This story originally appeared on Travelandleisure.com.
The lightning bugs, which are actually beetles, are the only type of firefly in America that are able to actually synchronize their flashing light patterns to create a dramatic nighttime spectacle.
For this reason, visitors travel to locations like Great Smoky Mountains National Park each year to catch the natural phenomenon and the array of twinkling lights they create.
While no one is quite sure exactly why the fireflies synchronize their flashes, the display is known to occur during their mating season, with NPS representatives stating the flashes could be a way for male fireflies to try to catch the attention of female fireflies.
One theory is that the male fireflies all flash around the same time due to competition, with each trying to be the first to flash. Another theory is that the males could be choosing to flash together to have a stronger chance of being spotted by a female firefly, who can them make comparisons.
The fireflies don’t always flash in unison, though, and can sometimes treat viewers to waves of flashes that appear across hillsides and random flashes across dark skies before going into bursts of synchronized flashing.
Factors like temperature and soil moisture play a role in the phenomenon, making it impossible to predict the exact date it will start and peak, though park representatives at Great Smoky Mountains say peak dates typically fall between the third week of May and the third week of June.
The park is one of the most popular locations to witness the display, which is why visitors hoping to witness the fireflies in the Smoky Mountains will need to enter a lottery due to the large numbers of those interested.
The lottery will open up on Friday, April 26 at 8 a.m. on the Recreation.gov — Firefly Event page and close on Monday, April 29 at 8 p.m., with winners notified on May 10. This year, winners will also need to pay a $25 reservation fee that will go towards viewing supplies and personnel that manage the viewing grounds each night.
For those who don’t happen to get a pass for Great Smoky Mountains’ viewing, several other locations offer the opportunity.
South Carolina’s Congaree National Park, which is also home to some of eastern America’s tallest trees, hosts a Fireflies Festival in May.
This year’s festival, which runs from May 10 through May 27, will include a Fireflies Trail to give visitors access to the top viewing areas in the park. The trail will start at the Picnic Shelter and end at the Harry Hampton Visitors Center, and no reservations are required to enter the park.
Rangers advise that those planning to stick around for evening views arrive ahead of time (the best time to view fireflies is usually between 9 pm. and 10 p.m.), with recommendations to bring a picnic lunch and spend some time enjoying the park to avoid access difficulties later in the evening.
Pennsylvania’s only national forest, the Allegheny National Forest, is also home to synchronous fireflies.
A festival takes place in the forest each year, though there are several locations within the forest as well for those who don’t happen to have tickets to the festival itself.
Synchronous fireflies have been spotted at locations like the Branch and Salmon Creek and at the Little Minister Creek behind Black Caddis Ranch, as the fireflies are known to head to locations that have a dark canopy and nearby water sources like a creek, bog, or pond.
In the past, they have also been spotted at the Buzzard Swamp recreation area and wildlife refuge, the Minister Creek campground, at the Kelly Pines campground, and at the Heart’s Content National Scenic Area, though travelers should keep in mind that it can be difficult to guarantee spotting the fireflies.
According to forest representatives, the synchronous firefly display is only noticeable five to 10 nights each year, with precise dates varying each year though the best times have typically fallen between mid-June to early July between 10:45 p.m. and midnight in the past.
The forest is also home to Chinese lantern fireflies, which fly lower to the ground and are known to emit shines that are close to 50 percent brighter than most firefly species. The best time to see them is June to early July, from 9:30 p.m. to midnight.
At Molly Branch Fireflies in Corryton, Tennessee, the Bennett family has opened the doors of their private property to allow visitors to take in the displays that the snappy sync synchronous fireflies create on their grounds.
While the family has lived on the property for more than 30 years and had the opportunity to witness the magnificent displays the fireflies put on for years, they decided to open their property to the public for the first time last year to honor mother and wife, Jeanette Bennett, who passed away in March of 2018 and enjoyed watching the firefly displays with her family.
Tickets will be $10 and available for purchase once exact dates are determined, though viewings are expected to likely start between June 10 and June 12 and last for two weeks. The firefly viewing area is near a wooded hillside where wildflowers bloom to make for a relaxing setting to see the twinkling show.
There are certain guidelines to follow when going to view fireflies that visitors should keep in mind. These include keeping noise levels down, staying on designated trails, collecting all garbage to protect the fireflies’ habitat, and refraining from catching or collecting any of the creatures.
Park representatives also recommend using flashlights only when necessary and turning them off once you reach the viewing point. They also recommend pointing flashlights straight down to the ground and covering lights with red or blue cellophane to avoid disturbing viewings.