and the Cobwebs of Myth about Them

Number 31 August 1, 1983

LayPeople often wonder why their tax spiders, could find “no obvious justifica- dollars should support science that tion for so dkproportionate, so wide- seems to have no relevance to everyday spread, so illogical a horror, which may problems. Why, for example, should welf have been an obstacle to serious they give money to people to study arachnology. ”1 Savory believed that the spiders or scorpions? What makes fear of spiders is complex and no single arachnology, the study of these crea- explanation can cover all cases. Like tures, relevant? The importance of many other phobias, however, it can arachnology became apparent to me often be traced to early chfldhood. Per- many years ago. As I lay on a mound haps a chdd, warned about poisonous during an Army maneuver in Texas, I and ferocious , transferred the felt a shooting pain move down my left fear to spiders. Or maybe the child was arm toward my chest. I thought I was once frightened by a . As Savory having a heart attack. It turned out to be notes, “Few creatures are more likely a scorpion sting. Many years later, I was than a house spider to appear unexpect- reminded of the relevance of arachnol- edly and give a shock to a child.”1 ogy while living on an asparagus farm Anthropologist Marvin Harris, Uni- with my son in New Jersey. A small child versit y of Florida, Gainesville, agrees was bitten by a black widow spider in an that the fear is learned in childhood. outhouse. Fortunately, the child sur- Since some spiders can be dangerous, he vived. says, it makes “good cultural sense” to Apart from the relevance of such ob- teach chddren to stay away from them. scure subjects as arachnology, scientists The fear need not be permanent. Hu- have another problem. We seem to en- mans can learn to love spiders and let joy what we do too much. The average them walk on their arms without fear.z person can’t comprehend why anyone Edward O. Wilson, Harvard Univer- would enjoy working with all those sity, Cambridge, Massachusetts, be- “things” they fear most: spiders, iieves the phobia is rooted in our genes. corpses, diseases, etc. Scientists need to “Wh~le there is a strong predisposition to be reminded that our lay friends have develop phobias against spiders, snakes, not acquired the knowledge that over- closed places and cliffs-the ancient comes common myth and superstition. perils of humankind—there is no predis- Like snakes and wolves, spiders have re- position whatever to form phobias ceived a bum rap. Perhaps this essay will against knives, electric sockets and au- indicate why. tomobiles, which are far more danger- Few animals are more universally ous in modem society.”z feared than spiders, Why people fear Whatever the root of human fear of them has never been precisely ex- spiders, these creatures have held a cer- plained. The late Theodore H. Savory, a tain fascination as well. Spiders figure in British author of textbooks about ancient myths. In 8 AD, the Roman poet

237 Ovid told the story of Arachne, a peas- legs allow them to step quickly over rug- ant girl who challenged the goddess ged temain. Chitinous exoskeletons Athena to a weaving contest. The wom- make them unappetizing to many preda- en produced cloth of equal beauty, but tors. And venoms, in tiny amounts, par- the jealous Athena punished Arachne, alyze their insect prey. A spider caught changing her into a creature that spends by the leg can leave it behind and grow its liie weaving silk: a spiders another at next molt .s Thomas Eisner Spiders belong to the phylum Arthro- and Scott Camazine, Cornell University, pods, which they share with insects and Ithaca, New York, recently made an crustaceans.q Arachnida, the subdivi- amazing dkcovery. When a spider is sion or class of spiders belong stung in the leg by a venomous insect, to, is named after Arachne. It afso in- such as a wasp or honeybee, it lets go of cludes worpions, mites, and ticks. LAe the leg within seconds, before the venom most of their fellow , spiders spreads through its body,g are air-breathing invertebrates. Their In addition to these adaptations, the bodies have two ditilons, four pairs of spider’s use of sifk is one of its tools for legs, and no antennae.s Unlike other survival. According to F. Lucas, Shirley arachnids, all spiders spin silk, though Institute, a fiber-research organization not alf build webs.b in England, spider silk is stronger than Most spiders have eight eyes, though nylon. It is also finer, lighter, and more some have fewer. Most spiders tenacious than silk from the common secrete venom, although only about silkworm, Bornbyx men”.lo All silks are 12 species are harmful to humans. Their made of a protein called fibroin. Spiders main diet is insects. They eat by first in- produce it in up to six sets of glands in jecting the victim with venom and treat- their abdomens. They secrete it through ing it with digestive enzymes that dis- valve-like openings, or spinnerets, solve its inner organs. Then they drink which help regulate the flow. 1I the resulting nutritive broth. Spiders Spiders’ silk is the basis for one of their hatch from eggs and change little as they most prominent survival tactics: the mature, except in size. They usually web. About half of all spider species molt (shed their chttinous outer skin) build them, Peter N. Witt, an arachnolo- seven or eight times before maturing. gist-pharrnacologist retired from the Females are often larger than males, and North Carolina Department of Human sometimes devour males after mating.b Resources, points out in a recent news There are about 35,000 known species story that webs are great energy savers of spiders.b Some scholars, including for spiders. Web-builders do not have to Norman 1. Platnick, American Museum roam in search of prey. They simply wait of Natural History, New York, befieve for insects to get caught in the web. that at least 100,000 species inhabh the Buildlng a web costs a spider the energy Earth.7 During the course of their 400 equivalent of two or three insects; on an million-year history, spiders have average day, a spider may catch 30. And adapted to almost every climate and many spiders recycle their webs, They every ecological niche, Accord~ng to eat all or part of the silk at the end of the Paul A. Zahl, National Geographic day and use its amino acids in their next Society, Washington, DC, they exist in web.lz great variety among the trees, bushes, According to Witt and colleagues, and grasses of every forest in the world. spiders build their webs according to in- Spiders are found from the tropics to the structions encoded in their genes. They Arctic. And some species, though they can build the day they hatch, though breathe air, live underwater.a most produce their fwst web after two Spiders clearly have efficient survival weeks, 13 W hlle each species spins a mechanisms, since they are so numerous characteristic web, individuals vary it in and widespread. Newly hatched spiders minor ways, making each web almost as are as mobile and fierce as adults. Eight distinctive as a fingerprint. And even

