The San Juan Worm

We’re digging into a controversial one here.  Opening a can of worms, if you will (I’ll stop now).

Bad jokes aside, this simple pattern has caused more debates and arguments among fly anglers than, I think, any other in existence.

A lot of purists will tell you that fishing the San Juan Worm isn’t fly fishing at all.

I’m not going to wade too far into the is-it-or-isn’t-it debate.  The fact remains that trout like to eat worms if they’re available and the San Juan is the best worm pattern that fly anglers have access to.

What Does the San Juan Worm Imitate?

The San Juan worm imitates any of a number of species of annelid – the ringed worms.  That includes earthworms, but also some twenty thousand or so other related species.

That’s really all there is to it.  It’s a worm.  Nothing more, nothing less.

It was tied initially to imitate red bloodworms, but a worm is a worm and the San Juan is a good imitation of any of them.

Fishing the San Juan Worm

While the San Juan is a great fly, it’s use is fairly narrow – after all it imitates worms and nothing else.  With that in mind, there are a couple of scenarios where it really shines:

When rivers are running high, either due to spring run-off, rainstorms, or if you’re fishing in a dam tailwater.  And, In big trout rivers in the winter.

Fish the San Juan Worm in High, Dirty, Water

Worms, of some species or other, are found in water all over the world.  There’s a reason that the worm-under-a-boober is such a fishing stereotype.

A lot of anglers have the most success fishing the San Juan after heavy rains or during runoff events.  When the soil is saturated, worms tend to come up out of the ground, and, as these animals tend to be waterlogged and sluggish as they get washed into the river, they’re easy prey for hungry fish.

This fly does work great during high, stained water conditions.

Fish the San Juan in the Winter

I’m not certain of the worm biology at work here, but there’s no mistaking the fact that it is effective.

I have a suspicion that the San Juan may be acting as an attractor pattern here.

While cold, sluggish, fish may be unresponsive to most flies, even when dangled in front of their noses, this big red worm may look like such a big, easy, meal that they simply can’t resist.

How to Fish the San Juan Worm

The simplest and easiest method, in moving water, is to dead drift it, just like you would a nymph.

Especially effective is running a combination of 2 or 3 San Juan Worms under an indicator.

This helps ensure that you’re getting a worm down deep, as well as leaving one for any fish looking high in the water column.  It’s not exactly fly fishing at its purest, but it’s effective.

If you’re having trouble getting your worm down near the bottom, you can switch to a bead-head version or add some split shot or soft weight to help drag it down faster.

One would think, given the worm-and-bobber stereotype that this would be a good stillwater pattern, but I’ve never heard of anyone having much success this way.  Maybe someone can enlighten me, but for now, I’m fairly convinced that this is best suited to faster waters where the worm can be swept downstream.

History of the San Juan Worm

Nobody knows exactly when, or by whom, the first San Juan worm was tied.  We do know that it originated among anglers along New Mexico’s San Juan River.

We do know that the pattern emerged in the 1960’s or 1970’s, and quickly grew in popularity, spreading far beyond its New Mexico roots.

The San Juan is a tailwater fishery, and water levels can fluctuate wildly as water is used for irrigation.  Little red bloodworms are apparently abundant in the area and emerge from the riverbed during periods of high turbulent water.

As these were a major food source for San Juan River trout, especially during spring run-off events, anglers began searching for a pattern to imitate them.

Tying the San Juan

Full disclosure – I’m not much of a tier.

But, if tying is something that you’re looking to get into, the San Juan Worm is a perfect learner pattern.

It’s so simple – just a length of chenille tied to a hook – that even I, with my blunt, clumsy, fingers can tie it without too much difficulty.


While some people hate this pattern, there’s no denying its effectiveness.  And for me, that’s the most important thing.  While it’s a noble thought, delicately presenting mayfly patterns all day doesn’t always jive with biology.

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