Why Do Some Animals Glow in the Dark?

Bioluminescence — light produced by living organisms — occurs in over 1,500 fish species, most cephalopods, many jellyfish, and countless deep-sea creatures. The chemistry typically involves a light-emitting molecule (luciferin) and an enzyme (luciferase), though the specific molecules differ across lineages. In the deep ocean, where over 90% of animals are bioluminescent, the uses are diverse: anglerfish lure prey with glowing lures, some squid use ventral light organs for counter-illumination camouflage (matching the faint light from above to hide their silhouette), and many species produce blinding flashes to startle predators. On land, fireflies use species-specific flash patterns for mating. Biofluorescence, a related but different phenomenon, has been discovered in corals, scorpions, flying squirrels, and even platypuses.