Ant foragers might present variation and universal property in their movements.

Investigating the locomotion mechanisms of animals improves our understanding of both their inherent movements and responses to external stimuli. Moreover, identifying the movement patterns of animals reveals their foraging search efficiency. The navigational mechanisms of foraging ants have been well studied; they present typical search strategies for pinpointing their goal. However, the detailed movement patterns of ants and the properties of their exploratory behaviors have yet to be fully studied, perhaps because of the inherent difficulty in investigating ants on a restricted flat field (on which they tend to walk along walls and stop moving around corners). Here, we address this problem using a spherical treadmill system (ANTAM), and we use this system to investigate the diffusiveness of Japanese wood ants' movements. On the treadmill, the ants walked over long distances without any restrictions. We found that the diffusiveness of movements varied across individuals and depended on time. Interestingly, further analysis indicated that the evolution of individual walkers' travel paths exhibited pink noise, even if individuals apparently produced different types of trajectories. Such complex paths may be related to optimized search strategies since ants produced both small and long paths unpredictably.