A Bright and Shining Bug

A firefly by any other name would shine as brightly. They are sometimes called lightning bugs or glowworms. But fireflies aren’t flies at all. They are beetles.

When an insect (or any living organism) is described scientifically, it’s given a scientific name composed of two parts, genus and species. The names use Greek or Latin roots and usually describe aspects or features of the organism.

Members of the firefly genus have had some clearly admiring descriptive species names given to them, like Lamprocera, which means brilliant and wax-colored, Microphotus and Macrolampis, big and little light, Pyrogaster which is fire stomach and, the perennial favorite, Pyropyga, which means fire rump or fire butt.

All known firefly larvae have photic organs and produce light. The behavioral function of the light has received considerable speculation with several theories proposed. The most generally accepted idea is that firefly larvae use luminescence as a warning signal, communicating to potential predators that they taste bad. Their glow indicates the presence of defensive chemicals in their bodies. Glowworm larvae increase the intensity and frequency of their glow when disturbed, giving merit to the theory.

Not all firefly species are bioluminescent as adults, but when they are, one or both sexes use a species-specific flash pattern to attract a member of the opposite sex. Not as specific as Morse code, perhaps, but the bioluminescent signals can be a continuous glow, discrete single flashes, or "flash-trains" with multi-pulsed flashes.

In most species of North American fireflies, during a certain time of night, males fly about flashing their species-specific flash pattern, often near ponds, streams, marshes or even depressions or ditches that retain moisture longer then surrounding areas. Females of the same species tend to be perched on vegetation, usually near the ground. If a flashing male catches a female's fancy, she’ll respond at a fixed time delay after his last flash. A short flash dialogue follows as he locates her position and descends to meet - and mate.

Non-lighting fireflies are left to locate mates the old fashioned way - through pheromones, church groups or introductions by friends.

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 the signal components that, to bugs, are quite sexy.

Too much light interferes with the firefly’s luminous signals, making it harder for fireflies of many species to locate mates. Also, many firefly species are active only during a certain period of the evening. They determine what time of night they will flash by the intensity of ambient light, so there aren’t many fireflies flashing on clear nights when the moon is full.

There are several theories, none involving a switch, on how fireflies control the "on" and "off" of their photic organs. It’s thought to be a chemical reaction, but the exact mechanism hasn’t been worked out.

The "Oxygen Control Theory" proposes that fireflies turn their light on and off 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 that release a messenger molecule in the photic organ, initiating activation of the chemical reaction. No matter how they turn themselves on and off, the production of light is very efficient, with very little heat being given off as wasted energy.

Thank goodness. Lightning bugs that got as hot as light bulbs would be an unwelcome addition to the party. It might be uncomfortable for the bug, too.

Although isolated sightings of luminous fireflies have occasionally been reported from the western U.S., fireflies that glow aren’t usually found west of Kansas. No one knows why- it’s another unsolved mystery of lightning bugs, like why they got a photic organ while people have to rely on cell phones.