Fireflies use nitric oxide gas to turn their biological lights on and off.

For a long time, scientists did not know how fireflies flashed so quickly. It turns out they use nitric oxide gas. Normally, tiny cellular power plants called mitochondria keep oxygen away from the light organ. When the firefly wants to flash, it releases nitric oxide. This gas tells the power plants to let go of the oxygen, which rushes into the light organ and triggers the chemical flash.