The USD Dun - Imitation Simplified The USD (Up-Side Down) Dun was originally developed by John Goddard, the renowned English tier/writer. It was the result of many hours looking back up from under the surface at the fly and the natural floating by.

Goddard realised that the surface of the water did not act as a true mirror. Because of refraction and the piercing of the surface by, amongst other things, hackle points, a certain amount of the top of the fly could be seen, even when viewed from directly underneath.

He then developed the USD fly, which had cut or burnt hackle wings situated on the underside of the fly hook shank and a parachute hackle on the topside of the shank.

This gave the fly a more natural attitude on the water (particularly in smooth water).

I have found though that it still left considerable room for improvement:

1) The hackling method was fiddly, flimsy and resulted in a fly which landed upright only 5 times in ten,
2) The hackling method also resulted in a messy thorax area,
3) The winging method was fiddly and hard to cast,
4) The tail of the fly lay flat on the water or even under the surface film,
5) The body was too short and in most cases too thick compared to the natural,
6) The body often lay under the water,
7) The fly took far too long to tie.

The above points were corrected by the following:

1) The parachute was changed to a standard parachute hackle tied on a post,
2) The thorax was neatened and made more realistic by the using a post and by the careful use of body materials,
3) The wings were omitted and a relatively thick parachute post used instead,
4) The tail was tied part of the way round the bend of the hook so that it pointed away from the water, as the naturals do, and was then cocked by use of a thread ridge under the tail, as per AK Best,
5) The hook was changed from a standard dry fly to a 3X curved shank nymph/hopper (Tiemco 200R or Talon Peregrine Caddis),
6) The change of hook made the body balance better and the choice of body materials helped,
7) The above changes simplified the whole pattern.

The whole fly is now recognisable as a USD but is significantly different. It has a cocked tail, which imitates the natural dun, a body that lies flat on the surface near the thorax, but the abdomen curves up and away from the water surface. The body of turkey barb makes a more natural looking, higher floating body. The parachute post of either dun or white t-base feathers (or white calf body hair) in the larger sizes makes an easy to cast, and easy to see fly.

Materials: Hook: Tiemco 200R or Talon Peregrine Caddis # 6 - # 22
Thread: brown or cinnamon 8/0 or Talon Unbreakable Thread
Tail: hackle fibres or Coq de Leon, tied cocked.
Abdomen: turkey tail barb.
Wing post: t-base turkey or calf body hair.
Hackle: brown, dun or grizzly tied as a parachute
Thorax: as per body
Head: 3 turn whip finish

Tying Instructions Note: this is a fly that lends itself to using a true rotary vice .

1) Tie in thread half an eye length behind eye - leaving a small gap is crucial.

2) Take thread 5 eye lengths back along shank and cut excess, take on wrap to cover tag then take 2 wraps forward to build a thread 'dam'.

3) Turn hook upside down (this is where the rotary earns its way).
4) Tie in parachute post by holding with tips pointed at 45-degrees down on the front of the shank.

5) Post should be pointing forward over hook eye.
6) Tie post into upright position, post should be 1.5 times the size of the hook gape.

7) Take turns back over part of butts of post, trim at an angle and cover in tight turns of thread
8) You should have a post that stands at 90 degrees from the shank on the same side as the point. It should be built up into the start of a thorax shape.

9) Turn the vice so the hook is right side up.
10) Take tight, close turns of thread to a point just behind the barb. This should be part the way around the curve.

11) Take one turn back over the last turn to make a very small thread 'dam'.

12) Tie in the tail. The tails should be tied in as the post was and should be equal to the length of the flat part of the shank. As you tie in the tail, continue to hold it at the 45-degree angle. This combined with the thread dam will result in the 'cocked' tail.

13) Tie in the body of turkey tail barb. 2 barbs will do for # 6-# 14, 1 barb for the sizes below. Tie this in with the thinner end at the tail and proceed to wrap it forward as far as the base of the parachute post.

14) Tie in the parachute hackle. The hackle should be 1.5 times the gape of the hook although a little either way will not make any difference. The hackle should be lashed to the post as far as the top layer of thread.

15) Tie in another turkey tail barb and wrap for the thorax.

16) Wrap the parachute hackle anticlockwise, using your dubbing needle to ensure that each wrap lies under the previous wrap.
17) Tie off on the shank where it was left bare.

18) Whip finish 3 turns building a small but neat head.
19) Varnish head (optional).