In the first few weeks of June, visitors to the Great Smoky Mountains of eastern Tennessee, United States, are treated to a rare natural spectacle — thousands of fireflies blinking in unison like strings of Christmas lights hanging in the night air. The species responsible for the performance is Photinus carolinus, one of the few in the world that is known to synchronize their flash patterns, within a tenth of a second of each other.

Fireflies are actually winged beetles that use bioluminescence during twilight to attract mates. The light is produced in their lower abdomen where the insects combine the chemical luciferin with the enzyme luciferase in the presence of magnesium ions and oxygen to produce light. Fireflies are extremely efficient at what they do. Nearly hundred percent of the energy produced in the chemical reaction is converted to light. For comparison, an incandescent light bulb converts only 10% of the energy into light with the rest 90% given off as heat. Because of the absence of heat, the light produced by fireflies are called “cold light”.

Photo credit: Ryan Atkins/Flickr