Luciferin

Wriggle Nightbug's Spread Shot (a Touhou LW original). She attacks by emitting beams of light that act as signals. It's said fireflies developed bioluminescence as a way to warn away predators, however, in reality, not all fireflies light up. The ones that do, though, are believed to shine as eggs, larvae, and pupae. In other words, throughout their entire life cycle.