Fireflies appear twice in the poem. The first time they appear they “open and vanish” (Line 8); later, they manifest as displays of energy. It’s been suggested that the “sparks” of the fireflies are metaphors for a climactic release of sexual energy; whether symbolic of physical release or simply an indication of joy and wonder, the fireflies represent a sense of change and forward momentum in an otherwise unchanging place. They also offer a visual contrast of golden light against the silver light of the moon.