From Joe at It's OK To Be Smart, who explains the phosphorescence:
Wow. This one is simply stunning. A wonderful new time-lapse from Vincent Brady, with music from Brandon McCoy, captures fireflies like Earthbound shooting stars against the backdrop of the night sky that we usually see in videos like these. Using long exposures and stacked images, this time-lapse operates on two scales: Terrestrial and astronomical.
Ahhh, good ol’ Photina pyralis, those harbingers of warmer days, those bearers of chemical candlelight, those blinking lovers calling out for a mate on long summer nights.
Photina creates its light using a process called chemiluminescence, mediated by an enzyme called luciferase. The luciferase protein, a name which stirs images of fiery spirits, grabs on to its chemical target, a molecule called luciferin, sitting ready, but dark, in the active site of the protein, like an unlit firework. Luciferase then reaches for a molecule of ATP, every living cell’s energy source, luminescent or not, capturing its chemical energy like a sprinkling of gunpowder on a fuse. It breaks apart that ATP into AMP and pyrophosphate, and with the release of that fiery-sounding byproduct, the invocation of fire begins.
Now oxygen gas, the very fuel fire needs to burn, rips away the AMP and sits down in its place. The fuse is burnt, the fire has food, and it’s time to ignite. Exhaling carbon dioxide, the luciferin molecule is excited into oxyluciferin, its atoms charged full via oxidation. Almost instantly, it relaxes back to a resting state, shooting out a photon like a quantum bullet.
And so it happens, millions of times a minute, in invisible pyralis posteriors that only betray their location in fleeting flashes of chemistry as they streak across the twilight sky.