The dun, scientifically called sub-imago, is typically fished on imitations with upright wings. In this stage the insect has surfaced and stretched its wings out of the wind-case, waiting to get them dry and fly away. Depending on the species and the humidity of the air, duns may drift very long before taking off. Left: a male spinner of Rhithrogena gratianopolitana. Right: the same insect in the dun phase.