The Troutline Skinny Black Dun Micro Mayfly is a delicate cdc dry fly that works great all day long. We advice to be used on medium and slow running waters for picky fish. The "biggest" sizes like #16 and #18 should be used early in mornings or in the last part of the day and size #20 should be used all day long. Especially when is cloudy outside this fly is a grayling killer and for this reason we advice to be used with moderation!
