Synchronous firefly
A woodland beetle of the southern Appalachians whose males flash together in waves on June nights, one of the few in North America that blink in unison.
Synchronous firefly at a glance
Photinus carolinus sin-KRUH-nus FYRE-fly; Photinus carolinus is foh-TY-nus kair-oh-LY-nus
- Type
- Invertebrate · beetle
- Diet
- Carnivore
- Size
- An adult is only about half an inch long (about 1 cm), roughly the size of a grain of rice or a pencil eraser.
- Lifespan
- The whole life takes about two years, but almost all of that is spent as a larva in the soil. The flashing adults live only about two to three weeks.
- Conservation
- IUCN Least Concern (assessed 2020). Its display still depends on dark, undeveloped forest, and viewing at the Great Smoky Mountains is limited by a lottery to protect it.
Eats snails, slugs, earthworms (as a larva)
For most of its two-year life a firefly is a larva living in damp soil and leaf litter, where it hunts snails, slugs, and worms. The glowing adults you see in June barely eat at all. They live only a couple of weeks, just long enough to flash, find a mate, and lay eggs.
Should you worry?
None. Fireflies do not bite or sting people and are not poisonous to touch. The best way to enjoy them is to keep flashlights off or dimmed and covered with red film, since bright white light drowns out their signals and confuses them.
For a couple of weeks in early June, a stretch of forest in the Great Smoky Mountains does something almost nowhere else does: thousands of fireflies flash at the same time. Each male beetle repeats a set pattern: five to eight quick flashes, then about eight seconds of darkness, then again. When the whole hillside falls into rhythm, waves of light seem to roll through the trees. The light itself is a cold light. Nearly all the energy becomes glow and almost none becomes heat, so the beetle can carry a lantern and never burn.
The flashing adult is the short, showy end of a long, hidden life. A synchronous firefly spends about two years as a larva in damp soil and leaf litter, hunting snails, slugs, and worms on the forest floor. The glowing beetle it finally becomes is only about half an inch long, the size of a grain of rice, and it barely eats at all. It has two or three weeks to flash, find a mate, and lay eggs, and then it is done.
The show only happens in the dark, which is why it is easy to wreck by accident. Bright white light drowns out the fireflies’ signals and confuses them, so visitors keep flashlights off or dimmed under red film, and the Great Smoky Mountains hands out viewing spots at Elkmont by lottery to keep the crowds and the headlights down. The fireflies do not bite or sting, and they are not poisonous to touch. The only care they need is a dark night.
Did you know?
- Each male flashes a set pattern: five to eight quick flashes, then about eight seconds of darkness, then the pattern again. When thousands do it together, waves of light seem to ripple across the dark forest.
- A firefly's glow is a "cold light." Almost all of the energy becomes light with hardly any heat, so the beetle never burns, unlike a light bulb.
- This is not the only firefly that flashes in unison. Congaree in South Carolina has its own synchronous species, a different beetle called Photuris frontalis, so the two parks each protect their own light show.
Common questions
Do fireflies bite or sting?
No. They are harmless beetles. You can let one walk on your hand.
Why do the fireflies flash together?
Males flash in the same rhythm to signal females. When many of them join in, the flashes line up into waves of light.
How do fireflies make light?
Chemicals inside their bodies mix to make a cold glow that gives off light but almost no heat.
When and where can I see them?
Late May into June in the southern Appalachians. At Great Smoky Mountains you need a lottery ticket to visit Elkmont on viewing nights.
Are fireflies disappearing?
This species is listed as Least Concern, but bright lights and lost forest hurt fireflies everywhere, so parks protect their dark viewing spots.