Fluid ejection via micron-scale soft nozzles enables Marangoni propulsion in tiny water skaters

When threatened, tiny water walkers (Microvelia) deploy their proboscis at the air-water interface to release surfactants, triggering rapid Marangoni propulsion. This process creates surface tension gradients that drive interfacial flow away from the low surface tension regions created by the released surfactant fluid. Additionally, these insects fold their limbs during Marangoni propulsion, likely to reduce drag from limb-water interactions. Such fluid dynamics enable Microvelia to achieve speeds up to 100 times their body length per second, far exceeding their typical skating speeds. Using high-speed imaging, particle imaging velocimetry (PIV), and micro-CT reconstruction, we systematically study biomechanics and interfacial fluid dynamics of Microvelia during Marangoni propulsion, while evaluating the role of their micron-scale soft nozzles morphology on interfacial fluid ejection. Our findings provide insights that could inspire the design of untethered, chemically driven micro-robots with enhanced propulsion at air-water interfaces.