Back in the 1990s, a naturalist from Tennessee named Lynn Faust read a report by a scientist named Jon Copeland that there were no fireflies in North America. Faust knew that what he had been seeing for years in the nearby forest was strange.
Faust invited Copeland and Moiseff, his partner, to see the wildlife in the Great Smoky Mountains. Photinus Carolina. Clouds of male fireflies fill the forests and hillsides, hovering at almost human height. Instead of flashing in a tight sequence, these fireflies emit rapid flashes within a few seconds, then go silent several times before emitting another burst. (Imagine hordes of paparazzi waiting for celebrities to appear from time to time, snapping photos at each appearance, and then twiddling their thumbs during the breaks.)
Copeland and Moiseff’s research shows that they are mutually exclusive P. carolinus fireflies actually tried to light it with a neighboring firefly—or an LED light—in a nearby jar. The group also set up high-sensitivity video cameras along the edges of fields and thickets to capture the light. Copeland went through the pictures frame by frame, counting the number of fireflies illuminated each minute. Analysis of this carefully collected data has confirmed that all the fireflies inside the camera that are visible at the scene did indeed produce a coherent burst of time.
Twenty years later, when Peleg and his postdoc, astronomer Raphaël Sarfati, began collecting firefly data, better technology was available. They created a system for two GoPro cameras that were placed at a distance. Because the cameras took 360-degree video, they were able to capture the energy of the fireflies from the inside, not the sides. Instead of counting flashes by hand, Sarfati developed processing algorithms that can flash three times on a firefly that is captured by both cameras and then record not only when each flash occurred but also where it occurred in three-dimensional space. .
Sarfati brought this system to the field in Tennessee in June 2019 for a P. carolinus the fireflies that Faust made famous. This was the first time he saw the exhibition with his own eyes. He had been thinking something like the synchrony of fireflies from Asia, but the Tennessee explosion was terrifying, with bursts of eight rapid flashes about four seconds apart and repeated about every 12 seconds. But the confusion was interesting: As a physicist, he felt that a system with natural variability could be more instructive than one that did well. “It was difficult, it was confusing in a sense, but also beautiful,” he said.
Random but Kind Highlights
In his brush with higher education and conciliatory fireflies, Peleg learned to understand them through a model developed by Japanese physicist Yoshiki Kuramoto, building on the early work of biologist Art Winfree. This is the ur-model of synchrony, the grandchild of the mathematical models that explain how synchrony can occur, often without fail, in everything from the pacemaker cells in human hearts to alternating currents.
At the most basic level, communication system models must specify two methods. One is the inner strength of the individual—at this time the firefly is alone in the jar, governed by the law of the body’s movement or behavior that makes itself known when it shines. The second is what mathematicians call correlation, how the flickering of a firefly affects its neighbors. With the fortuitous combination of these two parts, the sounds of the various bands can quickly pull themselves together into a perfect chorus.
In a Kuramoto-esque description, each firefly is treated as an oscillator with a favorite tune. Behold the fireflies have a hidden pendulum swinging steadily within them; Imagine a worm shining every time its pendulum sweeps down its arc. Suppose also that seeing a nearby flash swings the firefly’s pendulum slightly forward or backward. Even when the fireflies become disorganized, or their internal rhythms diverge, the group guided by these rules often connects with a coherent flash.
Several variations on this scheme have emerged over the years, each changing the internal rules and connections. In 1990, Strogatz and his colleague Rennie Mirollo of Boston College proved that simple devices like fireflies can always communicate if you connect them, no matter how many people you put together. The following year, Ermentrout explained how groups of Pteroptyx malaccae Southeast Asian fireflies can coordinate by speeding up or slowing down their internal wheels. As recently as 2018, a team led by Gonzalo Marcelo Ramírez-Ávila of the University of San Andrés in Bolivia developed a complex system in which fireflies switch back and forth between “charging” and “discharging” when they glow.
