Dynamic self-organization in fire ant rafts underpins collective longevity and threat responsiveness

Many living collectives must balance strategies between long-term energy conservation and short-term threat response; the ability for groups to dynamically self-organize into a variety of structures to address these needs is therefore essential. We show that fire ant Solenopsis invicta rafts which form buoyant bilayers in hostile flooded environments, adapt to conserve energy by separating into active and stationary phases. A simple kinetic model incorporating motility induced phase separation provides a useful framework to understand this transition, where ants form clusters by slowing down to participate in social interactions. We find that external stimuli either weakens or strengthens these interactions. The former leads to dissolution of clusters and fast-mobilization of surface ants, revealing how clusters could serve a secondary purpose with rapid mobilization aiding exploration through formation of bridges. These results highlight how swarms and other living groups can adapt survival strategies even in the absence of central control or global knowledge.