The San Juan Worm and the natural it imitates. (Bob Krumm photo)
October 06, 2025
By Bob Krumm
Editor's note: Flyfisherman.com will periodically be posting articles written and published before the Internet, from the Fly Fisherman magazine print archives. The wit and wisdom from legendary fly-fishing writers like Ernest Schwiebert, Gary LaFontaine, Lefty Kreh, Robert Traver, Dave Whitlock, Al Caucci & Bob Nastasi, Vince Marinaro, Doug Swisher & Carl Richards, Nick Lyons, and many more deserve a second life. These articles are reprinted here exactly as published in their day and may contain information, philosophies, or language that reveals a different time and age. This should be used for historical purposes only.
This article originally appeared in the July 1992 issue of Fly Fisherman magazine. Click here for a PDF of the print version of "San Juan Worms."
My client whooped and laughed and shouted as the trout he had just hooked took off another run. “This is the best day of fishing I’ve ever had; I can’t remember catching so many nice trout in one day. This San Juan Worm sure catches fish," he exclaimed.
The San Juan Worm has been around for several years. I discovered the fish-catching ability of it on the Bighorn River in June 1986 when Mike Craig, owner of the Bighorn Angler at Fort Smith, Montana, gave me a half dozen worms. "Try them," Mike said. "Holly and I fished with them yester day and caught a bundle of fish."
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I looked at the flies and almost laughed. They were just pieces of red Ultra Chenille tied to a wet-fly hook. The ends of the chenille dangled an inch or so beyond the bend and the eye. As I left the shop, I decided that if the old standby Bighorn Shrimp and Red-fox Squirrel Nymphs didn't work, I'd try the worm ... but only if other guides weren't around.
Fortunately my first choices didn't work for my clients, so I gave them the San Juan Worm to try. As a hedge against the fly's possible failure, I told my clients that if fishing with a bobber and "worm" didn't work in a half-hour, we'd try something else. They never needed to change flies. Using the worm, they caught as many as 12 fish from a single riffle. And the trout were dandies-many of them from 16 to 22 inches long.
In the following days I found the San Juan Worm to be as effective as any pattern used on the Bighorn River. And since then reports from other areas indicate that the San Juan Worm is a productive fly in many waters.
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Cork Bobbers Guides have universally picked up on the "worm and bobber," or strike indicator, technique. The technique is used on most rivers where float-fishing is the norm, and the San Juan Worm is the pattern of choice when the guide must get the customer into fish.
The strike-indicator-and-worm technique is the ultimate in simplicity. You thread a cork bobber onto the leader and tie the San Juan Worm to the tip pet. Fasten a split-shot or two to the leader just above the fly and then adjust the cork to permit the fly to get down to the fish.
You must choose the right size bobber to permit it to float while the fly is under water in the fish's feeding zone. You adjust the position of the cork, which can vary from the size of a pea to marble-size, according to the water being fished, to permit the fly to sink to the level at which the fish are holding. A toothpick or wood splinter slipped into the hole in the bobber holds it in place on the leader with a friction fit, but it can be adjusted easily by slipping the toothpick out, moving the bobber along the leader, and re inserting the toothpick.
From a drifting boat, long drag-free drifts are possible if you continuously mend upstream while you are floating over good holding water. The bobber, which is painted a bright fluorescent color, is always in sight, and when it stops, twitches, or does something that looks unnatural, you set the hook. Sometimes you will snag on bottom or rip underwater vegetation, but you will often hook a fish.
The San Juan Worm can also be fished with a standard nymphing technique while you are wading, and it can be fished with or without your favorite strike indicator-yarn, foam, or cork bobber.
Garden-hackle Imitation? San Juan Worms work best on rivers with red worms such as the Bow River in Canada. (Philip Hanyok photo) Some fishermen contend that the San Juan Worm imitates earthworms that are washed off the banks of a stream. Others say it imitates Chironomid larvae. But after investigating the riffles of the Bighorn, I find that there is an aquatic worm that lives in the moss growing on the cobble in the riffles. The worm is in the class Oligochaeta and is probably in the genus Lumbricus. It is from 2 to 2 1/2 inches long and about 3/16 inch in diameter, and it looks like the red worms I used as a kid when I fished for bluegills.
