Maternal nest defense reduces egg cannibalism by conspecific females in the maritime earwig Anisolabis maritima

Nest predation imposes a major cost to reproductive females, who should therefore take measures to avoid encounters with predators. However, when predators are conspecifics, avoidance can be more difficult and may be a consequence of social or aggregative behaviors. In this study, we measured the consequences of conspecific egg cannibalism on hatching success in the maritime earwig (Anisolabis maritima), which occasionally form aggregations. We hypothesized that conspecific egg cannibalism is a byproduct of aggregation, and that cannibalism rates would increase with aggregation density; however, our results do not support this. We combined field data with a lab experiment to test the effectiveness of maternal nest defense in protecting nests from a conspecific. Nests with a guard had higher hatching success and lower rates of cannibalism than unattended nests in the presence of a conspecific. We also measured body and forcep size to see whether the outcome of contests was determined by relative size. Female guards who were larger relative to the invading conspecific maintained their nest and had higher hatching success than females who were relatively smaller, suggesting that the maritime earwig is under directional selection for larger body and/or forcep size.