Trout Unlimited
Top Trout Flies Course

Lesson 5 – The San Juan Worm

Scroll Down to Read

The San Juan Worm

One of the Top 10 Trout Flies Ever Created

This fly, and all worm flies for that matter get a bad rap. I think anglers like bad mouthing this pattern on one end, and then fishing it like crazy and catching loads of fish an hour later. It’s the fly we all love to hate and love to fish. The reality of this fly, though a bit uncultured in its look and design, is actually just as accurate of an imitation of natural food sources in the water as a zebra midge or WD-40. It imitates something called an annelid, which is just a fancy word for an aquatic worm or a nightcrawler looking worm that lives underwater for its whole life. It doesn’t need a whole lot of additional variations or flash or anything to be successful, it simply needs to be fished and fished often. Let’s learn a little more about this fly, and why it’s so successful.

The Details

Invented for the famed waters of the San Juan River tailwater in New Mexico, the san juan worm was used on this river exclusively for quite some time before it became a staple in fly fishermen’s boxes across the US. As all great patterns start, it was looked down on for being too simple and too effective. People felt like it was cheating. “Why don’t you just throw a real worm on a hook and fish why don’t ya?” was the common criticism for some time. If you are used to fishing catskill style dries on the famous private waters of the East or was told nymphing is just something you don’t do unless you’ve sold your soul to the devil, then the san juan worm was hard to understand and accept. Overtime however, more and more guides used them, which in turn built confidence and acceptance to the fly and it slowly fed into fly shops and into anglers boxes everywhere. The san juan worm is incredibly simple fly to tie and holds up pretty well when tied correctly. Though it really only imitates an aquatic worm, these annelids are always in the river system and are in the rivers in big numbers. Trout always see them on the menu and I can count on one hand the number of days a san juan worm hasn’t put a fish to my net if I fish it for more than 30 minutes. It simply works and the sooner you get off that high horse and add it to your box, the sooner you’ll be catching more fish and making the most out of your fishing trip.


Graphs – Seasonality, Size and Color

So there is no need for the same graph as the other patterns because you can fish a san juan year round and color seems to be more the preference of the angler than the trout and all colors seem to work pretty well, with some colors doing better on other days than others.  It’s important to have a few colors of a few sizes in san juan worms in order to be prepared anytime of the year.  

With that said, here’s the size, color and variations we’d have in our box year round:

  1. San Juan Worm – 2 of Each Beadhead and Beadless
    1. Colors: Red, Pink, Brown, Green, Purple
    2. Sizes: #12 -#16 though often all you’ll need is #12 and #16
  2. Squirmy Worm – 2 of Each Size/Color below with Tungsten Beadheads (no need for beadless options here)
    1. Colors: Red, Pink, Green, Purple
    2. Sizes: #12 – #16 | Just a #12 and Just a #16 if you want

We will list and show a few different variations below, but you really only need these two options and you can add a third or fourth really just for fun or to mix it up.  Annelid imitations are pretty easy compared to most other insects we imitate as anglers which is a good thing cause you just need a few for each of your boxes and you’ll always be prepared.


The Secret to Why This Fly is So Productive

The secret? It’s no secret actually.  It works because fish love worms.  Nightcrawlers did it for you as a child and the san juan is doing it for you now as a nymph angler.  Annelids (aquatic worms) are readily available to trout, especially during periods where flows have recently increased.  Annelids are poor swimmers and easy, high protein food for trout.  It’s hard to pass up as a trout looking for a meal.  Aside from a few categories of insects, there aren’t any bugs in the water that are this numerous on a year-round basis.  The abundance of this insect and that it is always on the menu is what makes this fly so productive.  While it seems there is never a bad time to fish any of these top trout flies on our course, the san juan worm, more than any is an always have in your box, never hurts to throw it, kind of pattern.  Let’s dive into a little entomology on this fly, though short, and then focus on a few key signals and presentation tips to maximize your success on this fly.


The Entomology Knowledge on This Fly

This section will be different and substantially shorter than the other lessons, because it is the only pattern on the list that really only imitates one insect, the annelid.  Annelids spend all their life underwater and burrow and feed off the earth just like an earthworm, but in the river.  They play a vital role to the eco system and other insects ability to survive and thrive.

They are found anywhere and everywhere there is running water and trout.  The sizes range from a #6 to an #18 with the average sizes being #10 – #14 that I’ve sampled and found over the years.  They are pink, red, brown, tan, and purple from what I’ve seen though additional colors like bright green can work well too.  Fish find the san juan worm part imitative to an annelid and part attractor because it is bright and large and just looks tasty.

Chenille, sili worm material or squirmy worm material, pipe cleaners and rubber and spanflex have all been used to imitate annelids with the most popular being the micro chenille used for the traditional san juan worm.

That’s about all you need to know as they are easy to identify if you find them in rivers, though finding them isn’t as important as just trying them every time you fish during the day, because they are always in the water.  It really doesn’t get any easier for a beginner than to fish a san juan worm because at least you can have the confidence that you are matching something in the river at that time that trout are almost always willing to eat if you get it in front of enough of them.


Identify the Signals the River Provides to Learn When to Fish It

As I’ve mentioned earlier, there isn’t a bad time to fish this fly.  The key is finding the right color, the right depth and the right opportunity to fish them.  I have found that fish are either on the worm for the day or they are not.  If they are on, it can be lights out good, if they are off, you’ll end up with 1 – 5 fish that eat it.  That’s still a good day in most peoples book, so that’s why I say there isn’t a bad time, but there is a best time and that’s what we’ll discuss now.

