Yellow Sallies (Isoperla) are smaller stoneflies that are common in many streams across the country. They are smaller than most stones and often come off unexpectedly when other mayflies are hatching, and thus they are often overlooked. A common indication is the red butt on the fly. The Yellow Sally is a very effective fly and often the start to a great day when the fish are keyed in on them. Color, Natural.Fly in sizes: 14, 16, 18.