Developed by Mike Mercer of Redding, CA around 1989. Mike designed both a nymphal form and an emerger form for Pale Morning Dun, Blue Wing Olive, Callibaetis, and Green Drakes. Aspects that highlight his pattern are the use of materials to represent gills behind the thorax and the hard shiny epoxy covering of the wingcase. The use of epoxy on the wingcase had been used by earlier tiers, such as Hal Janssen, but Mike utilized this material on a number of patterns and became known for it's use. Epoxy had been a time consuming step that took time to mix, apply, and harden. Mike also had to use two Turkey segments for wingcases since the epoxy would seep into the thorax dubbing if only one segment was used. This all changed with the use of UV Fly Finish that hardened in seconds with the use of a UV light and requires no mixing. The material is quite viscous and only one segment of turkey is required for the wingcase. Today, the use of UV epoxy is quite common and is an important step to protect the weak fibers of the wingcase. The gills are marabou tips that are placed on each side of the shank in front of the abdomen. The length of the gills is adjusted to not exceed the base of the shuck or tail. This works well with sizes 14-18. However, in sizes 20-22, one wrap of the marabou fibers around the shank will accomplish the same thing and is much easier.
Mike believed that fish are attracted to light/dark contrasts and the darker wingcase with the lighter thorax provides that contrast. His patterns also use dark/light segmentation in the abdomen using pearl flashabou or pearl krystalflash ribbing with a stripe of Turkey tail that is about 3-4 fibers wide. All of his patterns have this stripe except the Callibaetis. The thorax and abdomen dubbing is a blend of colors. Try to include at least three Antron colors to come up with the proper hue. This spectrum will give the fly a mottled effect, more of the natural coloration. Mike formulated a dubbing blend that was sold within a dispenser but this dispenser is no longer distributed nationally. However, you might find it available through The Fly Shop. Spirit River formulated a number of blends that are very similar and are currently sold as Antron Dubbing. The emergent forms generally show a darker wingcase, a trailing shuck, and an addition of a forward wing with hackle. The nymphal form will have a tail represented by 3 Pheasant Tail fiber tips or 3 Ostrich herls, legs represented by partridge or Grouse fibers, a small dubbed head and is usually weighted.