The best time to fish this fly is when streamflows go up.  When streamflows increase, the more and the faster the better, it flushes the worms out of their holes and puts them free floating in the current.  People used to, and still might as far as I know, do what is called a san juan shuffle on the san juan river.  The fish have learned that when you walk around in the San Juan River, that you disrupt the streambed, kicking up insects, and the trout will sit behind you and eat flies that you kick up.  Shuffling your feet can make a near feeding frenzy on the food that gets dislodged.  The san juan shuffle is what they used to call this and it imitates quickly rising streamflows.  When this happens naturally more food is dislodged for trout and many of those are annelids making the worm fishing a solid choice. It’s a guess per river and per day which color is best, but with their only being 3 or 4 commonly productive colors, it isn’t hard to spend a few minutes tying different colors and fishing the hole until one connects and produces.

That’s the best tip we can give you at this point for identifying the right signals on the water.  Look for high water, or rising streamflows and get a heavy weighted worm in the strike zone for some excellent fishing opportunities.


Presentation Tips on the Fly

There are a few nice tips we’ve found over the years when fishing a san juan worm that will help you catch more fish.

Fish it Deep with Splitshot or a Beadhead – Or Both!

Fish will eat this fly down deep and they don’t seem to be very shy about eating it either. Getting it down deep is key and can make the difference between a 2 fish and 20 fish day. Make sure to get it down deep and make it the middle or last fly in a 2 or 3 fly set up.

Fish Without a Bead but Use Splitshot

Sometimes, fish can get picky on how this fly is presented and if you are seeing higher flows, and all the right signals to throw a worm and you’re fishing it heavy down deep and you’ve tried the color options and it still isn’t working, the last thing I try is to use a weightless san juan worm, the ole’ chenille on a hook and then use some split shot about 6 to 12 inches above the fly. This helps it get down deep, but doesn’t make the fly so heavy. Instead the fly floats more free and natural in the flows, but still gets in the strike zone. This can make the difference some days, but if you’ve tried this, and the other tips and it still isn’t working, then find some new water or try some other flies, cause you’ve done all that is needed to find success with the san juan worm at that point.

Peg That Worm!

Now it’s time to get real sneaky on the trout. If you peg the chenille or squirmy material on the line above a bare hook, even the most pressured of trout won’t figure out the difference between your offering and the real thing. I personally just tie a triple surgeons knot 2 inches above there I attach the hook, then do an overhand knot to cinch the squirmy material or chenille onto the hook. This seems to keep it all in place without many issues. It’s hard to go wrong when pegging an egg or a worm, but a squirmy worm pegged is as easy as fishing gets on the fly and a near guarantee if fish are even remotely interested in annelids that day.


Common Variations and Ways to Modify the Pattern for Success

There are not many ways to improve on the san juan worm, but as new materials surface in the fly fishing world, a few notable variations exist

The Squirmy Worm or Sili Worm

Named after the material used, this soft, stretchable rubber is like something that comes off a kids toy or doggy chew toy and is stretchy and easily broken. For the life of me, I can’t get these flies to last me more than 10 fish before something breaks, but the fact that it sometimes only takes 15 minutes to catch 10 fish makes it worth the lack of durability. To tie this pattern, simply do whatever you’d do when tying a san juan worm, just be gentle on the material and tie in the squirmy material instead.

I’ve given up tying these I’ve decided and now if I fish them, I just peg them instead. It’s just as durable if not more and I don’t have to retie every 10th fish, but instead when the material busts, I just tie a quick overhand knot onto the line with another squirmy. You can also trim them to whatever size you want this way while on the river. If you tie a size #10 and they are eating #16’s then it’s nice with a pegged worm to just trim a bit off each side to make it smaller.

Spanflex Worm – AKA Son of San Juan Worm

This is a sparsely tied version of the san juan and uses spanflex or small round rubber as the main material. This makes for a very skinny annelid pattern and is very effective on waters where regular san juans have lost their potency from everyone fishing them and the fish becoming educated. They have great movement just like the squirmy does and is better than chenille in that sense, but also less durable. It’s a trade off but having 3 or 4 of these in a couple sizes in your box is a good bet on those picky days as a sort of “secret weapon” to unleash when needed.

Depth Charge Annelid

This is a wire wrapped san juan worm that I developed for high water periods when I know worms work well. The tungsten bead in the middle plus the full wire wrapped body makes for an incredibly slim and heavy pattern that gets down deep. When water is fast and high, or when fishing deep holes where you need some weight, try this depth charge, its one of my favorites next to the squirmy worm and traditional san juan worm and is perfect for those times where a split shot just isn’t enough.

The standard san juan worm will work for 90% of occasions, I prefer squirmy worms because it’s newer and exciting, but they work as good as san juan worms in my opinion and are all in the same category of the san juan worm which is an excellent fly to fish anytime of the year, but especially during periods of increased flows or for beginners. It’s a great fly to have in your box and I always have at least a dozen in assorted sizes and colors in my box.

Image Gallery of Variations and Colors of the Fly

Join Trout Unlimited

Become a member of Trout Unlimited and support conservation on your local waters

Read Introduction Here

Read THE BASICS Lesson

Lesson 1
Lesson 6
Lesson 2
Lesson 7
Lesson 3
Lesson 8
Lesson 4
Lesson 9
Lesson 5
Lesson 10

Read Conclusion Here