WD40 Grey. A newer generation fly the Grey WD40 is a awesome performer and has quickly proved itself as an emerger not to be without. Available in a variety of colours the Grey WD40 is a good general imitation of both Mayfly and Emerging Midge Nymph pattern. The Grey WD-40 is best fished on a dead drift as a Pupa Midge at the end of your drift lift your rod to bring your WD40 to the surface replicating the natural movement of the emerger. Try these out on you favourite tailwater or creek you won't believe the results.