All Together Now, Fireflies Flash in Sync : Smoky Mountains: Expert says the patterns vary from those in Southeast Asia, where they get in a tree, flash in unison, “so it looks like a Christmas tree.”

Every June for 40 years, members of the Faust family have watched their very own springtime light show from a darkened cabin porch in the Great Smoky Mountains.

On the hill across the creek, a wave of light flows down the slope, stops, then starts over again at the top.

The light is the glow of hundreds and hundreds of fireflies, flashing in unison.

On the flat land nearby, their pattern is different. The fireflies flash simultaneously, on-and-off, five or six times, then stop for 15 or 20 seconds. Then they start over. On-and-off, on-and-off, all together.

So Lynn Faust was a little scornful when she read a magazine article saying the Western Hemisphere has no synchronous fireflies.

“I thought maybe it wasn’t synchrony, but it sure looks like it,” the Knoxville resident said.

The magazine’s editor put her in touch with John Copeland, an ethologist, or someone who studies creatures’ patterns of behavior, at Georgia Southern University in Statesboro, Ga.

When her message arrived, Copeland was roaming Southeast Asia studying what were thought to be the world’s only synchronous fireflies.

Evidently, he could have stayed much closer to home.

“This whole thing has been magical,” Copeland said of the show in Tennessee. “At the height of the season, it takes your breath away.”

Flashing is part of fireflies’ breeding pattern, but the flashes are usually random and individual.

Copeland said the patterns of synchronization in the Smokies are different from those in Southeast Asia, where the fireflies get in a tree “and flash congregationally, so that it looks like a Christmas tree with lights flashing on and off.”

In the Smokies the insects don’t gather in trees and their blinking is not as precisely uniform. “But you can tell with the naked eye that they’re flashing synchronously, or almost synchronously,” Copeland said.

The firefly in question is photinus carolinus. Its range is along the Tennessee-North Carolina state line, which forms the spine of the Great Smoky Mountains National Park.

Copeland and his colleague, Andy Moiseff of the University of Connecticut, began studying the Smoky Mountain fireflies only last summer, so there are things they don’t yet understand.

Copeland said no one has determined what synchronization is for.

“Folks have hypothesized nine different reasons for the Southeast Asia synchrony, but nobody really knows,” he said. “My guess is they do it to preserve the male pattern, so the females can discriminate the males of the species from other firefly species present at the same time. That’s a guess.”

As for why synchronization should show up in Tennessee and Southeast Asia, that’s another thing he’s not sure about.

“I wish I knew,” he said. “It evolved for some reason. The behavior costs energy and it’s unusual. Therefore, it has to have some evolutionary meaning.”

One possibility is that the females are sparse and unevenly distributed in the area, and unified behavior by the males is a way of amplifying their mating flash.