Visual and tactile learning of ground structures in desert ants

Place defining landmarks that have been studied intensively in insect navigation are large, voluminous objects visible to the insect from quite some distance. Here, we show that in desert ants, Cataglyphis fortis, local variations in ground properties can also serve as landmarks. The ants were trained to forage within a linear channel, in which the floor adjacent to the nest entrance was altered in optical and tactile properties. When ants were later tested within a test channel that ran parallel to the training channel, they recognized this landmark and centred their search on the part of the ground structure during training that was closest to the nest entrance. Hence, physical properties of the ground can be learnt and used as cues defining, for example, the position of the nest. In a second series of experiments the ants were presented with ground structures that differed in their visual and tactile properties from the training structure. We show that the absence of either the correct tactile properties or the correct optical properties of the ground structure make the ants reject the previously accepted structure. Hence small ground structures are recognized by the ants as familiar landmarks only if both visual and tactile information coincides with what the ants have experienced during training.