Non-linear mechanical properties of fire ant aggregations

Fire ant aggregations are inherently active materials. Each ant converts its own chemical energy into motion, and it is the overall motion of all individual ants that contributes to the bulk material properties of the aggregation. However, the activity level in fire ant aggregations is not constant in time. This lets us measure the material properties of this active material at different activity levels. Here we investigate the non-linear mechanical properties of fire ant aggregations using large amplitude oscillatory shear rheology at varying activity levels. For each oscillatory experiment we generate Lissajous curves and calculate common non-linear moduli used to characterize the non-linear behavior. Our data suggest that strain stiffening correlates with activity.