Variations on a Rock Worm

Guest Blogger: Mike Cline, Bozeman, Montana

“Nature is so delightful and abundant in its variations that among trees of the same kind there would not be found one which nearly resembles another, and not only the plants as a whole, but among their branches, leaves, and fruit, will not be found one which is precisely like another.”  –Leonardo da Vinci

This sentiment would be an anathema to commercial fly tiers. When you see one commercially tied Royal Wulff, you can marvel at its form, proportions and intricate combination of materials. But when you see 100s or 1000s of the same fly, it is truly awesome at the ability of commercial tiers to eliminate variation and replicate a precise pattern seemingly infinitely—almost robotic. Their customers demand such precision. Such is not the case for the amateur fly tier. We are not beholding to precision in our tying unless we so choose. Thus I make the case for Variations.

“In music, variation is a formal technique where material is repeated in an altered form. The changes may involve melody, rhythm, harmony, counterpoint, timbre, orchestration or any combination of these.” – Wikipedia. Let’s alter that–In fly tying, variation is a technique where elements of the fly are tied in an altered form. The changes may involve tails, bodies, ribs, thoraxes, eyes, wings, hooks, weight, materials, etc. or any combination of these. So to start my journey on variations, I chose the lowly rock worm or larva of 100s of species of Rhyacophilidae caddis flies or (Green Sedges). A nifty You Tube video gives us a good view of this larva’s behavior.

I couldn’t find any reliable information as to when we anglers started calling the free swimming larva of Rhyacophilidae caddis “Rock Worms”. In late 19th and early 20th century literature, such worms were lumped into a category called “creepers” and there weren’t to my knowledge any specific patterns to replicate them. However, in Montana Flies (Grant, 1981) George Grant gives Franz Potts of Missoula, Montana credit for the term “Rock Worm”. In the 1920s and 30s, Potts was known for his “woven hair” flies and he obtained his first patent on a pattern he called the Rock Worm which was intended to be an imitation of various caddis larva. In Flies-A Dictionary of 2200 Patterns (Leonard, 1950) such worms are acknowledged as caddis worms with an unnamed pattern composed of a white chenille body and either black chenille or peacock herl thorax. Strangely enough among the trout patterns Leonard lists, there is a “Rock Worm” but the pattern is comprised of a tan linen body and badger hackle which doesn’t compute with his description of caddis worms. One of the staples pieces of fly pattern literature in the 1970-80s was American Nymph Fly Tying Manual (Kaufmann, 1975). In print for over 20 years, the manual is indeed an important reference for nymph patterns. Kaufmann only lists one caddis larva pattern—the “Caddis Larva” with no mention of “Rock Worms”.

In a bit more contemporary reference, Flies for Trout (Stewart and Allen, 1993) they list six larva patterns that could fall into the “Rock Worm” category. One of those, Oscar’s Rhyacophila Nymph is a close match for the “Green Rock Worm” we know today. Finally, in an acknowledged seminal reference on trout fly patterns: Trout Flies—The Tier’s Reference (Hughes, 1999) there appears the Green Caddis Larva or Green Rock Worm. As I embarked on my Variations of a Rock Worm, this was the starting point.

Green Rock Worm

Hook: Firehole XXX 12-16

Weight: .015 Lead Free Wire

Thread: UTC 70 Black

Body:  Olive or green fur or Antron yarn

ThoraxDark brown fur

The defining features of the Rock Worm are a fat segmented body with a contrasting thorax.  Legs are minimal and usually merely picked out thorax dubbing. The more realistic versions use lead wire for weight and bulk, but beaded worms are not uncommon. Body colors vary from bright green through tans and browns.

Variation #1

Variation #2

The necessary segmented look of the rock worm can be enhanced by the addition of a variety of ribbing.

Variation #3

Body: Jute chord colored green or brown with marker

Jute chord is a common beading material and accepts permanent marker colors well. Its versatility allows subtle use of colors and provides a natural segmentation.

Variation #4

Variation #5

A variety of materials can be used to establish the thorax of a rock worm. Herl is commonly used, but any type of dubbing material works as well.

Variation #6

Variation #7

  • Body: Small or Medium Vinyl Ribbing underlaid with Polarflash

Vinyl bodies give the Rock Worm an immediate appearance of segmentation and translucency and with underlain Polarflash a flashy appearance if desired.

Undoubtedly, given the extensive availability and variety of natural and synthetic materials we enjoy today, the possible permutations of variations of the “Rock Worm” are essentially infinite. The constant however, when embarking on “Variations” is to sustain the fundamental characteristics of the pattern. In this case, a fat segmented body and contrasting thorax with minimized legs. Caddis larva, particularly free swimming larva, are found throughout the U.S. Whether such larva are a staple food source in any particular watershed is something to discover. Having a few variations of the “Rock Worm” in your fly box is an easy task to accomplish.

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