That a trout or any other fish could possibly mistake a wet fly used in the regular wet fly way for the natural fly of which it is supposed to be an imitation, was always to my mind a very doubtful question; but now it is so no longer. I am sure the fish takes it for something else.

If we consider what would happen to a natural fly which had by some mishap become submerged, we can come to no other conclusion than that it would be carried along by the current, without any power of its own of altering the direction in which it was being moved by the water. Does this ever happen to the sunk fly? I think not. In fishing across and down stream it certainly does not; and even in up stream fishing, in order to keep his line straight, the fisherman must keep a certain amount of tension on it, and very probably draws it through the water with much the same sort of movement he would give it if not fishing up stream.

This movement through the water which is given to the artificial must be absolutely unlike any movement of the natural fly when under the surface; for in the natural fly, if it were not already drowned, the only possible movement would be that of its legs and wings, which, not being intended as a means of progression through the water, and being absolutely unsuitable for that object, would be most unlikely to enable it to do so.

But here a very natural question arises as to what, if not the natural fly, the fish takes the imitation to be? In a communication to the Field in June, 1897, I described, under the heading of “A New Trout Fly,” the imitations of two CorixÆ. This seems to be a key to the whole question. The number of insects living in fresh waters, and possessing the power of moving through it, is enormous.

There are between 220 and 230 different species of Water Beetles in our waters. There are also very many different sorts of Heteroptera, including the numerous family NotonectidÆ. When we add to these the larvÆ of flies and water beetles, the Crustaceans, HydrÆ and Water Spiders, we must begin to realise that there are other things than a drowned natural fly for which the fish might mistake its imitation, with the materials of which it is made soaked in and drawn through the water.

The movement of many of these creatures through the water is fairly represented by the movement of the artificial fly in wet fly-fishing; and, when the shade and colour and size of the fly is the same as one of these aquatic creatures, I am sure that the fish takes it, not for a fly, but for one of them. Again, when the enormous number of these aquatic creatures is considered, it is most probable that one or other of the flies tried on any water by the fisherman will come very near in shade, colour, and movement through the water, at any rate, to one of them.

If this conclusion at which I have arrived is correct, as I believe it to be, would it not be wiser to try to imitate, not the natural fly, but some of these numerous aquatic creatures? They are numerous enough, and a large number of them are easy to imitate; but as yet but little has been done, except with regard to the spiders, in this direction. I am also sure that the success of the so-called spider patterns used in wet fly-fishing has been due to quite a different cause to that which those who first used them and those who use them now believe, as these imitations are made from the insect as it appears when out of the water. The spider goes from its nest to the surface of the water and back again by a thread stretched between, and so would hardly move through the water, as its imitation is made to do by the fisherman. Those of the so-called spider-flies which are supposed to represent some of the EphemeridÆ, are, for the reasons I have given before in speaking of flies in general, most unlikely to be mistaken for the natural insect by the trout.

A trout will undoubtedly sometimes take anything moving through the water which simulates life, if it be of a suitable size. This is shown by the manner in which they take the fancy flies; although here again, as one particular pattern of a fancy fly kills better than any other on one particular water, I think that very often this fancy fly is taken by the fish for some creature which is particularly numerous there. At any rate, if the fish only takes the artificial fly because it is apparently something alive and moving, I am sure that he would seize it with much more avidity if it represented one of his aquatic neighbours on which he has been feeding, and if its appearance reminded him of many previous pleasant meals. (Jan. 15, 1898.)[2]

My readers must not suppose that I intend to apply these remarks to any particular circumstances; I am only speaking of wet-flies in general. While it is probable that the natural fly does often sink under the surface, and may then be taken by the trout, the wet-fly of the fisherman does not as a rule behave as does the natural fly when under water. That the trout takes the wet-fly fished up stream, which is allowed to come down with the current without any drag and close to the surface, for the natural fly it represents, is also very probable; but these facts do not in any way tend to disprove my theory. This manner of wet-fly fishing is very much like dry-fly fishing, and is certainly not the way in which wet-fly fishing is practised in lakes, and is hardly the most general way in which it is practised on many rivers.

In dealing with this subject fully and to carry my theory to its necessary conclusion, it is of course necessary to find a probable explanation of what every form of wet-fly, fancy or supposed imitation of a natural fly, is taken for by the fish. This naturally leads us to believe that such a theory, if it approaches the truth, should include an explanation of why the salmon takes the fly.

We know but little of the world as it appears to the eye of the fish, but from the little that is known something may be deduced which carries this theory a little further. In the sea many and very various effects may be produced upon objects moving through the water when passing between the eye and the surface, by light, by the reflecting powers of the bottom of the water, and by the relative clearness of the water, all of which factors of the effect produced vary to an almost incalculable extent.

Given a bright sun, a light sandy bottom and clear water, a small crustacean swimming between the eye of the observer and the surface often will not appear to be like the creature when it is seen out of the water. The outline will be indistinct, and the whole will frequently appear to be brilliantly coloured. Not only is the body thus brilliantly coloured, but equally gaudy rays will be seen round it, probably produced by the moving legs and by refraction.

In this case the circumstances are all in favour of the production of an effect of brilliant colouration; but going to the other extreme, with a dull light, a dark bottom and cloudy water, we have the dullest-coloured fly accounted for, as the first conditions accounted for that which was most gaudy. This also explains the fact that the flies which go in various gradations of colour between these extremes are most suitable for various conditions of the weather, water, and locality.

In the case of the Salmon-fly, probably the salmon remembers, when he has reached fresh water, many an appetising morsel in the shape of a crustacean or small fish, and takes the fly for one of these.

In the case of the trout we know that crustaceans are very acceptable to them, and though probably fresh water will not produce the brilliant effect which is produced by salt water as I have described above, still, as fancy Trout-flies do not run to such gaudy colours as do Salmon-flies, still the effect should be sufficient to account for a fair amount of brilliant colour under similar conditions. No doubt some of the fancy Trout-flies are also taken for small fish.

In many waters, however, the effect could hardly be made brilliant, as shallow water, shade produced by weeds, &c., and muddy or dark bottoms would all militate against its being so, and in these waters probably only lures that imitate the actual colours of the object they represent would be of any use.

In fresh water and in the case of trout, as I have pointed out, there are many aquatic creatures which serve as food which have the power of swimming through the water.

My theory, stated briefly and more explicitly, I hope, than was the case in my article in The Field, is that under circumstances in which the wet-fly behaves more as does some creature having the power of swimming through the water, it is better to imitate this creature than any natural fly on the water, which cannot in any case behave in such a manner; and what I wish to advocate is, that imitations of these aquatic creatures should be made and used.