It’s that time of year when the rare synchronous lightning bugs of the Appalachians begin their spectacular annual display. This year, at Congaree National Park near Columbia, South Carolina, the fireflies have started the show a little earlier than usual.

Fireflies glitter in a forest
Fireflies blinking in unison is a rare and mesmerising sight.   

Fireflies are winged beetles that use bioluminescence during twilight to attract mates or prey. The sporadic blinking of fireflies is a common but invariably magical sight at dusk in the eastern United States. But the sight of thousands of bugs blinking in unison is as rare as it is mesmerising. The biology behind the phenomenon isn’t fully understood, but it’s believed to be part of a collective mating ritual.

Catching a glimpse of the show requires some planning ahead for two reasons: the season is brief, usually kicking off sometime in the second half of May and ending in early June, and the bugs seem to congregate in places that can be hard to access.

The bugs also blink in unison at the Great Smoky Mountains National Park in Elkmont, Tennessee, but the season there is shorter (this year, May 31 to June 7), places are only available by lottery conducted weeks earlier, and transportation to the viewing site is via a shuttle.

At Congaree National Park, on the other hand, the crowds are smaller and the bugs conveniently gather near the visitors’ centre. Congaree, South Carolina’s only national park, is a 27,000 acre floodplain known for its astonishing biodiversity. According to the National Park Service, it boasts “the largest intact expanse of old growth bottomland hardwood forest remaining in the southeastern United States.”

Congaree National Park in South Carolina
Congaree National Park in South Carolina

Synchronous fireflies are also known to exist in Pennsylvania’s Allegheny mountains and in southeast Asia. It’s recommended to see the fireflies as early as possible, as later in the season observers must contend with that other, more ubiquitous twilight bug, the mosquito. The light peaks at around 9pm, and visitors are encouraged to avoid flash photography and to use flashlights sparingly and discreetly to avoid disrupting the display.

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