Hydrodynamic responses of springtails to raindrop collisions on stagnant water

During rainy sessions, we typically seek shelter under a roof at home, but how do tiny organisms manage to survive the downpour? Our research investigates how raindrop collision in stagnant water affects jumping soil-based hexapod Fosomia candida springtails. Using high-speed cameras, we observe that the outcomes of collisions depend on factors like raindrop size, springtail morphology, and organism size. When hit by a drop (~ 3 m/s), springtails can be propelled up to ~150 times their body length into the air, spinning and tumbling. Our finding indicates that springtails often attach to a thin liquid sheet (crown formation after 20 ms) by the drops' impact, where springtails remained intact, but few remained in the crater. Subsequently, a Worthington jet evolves where some springtails remain intact within the jet while others are propelled into the air and allowing them to spin until they re-enter the water surface. We also explore the possibility of springtails triggering Raleigh Plateau instability, which occurs with the elongation of the Worthington jet and the formation of satellite drops. By combining experimental observations with theoretical analysis (using dimensionless numbers), this research enhances the understanding of the hydrodynamic forces acting on tiny organisms and the kinematics of their motion during raindrop impact.