Highlights • gli1 is essential for male schistosomes to induce female sexual development • Male:female pairing induces male Sm-nrps expression in a gli1-dependent manner • Sm-nrps is essential for male worms to induce female sexual development • SmNRPS makes β-alanyl-tryptamine, a pheromone that stimulates female development Summary Schistosomes cause morbidity and death throughout the developing world due to the massive numbers of eggs female worms deposit into the blood of their host.