ANGLERS have been trying to catch trout on artificial flies for thousands of years. According to Aelian, writing in AD200, the Mesopotamians were even then catching “speckled fishes” on hooks adorned with feathers and bits of wool.

In 1496, Dame Juliana Berners showed a range of fishing flies in her Treatyse of Fysshynge wyth an Angle, the first book on the sport in the English language. In the 1880s, F. M. Halford and G. S. Marryat popularised the study of real insects in close-up and designed large numbers of flies to imitate them, even creating separate representations of males and females of the same species.

Since then, imitative fly dressing has become ever more sophisticated and the study of entomology and the development of increasingly effective representations has become the central thread of this branch of angling.

Some enthusiasts have gone way beyond fishing effectiveness and have pursued exact imitation of natural bugs as a goal in its own right. Every year, throughout Europe, the United States and Japan in particular, exhibitions are held where enthusiasts can show their work and compete with one another.

Paul Whillock, of Solihull, must have known that he was getting something right when, in 2001, he sent a package of flies for exhibition in New Jersey and had them impounded by US Customs. When he inquired what the problem was, he was told that “it is an offence to import insects” into America.

Whillock tells the story in Flies as Art (www.paulwhillock.com, £34.99), an apparently self-published yet beautifully produced book that sets out his approach to both “art” flies and what he calls “realistic fishing flies”. The book shows examples of his own work so real that they must have his neighbours reaching for the swat. Some have taken up to 160 hours to create.

Astonishing though Whillock’s flies are, the pursuit of exact imitation is unnecessary in day-to-day fishing. For underwater artificial bugs, which the fish can see undistorted at the ends of their noses, a clear resemblance to the natural bugs all around them is an advantage, but no more. The beautifully crafted yet practical nymphs produced by Oliver Edwards, of Wakefield, are as far as even the most pernickety practical fisherman would want to go. Vast numbers, including me, would settle for much less, without adverse impact on their catches.

Exact imitation is even less important in flies to be fished on the water’s surface. These flies, when viewed from below where the fish is, dent the surface film where they touch it, so the underwater view of them is distorted by refraction.

Having made and long since published an intensive study of the way light distorts surface flies viewed from underwater, I now trouble with imitation very little. Years ago I reduced my everyday fly box from dozens of patterns designed to imitate different flies at different stages of their development to just a handful. The two I use most are a tiny fuzz of brown on a hook and a tiny fuzz of black. They take a couple of minutes apiece to tie and they are deadly.

What makes a fly deadly, provided that it broadly suggests the kinds of natural flies a fish is accustomed to eating, is the way the angler presents it. In the case of surface flies, that means having the ability to cast a fly of natural size and sometimes colour accurately and in an unalarming way to an unsuspecting fish on the lookout for surface food.

Fish are not capable of scrutinising any such fly for points of difference from the natural, they respond instinctively to similarities.

In the case of surface flies, they are not looking for something that has six legs, two antennae and green eyes but for something that, distorted by refraction, broadly suggests the natural flies they have been eating since birth. When they see that, they mostly respond automatically. All my experience demonstrates this.

It is this practical, everyday experience that makes Whillock’s discussion of what he feels are the most important features not of an “art” fly but of a practical fishing fly bizarre. “I try to include only details that regularly act as genuine ‘trigger factors’ — those small additions to a fly that just seem to ‘turn on’ a trout,” he says.

He lists these essentials, in order, as silhouette — by which he presumably means overall shape — antennae and tails, eyes and legs. This is, after shape, a list of preposterous minutiae, one that suggests he has spent far too long peering down a microscope and not enough time watching the behaviour of his quarry.

By far the most penetrating view of trigger factors was that articulated by Richard Walker in the 1970s. Walker observed that certain flies and prey fish have features that are distinctive and could benefit not from exact imitation to increase their effectiveness, but the opposite — exaggeration.

He likened the principle to that of the cartoon. A Scarfe cartoon of Tony Blair, he would have argued, is instantly recognisable because of the way Scarfe exaggerates key Blair features — but no one unprotected by parliamentary privilege would argue that Blair actually resembles the caricatures Scarfe produces. It is the same with fishing flies. They don’t have to look ultra-realistic; all they have to do is to give the fish enough information to decide, in a moment, that “that’s ’im!” The instinctive response almost always follows.

Whillock’s book is not perfect and his whole text would have benefited from professional editing. Nonetheless, it opens the door on one of fly fishing’s many fascinating cul-de-sacs. His illustrations are first-class and his dressings are quite astonishing. One for the obsessives — but for art’s sake alone and not angling.

• Brian Clarke’s fishing column appears on the first Monday of each month.

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