It seems, however, judging by the standard works on the subject, that there is practically but one recognised position for the wings of the artificial fly, as the difference between the position of divided wings and wings dressed flat together is, after all, but slight. No one seems yet to have realised the fact that the wings of a May-fly do not lie in the same relative position to the body as do those of the Blue-bottle, whilst in the case of the Alder there is a further marked distinction from both.
The wings, in the different families of flies upon which trout and grayling feed, lie when at rest in three distinct positions in relation to their bodies.
In the Ephemeridæ they lie in planes approaching the vertical, slightly diverging from each other towards their extremities. [Fig. 1] gives a sketch of one of the Ephemeridæ, and [Fig. 2] a transverse section through the line α β of [Fig. 1]. These drawings show the relation of the wings to the body. All flies have so far been treated by writers on fly-dressing as though their wings were in this position.
In the Caddis-flies (Trichoptera) and the Alder-fly (Sialis lutaria) the wings lie on each side of the body, meeting at their upper edges in front, gradually diverging towards their lower edges and posterior extremities.
[Fig. 3] gives a sketch of an Alder, and [Fig. 4] a transverse section through the fly, showing the position of the wings.
In the Diptera (Blue-bottle, Cow-dung, &c.), and Perlidæ (Stone-fly, Yellow Sally, &c.), the wings lie in a horizontal plane. In some Diptera the wings diverge from each other towards their extremities, as in the Blue-bottle, shown in Figs. [5 and 6]. In some other Diptera and in the Perlidæ, the wings lie over each other, as shown in Figs. [7 and 8,]. It will be seen that the wings in both these cases lie in a horizontal plane.
In [Figs. 2, 4, 6 and 8] β represents the section of the body, α and γ the section of the wings.
I wish it to be thoroughly understood that these positions are the positions of the wings of the natural fly when at rest.
Many flies when they fall on the water buzz round in circles periodically, apparently with the object of disengaging themselves from the surface. Between these efforts, however, their wings generally assume the normal position of rest. The only way to imitate the fly when it is buzzing is by dressing it without wings, and with extra hackle; and this is, after all, but a poor imitation. In most cases it is better to imitate the wings at rest; and if this is done accurately, it will present to the trout an accurate imitation of the natural fly as it appears to him when not trying to raise itself from the water.