The WD-40 is another simple pattern meant to imitate midge pupae and Baetis nymphs. I believe it originated somewhere in Southern Colorado and was popularized on the San Juan River in New Mexico. This pattern is a quick, easy tie that uses just two materials besides thread. This is a great fly to fish with no lead on the leader, just under the surface as well as with more traditional nymphing techniques. Color variations include chocolate brown, grey and black.
Hook: TMC 2487 #16-24
Thread: Tobacco Colored Danville 6/0 thread
Tail: Mallard Flank Dyed Wood Duck Gold
Abdomen: Tying thread
Wingcase: Leftover butts of the tail
Thorax: Muskrat Dubbing, grey
Place the hook in the vise with the front end angled slightly down to allow clearance around the bend. Start the thread and build a thread base back about halfway down the bend of the hook.
Peel a bunch of fibers from a dyed mallard flank fether. Notice that the natural tips are very thin and wispy.
Bunch the mallard fibers up in a bundle. Break the tip ends off with your thumbnail to even them and get down into a thicker portion of the feather. This will help with the durability of the tail.
This picture shows the fiber tips after being pinched off. They are still somewhat irregular in leng
Tie the broken tips in at the back of the thread base with a couple turns of thread. Be sure the tail is centered on top of the hook.
Wrap forward over the butt ends of the mallard fibers to the eighty percent point on the shank (a couple eye lengths back from the hook eye) forming a slightly tapered thread abdomen.
Reposition the hook in the vise so it is more parallel with your tying surface. This will keep the thread from jumping off the hook during the wingcase procedure to follow.
Pull the remaining butt ends of the mallard flank back over the top of the abdomen and bind them in place with a few turns of thread back to the seventy percent point on the shank.
Dub a rather large, round thorax with the grey muskrat dubbing from the base of the wingcase to the index point.
Pull the mallard flank forward over the top of the dubbed thorax, making sure to spread it across the top of the thorax.
Bind the wingcase down at the back of the index point. Clip the remaining butt ends flush and make a few turns of thread to cover the stubs.
Build a smooth thread head and whip finish behind the hook eye.
Top view. Note that the wingcase is evenly spread across the top of the thorax and the tail is about one half a shank length long.