The Top Arachilia ”

he earth is literally crawling with But in recent years this view has come spiders. Some 30,000 species have in for considerable revision. New breeds been tallied to date, and the guess is of arachnologists have emerged—arach- that half as many more still await nologist-cum-behaviorist and arach- discovery.■ Yet, despite their abundance nologist-cum-ecologist—specialists con and their ubiquity, spiders—members of a cerned with what spiders do, and where class of organisms called arachnids that, and how. And out of this pair of new also includes ticks, mites, scorpions and research foci, among others, is coming f M H H daddy longlegs—were long presumed to evidence that has all but demolished the be little more than evolutionary relics. supposition of spider irrelevance. Far The prevailing notion was that spiders from being trivial, spiders are now were ecologically irrelevant, vestigial believed not only to be critical con threads in the web of life. tributors to the balance of countless the Top "When researchers looked in the past," terrestrial ecosystems but to be a says arachnid ecologist Susan Riechert of superlative form of invertebrate life on the University of Tennessee, "they con earth as well. To Peter N. Witt, a 30-year cluded that spiders were ineffective veteran of spider investigation, the com Arachilia ” regulators of the insect populations plexity of spiders' neurally programmed because they failed to increase their own behavior, as reflected in the orb or numbers in response to increasing prey cartwheel web, is the ultimate expression populations,". With that verdict of in of superior, highly integrated in significance, it was hardly surprising that vertebrate brain function. arachnologists studying the spider king Not all spiders build webs. Of the 30 to dom traditionally confined their pursuits 50 families known, perhaps' half don't. largely to the realm of systematics or Many are insect trackers, vagrant preda Spider experiments. Behaviorist Peter M. Witt, work ing with Araneus diadematus, finds that taxonomy, the business of identifying tors. One such, the tarantula, is the most, spider webschange with the spider's age and that creatures according to family, genus, primitive spider of all. Spiders, nonethe drugs have an impact. The web at the far right, reflect species, etc. Trifling significance was less, conjure in most minds the image of the influence, of amphetamines, is compared to the attached to research efforts inquiring into intricate webs. adjacent normal web. the biodynamics of spider behavior or Different species weave different kinds Peter Witt their role in ecological systems. of webs. But generally the architecture Social spiders.SShe Mexican groufpiolerant spiders-, Mallos g re galls (left)^|||s®en mássé in a laboratory web (top right). The weScompl#x spider, Metepelra spinipßs, build! orb webs (above) in close proximity tp'.®ih othert ABoximity grid (right), applied to other species as well as^spiders^uggesM prinCiples ability. J. W. ípi rgeés^^hn^ll^.ury the spider never missed a day building. highly refined statistical techniques. Fits one of three basic blueprints: the important functions in the head]. In man, spirals. (Witt never seeks to stress spiders to Over the years Witt has gotten so good sheet web (a two-dimensional structure the number of nerve cells in the brain far Poor vision seems to go along with web death in his experiments. "I love these at identifying webs that, if any of his showing no symmetry, the threads outstrips that seen elsewhere in the spinning; spiders need their webs to creatures, and that would break my crisscrossing each other in apparently nervous system. In spiders, cephalization extend their sensory and capture range. charges moves from one part of the heart," he says.) helter-skelter fashion), the space web (a is even more concentrated than in man." To show the importance of the web to laboratory to another, he can tell at a Even among members of the same scattered, three-dimensional, multilevel Among spiders, orb webbers, of which spider survival, Witt performed a series of glance where it has taken up residence. He species—or the same litter—no two arrangement) or the geometric orb (the some 6,000 species are known, may have near-starvation studies on his research can also tell, just by looking, how old the spiders build to exactly the same orb familiar two-dimensional cartwheel). The the most highly developed brain function, favorite, Amneus diadema!us, the orb spider is; web cha rae te r is t ips are age design. "Each web is tike a person's face, ultimate web—the most material- and since the orb web is the most patterned, spinning corn spider commonly found in dependent. fingerprint or signature—unique," Witt labor-efficient and most effective in the most preprogammed