Why do fireflies glow?

Fireflies have a special part under their tummy. It has cells that make light. Inside these cells is a substance called luciferin. When luciferin mixes with oxygen, it makes light. This is called bioluminescence.

Fireflies don't waste this light. They flash it on and off to send signals to each other. Each kind of firefly has its own special flashing pattern. This helps them find a mate from their own kind.

The light also works like a warning to enemies. Some fireflies taste bad. Their glowing light tells birds and other animals, "Don't eat me, I taste bad."

This light has something very special about it: it gives off almost no heat. Light bulbs made by people turn most of their energy into heat, but a firefly's light turns almost all its energy into light.