Temnothorax longispinosus acorn ant colonies respond to parasitic raids by emigrating

Social insects face many threats from predators and parasites, and so have evolved a diversity of behavioral defense strategies to evade and combat enemies. Previous research has focused extensively on the evolution of front-line defense strategies that allow social groups to successfully avoid detection by enemies, defeat them during an attack, or mitigate fitness losses upon successful invasion. However, in the case of social insects, we must also consider how colonies have evolved to alter their behavior when they survive attacks. During an attack, colony fitness can be negatively affected while the colony itself survives. There may be selective pressure for surviving individuals to respond strategically to decrease the risks of future attacks by the same enemy. In this study, we tested whether colonies of Temnothorax longispinosus acorn ants emigrate when they experience a raid by the obligate social parasite T. americanus. We found that T. longispinosus colonies that experienced a raid moved to a different nest of equal quality significantly more than genetically matched colonies that had not experienced a raid event. We also found that raided colonies moved significantly more than we would expect by random chance. This result suggests that emigration may be an induced defense against re-raiding in this host-parasite system.