What makes a firefly light up?

Question

I was outside tonight (Lives in south TX) and I saw several firefly's randomly fly around my backyard, Anyways, I got up close to one of them and I noticed two shiny dots on each side of it which makes it glow. But how is this possible?

Well, I know it's possible, but how does the insect do that?

Answer 1

it just glows
i know that answer is stupid.