The San Juan Worm pattern originated in New Mexico for use on the San Juan River . Chuck Rizuto and Roy Stoddard's book Fly Fishing the San Juan Chironomid larvae imitations. He goes on to say that as word of the success of the Chironomid pattern spread, inexperienced fly tiers tied the pattern on larger hooks and still had success. Soon they were catching fish on # 10 hooks. Still most people didn't realize that there were aquatic worms in the San Juan River. Rizuto started tying the Ultra Chenille pattern nine or ten years ago, and it is this version that made it to the Bighorn River.
Jim Aubrey, another New Mexican, says he developed a similar pattern back in the 1950s as a shrimp imitation for Trapper's Lake in Colorado. He tied the fly on a #10 Mustad 3906 or 3906B hook with orange chenille. First he wrapped the shank with lead wire, then he wrapped chenille around the hook to the center of the shank, where he wrapped in red floss and made a red band. He then finished wrapping the chenille forward, tied it off, and whip-finished it.
After Aubrey left Grand Junction, Colorado, and moved to Albuquerque, he had little use for the pattern and gave some of the flies to his cousin for Christmas. During a 1968 fishing trip to the San Juan, both Aubrey and his cousin were getting skunked, so Aubrey's cousin tied on one of the orange monstrosities and promptly caught a nice trout. Aubrey thought it was a dumb trout, but when his cousin took another good fish, he switched to the worm pattern. Both men had a ban ner day. Aubrey contends that fly tiers modified his original pattern over the years to come up with the present patterns.
Baiting the Hook This article originally appeared in the July 1992 issue of Fly Fisherman magazine. There are two patterns that are most popular: one made of Ultra Chenille and the other tied from floss or yarn with a silver or gold wire or oval tinsel ribbing.
My favorite is the Ultra Chenille pattern. I tie it on Tiemco 200, #8 hooks. I use red (#56) Danville Fly Master Plus thread-a single-strand, waxed floss–to cover the shank of the hook. Then I tie in a four-inch segment of .008" Maxima tippet material to use as ribbing. Next I tie in a three-inch piece of red Ultra Chenille, leaving about an inch dangling past the hook bend. I wrap the floss forward to about 1/4 inch from the hook eye, then I pull the Ultra Chenille forward and wrap the floss over it enough to secure it at that point. I rib with the Maxima, tie it off with the floss, then pull the Ultra Chenille out of the way and whip-finish. There should be an inch or so of "tail" and "head" dangling from both ends. After cementing the thread wraps, I burn the ends of the Ultra Chenille just a bit to keep the chenille from unraveling.
The other San Juan Worm pattern is simple and effective. It is tied on a Mustad 37160 hook, #4 or #6. Use either two-strand red yarn or four-strand floss, red tying thread (the 3/0 prewaxed works well), and gold or silver wire or small oval tinsel.
First pinch down the hook barb. Then attach the tying thread near the eye and wrap it back through the bend. Tie in the yarn and wire. Next wrap the thread to the eye, then wrap the yarn to the eye without leaving any gaps. Rib the body with the wire and then whip-finish the head.
All the Bighorn guides I know don't like using Mustad 37160 hooks, because the large bend of these hooks causes the hook to rotate when it is set, and the point frequently lodges in the trout's eye. Rizuto contends that you can alleviate this problem by bending the hook just a bit to the right or left to offset the point.
While the San Juan Worm works best in tailwater fisheries, it works in many trout streams, because aquatic worms are so widespread. Also, heavy runoff causes earthworms to be dis lodged, so the San Juan Worm is a good choice after rainstorms.
The San Juan Worm is simple but effective. If you use a bobber for a strike indicator, you'll have a nostalgic fishing trip. Think of it–fishing with a bobber and a worm.
Bob Krumm, a freelance writer, fly tier, and guide, lives in Sheridan, Wyoming, in the winter and spends his summers guiding on Montana's Bighorn River.
