Denny Rickard's Callibaetis nymph is extremely simple but more deadly than the other, fancier, shop flies I have tried. I'ts just lemon wood duck fibers for the tail, hare's ear dubbing for the body, three turns of grizzly, gold ribbing if you want, and then pull some wood duck over the top for the back. Very easy. Looks very simple, but man, it sure is effective!
Happy tyin,' Bryan
