The San Juan Worm – Fly Tying Guide

The San Juan worm is one of those flies that will always be at the center of a fly fishing conversation.

This unassuming little fly has caused many debates among fly fishers as to whether fishing with this worm pattern is true fly fishing or not. Almost as many problems as the great catch and release debates!

Whether loved or hated in the fly fishing world, the San Juan worm fly can be found in many fly fishers’ fly box around the world, and regardless of what is said about the San Juan fly, it catches fish!

Designed by the fly fisherman in Mexico, they originally used the file on the San Juan river with huge success. It has since spread globally as a deadly worm imitation pattern and is used to catch many other species worldwide.

From a Brown trout on a stream in the USA to a Smallmouth Yellowfish in South Africa across to a Grayling on the River Frome, Dorset, UK, the San Juan fly is a very effective fly pattern and very basic to tie. It is one of the first flies you should learn in fly tying.

How to Tie a San Juan Worm Fly

  • Place hook in the vise (if you want to add additional weight, you can add a small bead at this stage)
  • Create a solid thread base (if you have added a bead, tie it in the center of the shank)
  • Singe the chenille on both sides.
  • Tie in the chenille at the base of the bend.
  • Tie in the second point in the middle ( if you have a bead, then tie either side of it)
  • Tie in the third point behind the eye.
  • Whip finish and apply head cement.

Recommended Resellers:

San Juan Worm Materials

Hook: scud, caddis hook, #10-16 ( SBS Mouche 8464 #14)

Thread: Griffith Sheer 14/0 red ( any similar flat thread)

Body: Chenille body material, red, brown, purple, and pink ( pink is a popular trigger)

Cement: Solarez Thin Hard

How To Tie A San Juan Worm Fly Step-by-Step

How to tie a San Juan worm fly step 1 Place your scud or caddis hook in your vice, making sure it is secure and not too close to the tip of the jaws as the hook may slip when you apply tension to it. I advocate using barbless hooks where possible to ease the removal and minimize the damage done to the fish.

How to tie a San Juan worm fly step 2

With your thread, start behind the hook eye and wrap backward towards the back end, ending two-thirds down the shank, creating an even and level thread base to work from. If you have red thread, great, you can also use a white thread and color it with a red marker a little bit as you go. There are no hard rules in tying.

How to tie a San Juan worm fly step 3

How to tie a San Juan worm fly step 4

Cut your red chenille three times the length of the hook shank. With a lighter, lightly singe the tips and quickly roll them between your thumb and forefinger to create a little point. This handy tip is to create a head on the San Juan worm and prevent the chenille from unraveling.

How to tie a San Juan worm fly step 5

Tie in the chenille at the end of the thread base. Wrap in the chenille on the top of the hook shank with two tight wraps.

How to tie a San Juan worm fly step 6

Lift the front part of the chenille and wrap it under and forward to the center of the shank. Secure the chenille again in the center with two tight wraps. You want the chenille to ride on top of the hook shank as you move forward with your thread.

How to tie a San Juan worm fly step 7

Finish with your third and final few wraps. Secure the chenille with two final wraps. Lift the front part of the chenille and add a few thread wraps underneath the chenille.

This will allow the chenille to stand out and up, giving the worm a more lifelike appearance. Whip finish and apply your choice of head cement. This San Juan worm is a straightforward pattern in fly tying and one of the most effective patterns to fish in fly fishing.

About the San Juan Worm

The San Juan Worm is a small pattern that imitates aquatic worms, also known as annelids. With its simple construction and convincing presentation, many anglers love to fish this pattern during heavy spring rains.

The worms are at their most active from March to May. After torrential rain or runoff, they rise through the mud and silt and are often swept off into the current, where the trout just love to snack on them.

Worms are easy prey for trout and a big burst of protein and energy, too. As the worms tend to become waterlogged and sluggish in the water, the trout can easily catch them.

Lots of fly anglers use the San Juan worm to lure out big old brook trout from their hiding spots along riverbanks. But where did this fly first come from, and why was it created?

