Ok, so it doesn’t really look like the offspring of a San Juan Worm but this little guy may be even more effective particularly during clear, early spring conditions. Although about as long as a traditional San Juan Worm, as you can see, it has a way slimmer profile and is carried on a much smaller hook.
For the hook, Dai-Riki #135 in size 20 works exceptionally well. Start by gently mashing the barb and getting the hook firmly secured in the jaws of your tying vise.
For thread, UTC 70 Denier in red looks good but so do pink, tan and brown. Start your thread on the hook shank behind the eye and take a few wraps rearward before snipping or breaking off the tag.
The only other material needed for the fly is a length of small, round rubber legs. Here I’m going to use red but any color you use for a regular San Juan Worm will work just fine. One strand is enough to make about a dozen flies. A Dai-Riki hook box comes in handy for measuring the material and cutting it to length. Fold the cut segment in half to create a small loop that’s held in the fingertips of your left hand. Place it so about 1/4” sticks out over the hook eye and use a pinch wrap to secure it to the shank. While pulling on the material to stretch it rearward, continue taking wraps of tying thread all the way down to the hook point, binding the material to the top of the hook shank as you go. Then, make open spiral wraps forward and leave your thread about an eye-length behind the eye.
Get hold of the rubber leg segment on the far side of the hook and start making touching wraps up the shank while pulling to keep mild tension on the material. When you reach your tying thread, take a few turns to secure the rubber segment to the hook shank. Then pull the segment straight up and snip it off.
Pull the front loop taut and snip one side of it off right by the hook eye to leave a single, long front segment. Take wraps of tying thread to build up a short segment of thread that’s the same level as the body. You can then do a 4 or 5 turn whip finish and snip or cut your tying thread free.
I like to snip the ends at an angle leaving about 3 full hook lengths of round rubber leg material extending off both the back and front of the hook.
A drop of head cement or in this case, Hard as Nails, will help to insure the thread wraps don’t come unraveled and also add a bit of shine to the small thread segment.
I know the ends look too long with respect to the body and the hook size but I think motion is absolutely key to the success of this little pattern. Here the rubber legs have been cut to a more reasonable-looking length but as you can see, the front and rear segments don’t have much motion. The same is true when they’re underwater. With longer front and back segments, you get a lot more motion, particularly underwater.
The Son of San Juan Worm is a quick, easy and cheap tie and absolutely deserves the small amount of space it’ll take up in your fly box.