Download the audio of On Six Legs: MP3, WMV.
Fascination with Flickering Fireflies Part of Hot Summer Nights
From the Rockies to the Atlantic and from the Gulf Coast to the Canadian prairies, one of the real treats of hot summer nights is the flashing of fireflies. Few insects have managed to capture the admiration of humans as pervasively as these pyrotechnists of the six-legged world have.
Generally known as either fireflies or lightningbugs, these light-producing insects are scientifically neither flies nor bugs; they are beetles. Fireflies are known as soft-winged beetles, reflecting that the outer wings of these insects are not as rigid as are the shell-like outer wings of many other beetles. But beetles they are and technically should not be called bugs or flies.
While names commonly used for these insects might not meet the approval of entomologists, the biology of the insect certainly does. The common names firefly and lightningbug reflect the ability of the insect to produce light, and that process has fascinated scientists and the general population alike. Insect flashers truly attract attention!
So what is going on with these insects that Paul Fleishman described in his book, "Joyful Noise" as "Six-legged scribblers of vanishing messages?" The insects are using flashing to attract mates. Each species of firefly has a distinctive type of flash. The light produced by a species is of a distinct color, either yellow, blue-green or amber. In addition, the flashing pattern of each species is specific. The pattern is a bit like Morse code, a series of dots and dashes of light.
The process works this way. On warm to hot summer nights from late May until September as darkness settles on the earth, male fireflies begin to take flight from the vegetation where they spend daylight hours. The male begins aerial forays in and over the type of vegetation in which the species lives. While on the wing, the male produces specific light flashes, say dot-dash-dot. One purpose of the flashing is to produce a courtship signal. This behavior was captured in a line from the Mills Brothers hit song about fireflies from the 1950s. The song, called "Glowworm," has the line, "glow for the female of the species."
Female fireflies generally sit on the vegetation and observe the male fireflies doing their aerial acrobatic light shows. Females will respond with the flashing pattern specific to their species. When this happens, the two insects communicate with each other using neon hieroglyphics until a deal is struck. At which point the male lands and the fireflies mate.
The light is produced by a chemical reaction in photocyte cells in the abdomen of the firefly. The reaction involves two chemicals called luciferin and luciferase and is somewhat like a fire in that oxygen is needed for light production. In the firefly, when the chemicals are exposed to oxygen carried by ATP the light is produced. When oxygen is removed the light goes out. So by using nitric oxide to control the availability of oxygen to the photocytes, the firefly is able to produce the characteristic flashing patterns we have come to associate with their aerial displays.
In a practical example of how the system works consider the following. When a firefly gets smashed, say on the windshield of a car, the light glows constantly. The reason is that fireflies can no longer control the flow of oxygen to the photocytes. Under these circumstances, the reaction will continue until the luciferin and the luciferase are destroyed in much the same way that a fire in the presence of oxygen will continue to burn until the fuel is consumed.
When we are watching fireflies flashing over forest and meadow on hot summer nights, most of us are not thinking of the amazing chemical reaction that is producing the light. Or that it is a cold light with very little heat produced. Or that the insects are really beetles, not flies or bugs. What we should be thinking is that one of the most spectacular sights in nature is in our own backyard on a hot summer night!