Fireflies are also known as lightning bugs. The green-yellow characteristic glow is a chemical reaction which takes place in the fireflies abdomen. The chemical reaction takes place with the help of 3 ingredients :
1) Luciferin-It is a heat-resistant substrate which acts as a source of light.
2) Luciferace-It is an enzyme(that triggers light-producing chemical reaction)
3) Oxygen-As oxygen supports burning-in this situation it it provides fuel for the reaction to proceed.
thats all my mother and I know.Shes an expert in science so helps me answer such questions.