expression of an New England and many parts of Europe. Of the 6,000 or so orb-web species that explains, having established this snaring prey—is the orb web, says Witt, a exquisitely exacting blueprint written in When deprived of food, A. diadematus does ha vie been identified, all, follow pretty singularity only after ten years of pains- behavioral scientist who heads the North the genes. not spin a smaller web as a means of much the same behavioral pattern: each :aking analysis of web construction. Carolina Department of Mental Health There is no generation-to-generation conserving its protein resources. ,Np;r builds a new web every day—a task that The task required the identification of Research in Raleigh. teaching of web spinning among spiders; does it build a larger-than-normal struc generally takes less than a half hour to 1,000 distinct points on the web (where A. newborn spiderlings don't see their ture as a last-ditch effort to increase complete. The silk for web manufacture Uadematus fuses thread to thread), Cephalization and economy parents. For it to survive, a spider must capture capability. Instead, in Witt's emanates from sp inn erets, valveiike measurement of thread angles and dis Web spinning, which calls for many spin a letter-perfect web from the outset. experiments, every morning A. dmianutus structures on the posterior portion of the ntegrated behavioral functions, bespeaks There is, however, some flex in the continued to build its web to exactly the tances between spirals, quantification of spider's abdomen. Most spiders can spin a highly developed central nervous sys program, some plasticity, as Witt dis same dimensions as it had prior to the shape (e.g., whether the web was longer several kinds and thicknesses of silk^ aii tem. In fact, if brain volume and neuronal covered when he took a spider out of ||s days of famine. To obtain the necessary :han wider and by how much), tallying of Rafiy a^eyén j||some cases. Not all of it density are keys, Witt contends, then web midway through eoi^truc^6P<? protein for silk, it borrowed protein from :urning points (where the spiral changes goes for web spinning. Some may go for spiders are probably the most advanced drained it of its silk and then replaced it. itself—losing weight in the process. Even direction between radials), evaluation of the production of a drag line to provide pecies on the invertebrate evolutionary The spider immediately picked up where when it had shrunk to half its size, it still 1 entricity (how symmetrical the web is), the spider with transportation, for wrap «dder. "As animal species grow more it had left off. But it adapted to its own spun a full-size web, but with a wider 1 he development of a complex computer ping prey, for lining a burrow or shelter or mplex," Witt observes, "there is in- material depletion by finishing the web mesh. Only after six weeks of starvation 1 •rogram (which in itself took three years fer en(flosing egg sacs in cocoons. Í: a sed cephalization Iconcentration of with abnormally wide spacing between did web size begin to shrink. Even then 1o elaborate) and the application of some The spiders build their webs modularlv. web—not the next day, but 48 hours later. aerially, through a process called balloon man zoologist who was affectionately This was demonstrated by in ing. At the appropriate time, depending known as "the spider web man." Peters collaboration with David Peakall, a on atmospheric conditions, the now- was gager ft© make a movie about web biochemist, then at Cornell University. arachnophobic spiderlings each dangle a building. But he was stymied by the fact In their experiments, Peakall and Witt thread of silk for capture by the wind, and that his spiders built their webs at 4 A.M., fed A. diademalus radioactively tagged off they soar. Alighting wherever the when ambient light for filmmaking was alanine, the principal amino acid in web breeze deposits them, the spiders actively lacking. protein, prompting the spiders to weave a seek out sites to spin their first, flawless, Peters asked Witt to se.e iiT Ihe could "hot" web. The original spiders were then orb webs. (Ballooning is a treacherous come up with a drug that would shift web removed and "cold" spiders placed on the business, which probably explains why so building activity to a later, more conven hub in their stead. Forty-eight hours later many more eggs are produced by wind- ient time. Witt gave various stimulants the new spiders, having eaten the webs to scattered species than by species whose and sedatives a try. All failed to alter the which they had been moved, were spin spiderlings disperse along the ground.) time of construction, but they did elicit ning the ingested, radioactive alanine into ff spiders are such aggressive, some some unexpected behavioral changes.

Load more