Mechanisms for turn alternation in woodlice (Porcellio scaber): The role of bilaterally asymmetrical leg movements

Angles of free turn were observed in woodlice (Porcellio scaber) after they had been forced to turn left or right in runways. Alternation angles were increased by greater forced-turn angles and number of successive forced turns in one direction. Removal of one or both antennae had no effect on alternation. It was also repeatedly observed that the closer a woodlouse remained to the far wall while traveling along the exit alley of a runway, the greater was its angle of alternation. However, orientation toward this far wall bore no relation to alternation. When given three successive left or right forced turns followed by a fourth in the opposite direction, woodlice moved further away from the exit-alley far wall and repeated the last forced turn at the choice area. Along with results of the other experiments, this result in particular supported an explanation for woodlouse alternation based on bilaterally asymmetrical leg movements (BALM) arising from the negotiation of forced turns. Such asymmetry is seen as biasing an animal to turn in the opposite direction to a preceding forced turn.