Self-Organized Floating of Aquatic Worms*

California blackworms (Lumbriculus variegatus) are detritivorous freshwater organisms that harness surface tension forces to assemble collective structures beneath the water's surface. These worms exhibit thigmotaxis-driven self-organization, forming protective entangled collectives. However, their aerobic respiration necessitates a sufficient dissolved oxygen (DO) supply, which can limit population density. Blackworms employ a unique adaptation to supplement oxygen intake. When submerged in shallow water, they extend their tails to breach the air-water interface, bending them at a 90-degree angle. This action creates localized dewetting on their body segments, effectively pinning their tails through surface tension. This posture allows blackworms to respire directly from the air rather than solely relying on DO. Consequently, this shift in oxygen source mitigates population constraints, enabling the formation of tightly entangled collectives, which we called “worm buoys.” We hypothesize that the emergence of worm buoys is intricately linked to the degree of entanglement influenced by oxygen levels, which we test by systematically monitoring DO at various population densities. Employing transfer entropy analysis, we elucidated a stigmergic relationship between the number of tails latching and DO levels over time. Finally, in internal 3D topological simulations using Kirchhoff elastic filament modeling, we unveil the intricate interplay between a buoy’s entanglement and its vertical lift.