Fig. 2.
As further evidence showing how much more ants depend upon scent than upon sight in finding their way, the following experiment may be quoted. In the accompanying woodcut (Fig. 2) the line marked 1, 2, 3 represents the edge of a paper bridge leading to the nest; A the top of a pencil which is standing perpendicularly upon a board, represented by the general black surface; B the top of the same pencil when moved a distance of a few inches from its first position A. On the top of this pencil were placed some pupæ. Sir John Lubbock, after contriving this arrangement, marked an ant and put it upon the pupæ on the top of the pencil. After she had made two journeys carrying pupæ from the pencil to the nest (the tracks she pursued being represented by the two thick white lines), while she was in the nest he moved the pencil to its position at B. The thin white line represents the course then pursued by the ant in its endeavours to find the pencil, which was shifted only a few inches from A to B. That is, 'the ants on their journey to the shifted object travelled very often backwards and forwards and round the spot where the coveted object first stood. Then they would retrace their steps towards the nest, wander hither and thither from side to side between the nest and the point A, and only after very repeated efforts around the original site of the larvæ reach, as it were, accidentally the object desired at B.' Therefore the ants were clearly not guided by the sight of the pencil.
Fig. 3.
Fig. 4.
Fig. 5.
The same thing is well shown by another form of experiment. 'Some food was placed at the point a (Figs. 3 and 4) on a board measuring 20 inches by 12 inches, and so arranged that the ants in going straight from it to the nest would reach the board at the point b, and after passing under the paper tunnel c, would proceed between five pairs of wooden bricks, each 3 inches in length and 1¾ inches in height. When they got to know their way they went quite straight along the line d e to a. The board was then twisted as shown in Fig. 4. 'The bricks and tunnel being arranged exactly in the same direction as before, but the board having been moved, the line d e was now outside them. The change, however, did not at all discompose the ants; but instead of going, as before, through the tunnel and between the rows of bricks to a, they walked exactly along the old path to e.' Keeping the board steady, but moving the brick pathway to the left-hand corner of the board where the food was next placed (Fig. 5), had the effect of making the ant first go to the old position of the food at a, whence it veered to a new position, which we may call x. The bricks and food were then moved towards the right-hand corner of the board—i.e. over a distance of 8 inches (Fig. 6). The ant now first went to a, then to x, and not finding the food at either place, set to work to look for it at random, and was only successful after twenty-five minutes' wandering.