Synchronous Fireflies

2025 firefly viewing opportunity information to be announced

Estimated information for the 2025 annual firefly viewing opportunity:

• Late-April 2025: Lottery for vehicle reservation applications
• Mid-May 2025: All lottery applicants will be notified if their application was successful or unsuccessful
• Early-June 2025: Annual firefly viewing opportunity

For reference: 2024 firefly viewing opportunity details

Logistics

• Parking Confirmation will be distributed via a lottery on Recreation.gov – Firefly Event page.
• During the lottery application, you may choose two dates you would like to attend—your preferred choice and an alternate date.
• All lottery applicants will be notified that their application was SUCCESSFUL (and are awarded vehicle parking confimation) or UNSUCCESSFUL (and were not awarded vehicle parking confirmation).
• **Lottery applicants will be charged a $1.00 application fee. Successful applicants will automatically be awarded parking passes and $24.00 will be charged to the same credit or debit card used for the application fee (collected on Recreation.gov) to help cover the cost of viewing supplies and nightly personnel to manage the viewing opportunity near Elkmont Campground.

 

Fireflies (also called lightning bugs) are beetles. Most of their lifecycle is spent in the larval stage (1-2 years), where they feed on snails, worms, and smaller insects in the leaf litter on the forest floor. Once they mature into the adult form, they only live for about 3-4 weeks and many do not feed.

Firefly flash patterns are part of their mating display. Each species has a characteristic pattern that helps male and female individuals recognize and find each other. Most species produce a greenish-yellow light, but others have more of a blue or white light. Males typically flash while they are flying, and females, which are usually stationary, flash in response.

The production of light by living organisms is called bioluminescence. Fireflies are a good example of an organism that produces light, but there are others as well, such as certain species of fungus, fish, shrimp, jellyfish, plankton, glowworm beetles, and gnats. Bioluminescence involves highly efficient chemical reactions that result in the release of light with little or no emission of heat. Fireflies combine the chemical luciferin and oxygen with the enzyme luciferase in their lanterns (part of their abdomens) to make light. The light produced is referred to as a "cold" light, with nearly 100% of the energy given off as light. In contrast, the energy produced by an incandescent light bulb is approximately 10% light and 90% heat.

Synchronous fireflies (Photinus carolinus) are one of at least 19 species of fireflies that live in Great Smoky Mountains National Park. They are one of only a couple species in North America whose individuals are known to synchronize their flashing light patterns.

 

Synchronous fireflies produce light in their lanterns, the pale area of the abdomen visible on the underside of the insect above.

Why synchrony?

Scientists studying the synchronous firefly have determined that the males flash in unison as a way for the female to be certain she is responding to one of her kind. There are other firefly species flashing at night, and some of them are predatory, so she must be able to recognize males of her species.

The flash pattern of Photinus carolinus is a series of 5-8 flashes, followed by a pause of about 8 seconds, and then this pattern is repeated. Initially the flashing appears random, but the period of darkness is synchronized. As more males start joining in, the flashing will also begin to synchronize and entire sections of the forest will be pulsating with light.

Timing of the Display

The mating season of Photinus carolinus lasts for approximately 2-3 weeks each year. The dates that they begin to display varies from year to year based on temperature and soil moisture. We use daily temperatures and predicted temperatures to set the dates of the public viewing event, but any natural phenomenon is highly variable and difficult to predict exactly.

As the season begins, a few insects start flashing, then more join the display as the days pass. They reach a peak and then the numbers gradually decline each day until the mating season is over. Since 1993, which is when dates were first recorded, this peak date has occurred at various times from the third week of May to the third week in June.

During the mating season, nightly displays can be affected by environmental factors. For example, fireflies typically won’t flash in heavy rain, but on misty, drippy evenings they will likely still display under the forest canopy. Cool temperatures, below 50º Fahrenheit, will also shut down the display for the night.

Light Show Etiquette

Flashlights disrupt the fireflies and impair people's night vision. The light show is best when you:

• Cover your flashlight with red cellophane or use a flashlight with a red light filter.
• Use your flashlight only when walking to your viewing spot.
• Point your flashlight at the ground.
• Turn off your flashlight when you find your viewing spot.

You can also help protect the fireflies and their habitat:

• Do not catch the fireflies.
• Stay on the trail at all times.
• Pack out all of your garbage.