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Blue-Winged Olive

Scientific Names: Family Baetidae, genera Baetis, Diphetor, Acentrella, Plauditus; Family Ephemerellidae, genus Attenella

Common Names: Blue-winged olive, tiny olive, BWO, pseudo


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NYMPH SIZE: 4-12 mm (3/16-1/2 in)

NYMPH COLOR: Dark brown, olive-brown, olive

DUN SIZE: 4-10 mm (3/16-3/8 in)

DUN COLOR: Wing smokey. Abdomen olive to olive-brown

SPINNER SIZE: 4-12 mm (3/16-1/2 in)

SPINNER COLOR: Wing clear. Abdomen olive-brown, reddish brown.

OTHER CHARACTERISTICS: Nymphs of Baetis and Diphetor have three tails with fringes; middle tail is shorter than others. Duns have two tails. Adult males have turbanite eye. Unlike the others in this group, Attenellas are not swimming mayflies and have some physical differences; for fishing purposes, however, they can be grouped with the other blue-winged olives.


Mouse-over for alternate views: Nymph    Attenella nymph    Dun    Spinner 1    Spinner 2

About Blue-Winged Olives

These tiny mayflies are rarely absent from the river. Fishable hatches can begin as early as February and continue through April or May, then start up again in September and last until really cold weather sets in, usually around the end of October or early November. In mild climates they never completely disappear in winter, but in the cold seasons of the Rockies they will take a break from November through February.

The blue-winged olives are diverse. The genus Baetis is the most significant to fly fishers. Many anglers call the whole group "Baetis," although the more anal ento-types start to fidget when they hear it. You still hear anglers refer to the genus Pseudocloeon ("Pseudos"), the size 22 tiny olive, but this insect has now been lumped into the genus Baetis. On Westfly, all four major genera of the family Baetidae, plus the genus Attenella from the family Ephemerelliade, are refered to as "blue-winged olives" because the imitations and tactics are so similar.

Nymphs live in almost all types of running water, but slow to moderate runs hold the largest populations. Nymphs have a habit of purposefully drifting short distances in the current to find a new home; sunrise and sunset are the prime times for this activity. Thus nymph imitations are can be productive even when there is no hatch in progress.

Winter/early-spring hatches usually start about 1:30 p.m. or 2:00 p.m. (standard time). In the far West, the best hatches occur on overcast or drizzly days. While slow runs can be good places to fish, some of the best fishing is in backeddies, where little duns seem to circle endlessly--or until a trout sucks them down.

Emerger patterns are especially useful during the hatch. When fishing a massive hatch, you might try a dun or cripple pattern that is slightly darker than the natural. The trout don't seem to care, and it's easier to pick out your fly from the hundreds of naturals.

Spinner falls are important, so you should always carry a few patterns during the blue-winged olive season. Some spinners actually swim or crawl below the water to lay their eggs, so sub-surface spinner patterns and tactics should be part of your arsenal.

Articles About Blue-winged Olives

Click headline to read entire article

Paraloops The paraloop style of hackle/wing has long been overshadowed by the more popular parachute style. But why? And how do you effectively construct a paraloop? Jeff Morgan

Hidden Adults Some adult insects dive or crawl underwater to lay their eggs. What's the best way to imitate this behavior? Jeff Morgan

Go Below for BWO Is a dry fly the best answer during a Baetis hatch? Not always. Scott Richmond

Fishing the Blue-Winged Olive Hatch If you trek to a river to fly fish for trout in the next couple of months, you'd better know how to fish the blue-winged olive hatch. Find out here. Scott Richmond

Quick Tip: A Little Known Two-Fer-One September offers a special opportunity for alert fly anglers. Scott Richmond


Nymph. (photo © 2006 Arlen Thomason. Used by permission.)

attenella nymph

Attenella nymph. (photo © 2006 Arlen Thomason. Used by permission.)


Dun. (photo © 2006 Arlen Thomason. Used by permission.)


Male spinner. (photo © 2006 Arlen Thomason. Used by permission.)


Female spinner. (photo © 2006 Arlen Thomason. Used by permission.)

Matching Blue-Winged Olives

Only standard fly patterns are shown. Click here for all matching flies in the database.







Hares Ear, Pheasant Tail, A. P. Nymph

16-22/Brown, brown-olive

Indicator, Tight line, Rising nymph

Moderate runs, just below riffles


Floating Nymph

16-22/Olive, Olive-brown

Shallow nymph

Flats, runs, backeddies


Parachute Baetis, Sparkle Dun, Comparadun, No Hackle, Thorax Dun

16-22/Olive, Olive-brown

Standard dry fly

Flats, runs, backeddies


Rusty Spinner

16-22/Olive-brown, red-brown

Standard dry fly

Flats, runs, backeddies


Diving Caddis

16-22/Olive-brown, red-brown

Surface swing

runs, slowish riffles

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