Chironomids are midges found in lakes and ponds that make up the backbone of a trout’s diet.  These larva range from #10-#22 but the Stillwater trout are particularly fond of the larger ones.  While fish will key in on the adults on the surface from time to time, the vast majority of chironomid fishing is sub surface.  You can fish these patterns on a long leader using a slip bobber, or trail them off a larger fly using an intermediate sinking line.