August 2014 Featured Paper

"A New Type of Synchronized Flashing in a North American Firefly" by Andrew Moiseff and Jonathan Copeland. Journal of Insect Behavior, Vol. 13, No. 4, 2000.
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Synchrony in fireflies is described as concurrent rhythmic group flashing. In other words, fireflies are flashing at the same time, and repeatedly, at a set time interval. The best known synchronous firefly is the Southeast Asian firefly Pteroptyx malaccae, where the males perch in a tree and flash synchronously for hours. While there were many reports of synchrony in North American fireflies (some species like Photinus pyralis and Photinus macdermotti will flash in synchrony only rarely), it wasn’t until the discovery of Photinus carolinus that a true synchronous firefly was discovered. This paper reports the existence of a second North American synchronous firefly — Photuris frontalis.

In a large population of fireflies, random flashing can easily be mistaken for synchrony. Not only is the timing of each firefly critical, but all the fireflies must flash in unison, and the synchronous flashing must continue throughout the fireflies’ activity period. To ensure that the researchers were observing true synchrony, they recorded the flashes on video and statistically analyzed the results.

Photuris frontalis is a forest species. Males begin flashing about 20 minutes after sunset and flash over a period of 30 to 60 minutes. The flash duration is about a quarter of a second and is repeated every 0.8 to 0.9 seconds. In the study site located in Savannah, Georgia, the forest floor is relatively flat with few bushes or shrubs between the trees, making the observation of large numbers of fireflies possible. Still, a firefly could only be observed for up to 20 meters before it was lost to view. Consequently fireflies were also studied in the lab where they could be monitored continuously.

Two questions are explored in this study:

  1. Is Photuris frontalis a true synchronous firefly?
  2. Is the synchronous flash of an individual firefly continuous; i.e., does each firefly continue to flash throughout the synchronous period without a break in its flashing?

When observed from a distance, Photuris frontalis seemed to flash synchronously in discrete groups. One group of fireflies appeared to flash for up to 20 seconds, then stop. In a different area of the forest another group would begin flashing. These distinct flashing groups would appear and disappear throughout the evening.

When observed more closely, pairs of fireflies behaved differently. They would fly towards each other while flashing synchronously, flash a few times in close proximity, then fly apart, still flashing synchronously. They do not appear to form flash pairs.

The video recording data revealed that all the flashes occurred within less than a tenth of a second of each other, a timing that appears synchronous to the human eye.

In the lab, two fireflies were placed in boxes with a barrier between them, preventing their seeing each other. These fireflies flashed independently. When the barrier was removed, they began to flash in synchrony.

In the field, the researchers found it difficult to determine whether an individual firefly flashed non-stop during the synchronous period, whether its flashing stopped and restarted intermittently, or if it stopped flashing completely. The researchers could not follow an individual firefly for more than five to eight cycles before it was lost to view as it flew in an irregular path around the trees. To determine if each firefly flashed continuously throughout the synchronous period, six fireflies were set up in the lab and their flashes recorded. The results showed that each firefly might flash for a period of time, stop flashing for a cycle or two, and then resume synchronous flashing. Although an individual firefly might stop and start, the overall effect of the group was of continuous flashing.

The synchrony of Photuris frontalis differs from that of the Southeast Asian firefly Pteroptyx malaccae in a couple of ways. P. malaccae flash while perched in a tree; Photuris frontalis flash while in flight. As a group, the synchronous flashing of P. malaccae lasts for hours, while that of P. frontalis lasts only minutes, stops, and then resumes. This means that Photuris frontalis must synchronize with each other many times during the night while Pteroptyx malaccae need synchronize only once. In both species, a male may drop out of the group for one or two flashes before rejoining, but a Pteroptyx male may flash hundreds of times before pausing while Photuris frontalis may pause after only a few flashes.

Photuris frontalis is a true synchronous firefly — its flashes are precisely timed and are synchronous throughout its active period. P. frontalis is the only member of the Photuris fireflies to display synchronous flashing.


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