Black soldier larvae actively modify packing density under ramping airflows

In air-fluidized beds containing inert granular media, particles remain immobile for increasing airflow (fluidization) until the pressure drop through the medium balances the weight per area; at this point, the medium expands with increasing flow. Decreasing flow from a fluidized state (defluidization) results in the evolution of the bed height along a different trajectory. In a fluidized bed (9.5 cm in diameter) of active granular media consisting of 300 and 600 g of black soldier fly larvae, we observe no hysteresis in a fluidization/defluidization cycle, while dead (freshly frozen) larvae behave like inert granular media. During fluidization, the active larval bed expands smoothly below the pressure-based fluidization condition, while during defluidization, active larvae pack more densely than their dead counterparts. 2D simulations coupling CFD and agent-based algorithms recapitulate these effects; in particular, beds with Gaussian random forcing show no hysteresis, indicating that the larvae are not actively responding to flow effects, but randomly crawling through the bed (and squeezing past each other) with dynamics independent of external forcing.