Jul 10, 2021 - Science

How fireflies coordinate their flashes

A stacked image of Photinus carolinus in the Smoky Mountains. Credit: Peleg Lab at CU Boulder
A stacked image of Photinus carolinus in the Smoky Mountains. Credit: Peleg Lab at CU Boulder

The synchronized flashing of fireflies is a summertime wonder — and a scientific mystery. New research maps the flashes in a swarm and suggests how these glowing displays are coordinated.

The big picture: Synchronization occurs in many systems — from the cells in our heart that contract at the same time to pump blood and neurons in the brain that synchronize at the onset of seizures.

  • "As physicists, we're always looking for universalities in many systems," says Orit Peleg, an author of the study and assistant professor of computer science at the University of Colorado, Boulder.
  • Modeling synchronization could help to inform efforts to decentralize telecommunications networks or to control swarms of robots, she adds.

How they did it: The researchers recorded video of thousands of fireflies in the Great Smoky Mountains of Tennessee in June 2020 using two cameras.

  • The video was then used to reconstruct where the flashes occur in 3D space and at what time.
  • Flashes from the male Photinus carolinus fireflies started in one location — once there was a critical density of individuals — and then cascaded across the swarm, according to the study published this week in Science Advances.
  • The phenomenon can be seen with the eye, but the empirical data helps the researchers to model how the flashes propagate.
  • The researchers suggest the fireflies take visual cues from others near and far in the nightly ritual to attract females on the ground.

The team also measured the velocity of the fireflies and found they move at about 1 foot/second, but the wave of light propagates at about 10 feet/second.

  • "It is information that is moving along, not the matter of fireflies themselves," says Raphael Sarfati, a physicist at the University of Colorado, Boulder, and an author of the study.

The big question: Are there leaders and followers? In future experiments, Peleg says they want to track individuals rather than the group to try to understand what or who decides to start the first flash.

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