Ten thousand fireflies, no conductor

Once a year in the Great Smoky Mountains, thousands of fireflies flash on and off together, down to a fraction of a second, for hours. No leader calls the beat. Each insect runs its own inner clock, and a nudge from a neighbour's flash is all it takes for the whole swarm to fall into step.

This piece walks through the pulse-coupled oscillator idea that explains synchrony from Appalachian forests to Southeast Asian mangrove trees, plus a twist: some fireflies don't even keep their own rhythm alone. A build-your-own swarm lets you dial up coupling and eyesight, scramble the field, and shine a torch to break it apart.