The WD-40 Is a very proven pattern for fishing streams and rivers for trout. It can be used as a BWO Baetis emerger or even a very effective searching pattern. The trout seem to not be able to say no to this fly! Its one of those patterns that just works, and is fairly easy to tie. You only need mallard flank feather, thread, and some type of fine dubbing.
Hook: Umpqua U202 size 18 (but you can use any curved hook in a wide range of sizes).
Wing/Tail: Mallard Flank
Casing: Super Dry Dubbing
Thread: 8/0 brown/olive thread (commonly tied olive, black, brown, and gray)
Music: Sunny, Happiness - Bensound.com