Part of being an experienced traveler is having at least one good story about experiencing bioluminescence (and knowing what the word means). For the uninitiated, it is what it sounds like: creatures that make light. Both land and sea organisms have this ability, including bacteria, plankton, fireflies, worms, snails, fish, jellyfish, and even sharks.
Certain places across the world attract people who go simply to be awed by the magical, glow-y spectacles that bioluminescent critters create: forests full of fireflies, caves populated by glowworms, far-flung island shores. Some travelers even plan seasonal vacations around the mating, glittering fireworms in the Maldives or the bright-blue firefly squid that surface by the thousands in Japan.
Across the world, these creatures produce a light-emitting compound called luciferin, or they eat or live with something else that makes luciferin. The chemical is helpful for a few different reasons, none of which involves entertaining humans. Some animals get sparkly because they are stressed out about being hunted: making light forces predators to worry that something even higher up the food chain will move in. Others use their light to attract mates, camouflage themselves, lure prey, communicate with friends, or confuse enemies.