Glow-worms and fireflies are neither worms nor flies, but beetles. Glow-worms are flightless females of fireflies. They have light organs located under their abdomens. The insects take in oxygen and, inside special cells, the enzyme luciferase combines it with a substance called luciferin to produce light with almost no heat. Fireflies usually flash in patterns that are unique to each species, which helps to find potential mates. The female of some species may imitate the flashing patterns of other species and when a male arrives to investigate, she eats him.