The Blue Dun fly is a classic and versatile pattern used in fly fishing. It typically imitates the dun (sub-adult) stage of mayflies. This fly often has a body made of blue-gray or olive dubbing, representing the insect’s body, and may feature a split tail. The wings are usually a light, translucent material to mimic the delicate appearance of mayfly wings. Blue Dun flies are effective in various water conditions and are commonly used for trout fishing.