San Juan worm

History of the San Juan Worm

As the name suggests, the worm was first developed by a fly angler fishing the San Juan River in New Mexico. Little red bloodworms are prolific in the San Juan River, and this fisherman wanted to come up with a fly to imitate them effectively. Thus, the San Juan pattern was born.

The San Juan River is a tailwater fishery, and the water levels fluctuate wildly because water from the river is used further downstream for irrigation.

The high water levels of this fast-flowing river cause the worms to emerge from the silty riverbed and muddy riverbanks, and high numbers end up in the water. This makes them one of the major sources of forage for trout and other fish, particularly during the spring. It was just a matter of time before someone came up with a worm pattern on this river!

There are rumors as to who this fly fisherman was, but no clear evidence pointing to one individual. However, since its creation in the late 1960s or early 1970s, this little worm has earned its place in fly boxes all over the country. While it was first developed for the San Juan River, it has seen success much further afield, too.

the san juan worm

Where To Fish Your Worm Fly

From the great western rivers to smaller trout streams, this pattern works exceptionally well for catching trout and bass. It’s particularly suited to silty rivers, streams, and lakes, but it’s not just limited to these locations.

Aquatic worms are found in waters all over the world. If you haven’t tried fishing the worm in your local river, we recommend that you give it a go and see if you get any bites!

Having said that, it’s well-known that the San Juan fly fares especially well in murky, dirty water conditions. You’ll be surprised how well this attractor pattern does, even in coffee-colored waters.

If the conditions are right, with high water levels, this worm pattern won’t disappoint.

How to fish San Juan worm fly

How to fish San Juan worm fly

You generally fish a San Juan worm, like you would any other nymph pattern. On a euro nymph rig, single nymph, or dry-dropper rig if the situation presents itself.

The worm pattern is rather small so getting them down to the bottom is often the problem.

Use the worm as a dropper with a heavy point fly to get it down, or you can use the weighted version as mentioned earlier. It is handy to have a few different weighted worms in your box, giving you that versatility. A split shot is handy to have for this purpose.

Another method to fish the San Juan in fly fishing is ‘on the swing’ this method is particularly effective in faster, shallower water.

Whichever method you use to fish the worm, remember to get it near the bottom as this is where the annelids worms are commonly found.

You can also use this fly for tenkara fishing or Czech nymphing with a lot of success. The versatility of this fly makes it a great addition to every angler’s fly box and fishing gear. We also have a guide here on tenkara fishing knots that you might want to check out.

san juan worm wrap up


When to use san juan worm

The San Juan worm is a great pattern to use when fishing in slow-moving streams and rivers. It is especially effective in the summer months when fish are often found near the bottom of the water column. The San Juan worm is great for trout and bass and can be used as a dropper off of a dry fly or streamer, or as a stand-alone fly.

Do San Juan worms work?

Yes, San Juan worms are highly effective for trout and bass fishing. They can be used as a stand-alone fly or as a dropper off of a dry fly or streamer. San Juan worms are effective for slow-moving streams and rivers, and are especially effective in the summer months when fish are often found near the bottom of the water column.

What color is the San Juan worm?

The San Juan worm is typically a tan or light brown color. It can also be found in other colors, such as pink, red, orange, and yellow.

The Wrap Up

The San Juan Worm is a unique and immensely effective little fly if used in the right conditions. We think that it deserves a spot among your flies, fly fishing supplies, and accessories. Don’t let the purists get to you. Hook this beauty on and get back to catching more fish!

If you’ve enjoyed this guide/review of the San Juan worm, don’t miss our other fishing gear and accessories review and guides! Why not share this review online or drop us a comment or email with your thoughts? We love to hear from you guys.

Photo of author

Kyle Knight

I’m a South African based fly fisherman who has been fly fishing and tying for the past 20 years. I enjoy targeting numerous fresh water species ranging from trout, carp and bass as well as our estuary species Grunter, Garrick and Kob. I have a funny thing that I can only use flies I have tied myself to catch fish.

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