Self-corrective behavior for turn alternation in pill bugs (Armadillidium vulgare).

Pill bugs (Armadillidium vulgare) demonstrate a behavior called turn alternation that keeps their overall direction of movement straight after obstacles in experimental settings force them to deviate from a course. For example, this behavior is seen when they alternate their path choice on successive trials of the T-maze test. However, sometimes pill bugs stop after turning and change their direction (directional change). The function of this directional change has not been investigated because such individuals are usually omitted from the data. The present paper shows that pill bugs use directional changes to prevent them from turning in the same direction on two successive turns, a behavior called turn repetition. We examined the behavior of 36 pill bugs that each completed 130 successive T-maze trials. Directional changes appeared more frequently when individuals had begun a turn repetition than when they had begun a turn alternation. Furthermore, after correcting for turn repetition, turn alternations increased. These results suggest that pill bugs have an inherent mechanism that acts to maintain turn-alternating behavior.