Estimation of homing distance in desert ants, Cataglyphis fortis, remains unaffected by disturbance of walking behaviour.

Desert ants, Cataglyphis fortis, use a stride integrator as a distance gauge in their well-studied path integration system (while a skylight compass provides the direction gauge). To further scrutinize the mechanisms of the ant odometer, we tried to disturb the stride integrator by interfering with normal walking behaviour. First, legs that contribute to one of the two leg tripods alternately used in normal walking were selectively amputated. This prevented the normal tripod gait and should interfere with both the normal walking programme controlled by the central nervous system, and normal sensory feedback from the legs. Second, manipulation of the walking substrate in the form of regular corrugations was observed to interfere with normal walking behaviour, at least for corrugation wavelengths (12-25 mm) in the range of normal stride lengths. The animals fell and stumbled, or footfall patterns were entrained to the corrugation wavelength. The relationship between stride length and stride frequency was altered in several situations. Surprisingly, distance estimation and homing performance remained virtually unaffected even by the most severe interferences with walking behaviour. This demonstrates a remarkable robustness of walking behaviour and homing, and it suggests that stride length is determined by robust signals of leg sense organs.