From The Firefly Files


How do fireflies produce light?

Fireflies produce light via a chemical reaction consisting of Luciferin (a substrate) combined with Luciferase (an enzyme), ATP (adenosine triphosphate) and oxygen. When these components are added, light is produced. McElroy (1951) described the reaction as:

There are several theories on how fireflies control the “on” and “off” of their photic organs. However, the exact mechanism(s) has yet to be worked out. The “Oxygen Control Theory” is based on the firefly turning on and off its light by controlling the oxygen supply to the photic organ for use in the chemical reaction. The “Neural Activation Theory” hypothesizes that fireflies have neural control of structures called “tracheal end cells” which, upon stimulation, may release a messenger molecule in the photic organ which initiates the activation of the chemical reaction. Regardless of how fireflies control the “on” and “off” of their bioluminescence, the production of light in the above manner is very efficient, with very little heat being given off as wasted energy. Imagine what would happen if the beetle got as warm as a light bulb!

Why do fireflies glow?

All known firefly larvae have photic organs and produce light. The behavioral function of the larval light has received considerable speculation and several plausible theories have been proposed (Lloyd 1971; Sivinski 1981). However, the most generally accepted hypothesis is firefly larvae use their luminescence as a warning signal (aposematism) that communicates to potential predators that they taste bad because they have defensive chemicals in their bodies. These larvae also increase both the intensity and frequency of their glow when disturbed (Sivinski 1981). An experimental study of whether mice could learn to avoid glowing objects by associating a larval-type glow with a bad tasting object further supports the aposematism hypothesis (Underwood et al., 1997).

Not all firefly species are bioluminescent as adults, but of the species that are, one or both sexes use a species specific flash pattern to attract a member of the opposite sex (Carlson et al., 1982; Lloyd 1971; Williams 1917). These bioluminescent signals can take the form of anything from a continuous glow, to discrete single flashes, to”flash-trains” composed of multi-pulsed flashes (Lloyd 1966; Williams 1917).

In most species of North American fireflies, during a certain time of night, males fly about flashing their species specific flash pattern. Females of the same species tend to be perched on vegetation, usually near the ground, and if a flashing male catches a female’s fancy, she will respond at a fixed time delay after the last male’s flash. A short flash dialogue may ensue between the male and female as the male locates her position and descends to mate (McDermott 1958). The courtship patterns of Japanese fireflies seem to show many variations of this type of communication system, as well as courtship behaviors that include pheromones as well as photic signals (Ohba 1983). It is generally assumed that most non-luminous North American fireflies locate mates through the use of pheromones.

Aspects of male flash patterns are also thought to be affected by sexual selection. Female fireflies have been shown to prefer certain characteristics of a male’s photic signal (such as increased flash rate) and respond preferentially to males that possess these “sexy” signal components (Branham and Greenfield 1996).