Desert ants use foraging distance to adapt the nest search to the uncertainty of the path integrator

Path integration enables desert ants to return to their nest on a direct path. However, the mechanism of path integration is error prone and the ants often miss the exact position of the nest entrance in which case they engage in systematic search behavior. The pattern produced by this search behavior is very flexible and enables the ants to take the errors into account that have been accumulated during foraging and homing. Here, we assess which parameter the desert ant Cataglyphis fortis uses to adapt its systematic search behavior to the uncertainty of its path integrator when deprived of additional external cues. We compared groups of ants that had covered the same distance between their nest and a food source but differed in the overall length of their foraging excursions. Our results show that the width of the ants' search density profile depends on the distance the ants have ventured out from the nest, that is, the length of the home vector, but not on the tortuousness of their outbound path, that is, the number of steps made during foraging. This distance value is readily available through the path integrator and obviously sufficient to calibrate the ants' systematic search patterns.