Synchronized firefly swarms are like melting ice, or so physicist Raphael Sarfati sees it.
Ice remains solid until it is heated to a certain temperature and turns into a liquid.
Similarly, a loose swarm of fireflies will randomly flash the lanterns on its abdomen.
Synchronized fireflies in the Smoky Mountains National Park in Tennessee. Photo Floris van Breugel / Nature Picture Library.
But when the swarm reaches a certain density, the fireflies begin to blink in unison.
“Above that threshold, there is a near perfect timing“with coordinated, rhythmic light waves, explains Sarfati, a postdoctoral associate at the University of Colorado, Boulder.
The spontaneous synchronization of certain species of fireflies, such as Photinus carolinus from the Great Smoky Mountains of North Carolina and Tennessee, has long puzzled humans who observed the peculiar mating ritual, in which twinkling males struggle to attract the attention of females on the ground.
Scientists in the early 20th century dismissed the phenomenon as accidental or blamed it on gusts of wind or the trembling eyelids of the people who made these reports, according to a 1935 review in Science.
In the last 50 years, scientists collected anecdotal observations of these unified sparkles, but not enough empirical data to really study the mechanisms of firefly timing.
Now Sarfati and Orit Peleg, a physicist and associate professor also at the University of Colorado, have filmed the mating hordes of P. carolinus and mapped their blink patterns in three-dimensional space.
Their research, published Wednesday in the journal Science Advances, adds to the evidence that insects synchronize their flashes and suggests what can drive that coordination.
“I appreciate the excellent experimental work done by the authors,” Gonzalo Marcelo Ramírez Ávila, a researcher studying synchronization at the Universidad Superior de San Andrés in La Paz, Bolivia, who was not involved in the research, wrote in an email.
He added that the work will improve future firefly timing models.
“Their findings confirm what I have seen with my own eyes in nature during the last 30 years of fieldwork,” said Lynn Frierson Faust, author of “Fireflies, Glow-worms, and Lightning Bugs,” known as the Lady of the fireflies from Tennessee.
Peleg learned about the phenomenon in an undergraduate physics class, when insects were offered as an example of synchronization in nature.
When Peleg created her own lab, she knew it was her chance to study fireflies.
From previous research on fireflies in the Great Smoky, researchers knew that fireflies would only flicker if the swarm reached a sufficiently high density.
So they contacted the Great Smoky Mountains National Park, which holds an annual firefly synchronized viewing event, and coordinated with the park’s entomologists and Faust to find an ideal filming location amid the fog. luminescent mating in June 2020.
“We walked miles and miles,” Peleg said.
“But we never saw the end of the swarm.”
Peleg and Sarfati placed two cameras 13 feet apart on the ground with an overlapping field of view.
Like the producers of a movie set, they calibrated the shots with a checkerboard and an initial artificial light signal.
The overlaid images allowed the researchers to reconstruct a cone-shaped area from the fireflies’ flashes in three dimensions.
The researchers also placed two cameras in the middle of the vegetation to try to see the swarm through the eyes of a participating firefly.
As the cameras recorded, they waited silently at the edge of the clearing, watching the tapes of flickering lanterns.
The 3D reconstruction allowed the researchers to characterize several complex patterns in the swarm’s behavior.
Male fireflies did not blink instantly, but instead cascaded through the swarm.
For example, sometimes the flashes started at the bottom of the ridge and were directed towards the insects at the top.
This spread of sparkles in relay form suggests that the fireflies interact with the swarm locally, taking their signals from the fireflies around them, Peleg said.
This pattern of spread is also found in other swarms of animals, such as schools of fish, where local interactions between fish can spread to the entire group.
“I see my neighbor blink, so I do too,” Sarfati explained.
The reconstruction also revealed that the flashes typically occur in bursts in which a flickering firefly in motion prompts other slower-moving insects to blink as well.
This observation suggests that there is no clear leader fireflies or a single place of activity, said Andrew Moiseff, associate dean of behavioral and life sciences at the University of Connecticut, who has researched Great Smoky firefly timing since the 1990s.
Moiseff, who advised the researchers, said his findings confirmed what he had hoped for after years in the field.
“It’s spectacular,” he said, adding that the 3D approach had already provided insight into the mechanisms underlying the swarm that he had failed to address in his early investigations.
Although the new work offers a glimpse into the swarm of sparkles, it is still many factors are unknownsuch as the way individual fireflies respond to their relatives from varying distances or the multiple flashes of different individuals, Peleg said.
He believes that the holy grail would be a model capable of explaining how individual fireflies perceive the flashes around them and decide to flash themselves, thus reproducing the swarm’s community flash pattern.
“Then I could die in peace,” Peleg added.
Peleg is now conducting experiments on how fireflies respond to artificial light to refine his mathematical models.
Next June, you’ll be back in the Great Smoky Mountains, watching from the edge of the swarm.
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