The invasive mosquitofish (Gambusia holbrooki) chews off the tails of freshwater fishes and tadpoles, leaving the native animals to perish while dining on other fishes' and amphibians' eggs. In a study published December 16 in the journal iScience, researchers engineered a robot to scare mosquitofish away, revealing how fear alters its behavior, physiology, fertility—and may help turn the tide against invasive species.