Piloting in desert ants: pinpointing the goal by discrete landmarks

SUMMARY The inconspicuous nest entrances of the Namibian desert ant Ocymyrmex robustior are located on barren sandflats often devoid of any goal-defining landmark. Foragers that have returned by path integration to the rough area of the goal need a considerable amount of time to finally pinpoint the goal. Even a single landmark decreases the search time dramatically. By using artificial landmarks placed in the neighbourhood of the goal, we show that the larger the image transformations (caused by the landmarks) in the ant's visual field, the faster the homing ants localize the goal. While approaching the goal the ants do not try to fixate the landmarks frontally. Hence, even if provided with discrete landmarks rather than extended visual scenes, Ocymyrmex relies on image changes occurring in wide areas of its panoramic field of view rather than those occurring in a frontal fixation area alone.