Biolumiescence is the emission of energy that is caused by living, ecological things. The most common living creature that is able to emit energy is insects and they do this in the form of light. Insects such as fireflies emit light in the form of bioluminescence. Bioluminescence is the reaction that occurs when the pigment luciferin, oxygen, and the enzyme luciferase come together. Usually the reaction occurs once the luciferin and the oxygen react with each other to produce light either inside of the cell or outside of the cell of the insect. The enzyme, luciferase, like most enzymes, is helpful in speeding up the chemical reaction that occurs between the pigment and the oxygen. This is why the pigment and the oxygen are necessary for insects to glow, without each of these the insect would not have any glowing capability.
Bioluminescent Insects Glowing in the Darkness, Karl Fabricius