Figure 3.

Beetles were forced off course by either a fall from a ramp or by an induced 90° rotation. When continuing to roll, the beetles attempted to reorient back to their original direction of travel. The deviation from the original bearing was measured after reorientation in six different species of beetles, four diurnal species (G. unicolor, S. rugosus, K. lamarki and P. femoralis) orienting to the solar polarization pattern during the day (open symbols) and two crepuscular/nocturnal species (S. zambesianus and S. satyrus) orienting to the million times dimmer celestial pattern created around the full Moon (closed symbols). The mean and standard error of the angle of deviation after a fall from the ramp (squares) or a 90° rotation (circles) are displayed on the y-axis for each species, ranked in order of size from small to large. A deviation of 0° indicates perfect fidelity to the original rolling direction. The large diurnal beetle P. femoralis had not fully compensated for the induced rotation when reaching the perimeter of the small wooden disc and was consequently excluded from this experiment. The different species do not vary in their precision of reorientation after a fall from either the ramp (ANOVA, p = 0.14) or after passive rotation (ANOVA, p = 0.08). The consistent orientation performance of the beetles under these rolling conditions shows that the use of a celestial polarization compass at night allows the same fidelity to the original direction of rolling as during the day.