Nights at Congaree National Park are as inky black as any place in South Carolina.
But for a few weeks each year, the darkness is pierced by the synchronized flashing of tiny lightning bugs.
The annual spectacle began last weekend in what one retired park ranger says is an early start to the firefly season. Just off the main boardwalk, fireflies blinked in unison this week as visitors began to hear about the natural show at South Carolina’s only national park.
Standing close to her parents, 10-year-old Chloe Zavislak watched the lights in awe Tuesday night.
“I like it,’’ the Columbia fourth-grader said. “It looks like Christmas lights blinking, except it’s outside. And it isn’t cold.’’
Congaree National Park is one of the few easily accessible places in the country where people can see fireflies light up all at one time, rather than blink sporadically. The natural light show typically begins in mid-to-late May and ends by early June.
Long after daytime visitors leave Congaree National this time of year, parking lots fill up with the cars of folks seeking a firsthand look. The phenomenon has gained enough attention in recent years that owners of Columbia’s new minor league baseball team named their club the Fireflies.
“This takes seeing fireflies in your backyard to another level,’’ Columbia resident Chuck Steinfurth said. “We’re lucky we have this. It’s kind of mesmerizing to stare off into the woods and see it constantly light up.”
Synchronized blinking is believed to be part of a mating ritual by a species of firefly that lives in the 27,000 acre flood plain preserve southeast of Columbia. Unlike other species, these fireflies work together to find mates. But all the reasons for the phenomenon aren’t fully known.
The place to see fireflies at Congaree National is near the visitor’s center. A quick walk down the boardwalk brings visitors to a patch of high ground frequented by lightning bugs. The bugs seem to prefer areas such as this, as opposed to more watery spots along the boardwalk, park officials said.
Retired park ranger Fran Rametta, who said he first saw the phenomenon about 25 years ago at Congaree, said it appears to him the synchronized blinking has begun earlier than usual this year. He noticed it last weekend while leading a nighttime owl tour at the park. Usually, the blinking reaches its peak later in the month, he said. Park officials didn’t dispute that, saying Rametta has longtime experience with fireflies.
J.C. Chong, a Clemson University scientist who is studying fireflies, said many species of bugs are out sooner, likely because of the warm winter and spring the state experienced. It’s possible that’s attributable to climate change, although it’s difficult to say conclusively, Chong said.
It’s unknown how many places have fireflies that flash all at the same time. The website firefly.org, which provides information about lightning bugs, says there are relatively few spots in the world where synchronous fireflies can be found. Those spots include Great Smoky Mountains National Park in Tennessee, Allegheny National Forest in Pennsylvania, and a wildlife management area near Oak Ridge, Tenn.
The Smokies firefly show is perhaps the best known. It has become so popular that the National Park Service began requiring tickets for people who want to see the lightning bugs. Scientists say three species of fireflies synchronize lighting in North America. Many other species are not known to light up at the same time.
But research shows that southeast Asia also has fireflies that flash in unison. Chong said firefly synchronization likely occurs in places that people don’t notice, such as some urban areas, where man-made lights drown out fireflies.
“Artificial light dilutes the effect,’’ Chong said.
In contrast, Congaree National Park is in a remote area of Richland County and includes huge, old-growth trees that block light.
For Rametta, the annual return of synchronized fireflies to Congaree National Park is a treat. He’s regularly on the park boardwalk at night this time of year, soaking up the blinking scenery.
“It’s magical,’’ he said. “Every year, I’m waiting to see it again.’’
Visitors wanting to see the synchronized blinking of fireflies can visit Congaree National Park most any night from now through early June. Fireflies typically flash in unison from now through early June. Here are some tips from park officials about watching Congaree’s fireflies:
▪ Fireflies are most visible on a hilly spot just outside the back of the visitors’ center.
▪ Going now is a plus if you want to avoid mosquitoes, which become more numerous the closer it is to summer
▪ Don’t take bright flashlights on the boardwalk. Use a red cover over any flashlight. Park officials say bright lights could stop the fireflies from blinking in unison.
▪ Don’t use flash photography
▪ Images of fireflies are difficult to capture or video
▪ Swarms of fireflies appear to diminish as you get closer to swampy areas with standing water
▪ The best time to see fireflies is around 9 p.m.