Hundreds of drifting fireflies wander and flicker through a dark, misty nighttime forest.
Fireflies (family Lampyridae) produce cold light through bioluminescence: an enzyme called luciferase catalyzes the reaction of luciferin with oxygen inside light-producing cells called photocytes, converting chemical energy almost entirely into light with very little heat. Each species flashes in a distinct rhythm and color pattern that acts as a mating signal, letting males and females identify compatible partners in the dark. In a few remarkable species, such as Photinus carolinus in the Great Smoky Mountains, thousands of individuals flash in synchrony, producing waves of light that sweep through the forest. Damp forests and meadows near water are ideal habitats because firefly larvae need moist soil and abundant prey, and the still night air combined with ground fog helps flashes travel and remain visible over longer distances.