For two weeks out of the year, lightning bugs in the Smoky Mountains transform from random twinkling lights to a single, pulsing illumination. The collective lighting from the tiny bugs shines on the mountainside forest in an enchanting bioluminescence.

These fireflies that synchronize their lights have become a natural phenomenon attraction, and people drive from all over to visit the park and witness the coordinated flashing. In 2018, on any given night during the two-week lightning bug synchronization window, nearly a thousand people filled the park, and silently observed the lighting of the mountains to the rhythm of the fireflies’ cadence.

Lightning Bugs in the Smoky Mountains Will Flash Their Lights in Unison Once A Year at These Campgrounds

Because the lightning bugs in the Smoky Mountains have become somewhat of a celebrity, park officials have had to implement a lottery system to determine who gets in the official viewing areas to avoid overcrowding. However, there’s more than one place to view the fireflies.

Where to Camp to See the Firefly Synchronization

Elkmont Campground is the primary official viewing location for synchronous fireflies. Its soil and temperature conditions support a dense population of the synchronous lightning bugs in the Smoky Mountains. This campground is also only a short drive from Gatlinburg, and has the parking availability for park rangers to better manage the influx of visitors during the firefly synchronous flashing time period.

But the fireflies can be found in other areas of the park. Some have reported seeing the simultaneous flashing at Cades Cove and the Cataloochee Valley.

The Great Smoky Mountains National Park Service has confirmed that a primary reason Elkmont Campground serves as the official viewing location is due to the parking availability. “There are likely many places of similar habitats, low to mid elevations with rich, alluvial forests, where people may find fireflies displaying,” reads a National Park Service press release for the 2019 synchronous fireflies viewing season. “Unfortunately we are not aware of another location in the park with adequate parking to sustain visitation associated with firefly viewing.”

This is good news if you can’t get into the crowded Elkmont Campground during the synchronous viewing period. Chances are you can find your own viewing spot in a similar environment within the park.

When Does it Happen?

The fireflies in the Smoky Mountains synch their lights for two weeks every year, but the peak of the flashing lights season has historically occurred anywhere in the time frame from May to the third week in June. In 2018 the fireflies coordinated their lights from June 7 to June 14.

Although it’s impossible to predict the exact dates that the synchronous fireflies will begin their season, scientists have discovered that soil moisture, temperature, rain, and moon phase all have an impact on when the fireflies flash together.

Securing Your Spot with the Lottery

In order to keep the park from being overrun with firefly watchers during the flashing season, the Great Smoky Mountains National Park has set up a lottery system that allows people into the Elkmont Campground area. It is free to put in your lottery application, but if you’re one of the lucky selected then you’ll need to pay a $25 reservation fee.

In your application, you’ll select two dates, one preferred date and one alternative, for the lottery to either approve or deny. A randomized computer drawing determines which applications are selected. If your application is accepted, your parking confirmation is only valid for the date specified, this is when you must go to view the fireflies.

For the 2019 synchronous firefly season, the lottery application system opens Friday, April 26 at 8 a.m. Eastern Standard Time. The lottery closes on Monday, April 29 at 8 p.m. EST. The link to apply for the lottery is here, but keep in mind this link will be inactive until the actual lottery application system opens during the aforementioned dates.

On May 10, lottery applicants will be notified whether their application was successful or unsuccessful.

The Science Behind Nature’s Strobe Lights

Synchronous is a bit of a misnomer. The lightning bugs in the Smoky Mountains are actually only flashing in coordination with their gender. Female fireflies generally are stationary and flash together, and males usually flash back while flying. This is a call and response type ceremony that is part of the firefly mating ritual.

Not all fireflies exhibit this unison lighting behavior. There are 19 species of fireflies in the Great Smoky Mountains National Park, and only one species, the Photinus carolinus, light up together during their two-week mating season.

Tips for Best Lightning Bug Visuals

Because the firefly synchronization is an eerie and beautiful experience, it can be tempting to become more involved than simply being a witness. However, this is an important stage in the life cycle of a firefly, and it’s critical to have the least amount of human intervention as possible. Below are some tips to protecting the synchronization process, as advised from the National Park Service.

1. Keep flashlight use to a minimum, these can disturb and confuse the fireflies, and alter their pattern displays.
2. However, it’s difficult to walk to a viewing area in the night, so if you need to turn on your flashlight, cover it with red or blue cellophane and keep it pointed at the ground.
3. Turn off your flashlight once you have finished walking.
4. Do not catch the fireflies.
5. Stay on marked trails.
6. Leave no trace.

Viewing Synchronous Fireflies Outside of Great Smoky Mountains

While the Great Smoky Mountains National Park has the most dense population of the special synchronizing fireflies, there are other areas where the lightning bugs are known to flash together.

In Congaree National Park, South Carolina, Photinus carolinus synchronize their lights in the same time frame as the lightning bugs in the Smoky Mountains. The South Carolina subsect of the species is especially curious for surviving in the swampy conditions of Congaree National Park.

In Allegheny National Forest, Pennsylvania the synchronous fireflies are honored with a Firefly Festival. The festival celebrates all 15 firefly species found in the forest, but includes the Photinus carolinus species. The synchronizing firefly was only discovered in the Allegheny National Forest in 2012.

Even more recently, a different species of synchronizing firefly, the Photuris fontalis, was discovered in East Tennessee in 2015. At the Oak Ridge Wildlife Management Area near Knoxville, a firefly species nicknamed Snappy Syncs, distinguishes its collective lighting pattern by blinking about 30 times as a group, then some will quit blinking for a few seconds before joining the group again.