Nestmate interference in acacia ants varies with colony size and task specialization

In a society, several individuals can help to execute a task otherwise impossible to achieve individually. However, the unnecessary interference of another individual in a solitary task could delay task execution. We studied task interference in acacia ants (Pseudomyrmex spinicola) performing a foraging task. Foraging is solitary: a single worker carries a plant-produced food body and typically stores it inside the plant domatia, but sometimes workers discard them off the tree. Acacia ants have behavioural subcastes among workers with pronounced differences in task execution. Also, task specialization increases with colony size, hence smaller colonies have less specialized individuals. Here, we first assessed whether interferences on a solitary task provided any benefit to the colony, to counteract the delay in performing the task. We found that when nestmates interfered, food items were more likely to be stored rather than discarded. Second, we tested the role of the worker's task specialization on the occurrence of interferences. Specifically, we tested whether interferences (1) are a by-product of lacking workers specialized in foraging ('Jack-of-all-trades' effect), or (2) depend on having experts trying to take over the task ('expert effect'). We found partial support for the Jack-of-all-trades effect, because workers in smaller colonies were more often interfered with, but interferences lasted longer in medium-sized colonies; in larger colonies, workers had fewer interferences that resolved faster. Our evidence supports the 'expert effect', as experienced foragers had fewer and shorter interferences than workers not regularly foraging. Interfering in a solitary task in social insects parallels task conflicts and managerial issues in human organizations and may function as a quality control mechanism in a leaderless organization. Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour.