How do soldier crabs behave when seeing vibrating robots?

Metaheuristic algorithms are a method of searching for a suboptimal solution and are implemented by a large number of agents, such as a swarm of animals. In this method, it is very important to adjust the relationships and/or interplay between individual freedoms and constraints as a group. The phenomena related to this interplay are strongly relevant for self-organized criticality showing a power law distribution. Since individuals' independent behavior and translation as a group coexist in a swarm of soldier crabs, we conducted an experiment involving soldier crabs to estimate whether a power law distribution results from that interplay. The engine of translation was implemented by the directed movement of robot crabs. Soldier crabs confronting moving robot crabs were observed in the experiment. Here, we show that the interaction between robots and soldier crabs entails a Lévy walk characterized by a power law distribution of step length as well as the real swarm. This result suggests that soldier crabs could be attracted by the directed motion of robots and that combining a random walk with ballistic movement can realize a Lévy walk.