Troutline Skinny Blue Dun Micro Mayfly is a small and delicate cdc dry fly thatworks great all day long. We advice to be used on medium and slow running waters for picky fish. Our Pro Team use these kind of flies when the waters are low in volume in Summer and in Autumn time. This model works from end of August till late in Autumn for both trout and grayling and is tied on BL hooks!