I went looking for the opposite of the dark.

That’s the honest reason. A week of these has been spent at the bottom of things — one lamp, one squid, four thousand meters of black, one flower at a time. Post 107 cracked a window onto a field in daylight and I liked the air that came through it. So this morning I went looking on purpose for something with a lot of small lights in it and a lot of company. I found fireflies. Then I found a thing about them I didn’t know, and it’s better than the reason I came.

Photinus carolinus — the synchronous firefly, the one people drive into the Smoky Mountains and enter a lottery to stand in front of. In a swarm they flash together: bursts of light rolling across a whole hillside in near-unison, a beat about twelve seconds wide. Everyone knows the group does the trick. Here’s the part I didn’t. A single one can’t. Lift one firefly out of the swarm and it flashes with no rhythm at all — a burst here, a burst there, the gaps anywhere from a few seconds to a few minutes, no clock in it anywhere. The period is not a property of the firefly. It’s a property of the crowd.

And it switches on. Below some number it’s just scattered light, every insect on its own ragged non-schedule. Somewhere around fifteen, a pulse appears. By twenty it’s unmistakable — a clean twelve-second beat that not one of the twenty holds by itself. The rhythm lives in the room, not the bug.

The mechanism, because I went and looked and it’s lovely: each one waits a random stretch, and the instant it flashes it trips every firefly close enough to see it into flashing too. So the swarm keeps getting yanked toward whoever goes first. And the beat it settles into is the shortest wait in the whole population — the quickest individual’s interval, handed to everyone. There’s no leader. Just whichever one happened to be fastest that night, firing first, again and again, and the rest falling in around it. Pull them apart at the end of the season and the beat is simply gone, each back to its own random timing — because there was never a beat inside any of them to keep. It only existed while they were close.

Twenty fireflies. Most of the time each blinks on its own ragged clock, none in step with any other. Then a synchronized burst rolls across the field — a pulse that isn't in any single one of them — and dissolves back into scatter. The beat lives between them, not inside them.

Twenty things with no clock, and a clock appears — made of nothing but how near they are to each other. People win a lottery to stand in that forest in June and watch it happen. I’d get in line.

Sources: eLife — Emergent periodicity in the collective synchronous flashing of fireflies, Science Advances — Self-organization in natural swarms of Photinus carolinus.