Pa is right. WD40 is an awesome nymph. I have been using Chironomids, which are very similar to a WD40. A WD40 got it's name cause the little tail and the wing cast is out of Wood Duck. The bodys are generally just thread and there is a tuft of dubbing for the Thorax. Also, generally tied on a bent hook or a scud.
The Chironomids (and Pa, I have simplified them) is also a scud hook or it can be a nymph hook or even a 200R. They do straighten out, just like a scud.
I use a Bead Head (usually tungsten for the weight) and the body is thread or floss and wire. You can use Peacock for a thorax, but lately I just build a taper to the bead out of thread.
Best colors for me have been Black/White down deep, and Flashy Green/Gold OR and Lunker saw this, Blue wire on Black thread body, about two to three feet off the bottom.
I know we have no idea how deep Willow is so I start off with Nine feet and an indicator that will stand straight up if suspended, so Nine Feet is what I call deep. I work my way up from there.