Fireflies mainly emit light to attract mates, though this communication method is also used to defend territory. Though it is mostly adult fireflies that glow, there are some species where the larvae and the eggs also emit light.
pascalcampion: “ They’re back! No matter how old I am, each time I see fireflies it makes my heart beat faster, just like when I was a kid . I always think that feeling is gone forever and boom, it comes out of nowhere again and again. Kind of.