In a light show worthy of an underground rave, every May the fireflies of Congaree National Park, South Carolina, put on a coordinated display that illuminates the forest. Now researchers have worked out how they keep their flashes in synch. Their results are reported in bioRxiv.
Lots of animals collaborate with members of their own kind to create features that are bigger than they are. Think starling murmurations, termite towers and coral reefs. In the southeastern United States, thousands of male fireflies (Photuris frontalis) come together to attract mates, by producing a group display of synchronised, bioluminescent light pulses.
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“It’s magical,” says computer scientist Orit Peleg, from the University of Colorado Boulder. “At certain times of night, fireflies have a single rhythm for the entire group, and they’re very punctual.”
This is a mesmerising and much-loved natural spectacle, but it raises an important question. How do the fireflies keep the beat?
To find out, scientists captured individual males and exposed them to a dim LED light, designed to mimic another flashing male. Fireflies normally make one or two flashes per second. The LED made around one to three flashes per second, but when the tempo was increased or decreased, the fireflies matched it.
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The researchers found that the fireflies were most likely to change their rhythm when the LED was almost synchronous. If the LED blinked immediately before the firefly, the male often rushed its next flash to catch up. If the LED blinked right after, the firefly waited a little longer, then flashed. When the LED was completely out of synch, however, the firefly usually ignored it.
Based on these observations, Peleg and colleagues devised a mathematical formula, known as a ‘phase-response curve,’ which describes how the external light source drives fireflies to modify the timing of their flashes.
“This research opens the door to discovering other examples of synchronisation in nature that we haven’t seen yet,” says Owen Martin, who was also involved in the study.
In addition, conservationists could use this knowledge to help identify different species of light-emitting insects and monitor their population sizes. “Such advances could transform how we study and protect firefly biodiversity,” the authors say.
Meanwhile, engineers could also learn from the fireflies and use the relevant mathematics to help make better drones. Perhaps one day, we will see engineered swarms of drones that communicate with each other via firefly-inspired pulses of light.
Top image: Researcher Owen Martin uses a red light to hunt for fireflies in Congaree National Park, Credit: Owen Martin
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