Imitation Perlidæ, or Stone-flies, are more used in the North in wet-fly fishing than by the dry-fly fisherman of the South.
The best known species is the Stone-fly proper, but this fly does not seem to abound in the South, though I have found isolated specimens at Heathfield in Sussex on two occasions.
This fly is therefore omitted, and the Willow-fly and the Yellow-Sally only are described.
Perlidæ, unlike Diptera, have four wings. As, however, the anterior wings cover the posterior when at rest, it is as a rule only necessary to make the imitation with one pair of wings.
This posterior pair of wings in the Perlidæ often materially changes the colour of the anterior pair when they are at rest. Thus in the Willow-fly, though the anterior pair of wings are of a brownish colour, they appear of a dark slaty hue when the fly is seen crawling about. An illustration of natural fly is given on [Plate I].
Willow-fly (Leuctra geniculata, Steph.).
This fly comes on late in the season. In September and October it is taken freely by the trout and grayling. It is similar in shape to the Stone-fly of the North.
This fly has almost always been made buzz. Ronalds mentions in his Fly Fisher’s Entomology that it may be made with wings, but does not say anything about their position. I do not think that the hackle fly is a really good imitation of the natural insect, and it is quite possible to put the wings of the imitation in the same position as those of the natural fly.
It will be seen that there are on Plate II. three illustrations of the imitation Willow-fly. One of these has its wings in the position of rest, the manner of dressing which I have described in a previous chapter.
The other, which has its wings partially spread, I owe to a suggestion from Mr. G. E. M. Skues.