Synchronizing pile formation of black soldier fly larvae

When confined to containers, black soldier fly larvae aggregate together, piling up in corners. How do these piles form, and what causes them to eventually break apart? In this combined experimental and numerical study, we confine 300 larvae to flat vertical containers and measure their activity using both time-lapse film and particle image velocimetry. Within a pile, the majority of the larvae are unable to move because their bodies are jammed. Larvae enter the pile by crawling along the less jammed floor of the container and accumulating at the wall. Using PIV analysis, we observe events that are correlated with the breakup of a pile. We hypothesize that the pile disperses if there is a downward traveling larva that frees a path in the jammed pile. We test this hypothesis with both a horizontal and vertical intruder that enters the pile. We find that a vertical intruder can synchronize the creation and disassembly of the pile, reducing its disassembly time from 60 min to 20 min. The surprising ability of foreign objects to break up a swarm may provide utility in other systems from bird flocks to fish.