The San Juan Worm is a popular and effective fly pattern used primarily in trout fishing. It imitates various aquatic worms, such as the common earthworm or aquatic annelids, which can be a significant food source for trout, especially after rainstorms when worms wash into rivers and streams.

Key Features of the San Juan Worm:

Simple Design: Typically consists of a hook, thread, and a segment of chenille (often red, pink, or brown).

Versatile: Works well in both still and moving water.

Effective Year-Round: Particularly productive in high, muddy water or after heavy rains when worms are dislodged into the water.

Variations:

Colors: Red, pink, tan, brown, and even fluorescent hues.
Materials: Chenille, ultra chenille, or stretchy synthetic fibers for a more natural look.
Sizes: Usually tied on hooks ranging from #8 to #16.

How to Fish It:

Dead Drift: Like a nymph, often under an indicator.
Euro Nymphing: Works well as part of a tandem rig.
Swung (Wet Fly Swing): Can be effective in faster currents.

Why It Works:

Trout recognize worms as an easy, protein-rich meal. The San Juan Worm’s simplicity and realistic movement make it a reliable "searching pattern" when fish are feeding opportunistically.
Would you like tying instructions or tips on fishing it in specific conditions?