Some corners are more equal than others: Beetles linger longer in acute-angled corners than in obtuse-angled ones

The ability of animals to find shelter is vital for survival, providing protection from predators and harsh conditions. In lab studies, animals often favor walls and corners, suggesting a natural inclination toward enclosed spaces for safety reasons. Here, we investigated how shelter characteristics, specifically its size and corner angles, affect usage by the red flour beetle, Tribolium castaneum, a cosmopolitan pest of stored products, as well as the beetle's movement. The beetles remained longer in narrow shelters than in medium-sized shelters, with no significant difference from wide shelters. They spent less time in obtuse-angled corners than in right-angled ones, and more time in acute-angled corners than in right-angled ones, indicating their ability to differentiate among corners and choose suitable ones. Next, we examined whether movement through a corridor is delayed more strongly by the presence of obstacles forming acute angles with walls than by obstacles forming obtuse angles. Although there was no difference in the proportion of arrivals at the destination cell or the time required to cross the corridor, acute-angled obstacles caused a higher frequency of reentries into the origin cell, possibly due to the beetles' tendency to follow walls. This research may have applied importance, such as enhancing our understanding of beetle movement, strategies to delay their arrival in new areas, and the optimal placement of traps.