The thorax dun is best in medium to slow flows where a low profile pattern is required. Used in mayfly hatches, it sits with the body on or in the meniscus and can often induce a strike where a heavier dressed pattern might be ignored. The version illustrated is great for olive hatches. Size is chosen to match the hatch. In winter, early and late season, Blue-winged Olive hatches can often require size 22s.
How to fish:
Fish using standard dry fly presentation, maintaining a drag free drift at all times. This pattern is prone to sinking if fished in heavy broken water where a standard hackle or parachute pattern is more suited. In some circumstances an effective alternative to Vincent Marinaro’s pattern is the Comparadun.