Turn alternation of the pill bug Armadillidium vulgare and its adaptive significance

Abstract

The pill bug Armadillidium vulgare shows clear turn alternation behavior. As the mechanism underlying the behavior, the bilateral asymmetrical leg movement (BALM) hypothesis has been proposed. Pill bugs, however, showed a longer following when in a zigzag pathway than in a straight pathway, suggesting the presence of an innate turning pattern in their neural system. On the other hand, they showed clear thigmotaxis: they walked a similar distance along a single side-wall as along a straight pathway. The adaptive significance of this behavior was analyzed in an artificial arena. The turn alternation was more frequent in an escaping situation than in voluntary walking, and also the walking speed was faster when escaping than voluntary walking. These results suggest that the turn alternation of the pill bug functions as a behavior for effective escape from natural enemies.