Every year between late May and mid-June, synchronous fireflies gather into a sparkling, rhythmic light show in the forests of Great Smoky Mountains National Park. As part of their two-week mating display, the female lightning bugs synchronize their flashes with nearby males so that every few seconds waves of light ripple through the woods. Of at least 19 species of fireflies that live in Great Smoky Mountains National Park, Photinus carolinus is the only species with synchronous light displays, but they can also be found in Allegheny National Forest in Pennsylvania and Congaree National Park in South Carolina. Other species of synchronous fireflies are particularly prevalent in Southeast Asia.