238 though a spiderling rarely gets to meet its field Hills, Michigan, thw modest maze parents, its web closely resembles of tangled threads is attached to sur- theirs. 12 rounding structures in a haphazard- Different species of spiders build dif- looking way. lb Although the cobweb is ferent webs which vary greatly in their considered a nuisance by people who en- degree of complexity, One of the struc- counter it, Anne Moreton, an amateur turally simpler webs is the single line web arachnologist from Powhaton, Vir~la, of the tropical spider l%oroncidia studo. has found that it helps the spider catch The web consists of a strand or two of more than 1,000 , mosquitoes, and silk stretched across a path or stream. moths a year. 17 Observing in a forest near Yotoco, A more ambitious web is called the Vane, Colombia, WMiam G. Eberhard, sheet web. It’s a thick plane of hundreds University of Costa Rica, Costa Rica, of fine silk filaments placed very close found that insects move more slowly together. Some spiders crawl atop the when flying near the web, and end up be- mesh. Others, such as Linyphia triangu- ing caught by their feet. He concluded lmis, hang from beneath with specially that thk flying pattern indicates the pres- adapted toothed claws. ThK spider ex- ence of a chemical attractant, or phero- tends thin filaments from the web to mone, in the silk, 14 structures high above it. Insects into Another simple web, the cobweb, is the filaments and fall onto the web sur- spun by the common house spider face, where the spider can pull them Achaemnea tepidariomm. The cobweb through from underneath. lb (See Figure gets its name from the Old Englishword 1.) cob, for spider. 15 According to a 1964 Some spiders, such as the 1,300 spe- book by Laura B. Lougee, then with the cies in the fam~les Dipluridae and Cranbrook Institute of Science, Bloom- Agelenidae, weave their snares into the

F@ne 1t Linyphia trrhnguiaris hangs underneath its horimntal sheet web and pulls trapped prey through.

(From: The Worfd of Spiders, Bi+stowe,WS, William Collins Sons& Co. Ltd.)

239 shape of a flaring tube with a rim extend- web. 19 The word orb comes from the ing into a sheet web. At the apex of the Latin or-his, for ring, circle, or dkk.zo tube is the spider’s retreat, which maybe Savory and many naturalists before him buned underground or below vegeta- have found that in orb webs, dry silk fila- tion. lb One type of funnel weaver, the ments radiate from a central point like European water spider Argyoneta spokes of a wheel, while sticky threads aquatica, constructs an airtight silk cross over them in a spiral that ends near dome beneath the surface of slow-mov- the center.zl (See Figure 3.) The orb ing waters. It carries bubbles of air to its web of an adult can have up to 60 radii, web nest, where it lives, mates, lays its 80 spiral turns, and more than 1,500 in- eggs, and raises its young. la tersections, 19 One group of spiders builds the tr- Orb webs are so finely made that they iangle web which, unlike sheet and fun- are almost invisible, except when nel webs, Lougee notes, is characterized drenched with rain or dew. But, Witt by the careful positioning of each strand. notes, they are strong, efficient prey- The result is a strong, triangle-shaped catching devices. They stop fast-flying silk net anchored with a long thread to a insects and foif their attempts to escape. nearby plant, wall, or other structure. They support the weight of the spider, its One species, Hyptiotes ca vatus, anchors mates, and sometimes several accumu- the main thread to tree trunks and sits at lated prey.zz the junction disguised as a bud. It holds Witt and his colleagues have also the anchoring thread taut, and when found that orb-weavers take about half prey strikes the web, lets slack out of the an hour each day to build the web. Some line, further entangling the victim. lb work in the hours before dawn, others in (See Figure 2.) the early evening. One species, Zygiella About 2,500 species build the most .r-nokzta, keeps a 60 degree slice of the beautiful and complex of webs, the orb web free of sticky spirals, where it leaves

FIsure 2: The triangle web of ffyptio~er cavatus.

(From: The Wodd ./ Spid.r$. Bridowe, WS, William Collins Sons & Co. Ltd.)

