In the experiments of pill bugs (Armadillidium vulgare), some of them performed as if they had contained the models of themselves and the environment in view of computing their present state as a function of the prediction of the models. In a specific situation, they escaped from the experimental apparatus as if they had constituted spatial knowledge of it (open field surrounded by walls) in the process of exploratory behavior and used the knowledge. This species gets environmental information by tactile ability of antennae, not by visual one, and do not climb perpendicular walls in general condition. If they had not escaped in the experiment, they would have died of hunger or water deficit. In this paper I will present the result of this anticipatory behavior. I also discuss that the notion of anticipation, which is another name of autonomy, is inevitably introduced when one considers the process of understanding of animal behavior progressing without any common basis between animals and experimenters. ©1999 American Institute of Physics.