The same thing happened in the 1990s when a Tennessee naturalist named Lynn Faust read a scientist named Jon Copeland’s confident published claim that there were no synchronized fireflies in North America.
Faust realized at that moment that what she had been observing for years in the neighboring
Copeland and his partner Moiseff were asked by Faust to see a species known as Photinus carolinus in the Great Smoky Mountains. Forests and clearings are covered in the clouds of male fireflies, which are around the height of a person. These fireflies don’t blink in perfect unison; instead, they flash rapidly for a short period, then go silent for a considerable amount of time before flashing again. (Consider a group of paparazzi who wait for celebrities to show up at predetermined intervals, firing off a barrage of pictures at each appearance, and then idly fidgeting during the lull.)
According to Copeland and Moiseff’s research, isolated P. carolinus fireflies genuinely attempted to flash in time with an adjacent firefly or a nearby LED that was flickering. To record flashes, the team also placed high-sensitivity video cameras along the boundaries of fields and forest clearings. Copeland watched the video frame by frame, recording how many fireflies were visible at each split second. These painstakingly collected data were statistically analyzed to demonstrate that all of the fireflies in the cameras’ field of view did generate flash bursts at predictable, correlated intervals.
Better technology was available when Peleg and her postdoc, the physicist Raphael Sarfati, set out to gather firefly data two decades later. Two GoPro cameras are set up in a system that is spaced a short distance apart. The cameras were able to record 360-degree video, allowing them to observe a firefly swarm’s dynamics from all sides as well. Sarfati developed processing algorithms that could triangulate on firefly flashes captured by both cameras and then record not just when each blink occurred, but also where it occurred in three-dimensional space, as opposed to manually counting flashes.
Sarfati first brought this system into the field in Tennessee in June 2019 for the P. carolinus fireflies that Faust had made famous. It was his first time seeing the spectacle with his own eyes. He had imagined something like the familiar scenes of firefly synchrony from Asia, but the Tennessee bursts were messier, with bursts of up to eight quick flashes over about four seconds repeated roughly every 12 seconds. Yet that messiness was exciting: As a physicist, he felt that a system with wild fluctuations could prove far more informative than one that behaved perfectly. “It was complex, it was confusing in a sense, but also beautiful,” he said.
Random but Sympathetic Flashers
In her undergraduate brush with synchronizing fireflies, Peleg first learned to understand them through a model formalized by the Japanese physicist Yoshiki Kuramoto, building on earlier work by the theoretical biologist Art Winfree. This is the ur-model of synchrony, the granddaddy of mathematical schemes that explain how synchrony can arise, often inexorably, in anything from groups of pacemaker cells in human hearts to alternating currents.
At their most basic, models of synchronous systems need to describe two processes. One is the inner dynamics of an isolated individual—in this case, a lone firefly in a jar, governed by a physiological or behavioral rule that determines when it flashes. The second is what mathematicians call coupling, the way the flash of one firefly influences its neighbors. With fortuitous combinations of these two parts, a cacophony of different agents can quickly pull itself into a neat chorus.
In a Kuramoto-Esque description, each firefly is treated as an oscillator with an intrinsic preferred rhythm. Picture fireflies as having a hidden pendulum swinging steadily inside them; imagine a bug flashes every time its pendulum sweeps through the bottom of its arc. Suppose also that seeing neighboring flash yanks a firefly’s pace-setting pendulum a little bit forward or back. Even if the fireflies start of sync with each other, or their preferred internal rhythms vary individually, a collective governed by these rules will often converge on a coordinated flash pattern.
Several variations on this general scheme have emerged over the years, each tweaking the rules of internal dynamics and coupling. In 1990, Strogatz and his colleague Rennie Mirollo of Boston College proved that a straightforward set of firefly-like oscillators would almost always synchronize if you interconnected them, no matter how many individuals you included. The following year, Ermentrout described how groups of Pteroptyx malacca fireflies in Southeast Asia could synchronize by speeding up or slowing down their internal frequencies. As recently as 2018, a group led by Gonzalo Marcelo Ramírez-Ávila of the Higher University of San Andrés in Bolivia devised a more complicated scheme in which fireflies switched back and forth between a “charging” state and a “discharging” state during which they flashed.
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