Most of us have probably seen photos of a deep-sea angler fish luring prey right down to its mouth with its fleshy, glowing lure. The lure shines because it is bioluminescent—it is chemical light the fish produces through bacteria. Once thought to be rare, a new study in Scientific Reports—and the first quantitative analysis of deep-sea bioluminescence—estimates that more than three-fourths of all the animals living from the sea’s surface to 4000 meters below can light up. Fish, jellyfish, worms (like this deep-sea tomoptorid worm), larvaceans, crustaceans, squids, and octopus all have the talent. Some, like the anglerfish, rely on light-emitting bacteria, but most, like many jellyfish (which can light up like Christmas decorations) make their own through chemistry. Some use the light to hunt, others to scare off predators or attract mates. That makes bioluminescence in the ocean an “ecological trait,” the scientists say, a characteristic that animals living in this habitat should be expected to have.