The CDC Biot Spinner Callibaetis is an excellent mayfly imitation for summer evenings spent fly fishing. During a mayfly hatch in the afternoon when trout are rising is the prime time to tie on this fishing fly. With light tippet, floating, and a dead drift, you’ll be catching numerous fish using this fly. The best size for this trout fly would have to be a 16 but the larger sizes work well too. Be sure to pick up a dozen of these before heading out on the water this summer.