MARY LOUISE KELLY, HOST:
Fireworks are one of the flashiest summer light shows, but closer to ground is another, quieter spectacle - that beautiful dance of light in the woods put on by fireflies.
ARI SHAPIRO, HOST:
So next time you're out, try paying attention to something more - the rhythm of their flashes - because like the best dancers, some swarms have plenty of it.
STEVEN STROGATZ: The phenomenon of fireflies in sync has been known for hundreds of years going back to the 1500s, when Sir Francis Drake and his crew were traveling around the world and they saw these spectacular displays of male fireflies on the river banks in Thailand and Malaysia gathered in mangrove trees all flashing in perfect unison all night long.
KELLY: Steven Strogatz of Cornell - not a biologist but a mathematician. He came up with the first model to describe this phenomenon.
STROGATZ: And mathematically, it's very mysterious because in math terms, we're studying an enormous system of interacting so-called oscillators - things that have a rhythm, that go through a cycle and, in this case, a cycle of flashing periodically.
SHAPIRO: Physicists from the University of Colorado Boulder wanted to investigate some of the mystery behind that effect, so they packed their cameras and headed to the Smoky Mountains in June last year to see one particularly rhythmic species put on its show.
ORIT PELEG: So it's flash, flash, flash, flash, flash and then quiet for a few seconds and then again flash, flash, flash. And the flash part is, again, in unison, where many fireflies flash together.
KELLY: Orit Peleg and her colleagues filmed those fireflies flashing in sync night after night. Then they created a 3D reconstruction of that swarm and found that fireflies need to reach critical density before the rhythm kicks in. Here's Peleg's co-author Raphael Sarfati.
RAPHAEL SARFATI: The flashes tend to move pretty rapidly but not instantly from one point of the swarm to another. So there's really a propagation effect very similar to a wave of flashing information.
SHAPIRO: A relay, almost, where the fireflies sync themselves with those nearby, sending waves of light through the forest.
PELEG: Where, you know, fireflies that are further away start flashing in bursts and then a little bit closer to you and a little bit closer to you. And then they pass by, and you can really experience this wave that's just beautiful.
SHAPIRO: The study was published in Science Advances.
KELLY: Now, this light show is so complex, it's brought together the fields of math, physics and biology. And though it's rare among American species, Sarfati recommends watching your nearby fireflies.
SARFATI: And maybe you will notice something, you know, that is unexpected. Or maybe you feel like they are indeed on a dialogue sometimes and responding to one another.
SHAPIRO: Who knows? You might just see something magical.
(SOUNDBITE OF JON HOPKINS' "LIGHT THROUGH THE VEINS")
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