Run, robber, run: parasitic acacia ants use speed and evasion to steal food from ant‐defended trees

Ants that are obligate plant associates protect their host against herbivores and aggressively defend the resources offered by the plant. Workers of Pseudomyrmex nigropilosus Emery (Hymenoptera: Formicidae), an acacia ant that parasitizes the mutualism by not defending the tree, are seen stealing food from other ant‐defended acacia trees. In the present study, hypotheses of evasion, chemical crypsis, chemical repellence and temporal activity patterns are tested in the field aiming to determine how P. nigropilosus enters other acacia trees, successfully circumventing the defence of the resident ants. When parasitic ants are stealing, resident ants are evaded by stopping walking, changing their walking direction or walking faster. Resident and parasitic workers have similar temporal activity patterns. Parasitic workers can walk 2.6‐fold faster compared with any of the three species of acacia‐ants from which they usually steal food. Behavioural assays suggest that P. nigropilosus do not have chemical repellence but that chemical crypsis may be involved in the evasion strategy. This last hypothesis needs to be explored further by chemical and olfactory analyses. The combination of speed and evasive reactions allows parasitic ants to access well‐defended acacia trees.