This is particularly true of PMDs and to a lesser extent BWO. The real critters take a long time to get out of their shucks and many don't make it. This is why the rises to PMD are often so "businesslike," with little rush on the part of the fish. Compare that to a Green Drake rise where the fish go nuts, because once the drake is on the surface of the water it will go as soon as its wings are dry --which is why drake fishing is MUCH better when conditions are wet.