Synchronous fireflies (Photinus carolinus) are one of at least 19 species of fireflies that live in Great Smoky Mountains National Park. They are the only species in America whose individuals can synchronize their flashing light patterns.
Fireflies (also called lightning bugs) are beetles. They take from one to two years to mature from larvae, but will live as adults for only about 21 days. While in the larval stage, the insects feed on snails and smaller insects. Once they transform into their adult form, they do not eat.
Most species produce a greenish-yellow light; one species has a bluish light. The males fly and flash and the usually stationary females respond with a flash. Peak flashing for synchronous fireflies in the park is normally within a two-week period in late May to mid-June.
No one is sure why the fireflies flash synchronously. Competition between males may be one reason: they all want to be the first to flash. Or perhaps if the males all flash together they have a better chance of being noticed, and the females can make better comparisons.
The fireflies do not always flash in unison. They may flash in waves across hillsides, and at other times will flash randomly. Synchrony occurs in short bursts that end with abrupt periods of darkness.
As the season begins, a few insects start flashing, then more join the display as the days pass. They reach a "peak" when the greatest number of insects are displaying. After peak, the numbers gradually decline each day until the mating season is over. Since 1993, this peak date has occurred at various times from the third week of May to the third week in June.
During the two week long mating season, the quality of individual nightly displays can be affected by environmental factors. On misty, drippy evenings following rainfall, the insects may not readily display. Cool temperatures, below 50º Fahrenheit, will also shut down the display for the night. Moon phase has been observed to affect the timing of nightly displays-on nights with a bright moon, the insects may begin flashing a bit later than usual.