By now, we're all pretty familiar with the use of cul-de-canard (CDC) on dry flies and emerger patterns. This magical, nondescript feather is found near the preening gland of a duck, and has become a common, practical feature of many modern patterns.
This inherently buoyant feather gets its floating qualities more from its structure than its often-credited oils, and has become the material of choice for many low-floating emerger and cripple patterns. While CDC has no doubt revolutionized many floating patterns, this odd little feather has yet another unexpected trick up its sleeve when it comes to tying nymphs.
My first encounter with CDC on submerged patterns was the somewhat obvious use as a wing on patterns like the RS2 and other similar emergers. A tidy little CDC wing clump allows the fly to be fished dry or wet as needed, but seems to offer no real difference when it comes to the effectiveness of the pattern. There is the theory that CDC holds and traps air bubbles on subsurface patterns, but I have found that once the fly gets wet, the air bubbles disappear quickly.
The first time I heard of CDC feathers being used in place of a soft hackle on nymphs, I admit I was a little flummoxed as far as the thinking behind it. I just couldn't come up with any good reason to use a buoyant feather on a subsurface fly; it just didn't make sense. However, once I tied a few and fished them, I quickly became a believer.
As it turns out, a CDC collar on a nymph creates a beautifully flowing veil of fibers that are far livelier and more buggy-looking than any partridge or hen feather could ever hope to be. These fibers do a good job of imitating either dangling legs or emerging wings, and in some cases the bedraggled wings of a drowned adult insect.
The same structural features that make CDC float so well also prevent the fibers from sticking to one another when wet, thus making a collar that flows and breathes freely in the current, adding the illusion of life to nearly any fly pattern. The fluidity of the fibers creates a gentle, slimy movement, creating life even when fished in the slow currents near the bottom.
One of my favorite things about tying with CDC is its easy use and application. There are a variety of ways to add these magic fibers to a fly, from simply tying it down in a clump, to wrapping a whole feather as you would a traditional hackle collar. I use the latter method on the CDC Golden Stone to create a flowing set of legs on a pattern designed to be fished down deep and dirty. The slender strands of CDC flow back beautifully over the body, replicating the legs of a fluttering golden stone nymph. Of course, the colors can be altered to match darker stones as well.
It's easy to add or substitute a CDC collar on common patterns like the ubiquitous Prince Nymph or Pheasant Tail, and I find it especially useful on caddis pupae patterns. The fine straggling fibers of a CDC feather mimic the dangling legs and wingbuds of caddis emergers to a T.
Insects that shed their nymphal husks underwater (Western Green Drakes and Pale Morning Duns, for instance) are prime candidates for sunken patterns with CDC wings.
Hans Weilenmann's incredibly effective CDC&Elk pattern has a sparse deer-hair wing and uses a scruffy, wrapped CDC feather for a body. The CDC on this pattern is not used for floatation, but rather it is intended to become saturated, and dangle the body of the fly low in the surface, trailing loose fibers below the film. I have had incredible success fishing this pattern with split-shot down near the river bottom as well, another testament to the power of wet CDC.
These new CDC patterns have found a permanent home in my fly box, and in many cases have become personal favorites. The combination of soft and lively CDC, coupled with tungsten beads and a weighted wire underbody has proven to be a spectacular one, but I still carry a few smaller patterns with no weight in case I need to present them closer to the surface.
To get these unweighted patterns to sink, I wet them down with river water or saliva. Saturating the fibers takes a moment of working the water well into the fibers—the fish slime that coats your fly after a successful drift is perhaps the best method of keeping the fibers wet. Yes, there is always a catch.