Landmark guidance and vector navigation in outbound desert ants.

This study deals with the influence landmark information has on the foraging behaviour of the desert ant, Cataglyphis fortis, especially with the interaction of such landmark information with the ants' path integration system. We show in the first experiment that desert ants that are captured immediately after leaving their nest and then transferred to a remote test area search for the nest rather than activate their previous path integration vector. In a second experiment, the ants had been trained to a landmark corridor on their way to the feeder. In the critical test situation, they were again captured immediately after they had left the nest and transferred to a test field where they faced one of the following three situations: (1) the same landmark corridor as used during the training phase, (2) no landmarks at all and (3) a landmark corridor rotated by 90 deg. as compared with the training situation. Nearly all ants in test situation (1) eventually followed the landmark corridor but most of them never reached the fictive feeder. In situation (2), the ants searched around the nest entrance. In situation (3), approximately one half of the ants searched for the nest, whereas most of the other ants followed the landmark corridor, i.e. headed in a completely wrong direction. Hence, familiar landmarks do not only influence the foraging behaviour of desert ants, e.g. in making the ants start their foraging runs but can even out-compete the ants' path integration system.