Most organisms defend against predators. A defence that increases handling time but does not sufficiently prevent successful attack is apparently inefficient. However, predators often have a limited time for foraging. Owing to a predators’ avoidance of the prey whose defence increases handling time, increasing the handling time will be an efficient defence. We examined whether predators avoid the prey whose defence increases handling time.

A queen of Polistes chinensis antennalis founds a nest and rears larvae alone in spring. Queens need to leave nests to gather resources (e.g. prey). When queens are absent from the nest, conspecific females of other nests prey on immatures. To prey on pupae, females need to break the cocoon. Queens often attach nest materials to the surface of cocoons, which is predicted to increase the time spent in breaking a cocoon.

In the presence of queens on the nest, attacking females are always chased off by queens. Within the limited time when queens are away from the nest, females need to take away a pupa.

The time spent in breaking a cocoon increased with the amount of nest materials on the cocoon. Females selectively depredated on the pupa whose cocoon had lower amount of nest materials. These results suggest that females avoid the pupa that is more time-consuming to take away albeit their abilities to prey on the pupa.