The firefly produces light through an efficient chemical reaction using special photic organs, with very little heat given off as wasted energy. One or both sexes use species-specific flash patterns to attract members of the opposite sex (though not all firefly species are bioluminescent as adults).

These signals range from a continuous glow, to discrete single flashes, to "flash-trains" composed of multi-pulsed flashes. In most North American species of firefly (including Photuris pennsylvanica), the males fly about flashing their species-specific flash pattern, while females are typically perched on vegetation near the ground.

When a flashing male attracts a female, she responds at a fixed time delay after the male's last flash. A short flash dialogue may ensue between the fireflies as the male firefly locates her position and descends to mate.