National Geographic : 1971 Jul
Smoldering "headlight" and gleaming "windows" give a name to the railroad worm of Central and South America. Inch-and-a -half-long Phrixothrix tiemanni is one of the few insects known to emit red light. Fare for biologists rather than for gourmets, a platter of shrimp and fish glows eerily. To study lumi nous bacteria, scientists inoculated the raw seafood with Photobacterium phosphoreum, which quickly multi plied by the billion. Related single celled organisms often glow naturally in rotting wood. It would take 50 trillion such bacteria, each about 1/20,000th of an inch across, to generate one candlepower of light. Photograph without a camera: Western banded glowworms (Zarhipis integripennis,shown 21/2 times life-size) writhe on a sheet of color film, making their own portrait. This species and the related railroad worm, each equipped with 11 pairs of body lanterns, turn on their garish flares only when aroused, as if to warn or bluff intruders. of mucus (page 55). Upon arriving at one end of the tube, the larva would fold back on itself and slide in the opposite direction. A dozen or more exceedingly fine silken threads held the tube fast to the ledge. I counted 18 fishing lines hanging down from this larval case, each strung with pearls of deadly glue. When a victim becomes entangled, the worm bites a hole in the tube, seizes the line with mandibles and minute ventral bristles, and draws it up by successive waves of the body muscles. The worm bites its prey to quiet its thrashing, then eats it. Glowworms hatch 22 days after the adult female deposits about 130 eggs on a dark or shady moist surface, I remembered from a re port published by Dr. A. M. Richards. The larval stage is the feeding and growing por tion of the insect's life cycle and lasts for al most a year, the length of the period probably depending on the abundance of food. The larva next changes into a pupa the size of a large grain of rice. The pupal case hangs from ceiling or ledge by one silky thread, remaining thus for about two weeks. Finally the adult emerges-a fragile long legged fly. The female measures about half an inch from head to tail with a slightly longer wingspread; the male is a bit smaller. Male Waits Patiently for Emerging Mate Ian, who had been searching the cave for adults, suddenly called to me in a stage whis per. "Something you should see," he said as I waded to his side shin-deep in water. "The male of the species waiting for a mate!" There in a crack in the cave wall was a mosquitolike insect, absolutely still, clinging to a pupal case. A female heavy with eggs bulged within the case. "It's not rare," Ian added, "to see several males waiting for one adult female to emerge. Sometimes after mating and egg laying, the weakened adults get caught in the feeding lines, by which they're drawn up to be eaten by the larvae." Adults are seldom seen by the casual visitor to Waitomo, not only because the observer is too far away, but also because the mature insects are so small. Furthermore, their days are numbered-probably no more than three or four, even if they succeed in avoiding those lethal pearls. By now the intensity of our beams had caused most of the grotto's larvae to extin guish their lights, and it was time to go.