Lateral optic flow does not influence distance estimation in the desert ant Cataglyphis fortis

The present account answers the question of whether desert ants (Cataglyphi s fortis) gauge the distance they have travelled by using self-induced late ral optic-flow parameters, as has been described for bees. The ants were tr ained to run to a distant food source within a channel whose walls were cov ered with black-and-white gratings, From the food source, they were transfe rred to test channels of double or half the training width, and the distanc e they travelled before searching for home and their walking speeds were re corded. Since the animals experience different motion parallax cues when wa lking in the broader or narrower channels, the optic-how hypothesis predict ed that the ants would walk faster and further in the broader channels, but more slowly and less far in the narrower channels. In contrast to this exp ectation, neither the walking speeds nor the searching distances depended o n the width or height of the channels or on the pattern wavelengths. Even w hen ventral-field visual cues were excluded by covering the eyes with light -tight paint, the ants were not influenced by lateral optic how-held cues. Hence, walking desert ants do not depend on self-induced visual flow-field cues in gauging the distance they have travelled, as do flying honeybees, b ut can measure locomotor distance exclusively by idiothetic means.