What causes the light on a firefly (in England I think they are called glow worms)?

Senior Moments

Luminescent insects like glowworms produce almost no heat and nearly 100 percent light. Their bodies produce luciferin, a substance that combines with an enzyme plus oxygen to produce the light. Apr 05 02, 6:10 PM

Senior Moments

A bit more info - The glowworm is one of many creatures that naturally produce light (bioluminescence). The light is the result of a chemical reaction that involves several components: LUCIFERIN, a waste {product;} LUCIFERASE, the enzyme that acts upon {luciferin;} ATP, adenosine triphosphate, the energy {molecule;} and oxygen. These combined form an electronically excited product capable of emitting a blue-green light. Apr 05 02, 6:13 PM