National Geographic : 1962 Jul
Two luminous segments mark the male Photinus pallens, enlarged six times at right. Though bigger, the female (left) has smaller eyes and only one lighted segment. Adrena lin, given for study purposes, makes the lamps glow continuously. To find a mate, the male flashes a court ing code as he wings through the night. The female, who rarely flies, blinks her response while remaining at rest. male may repeat his signal several times, the female reacting each time with her own; thus he establishes range and closes in. Finally he finds her perch and courtship begins. The capture of living specimens was sim plicity itself. One had merely to hold a jar or widemouthed bottle under the light of any perched firefly, then with a quick brush of the hand sweep the insect or mating pair into the container. Once in the lidded container, the captives would flash frantically and try to get out. Before long, the crowded bottle would be giving off nearly as much light as an old fashioned kerosene lantern (page 51). A screen-topped terrarium on the desk of my room temporarily lodged two small Anolis lizards I had caught in the Sibley rock garden. One night I dumped a bottle full of fireflies in the terrarium to observe how the insects and the reptiles got along. Half an hour later I noticed that one of the lizards had snapped up a firefly and was holding it high, half swallowed (page 55). The firefly's lantern end, protruding from the reptile's mouth, glowed continuously, exactly like the insect I saw snagged in a spider's web on an earlier evening. Light Without Fire or Heat On another occasion I injected several fireflies with a tiny drop of adrenalin, using a fine-gauge hypodermic needle. Adrenalin has long been known to stimulate the chem istry of firefly luminescence. Almost immedi ately the lamps of the injected fireflies flamed up, maintaining a steady brilliance for an hour or more until, apparently, the drug's effect wore off. With a 20-power magnifier I examined the light organ of one of these specimens. The outer layer was transparent. I looked deeper within, at the layer of cells that comprised the generator where biochemical materials reacted to produce light. There I saw micro scopic eddies of churning radiance and whorls KODACHROMEI) NATIONAL GEOGRAPHICSOCIETY of brilliant incandescence, suggestive of the shimmering surface of a white-hot coal. Yet here was no fire and virtually no heat, only intense radiance-the phenomenon of bio luminescence.* This strange cold light, produced not only by fireflies but also by many bacteria, proto zoa, fungi, coelenterates, crustacea, and fish, is at present the subject of research in at least half a dozen major laboratories. Its dupli cation for man's use might someday lead to the development of a light-emitting bulb or wall panel in which no precious energy would be wasted as heat. Being so readily available for study, fire flies, or lightning bugs, and glowworms (actu ally neither flies, bugs, nor worms but beetles of the families Lampyridae and Elateridae) have supplied much of our understanding of biologically produced light. We know, for example, that a firefly's lan tern is fueled by a substance called luciferin (from Latin meaning "light bearing") that oxidizes in reaction to luciferase, an enzyme produced in the insect's body. Both of these * The author, long interested in the subject, has written other articles on bioluminescence for the NATIONAL GEO GRAPHIC: "Puerto Rico's Bay of Fire," July, 1960; "Night Life in the Gulf Stream," March, 1954; and "Fishing in the Whirlpool of Charybdis," November, 1953.