Blue-Winged Olive

Other Common Names: BWO, blue wing, tiny olive, pseudo
Scientific Names: Family Baetidae, genera Baetis, Diphetor, Acentrella, Plauditus, Attenella; Family Ephemerellidae

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.


How to Match a Blue-winged olive

Hatches are matched from Westfly's database of "standard" fly patterns.

Size 16-20 Pheasant Tail, Hares Ear. Olive-brown body, gray wing
Flats, runs, backeddies: indicator, tight line, rising nymph
Size 16-20 Hackle Stacker, Film Critic, Sprout Midge. Olive-brown body, gray wing
Flats, runs, backeddies: standard dry fly
Size 16-20 Hairwing Dun, Comparadun, Sparkle Dun. Dark body
runs, slowish riffles: standard dry fly
Size 16-20 Diving Caddis, Soft Hackle. Dark body
runs, slowish riffles: surface swing


NYMPH COLOR: Dark brown, olive-brown, olive

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

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

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

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

OTHER CHARACTERISTICS: Nymphs of Baetis and Diphetor--three tails with fringes; middle tail is shorter than others. Duns--two tails. Adult males--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.