Tie a bundle of coq de león fibers, evenly as possible. As long as the hook shank.
Go forward with the thread and then go back making a loop with the thread and the lower side of the fly. This loop will separate the tails.
Take one tip of the loop at each side if the hook, and go forward from the top separating the tail in two equal halfs. Tighten a bit the loop once tied with some turns. The tails should remain in a 45° angle.
Finish tying the loop, cut. Tie the cdc feather by its tip. This is the most effective color.
Wrap the feather through itself and carefully wrap it going forward. A third of the hook should remain not covered. Don’t worry if many cdc fibers overhang, watch that the segments formed for the abdomen have a growing diameter towards the front. This is made by wrapping the feather carefully controlling each segment.
Trim and cut the loose fibers to expose the abdomen. The picture shows the conic figure and segments.
Place 3 or 4 cdc feathers on the Marc Petit Jean tool to pass the fibers to the thread, to be opened with a needle. The length of the fibers should cover the wing of the fly. Cdc is tricky, if the wing is shorter we may get an emergent and not a dun, in spite it still would catch fish.
Separate the thread to insert the fibers, wrap the thread spinning the bobbin, to make a cdc brush.
Combing the feathers upwards and to the back, cover densely the vacant third of the hook.
Tie and cut the thread. Comb the cdc fibers upwards and to the back, trimming carefully the under part and the sides, until the wing –seen from the front- has a V-shape.
Trim the feather imitating the ephemeroptera wing to finish the fly. The silhouette is very good, 45° tails make it stable, and the base of the cdc wing makes it float naturally as it gathers air. On the water, it is so similar to the duns that we will soon confuse it with them.