Synchronized Fireflies at Congaree

Visitors to Congaree National Park have long been fascinated by synchronized fireflies and their unique ability to flash in unison with one another.

NPS Photo

The appearance of fireflies flashing in the evening is a welcome sign summer is near. Many have fond memories of watching fireflies twinkling at sunset, but sadly the experience of watching these fascinating insects come out to dance at dusk is not as common as it once was. This makes places that preserve the habitat and conditions fireflies need to survive, while also offering opportunities to view them, so important.

Congaree is home to several species of firefly, including the synchronous species Photuris frontalis. It is the ability of this firefly species to flash in unison with others that draws thousands of fascinated visitors to Congaree each May. To learn more about these fireflies, click the tabs below to see answers to some of the frequently asked firefly questions people ask park rangers and volunteers each year.

 

Is a firefly the same as a lightning bug?

‘Firefly’ and ‘lightning bug’ are different names for the same insect. Fireflies are not flies but instead are a species of beetle belonging to the family Lampyridae. There are over 2,000 species of fireflies found around the world, approximately 170 species of which can be found in North America. The species most are familiar with is the common eastern firefly, Photinus pyralis, which can be seen throughout the summer in yards and parks across the eastern and central United States.

How long do fireflies live?

Depending on the species, most fireflies have a lifespan of 1-2 years. Fireflies spend most of their lives in the soil as larvae, feeding on soft-bodied organisms like worms and snails, as well as other small insects. Once they emerge as adults, fireflies typically live for 3-4 weeks. As adults their only goal is to find a mate and reproduce. The adults of some firefly species are so focused on this that they do not even eat, and once they find a mate their life cycle is complete.

How do fireflies produce light?

Light produced naturally by a living organism is called bioluminescence. A variety of organisms can produce and emit light, including species of plankton, jellyfish, crustaceans, squid, and other invertebrates, as well as certain types of fungus. However, the bioluminescent lifeforms that we know best are fireflies.

Fireflies produce light through a chemical reaction that takes place in a part of the abdomen appropriately called the lantern. There the chemical luciferin combines with the enzyme luciferase, and along with oxygen, magnesium, and the energy producing compound ATP, produces light. Some firefly species produce a steady glow, while others blink at different intervals. Some produce a yellow-green light, while others emit a blue-white light. There are even fireflies that do not produce any light at all.

Why do fireflies flash or glow?

Fireflies communicate by light. Watch a specific species of firefly long enough, and you may notice they have different signals. A firefly’s flash might be an alarm, indicating potential danger, or it could be warning to another firefly to back off. However, the primary purpose of this behavior is to attract and communicate with a potential mate.

Often the brightest and most visible fireflies are the flashy males trying to attract one of the less often seen females. While the light produced by male fireflies is distinctive, female fireflies tend to have a paler, dimmer signal. After a female has selected a male that she thinks will be a suitable mate, she will point her lantern at him and flash out a signal letting him know she has chosen him out of all the others.

Are all fireflies capable of synchronization?

Complete synchronization is unique ability that only three of all North American firefly species are capable of. They are:
 

• Photuris frontalis – Also known as the Snappy Single Sync, these are the synchronous fireflies seen at Congaree National Park. Males fly low to the ground, producing a quick flash every .65 seconds. This species prefers to live on the edges of mature cypress/hardwood swamps and bottomlands, and are locally abundant across the southeastern United States. They are also present (though uncommon) as far north as Delaware and Maryland.
• Photinus carolinus – The famous synchronous firefly seen at Great Smoky Mountains National Park, males of this species typically fly 3-7 feet off the ground, producing a series of 4-11 yellow flashes, followed by a 6-9 second pause. This species may be found in isolated pockets of the Appalachian mountain range from northern Georgia to New York, preferring more mature cove hardwood forests with small clearings containing little or no underbrush.
• Photinus knulli – Native to the southwestern United States, scattered populations of this species can be found in wet areas of the deserts of southeastern Arizona and northern Mexico. Males may synchronize where populations are large enough, producing three yellow flashes about every six seconds.Complete synchronization is unique ability that only three of all North American firefly species are capable of. They are:

Why do fireflies synchronize their flashes?

Researchers have been studying firefly synchronization for many years to determine its purpose. While no definitive reason has yet emerged, recent studies have provided some interesting insights into this unique behavior. Scientists studying the behavior of female Photinus carolinus fireflies found that they were more likely to respond to males who were fully synchronized but would not respond to those slightly or completely out of sync. This has led to the theory that synchronization may function as a means of species recognition between males and females in a visually cluttered environment. Whether the same is true for Photuris frontalis fireflies at Congaree has not been tested, but future research will hopefully one day provide an answer to this enduring mystery.

Why does it look like some fireflies are slightly out of sync?

At first glance it may seem like all the fireflies you see are blinking in unison. While the fireflies you see at Congaree are synchronized, a closer look reveals that it is not a uniform synchronization. Researchers studying Photuris frontalis here at Congaree recently found that, rather than all fireflies being uniformly synchronized on the same tempo, some groups are on slightly different tempos others, making the fireflies as a whole collectively synchronized. This naturally occurring coexistence of both synchrony and asynchrony is known as a chimera state. Mathematicians and physicists in the past have only been able to observe this phenomenon in laboratories through carefully designed and controlled experiments, making the synchronization of fireflies at Congaree one of the only known observable natural occurrences of this phenomenon! You can read more about this research done at Congaree here!

Why does this phenomenon only occur in national parks?

While Congaree and Great Smoky Mountain National Parks have become two of the best-known locations where synchronous fireflies can be found, they are far from the only places. There are other places, often on private land or areas with little to no public access, where synchronous fireflies can be found. There are still other locations with synchronous fireflies that have not listed to prevent these fragile populations of flashy fliers from being loved to death. The Xerces Society for Invertebrate Conservation has a number of online resources on firefly tourism, including locations people can go to see both synchronized and non-synchronized fireflies.

Why did the park change how the viewing event was run?

For many years the synchronous fireflies at Congaree were something only a few people each year came to see. Word spread, however, and by 2016 large numbers of people were coming to Congaree to see them. Concerns that this rapid increase in visitation would have negative long-term impacts on the synchronous fireflies and their habitat led the park to hold its first managed viewing event in 2017.

Between 2017 and 2019 an estimated 25,000-30,000 visitors came to see the synchronized fireflies. The pandemic in 2020 gave park staff the opportunity to observe and compare synchronous firefly activity in both the viewing area and nearby locations that had seen little to no event visitors over the past three years. The results of this work found that synchronous firefly activity had visibly decreased compared to neighboring locations, raising concerns that with visitation only likely to increase in the future, this trend would only get worse.

To better protect firefly habitat from further damage and reduce overcrowding in the viewing area, the park implemented a lottery system modeled after the one that Great Smoky Mountains National Park has been using for their annual synchronized firefly event. Started in 2021, this new system not only allows park staff to provide a more comfortable and enjoyable visitor experience, it is also helping to ensure that there will be fireflies for the future.

If you would like more information about this annual event, including how to enter the lottery for a vehicle pass, please see our Firefly Viewing Event page.