Self- and air-driven fluidization of black soldier fly larvae

Active systems can be driven via internal activity of individual elements or via external mechanical forcing. Here we study a living system in which both internal and external activity can be varied. In laboratory experiments, we confine thousands of ~10 mm long black soldier fly larvae in an air fluidized bed (~4 larva lengths in diameter, 10 in height ) and study the collective and individual dynamics. When larvae are not externally fluidized, due to their internal activity they self-pack and the height of the column of larvae decreases over time to a steady state value. In steady state, larval motion is distributed heterogeneously and transiently, with regions of motion and clustering appearing and disappearing throughout the bed volume. These dynamics can be altered by gentle flow of air to the bed: like fluidized beds of inactive (non-living) particles, steady-state larval collective volume (column height) increases with increasing air flow, and the persistence of the transient regions change. Further, external fluidization has the same effect as the addition of food, where activity also causes large-scale mixing.