Perhaps no single evolutionary novelty in the animal kingdom has fascinated scientists more than the lantern of the firefly. Yet to this day, nothing has been known about the genetic foundation for the formation and evolution of this luminescent structure. But now, new work offers for the first time a characterization of the developmental genetic basis of this spectacular morphological novelty — the firefly’s photic organ — and the means by which this beetle successfully uses ancient and highly conserved regulatory genes to form its lantern.