Know Your Pattern: The San Juan Worm

When I was a boy, I caught trout with a bobber and a worm. I gave up bait fishing long ago. Now I use a fly rod. But I still catch a lot of trout with a bobber and a worm.

The bobber is a strike indicator. Yes, I like the little round plastic bobbers because they never get water-logged like the indicators I’ve tied with strands of nylon.

The worm is a San Juan Worm — a controversial “fly pattern.” Some fly fishers scoff at it. When they do, I simply smile, nod, and go back to catching fish. Here is the scoop on this beloved and maligned non-fly fly.

1. How it originated

There are as many accounts of this pattern’s origin as there are variations of it in the fly bins at your local fly flop.

What we know for sure (I think) is that a fly fisher developed this fly to imitate the red worms in the silt-coated channels of New Mexico’s San Juan River. The fly fisher is unknown to us, although I’ve heard several suggested names. The time period was likely the late 1960s or early 1970s.

The pattern is so simple that it is silly. It consists of a two-inch length of red chenille tied onto a scud hook — that is, a hook with a curved shank. That’s all. It’s the easiest fly in the world to tie. So it’s a great place for beginners to start.

2. How it has been modified

You might get dizzy when you think about all the colors and styles of chenille with which the San Juan worm has been tied.

I even experimented (at the suggestion of a friend) with putting a beadhead in the middle of the hook’s shank and then tying a one-inch piece of chenille on the front and then a one-inch piece of chenille on the back. This takes a lot of extra time and effort. It looks impressive, but I haven’t found it any more effective.

In the last six weeks, I’ve caught several trout in both Wisconsin and Montana on an odd assortment of San Juan Worm patterns. I’ve meant to tie some new ones, but I didn’t get to it. So I ended up using the left over patterns in my fly box — that is, some of the ugly ones I tied when I was experimenting with different sizes and colors (red, crimson, tan). The good news is that all of them worked.

There’s no need, then, to get hung up on size or color. Whatever you use will likely be “the only thing that’s working on the river today.”

3. Why it works

You don’t need a PhD in zoology to figure out why the San Juan Worm is so trusty. It imitates a worm — the kind which resides in a silty river bottom. Enough said.

4. When to use it

The San Juan Worm is a great go-to pattern in most conditions.

But it works especially well after it rains or when a river rises a bit. This results in churn that can loosen up the earth along a bank or the silt at the bottom. Worms get displaced by this churn. It’s hard for a trout to pass up such a large dose of protein for the little effort it takes to grab the worm as it drifts through the current or bobs along the bottom.

If a purist asks you later what you were using, tell him or her you were simply matching the hatch — imitating the aquatic life below the surface. You’ll be telling the truth.