Blue Wing Olives (BWOs) are arguably the most important mayfly hatch in North America. They emerge in cold, overcast conditions when other insects stay tucked away — which means they bring fish to the surface when nothing else will.

The hatch typically begins in early spring as water temperatures climb into the mid-40s. Look for emergences on cloudy, drizzly afternoons between 1 PM and 4 PM. The worse the weather, the better the hatch.

Match the hatch with size 18-22 parachute patterns, RS2 emergers, and pheasant tail nymphs in the days leading up to a hatch. Pay attention to the trout’s feeding rhythm — many fish key on emergers just below the surface rather than the duns themselves.

Late fall brings a second wave, often even more reliable than spring. Cold mornings keep fish lethargic, but by midday, you’ll see noses sipping in the slow seams. This is technical, rewarding fishing — and it’s why we tie so many BWO patterns.