Perdigon Nymphs were developed by Spanish anglers fishing the fast streams of the Pyranees. They are a simple pattern to tie and extremely effective since they get down into the depths of a fast moving stream wtih their streamline profile. You first notice that this pattern has no fibers protruding from the body that usually represent life producing aspects to a pattern. However, protruding fibers also provide drag to the fly and we want this fly to get down fast! The only fibers on a Perdigon is the Coq De Leon tailing fibers which also happened to originate in the Pyranees. The first Perdigon Nymphs were tied onto a competition style hook with a barbless wide-gape point but soon were tied onto jig style hooks since the inverted presentation decreased possible snagging on the bottom. The name, Perdigon, means Lead Pellets or lead ammunition in Spanish. I don't know if the Spaniards actually adapted their lead pellets to a hook but tungsten beads, either countersunk or slotted are the preferred method today. These beads get the flies quickly to the bottom where the fish lie within the slower currents of the stream. The Spanish anglers often fish this nymph with one fly on the rig and utilize short casting drifts. However, here within the Sierra, anglers often use a two fly rig or a dry-dropper combination. Colors and size of the flies are determined by the stream and the mayflies that are present at that time. Early in the season you might have discolored water and dark colors such as black, brown-olive, UV Purple, with red or orange hot spots will be effective. As the stream becomes clearer, copper or black nickel beads have a good attraction. During the early season, Mayflies will be in the larger sizes such as #12-14 and natural colors such as olive, cream, or ginger work well. At the end of the season, mayflies are much smaller in the #16 to #18 size, maybe in the #20's. These flies should be darker such as dark olive and olive with vivid hot spots.
Experiment with Pearl Flashabou and vary the thread underbody color.The UV Resin coating over the body will highlight the various shades you can develop by changing the underbody coloration. Another new material worth using is the Veevus Body Quill which comes in a wide range of colors. Coating the Body Quill with UV resin brings out a depth to the coloration of the pattern that offers a sense of translucency.