Amphibians—the big-eyed, swimming-crawling-jumping-climbing group of water and land animals that includes frogs, toads, salamanders and worm-like caecilians—are the world’s most endangered vertebrates. One-third of the planet’s amphibian species are threatened with extinction. Now, these vulnerable creatures are facing a new foe: the Batrachochytrium salamandrivorans (Bsal) fungus, which is the source of an emerging amphibian disease that caused the die-off of wild European salamander populations.