Late one night, ecologist Jonathan Martin was searching for tree frogs in his Wisconsin backyard when he made an unexpected discovery. As he shined an ultraviolet flashlight in the direction of a high-pitched chirp, Martin saw a flash of bright pink at his bird feeder. That pink glow was coming from a flying squirrel. What was going on? You’re probably familiar with some kinds of glowing animals. Fireflies light up summer nights. Bioluminescent jellyfish and other sea creatures fill our oceans. But some animals glow only under ultraviolet light. This is called biofluorescence. That flying squirrel Martin found turned out to be one of the first-ever recorded sightings of a biofluorescent mammal. Follow along with Martin and his colleagues as they delve into the mystery of the flying squirrels and discover that they aren’t the only glowing mammals out there!