF, this species has been collected at elevations ranging from 26 to 9065 ft, with an average (median) of 5194 ft.

Species Range

Spinner behavior

The large turbinate (raised on stalks) eyes of the male imagos are the reason for this species' name. They are capable of molting quickly, and morning dun hatches often provide excellent spinner fishing that evening.

Nymph biology

The nymphs are stouter in proportion compared to other baetids, but their behavior is similar.

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

Described in Needham et al (1935) as Pseudocloeon carolina
Body length: 4 mm
Wing length: 4 mm

Abdominal tergites 2-6 of male imago wholly dark polished brown.

Turbinate eyes brown in dried specimen. Thorax and femora clear polished brown, darker than in P. turbidum (now a synonym of Acentrella turbida). Femora likewise polished brown. Wings hyaline, venation pale. Abdominal tergites 2-10 clear polished brown; sternites pale yellowish. Tails pale whitish, very slightly brownish at the joinings. Genitalia as in fig. 168.

The much darker brown of thorax and abdominal tergites, as well as the dark markings at the tail joinings, distinguishes this species from turbidum.

Described as P. turbidum

Body length 4 mm, wing length 4 mm

Abdominal tergites 2-6 of male imago entirely dark olivaceous brown.

Turbinate eyes are large, circular; considerably larger than in P. dubium (now a synonym of Plauditus dubius); reddish brown in living insect, deep red-brown to blackish in dried specimen. Thorax shining blackish; pleural sutures below the wings tinged with ruddy. All femora dark smoky brown; tibiae and tarsi pale yellowish white, those of the fore legs tinged with smoky. Wings hyaline. Abdominal tergites 2-10 entirely dark olivaceous brown; sternites pale yellowish white. Tails and forceps white.

This species is very similar to the eastern species P. carolina (now a synonym of Acentrella turbida), but not so deep a brown in color of body.

Specimens of the Mayfly Species Acentrella turbida

1 Male Spinner
3 Female Spinners

2 Streamside Pictures of Acentrella turbida Mayflies:

Start a Discussion of Acentrella turbida


Mayfly Species Acentrella turbida (Tiny Blue-Winged Olives)

Species Range
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