What can ants tell us about collective behavior during a natural catastrophe?

Abstract

The fire ant, Solenipsis invicta, has successfully invaded and colonized ecosystems worldwide. Like humans, fire ants build permanent domiciles to house family members, establish well-defined territories for foraging and fight to the death when invading neighbors breach the borders. One of the more striking behaviors of fire ants is their ability to form a living raft when springtime rains flood their domiciles. What are the survival benefits, if any, to collective behavior during a flood? To address this question, we quantified the survival of individuals as solitary swimmers compared to cooperative rafters. We found that large workers and matriarchs survived equally well as solitary swimmers or rafters. In contrast, small workers drowned whether they were solitary swimmers or rafters. However, when rafting with large workers or matriarchs, the mortality of small workers declined three-fold. We propose a behavior phenotype classification scheme to catalog the diverse behaviors observed in this series of experiments. Although the ultimate goal of rafting behavior by fire ant workers is to protect their matriarch, the proximate goal for the vast majority of fire ants is to save themselves first and to save others if the opportunity arises.