The Olive Dun Barbless is a general dry fly for matching adult upwinged olives on UK rivers. Its familiar olive body and upright-wing profile cover several species and sizes of dun. In particular, it is a strong imitation of the Large Dark Olive dun during its important spring and autumn hatches.
Choose a hook size that matches the insects present, then fish it upstream on a tapered leader with a drag-free drift. Concentrate on riffle edges, glides and established feeding lanes. It is most convincing during an actual olive hatch, not simply because olives are expected by the calendar.