National Geographic : 1971 Aug
National Geographic, August 1971 attachments, all engineered with mathemati cal precision. Another spider of the same species was busy spinning in a duplicate frame alongside. Ear lier, this spider had demonstrated its ability to weave a regular, symmetrical web. But now it had been fed a droplet of sugar water containing "speed"-dexedrine sulphate. Mrs. Scarboro sprayed the two webs with quick-drying white paint to make the threads stand out clearly. Then I saw the strange angles and illogical backtrackings in the weaving of the drugged spider. Laboratory measurements would record angles, affixment points, number of spokes, and other data for computer analysis. Experimenters have found that different drugs-caffeine, mescaline, and LSD, for example-produce characteristic variations in a spider's web. Some human mental illnesses seem to be accompanied by biochemical changes in the blood or tissue fluids. Could such fluids, ad ministered to a spider, measurably influence its weaving patterns? If so, spiders might perhaps be able to tell us-through the vary ing patterns of their webs-the particular illness affecting a patient, or even his progress under psychiatric treatment. This is only one potential of the experiments, which are still in exploratory stages. Spider Responds to Strange Vibrations Researchers are on more certain ground in the field of normal spider behavior. Dr. Peter N. Witt, distinguished research pharmacolo gist and director of spider investigations at the North Carolina laboratory, repeated an experiment for me. He tapped a tuning fork and touched it gently to a web tended by an Argiope. In stantly she rushed across the strands and furiously assaulted the quivering metal. With her legs she pulled a silken stream from her spinnerets, and in seconds the cold prongs were bound tight. "A slave to innate behavior patterns," said Dr. Witt. "Spiders can't alter their reactions, can't discern or evaluate subtle changes in external influences. The vibration of a tuning fork or a thrashing insect-it's all the same to them." Perhaps even more instinct-bound than the orb-web spiders are two enemies I encoun tered while spider hunting with young Nicho las Eltz, who was then helping scientists at the American Museum of Natural History's Southwestern Research Station near Portal, Arizona. Nicky's terrariums already held a dozen tarantulas. Battle's Outcome Rarely Varies The sun had set and the desert was losing its daytime heat as I drove slowly down a twisting roadway across rolling terrain covered with sage and cactus. Nicky perched on the hood, a flashlight in one hand and a wide-mouthed jar in the other. He had ex plained why at dusk in summer tarantulas leave their holes to forage or to find mates. "After dark it's cooler, and they're also safe from pompilid wasps." Abruptly Nicky signaled me to stop. He jumped off the hood, ran ahead, and suddenly dropped to his knees on the macadam. In the headlight glare I saw him scoop up something with his collecting jar. A moment later he was back with his prize-a tarantula with a body thicker than my thumb, a leg spread of five inches, and two formidable black fangs. We bagged six more specimens within an hour, then returned to the research station. Earlier that day we had netted a metallic blue, topaz-winged pompilid wasp and re leased it in a glass terrarium partly filled with desert sand. Now we dumped one of our new ly captured tarantulas in with the wasp. "First they'll wrestle," Nicky predicted, "but the outcome is usually the same." I watched the unequal struggle, the keen eyed wasp circling like a gladiator and sizing up the near-sighted spider, which could as sume only a threatening attitude until touched. The wasp quickly broke through the spider's guard. With a lightning-swift jab, she sank her stinger into the tarantula between its third and fourth leg sockets. (Continued on page 208) If it moves, it's probably food. The fishing spider, here feeding on a freshly caught minnow, devours insects, tadpoles, and even other spiders with equal gusto. Like all spiders, he must inject the victim with digestive enzymes before he dines, turning soft tissues into a soup that he can draw into his body. Venom for killing prey occurs in all but two small groups of spiders. DOLOMEDESVITTATUS,2 1/4 TIMESLIFE-SIZE, EASTERNU.S.; BY HARRYELLIS © N.G.S.