The Corixa sahlbergi, which is almost as common as the Corixa geoffroyi, is about half its size, but is otherwise very similar in appearance, as are nearly all the other smaller species.
The Corixa frequently comes to the surface to breathe, and a number of small air bubbles attach themselves to its body. These, when the insect is swimming under water, give its body a brilliant silvery appearance, with the yellow showing through in places. This effect is accurately reproduced by ribbing the body with silver tinsel.
The size of the hooks used must depend upon the size of the species of Corixæ inhabiting the water to be fished, and varies from No. 1 to 3, new size.
The Corixæ in any particular water may easily be found in order to observe the size. They congregate in great numbers among the weeds, &c., on the bottom of the water. They are very numerous in most millponds, pools, back-waters, sluggish waters and ponds.
The body is made with light yellow Berlin wool, teazed up with fur from the hare’s face, and ribbed with silver tinsel. A good space of shank should be left above the body.
The only legs which make any show in the water are the hind legs, and they are the only ones it is absolutely necessary to imitate; should, however, the fisherman wish to imitate the others, one turn of a ginger hackle may be used.
When I described the Corixa in the Field I directed that the hind legs should be made with a strand of peacock herle. I have however found a better imitation of these legs since then, in the end of a quill feather from a starling’s wing. This keeps up its spring even when soaked for a long period in the water, while the peacock herle legs after a time adhered to the body of the fly, and did not stand out on each side when the fly was at rest. The tip of the feather should be completely cleared of fibres on one side, and nearly so on the other, leaving however a few short stumps at the end, as shown in illustrations of imitation in [Plate III.], to represent the paddle-shape of the legs. These legs are then tied in at right angles to the body. I have found the best way of accomplishing this is to tie the legs in straight to the side, with the buts pointing towards the tail of the fly. Then bend them down, and put enough turns of the tying silk round the shank of the hook to keep them in the position shown in the illustration of the imitation.
The wings are made from the quill feathers of the woodcock, laid flat on the body one over the other, as described in the directions for tying Perlidæ, which have their wings lying one over the other. The head must be made large, and the whole fly when finished appear as shown in the illustration.
When used, this fly should be allowed to sink. The depth to which it must sink varying according to circumstances, and then drawn through the water in little jerks. Each of these movements through the water causes the legs, which stand out on each side of the body, to bend back; but at the end of the jerk, when the fly is momentarily stationary, these legs resume their original position. Thus the movement of the legs of the natural insect when swimming is accurately imitated. (June 12, 1897.)