Nobody is laughing now. Sea lice—rice-grain-sized crustaceans that have evolved to parasitise salmon fish and live inside them, munching away at their skin, protective mucus and blood—have been ravaging salmon aquaculture worldwide. The burden is heavy—infestations cost the British aquaculture industry alone more than £20m ($25.6m) each year—and, for now, there are no good, long-term solutions. The development of a successful louse-preventing vaccine could change that. Some teams think they might be close.