San Juan Worm
The San Juan Worm is exactly what it looks like - an aquatic worm in chenille form - and pretending trout don't eat worms has never once fooled the trout.
Aquatic worms live in every silty river bottom by the million, wash into the drift with every flow change, and get eaten with zero suspicion - facts the San Juan Worm converts into one of the most productive 'flies' ever wrapped. A length of red chenille, singed at the ends, that works precisely because it isn't clever.
What it imitates
Aquatic annelids - real worms that genuinely live in rivers (this matters to the fly's dignity) - plus every earthworm a rainstorm donates.
When & where it wins
Rising, off-color and post-storm flows above all (worm o'clock), tailwaters year-round, early season everywhere.
How to fish it
Dead-drift near bottom, usually as one fly of a tandem; in dirty water, upsize and slow every presentation.
Sizes & variants
10-16 in red, pink, wine, brown; the Squirmy Wormy's silicone version wiggles more (and dies faster in fish teeth).
Tying notes
Chenille + hook + lighter-singed ends: the first fly a six-year-old can tie, fishing forever after.
Common mistakes
Snobbery during a rising river (the one hour it's truly THE answer), and fishing it static in clear low water where nothing's washing worms in.