BWO (Blue-Winged Olive)

Mayflies

Jun 12

Latin: Baetis spp. — most commonly Baetis tricaudatus in Western North America Family: Baetidae Sizes: #16 – #22 (small) Where: Worldwide; iconic on every Western trout river

Overview

The Blue-Winged Olive is arguably the most important mayfly in trout fishing. Olive-bodied with characteristic dark blue-gray wings, BWOs hatch in two distinct seasonal pulses — spring (March–May) and fall (September–November). They especially love overcast, drizzly weather, when emergences can blanket the surface for hours. By November in Montana, BWOs become the focal hatch when most other mayflies have wrapped up.

Life cycle and angler relevance

Baetis nymphs are agile swimmers that hold in slower currents. Emergence happens in the surface film, where adults can struggle for several seconds — making cripple and emerger patterns deadly during the hatch. Spinners fall in the evening but are typically less heavily fished than the dun.

Imitating patterns

Adult duns: Parachute Adams (sizes 16–20 — generic but works), Purple Haze, generic small dark mayfly dries. Emergers: BWO Sparkle Dun, Sprout Baetis, Nyman's DOA Cripple Baetis. Nymphs: small Frenchie, small perdigons, generic small jig nymphs.