In this study, we report the observation and behavior analysis of Enchytraeus japonensis, a species of earthworm, as the first step for creating swarm intelligent micro robots. Several studies have been conducted on the earthworm's behaviors of constructing tunnels by biologists and agronomists. Earthworms make intricate network of tunnels in the soil. We presumed that earthworms use self-organization to make this intricate structure, and we investigated the Enchytraeus japonensis's behaviors. Two experiments to observe their behaviors and to confirm construction of tunnels with self-organization were done. As the results, we observed that their behaviors were both tracking the same direction with other individuals, and changing direction with sensing the surrounding environments of hardness. These behaviors emerge the intricate network of tunnels with self-organization.