The baetis BWO hatch is considered by experts to be the most important insect hatch. In fact, you are almost guaranteed to experience a blue wing olive hatch. Emergers have to wait until their wings are dry before flying. This “wet winged” parachute allows the fly to sit flush with the surface and make it easier to see in fast currents and heavy hatches. You’ll find BWO’s more active on overcast days and even in light rains.