Fireflies produce light due to

Light production in fireflies is due to a type of chemical reaction called bioluminescence. This process occurs in specialized light-emitting organs, usually on a firefly&;s lower abdomen. The enzyme luciferase acts on the luciferin, in the presence of magnesium ions, ATP, and oxygen to produce light. Gene coding for these substances has been inseed into many different organisms (see Luciferase - Applications). Firefly luciferase is used in forensics, and the enzyme has medical uses -- in paicular, for detecting the presence of ATP or magnesium. All fireflies glow as larvae. Bioluminescence serves a different function in lampyrid larvae from the function served in adults. It appears to be a warning signal to predators since many firefly larvae contain chemicals that are distasteful or toxic.