Blue Dun The Blue Dun is a classic dry fly pattern that is used to imitate the early mayfly hatches. It is a small fly, typically sized 12-18, and is made with a gray body, blue dun wings, and a grizzly hackle. The Blue Dun is a versatile fly that can be used in a variety of water conditions. It is especially effective in clear, slow-moving streams where the trout feed on the surface. Here are some tips for fishing the Blue Dun: a Cast the fly upstream and allow it to drift naturally with the current. a Use a fine tippet to help the fly float properly. a Make sure to mend your line regularly to keep the fly in the strike zone. a Be patient and wait for a good take. The Blue Dun is a great fly to have in your fly box, especially if you are fishing for trout in the spring or early summer. It is a simple pattern to tie and can be effective in a variety of conditions. Available in sizes: # 12 - # 18