National Geographic : 1971 Jul
National Geographic, July 1971 The Christmas lights also registered on the oscilloscope. The frequency and duration of their blinking was determined and altered by Dr. Polunin, so that the effect on the fireflies could be measured. He demonstrated that, to a limited extent, a firefly will follow the rhythm of the flashing bulbs. Dr. and Mrs. John Buck of the National Institutes of Health, who have done research on bioluminescence in Thailand and New Guinea with aid from the National Geo graphic Society, have made a number of interesting observations about fireflies. They have found that only the male occupants of a firefly tree are involved in synchronous flash ing. Females are there, or may soon be at tracted, but their dimmer flashes do not coin cide with those of the rhythmic males. From movies and photometric records of Pteroptyx in Thailand, the Bucks have shown that the insects' ability to flash together is much more precise than it would be if each firefly had to see another's flash before pro ducing his own. Somehow, each insect seems able to match his flash with that of neighbor ing fireflies. In related experiments, Dr. and Mrs. Buck have shown that blindfolded human beings have a similar ability to tap telegraph keys in unison. The Bucks suggest that large congre gations of synchronously flashing male fire flies attract mate-seeking females just as a theater marquee arrests the human eye with huge numbers of bulbs and insistent rhythms. "Glowworms" Are Not Worms at All The precise life cycle of Pteroptyx remains unknown. But on the basis of well-established facts about North American fireflies, one would assume that the eggs are laid on or near the ground, and that these hatch into larvae which, for a year or so, gorge on minute snails. The larvae turn into pupae, then hatch into adults. The latter probably do not feed. Their main activity is to join their fellows in one of those flashing trees to mate and, within a few weeks, to die. All fireflies are beetles, members of the order Coleoptera, and most glowworms actually beetle larvae-also belong to this order. Fireflies are members of the Lampyri dae family, while the spectacular railroad worm belongs to the Phengodidae (page 62).* Among these and other beetle families, several dozen genera exhibit luminescence, both in the mature and immature stages. There is yet another light-producing insect-the New Zea land glowworm-that is neither worm nor beetle but a cousin of the common housefly. Regardless of its source, the biological production of heatless light is perhaps the most efficient energy-emission system known. Scientists study how certain cells and tis sues produce the critical light-making com pounds, how these interacting substances are governed and related one to another, how drugs, enzymes, oxygen, pressure, tempera ture affect light-producing reactions. Physio logical principles underlying these problems involve the metabolic building blocks com mon to all living things. Ancient Mariners Awed by "Sea Fire" Robert Boyle, a pioneer in the laboratory study of bioluminescence, showed in 1667 that the light of luminous bacteria and fungi goes out if the organisms are deprived of oxygen. Raphael Dubois demonstrated in 1887 the existence of a specific compound he called luciferin, which interacts with an en zyme, luciferase, and oxygen to produce light. The late American physiologist Professor E. Newton Harvey spent a lifetime investi gating light production by living organisms. He and his students showed that there are many kinds of luciferin and luciferase-in fact, a different substance and enzyme for nearly every luminous species-which upon interacting undergo minute changes and release energy in the visible part of the spec trum, but without appreciable heat. Firefly luminescence involves energy-laden molecules of adenosine triphosphate-ATP -a compound found in all living cells.f Recent experiments have indicated that can cerous cells contain less ATP than healthy ones, and thus produce a less intense light when combined with extract from firefly lanterns. Scientists believe that firefly chemi cals may someday become important tools in the detection of the disease. The ancients, too, were impressed with bio luminescence. Nearly 2,300 years ago Aris totle wrote: ". . . some things, though they are not in their nature fire nor any species of fire, *A National Geographic Society research grant sup ported Darwin L. Tiemann's study of this fascinating creature, which he described in "Nature's Toy Train, the Railroad Worm" in the July 1970 GEOGRAPHIC. tSee Frederick G. Vosburgh's "Torchbearers of the Twilight," in the May 1951 GEOGRAPHIC.