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Lateral view of a Male Baetis (Baetidae) (Blue-Winged Olive) Mayfly Dun from Mystery Creek #43 in New York
Blue-winged Olives

Tiny Baetis mayflies are perhaps the most commonly encountered and imitated by anglers on all American trout streams due to their great abundance, widespread distribution, and trout-friendly emergence habits.

Dorsal view of a Skwala (Perlodidae) (Large Springfly) Stonefly Nymph from the Yakima River in Washington
This Skwala nymph still has a couple months left to go before hatching, but it's still a good representative of its species, which was extremely abundant in my sample for a stonefly of this size. It's obvious why the Yakima is known for its Skwala hatch.
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 Attenella margarita (Little Western Blue-Winged Olives)

Though having a national distribution, this species is considered by angling authorities to be important only in the West. In localized waters where it is abundant, it can be a significant hatch.

Where & when

Time of year : August

In 2 records from GBIF, adults of this species have been collected during July (50%) and August (50%).

In 4 records from GBIF, this species has been collected at elevations of 5230, 5420, 7589, and 8350 ft.

Species Range

Hatching behavior

Time of day : Mid-morning

Fred Arbona in Mayflies, the Angler, and the Trout says that trout prefer nymphs on the surface when the margaritas are hatching, so a floating nymph is the ideal tactic. He also says this hatch is unusually prone to producing stillborn and crippled duns.

However, Knopp and Cormier say that this species, like Attenella attenuata, emerges on the bottom of the stream and rises to the surface as a dun. This conflicts with Arbona's observation.

It may be that the nymphs of this species make several failed trips to the surface, like most in the family Ephemerellidae do, before deciding to emerge, and that Arbona observed feeding during this behavior. Or there may be a wider range of emergence behavior during this hatch than either author realized.

Spinner behavior

Time of day: Late dusk

Nymph biology

Current speed: Slow

Environmental tolerance: Best in consistently cold water

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.


Described in Needham et al (1935) as Ephemerella margarita
Body length: 9.5 mm

A species of the simplex (now a synonym of Dannella simplex) group, of which only the nymphal stage is known; dorsal abdominal spines present, but no occipital nor thoracic tubercles.

Head and thorax of nymph smooth. Legs pale; tibiae and tarsi banded at the middle, tarsi also at the tips. 8 to 9 denticles along the inner margin of each claw, the distal one being longest. General color olive brown with blackish markings. Lateral extensions of the abdominal segments are well developed, and terminate in long postero-lateral spines on segments 4 to 9; abdomen broadest at segment 7. Gills present on segments 4 to 7 only, semi-operculate on segment 4. Rather short dorsal spines are present on tergites 3 to 9. Two color phases are known. In the best marked phase, a median blackish spot is present on tergites 2 and 3, and 5 and 6; apical margin of 8 with a black streak; tergite 9 largely blackish except for the lateral extensions and two pale submedian apical dots. Lateral extensions pale, each crossed near the middle by a broad brown band. Brownish ventrally; sternite 8 largely pale yellowish; sternite 9 blackish brown. Tails yellowish white, with a broad black band across the middle and a narrow black band at the tip.

Specimens of the Mayfly Species Attenella margarita

1 Female Dun
1 Nymph

Start a Discussion of Attenella margarita


Mayfly Species Attenella margarita (Little Western Blue-Winged Olives)

Species Range
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