Marangoni effect enhances an ultrafast escape and its wake impairs predator's locomotion in water striders unlike rove beetles

Marangoni effect is used by water striders (Veliidae) and rove beetles (Staphylinidae) to induce an ultrafast escape response against inter- or intra-specific predators. However, it is unclear if the surfactants secreted by these insects that help reduce surface tension of water can also affect predator's locomotion during the chasing. We discovered that the wake produced by Rhagovelia and Microvelia bugs during Marangoni propulsion forms a wide persistent layer at the water surface that significantly degrades the locomotion performance of a pursuer. In contrast, we found that the wake left by Rove beetles during Marangoni propulsion is very narrow and dissipates quickly, which is ineffective to affect the predator's locomotion. This double advantage of Marangoni effect in water striders (speeding up prey escape and slowing down a pursuer) can be an adaptation not only against interspecific predators, but also to counteract cannibalism. Our results can be used for bio-inspired interfacial micro vehicles with the capacity to escape quickly and deter pursuers using the Marangoni effect.