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Blue Wing Olive CDC Biot Comparadun
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Blue-Wing Olive
CDC Biot Comparadun
By Dave Hughes

Matching Duns

It's not possible, at least for me, to understand why trout will be happy to accept one fly, then suddenly and arbitrarily begin refusing it and demand another. It can depend on the weather, the luck or lack of it that the insects might be having getting through the barrier of the surface film that day, or the preference of one trout for emergers over duns, another for crippled duns over fully formed duns, and a final fish that is a snob toward anything but a perfect dun. Whatever the reasons, you'll never solve all of these trout with any one-fly theory.

The truth is, you'll never solve all trout with any theory. But you'll solve a lot more trout with a few options in your fly boxes than you ever will with just one.

If you tie a series of fly styles to imitate mayflies, each of which floats in a different way, and therefore shows a different shape and silhouette to trout, you'll nearly always be armed with a dressing they will accept. You just need to have a style in your fly boxes in the right size and approximate color...

Blue-winged olives extend from tiny size 20 Baetis up through the lesser green drakes in size 12 and 14 to the largest size 8 and 10 green drakes themselves. Sulfurs, both eastern and western species of Ephemerella, begin at sizr 16 and 18, but can be enlarged to encompass the giant and widespread size 6 and 8 Hexs (Hexagenia). Blue duns, beginning with the tongue-twisting size 14 and 16 Paraleptophlebia, can be extended to include the size 10 and 12 gray drakes (Siphlonurus). Mahoganies and March browns, in the genera Paraleptobhlebia, Stenonema, and Rhithrogena, generally run the narrow range from size 12 to 16.

If you tie and carry flies to cover these themes, each in an appropriate range of sizes, you'll have most mayfly dun hatches covered. Extend the size range only when you encounter a specific hatch that demands it, on your own waters, in your own fishing. The goal is to wind up with a fly box or two that covers the basic mayfly hatches across the continent, and even worldwide.

Since the way they float gives them some of the aspects of emergers, we'll begin our continuum of dun imitations at the end of flotation on the smoothest water, with CDC Biot Comparaduns. This fly style was originated by the great young Colorado tier, Shane Stalcup.

Materials: Blue-Wing Olive
CDC Biot Comparadun

  • Hook:  Standard dry fly, 1x fine, size 12 to 20

  • Thread:  Olive 6/0 or 8/0.

  • Tail:  Blue dun hackle fibers, split.

  • Abdomen:  Olive turkey or goose biot - The biot is the short, sharp fiber on the leading edge of a wing primary feather. Buy feathers dyed to the primary colors you'll use to cover the color themes: olive, pale yellow, gray, and brown. Before beginning to tie, peel the number you need from the feather and place them between moist paper towels to soften..

Tying Steps:

1. Fix hook in vise and layer shank with thread. Form a slight thread hump at the bend with several turns of thread taken over each other. Select six to ten stiff and web-free hackle fibers, measure than the length of the entire hook, and tie them in at the bend. Use your fingers to split the hackle equally to each side, while taking thread wraps back against the hump to lock them in place.

2. Take one thread layer forward two-thirds of the shank length over the tail butts before trimming the excess. Take another ever layer of thread back to the tail base. It's important to form an even underbody for a biot body. Select a biot and tie it in by the tip, with the convex side toward the hook.

3. Use your hackle pliers to wind the biot forward over two-thirds of the shank. Tie it off and clip the excess. Be sure the raised edge of the biot trails, so that when wound the body is distinctly segmented.

4. Select the tips or strip the fibers from one side of a CDC feather. It's fine to trim the tips to even them. Measure them the shank length, and tie them in just forward of the abdomen so they are flared in an arc over the hook. It's often necessary to double the CDC if the first fibers are not enough. Peel or cut a section of mallard flank fibers from the feather, and tie it in over the CDC, at the same length. Trim the butts of CDC and mallard flank.

5. Twist fine synthetic dubbing tightly to your thread, to form a slender skein. Take one or two wraps behind the wings, then a wrap or two right against them in front, to lock the wings into an arced and swept-back posture. Taper the dubbing down to the hook eye. Form a neat thread head and apply your whip-finish.

Same Method - 3 Variations:

Sulfur CDC Biot Dun

Blue Dun CDC Biot Dun

Mahogany CDC Biot Dun

As always with CDC, never dress the wing with floatant. That will gum it up. Use desiccant and special CDC treatment and the flies will fish well through the catching of many trout.

CDC duns are effective on the smoothest water, though your use of them does not need to be limited to spring creek and tailwater flats. Many mayflies that live in riffles and even cascades as nymphs migrate toward less turbulent edge currents before emergence. Trout feeding on soft water that is fast can be just as selective as trout feeding on the smoothest currents. The CDC style dry fly floats well, is relatively easy to see, and should be in your fly boxes as one of your options to match mayfly duns. ~ Dave Hughes

Credits: Excerpt from Matching Mayflies by Dave Hughes, Frank Amato Publications. We greatly appreciate use permission.

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