Intruder alert: Factors influencing the success of maternal nest defense against conspecific egg cannibalism in the maritime earwig

Parental care is relatively rare in insects, where parents typically
maximize the number of offspring produced rather than investing in
individual offspring survival. However, some insects do guard nests or
clusters of eggs against predation risk or when conspecifics pose a threat
of cannibalizing offspring. The maritime earwig (Anisolabis maritima;
Order Dermaptera), an insect found under objects above the high tide line,
exhibits nest guarding against cannibalistic conspecifics. Because both
male and female cannibals exhibit size-based aggression but differ in
morphology and temperament, we studied how different intruder
characteristics influenced the success of maternal nest defense. Although
mothers were usually effective in protecting their eggs, we found that
both the relative size and the sex of conspecific intruders affected the
mother’s behavior and success in egg guarding. Specifically, we found that
mothers were more successful in defending their eggs against smaller
opponents and against females. Our results may reflect that smaller
opponents are generally less aggressive and that females are less likely
to invade nests than males. This study provides insight to how the
benefits of maternal care in response to cannibalism are likely to depend
on the sex ratio and size distribution of the colony.