THE LIGHT IN THE FOREST

Right around midsummer, in a quiet corner of Pennsylvania, a rare species of firefly puts on a dazzling, one-of-a-kind show.  

- GINA DECAPRIO VERCESI

LIGHT HAD FALLEN on Allegheny National Forest in northwestern Pennsylvania. It was a few days past the summer solstice that magical June evening when Robin Goodfellow and his troupe of fairies from A Midsummer Night's Dream emerge to frolic in the forest and hoodwink young lovers. But instead of Shakespearean sprites, I'd come in search of the rare Photinus carolinus, a charismatic species of firefly that puts on a spectacular, synchronised light show each year, just as spring slips into summer.

I first observed this glittering mating ritual, in which the males of the species illuminate in unison to attract females, on a 2016 trip to Great Smoky Mountains National Park. It was there, in 1992, that a naturalist named Lynn Frierson Faust helped scientists identify the Western Hemisphere's first synchronous fireflies. A decade later, after a tip-off from some campers, Faust and her Firefly International Research and Education (FIRE) colleagues confirmed the existence of P. carolinus in Allegheny National Forest, citing a particularly robust population near the blink-and-you'll-miss-it village of Kellettville.

The news came as a surprise to Peggy and Ken Butler, whose kellettville backyard turned out to be a hotbed of firefly activity. "We didn't know that the lightning bugs were anything special," Peggy Butler told me. "But then the FIRE team came and introduced us to the world of synchronous fireflies, and our lives changed."