Synchronic Firefly Research at Congaree

Humpback posture and hourglass headshield characteristic of Photuris frontalis.
Humpback posture and hourglass headshield characteristic of Photuris frontalis.

Lynn Faust

Synchronic Fireflies - Sophisticated Communication

The first historic accounts of synchronous flashing are from records that date back to the late 1500s of fireflies that grouped in trees along waterways in Southeast Asia. More recently, synchronous flashing was discovered in certain species of North American fireflies that do not congregate. Synchronous flashing fireflies that can be found in North America include: Photinus carolinus, Photinus knulli and Photuris frontalis.

The synchronous quick single flashes of male P. frontalis fireflies are typically observed at Congaree National Park for approximately two weeks between mid-May and early June. Synchronous flashing is defined as concurrent rhythmic group flashing. Although the males appear to be continuously synchronic, they are actually intermittently synchronous. Flashing of the group is continuous, but individual fireflies flash synchronously for several cycles and then pause for several cycles.

Research is being conducted on P. frontalis at Congaree National Park to improve understanding of this species' unique characteristics including rapid sychronous flashing and intermittently synchronous flashing. Scientists are interested in collecting more data on female P. frontalis in order to better understand the courtship and mating behavior of this species.

Background

Naturalists often appreciate insects for their fascinating visual displays. Unlike butterflies and moths, fireflies are often identified at a distance by their bioluminescent displays rather than their physical appearances.

When viewing free flying insects at night, factors such as depth of field, distinctiveness of flash patterns and the number of different species simultaneously active may confuse field recognition. Basic knowledge of seasonal variation, geographic range and flash patterns are helpful for identifying fireflies.

Firefly flashing is a sophisticated form of animal communication that is specific to each species. The male firefly's flash duration as well as the duration of the pause between successive flashes are components of this species-specific flash pattern. These specific flash paterns communicate information such as sex and species to other fireflies.

While patrolling, male fireflies of most species flash their species-specific pattern independently of other nearby males so that there is no discernible group-wide pattern among flashing males. In contrast, some firefly species flash in pairs or in coordination with a larger group (synchronous flashing).

The range of P. frontalis covers much of the southeast, including Alabama, Florida, Mississippi, North Carolina, South Carolina and Tennessee. Mature forests and wet bottomlands such as those found at Congaree National Park are the preferred habitat of this firefly. P. frontalis males are approximatey 1/2 inch (13mm) in length, and females are thought to be similar in stature Information on females is limited because they are difficult to find.

One possible explanation for the shortage of data on P. frontalis females is female firefly scarcity. The sex ratio of most fireflies is strongly male, especially early in the season. Females are susceptible to predation, so they are often hard to locate because they survive by being cryptic.

Synchronous flashing displays are rare among North American fireflies. The speed and rythym of P. frontalis flash pattern is unique and can be used to separate this species from other sychronous fireflies. Male fireflies produce sychronous quick single flashes twice per second. Flashing of the group may appear continuous, but individual fireflies join in and out of the sychronized display.

Another identifying characteristic of P. frontalis males is the height at which they fly. These fireflies usually patrol an area at a height of approximately 2 to 4 ft. (0.6 to 1.2 m) above the ground.

Flashing typically begins shortly after sunset and lasts for approximately one hour before the display dissipates. Smaller displays can also be viewed shortly before dawn.

Female fireflies typically view male displays from a stationary location and respond with their own species-specific flash pattern. The exchange of light displays between male and female fireflies is called a photic dialog. Photic dialog usually occurs between two fireflies but sometimes more than one male can court the same female. This photic dialog continues until male and female meet and ultimately mate.

Research Overview

Research is being conducted on P. frontalis at Congaree National Park to improve understanding of this species' unique characteristics including intermittently synchronous flashing.

Beginning in 2009, Congaree National Park partnered with Georgia Southern University to study flash communication and physiology of the synchronic firefly P. frontalis. Male firefly behavior is well documented, but mating flash communication has never been described for P. frontalis.

The male P. frontalis flash code involves a single flash repeated rhythmically every 0.6 to 1.0 sec., depending on temperature. Flying males fly into proximity, so that they are 1 ft. (30cm) apart and flash together repeatedly and rhythmically at the species-specific interval for several flash cycles. Then, one firefly will stop flashing while the others (if there are more than two fireflies) continue flashing. Shortly thereafter, the non-flashing firefly will resume synchronous flashing.

Results

Research suggests that the male-male activity of synchrony in this species serves to separate the flying flashing males. Previous studies found that males neither congregated in the field nor the lab. The flashing is likely a form of competition for females.

The precision and rapid start of synchrony may attract females. Likewise, males that are able to remain flashing may be preferred because they are more visible to females. The separation of males may allow females to choose a single partner for mating.

The lantern morphology of P. frontalis females is well known, but their behavior is not well studied. Neither courtship nor mating behavior of females have been observed or recorded.

Although mass sychrony of firefly flashing appears continuous, researchers found that individual flying males flash intermittently - they enter the flashing pattern sychronously. The intermittent sychrony of P. frontalis reinforces evidence that there is a diversity of sychronies in fireflies.

Research in Action

Researchers continue to study mechanisms associated with sychronous flashing. They continue to search for female P. frontalis in order to better understand their courtship and flash communication of this species. Ongoing studies contribute to the long term monitoring of status and trends of P. frontalis populations.

For More Information

  • Copeland, J. and A. Moiseff. 2004. Flash precision at the start of sychrony in Photuris frontalis. Integr. Comp. Biol. 44: 259-263.
  • Faust, L. 2015. Fireflies, Lightening Bugs and Glow-worms! Field Guide to the Fireflies of the Eastern US and Canada. The University of Georgia Press. Athens, GA.
  • Moiseff, A., J. Metcalfe, J. Copeland, and F. Palmieri. 1999. Sychrony in fireflies: Diversity, mechanisms, and model. In A. Roda and P. Snelling (ed.) Bioluminescence nce: Perspectives for the 21st century, pp 573-576. John Wiley and Sons, Chichester.
  • Printable and formatted version of this research summary (PDF 483 KB)

Last updated: May 6, 2015