Bob Wyatt adds some magic to the veteran Grey Duster to produce an eye-catching set of dry flies.

Out of some 400-odd flies in A Dictionary of Trout Flies, Courtney Williams called it the only fly that tempted him to become a ‘one-pattern’ angler, and one of the best, perhaps the best, pattern known to him. In a Mayfly hatch, he considered it to be at least as good as any Mayfly imitation, and found it difficult to find anything better. It has, he said, the “inestimable quality of bringing fish up” throughout the season. Williams also said he had no satisfactory reason for the Grey Duster’s effectiveness, apart from the rather desultory attribute that it rode nicely in rough water. I think the reason Williams was stumped by the Duster’s attractiveness was that, like most anglers of his time, he was looking for what insect a fly imitated, rather than how it behaves.

According to Williams, the Grey Duster appears to have been invented by the anglers of the Welsh Dee and its tributaries. He gives the impression that it was already well established on that watershed by the time he saw it, and those Dee valley boys also considered it the only fly you need to catch trout. I know I liked it the first time I laid eyes on one, and it entered my repertoire to become one of my most reliable go-to flies. It is beginning to appear on the American scene of late, and, like the Adams and the Gold Ribbed Hare’s Ear, will undoubtedly become established as one of the truly great trout flies.

Okay, so far so good. Courtney Williams wasn’t the only one to wonder why the Duster is so effective, and so far, I still haven’t read a satisfactory account for it. Most of those who have ventured an explanation reckon it’s to do with its dogsbody, match-any-hatch, general purposeness. That’s certainly true, but there’s more to that than meets the eye. The Duster’s special ingredient is something that isn’t there at all – a tail.

Not so fast, you say, some Duster enthusiasts tie it with a tail, and say it works better. Well, I have a hunch that a Grey Duster with a tail is the result of conventional thinking, that old question of what it can possibly imitate and coming up with the answer that it’s an ephemerid dun of some sort. My guess is the Duster doesn’t imitate a dun at all, but an Emerger. The lack of a tail just completes that impression.

Like WH Lawrie’s Hatching Nymph series, and VS Hidy’s similar Flymphs, the tail-less Grey Duster represents the sub-imago emerging from its nymphal shuck. The sunk abdomen of the emerging dun is a strong stimulus to the trout’s predatory instincts, and that’s just what the Duster behaves like.

I’ve even got an idea that the visible hook, rather than being a deterrent, may act as a supernormal stimulus. Such exaggerations of natural forms have been shown to stimulate much stronger responses in animals than the natural form it resembles. This is not so far-fetched as it may seem. Something’s got to account for the trout’s behaviour, and there is no doubt they can clearly see the hook.

Anyway, this sunk-abdomen thing has re-shaped the way I think about dry flies generally. Except for spinner patterns, most of my dry-fly fishing these days is done with a semi-dry or semi-sunk Emerger design based on principle of the Klinkhåmer Special. Inevitably, I’ve applied this design concept to several old favourites, such as the Grey Duster. My sunk-abdomen version makes a virtue of what is generally regarded as bad form for a dry fly. I call it the Dirty Duster.

The only way to really test-drive a fly is to fish it against another one. In fly-fishing, the number of variables is too great to make hard and fast conclusions, but if you are fishing in sight of an angler that you know is a good fly fisher, it at least gives you some idea of a fly’s relative merits in a certain situation.

On my first day on the river this season [2004], I was fishing with my pal Bob Morton. Bob features regularly in these articles, and he’s a very good angler. He likes the old wet Spiders for his spring fishing, and they work for him. On this day we were sharing the same big pool: he at the top riffle where he likes to play his Spiders, usually on a downstream line; me at the tail-out, where I like to work my upstream dries and Emergers.

Both are good places for trout, and both suit our different preferences for that time of year. The spring olives live in the fast stony riffles, and the wet Spider is an excellent way to represent the nymph as it swims to the surface. By the time the nymph has reached the surface and emerged, it has often been carried into the body of the pool. The duns, and any nymphs that have been slow to emerge or damaged in some way, float through the pool and into the tail, where more trout are waiting to pick them off.

There was no visible fly or trout activity when we started, so I put up a small Hare’s Ear Nymph to begin. I fished it through the good water with no results. After a few fruitless drifts, I saw a trout rise very near me. There were no flies on the water, but suspecting the beginning of an emergence, I quickly changed my fly to a size 14 Dirty Duster and ginked the hackle. I covered the spot where the fish rose and it took instantly, a cracking 15in brownie. I released it and on the next cast hooked another fish. This time it was a silvery sea trout, of about 1.5lb, that threw itself all over the pool. I brought it around and slipped it off the hook too.

I noticed a couple of rises further out into the current and had three more rises in the next few minutes, snatching at two and only pricking them. Then, suddenly, it was over. Typical spring fishing. There were a few olive duns on the water, being skated along by the wind, but saw nothing rise to them.

About the same time as I hooked the sea trout, I saw Bob hook up with one fish. This in itself doesn’t prove anything, but it’s an indication that when the trout are looking up, an Emerger is probably as good a bet as anything. I feel that it’s a lot more than that, otherwise I wouldn’t stick to it. The thing is, that little episode demonstrated that the sunk-abdomen Dirty Duster can hold its own, although I never doubted it for a moment. To me, it looked fishy from the outset.

I clip the under-side hackle to make sure the fly adopts the proper posture. You want its thorax to sit in the surface film, while the clipped hackle supports the fly to the sides. I trim the hackle just to the edge of the black centre stripe, leaving a bristly, high-contrast, black thorax, which I believe makes an excellent secondary trigger itself, like the peacock herl thorax on the Klinkhåmer Special. The untrimmed, upside hackle makes a good sighter out there on the water. There will always be a place in my fly box for the old standard Grey Duster, even for some with tails. By clipping the under-side hackle on a tailed Duster, you have a general-purpose spinner pattern that will seldom let you down.

I regard trout flies as ammunition; they should be as expendable as No. 7s are to a pheasant shooter. A trout fly should not be so precious that you can’t risk it on a tree limb. The Dirty Duster is an even simpler sunk-abdomen fly than my Deer Hair Emerger. A couple of my pals say they still have trouble tying the Deer Hair Emerger to my demanding specifications, especially in small sizes. So, rather than conquering this Everest of skill, they just bum flies off me. My supply-side problem is solved by the Dirty Duster, which is easily tied down to size 18 or 20. Best of all, the Dirty Duster is cheap as chips. You don’t even need good hackle. A cheapish badger saddle hackle and a hare’s mask will tie hundreds of ’em.