240 FfgrJre 3: Left: the orb web of Zygiel/a x-notata has a free sector with a signaf thread Ieadkg to the spider’s retreat, Right: the orb web of the cross spider Amneu$ diadematu$.

(From: Biology of Spiders. Foelix RF, Harward University Press.)

a single dry filament leadhg to its re- radial thread, orienting itself toward the treat. 13(See Figure 3. ) Some use special quadrant sending the strongest nbra- combs on their feet to knit dry spirals in- tion. If the spider feels vibrations that to loops of woolly lace. 12 are too strong, it may deem the captive Some species weave white, conspicu- too big or lively to handle. In this case, ous slashes, crosses, or ovals across their the spider cuts the threads surrounding orb webs. Until recently, thk puzzled the captive and lets it fall to the ground. arachnologists. Webs, after all, are sup- It does the same if a twig or other in- posed to be invisible, to trick insects into animate object fails into the web. It can flying into them. The mystery was solved determine the size and position of a twig in January 1983 by Eisner and Stephen by plucking the threads and “reading” Nowicki, Cornell. They reported that the reverberations. Of course, spiders these markers, called stabilimenta, serve also use these methods to find edible as detour signs for birds. Otherwise, prey, which they bite and wrap in silk to birds would fly through a web and de- eat or store.% molish it. They found that webs with Webs, besides helping individual stabilimenta have a 60 percent chance of spiders catch food, serve in some species surviving untif noon. Webs without as communal homes for up to several these markers have only an eight percent hundred thousand spiders. About 30 chance.~ species build communal webs in tropical The orb web is more than a trap. It and subtropical climates, where prey is compensates for the poor vision some superabundant. J. Wesley Burgess, Uni- spiders have. Diemut K~arner and Fned- versity of California, Davis, found a web rich G. Barth, Zoology Institute, Johann of the species gregalis near Wolfgang Goethe University, Frankfurt, Guadalajara in Mexico that covered the Federal Republic of Germany, have upper three-quarters of a 60-foot mimo- found that when prey strikes an orb web, sa tree. Most communal webs, however, the spider mns to the hub and feels each are smaller. The spiders collaborate in

241 the capture of prey, and in the Guadala- mth his, apparently enchanting her. in jara web, they attack insects much still other species, the male plays it larger than any that the five millimeter- safe—he presents his mate with a gift of Iong spiders could disable alone.zs neatly packaged prey to satisfy her hun- A less spectacular but still remarkable ger.m example of coexistence was found in the Not all spiders rely on webs alone US in 1982 by George W. Uetz and Wen- to catch food. An ogre-faced spider dy Allen, University of Cincinnati, Ohio. found in the tropics, for example, has Large numbers of Nuctenea sclopetan”a, developed a way of capturing ants from a solitary orb-weaver, were found at- colonies that combines web and hunting taching webs together near the River- techniques. The spider places itself front Coliseum Sports Arena in Cincin- above an ant trail and spins a small, nati, where floodlights had attracted a sticky web which it holds between its great deal of prey. Tolerance went only legs. When an ant crawls by, the spider so far, however. The spiders refused to lowers the net, gluing the ant by the share food with each other, and fiercely head. The captor then lifts the ant and defended their individual webs from in- wraps it in silk. The Robinsons have ob- truders.zb served ogre-faced spiders trapping many Webs and their manipulation can also ants this way while avoiding the poten- help male spiders survive the often dan- tially dangerous retaliation of other gerous rite of mating. The male, if mis- ants.sl taken for prey by the much larger fe- Some spiders do not use webs at all to male, faces certain death. Michael H. catch prey. According to Zahl, trap- Robinson and Barbara Robinson, Smith- door spiders, of which there are about sonian Tropical Research Institute, 750 species, dig retreats six to eight Balboa, Canal Zone, have studied spider inches into the ground, waterproofing mating in orb-weavers. They found that the dirt with saliva and lining it with soft some males, when they arrive at a fe- silk. These spiders construct hinged, male’s web, pluck the threads in a cer- carefully camouflaged doors at the sur- tain way to advertise their intentions. face. When threatened, they hold the Others attach a thread of their own to doors tightly shut. The trap-door spiders her web and pluck that. If the female are timid, rarely leaving their burrows behaves menacingly as she runs onto the and attacking only prey that comes thread, the male may cut the line and within easy reach. Even while attacking, run away, or try to tire her out by run- many keep the trapdoor open with their ning away while letting out line. 27 In hind legs, for an easy retreat.fJ some species, the male uses a few Jumping spiders, of which there are strands of silk to immobilize the female. about 4,000 species, pounce on prey In a few, males wait until the females eat from a distance of up to 40 times their something else before they get too body Iength.s Able to see up to 12 inches close.za away, they possess the best vision among Courtship survival strategies don’t rely spiders. Jumping spiders often live in exclusively on the spider’s skill and silk. close competition for resources within a Lyn M. Forster, Otago Museum, Dun- habitat. Forster has observed them per- edin, New Zealand, found that in some forming complex ritualistic dances to species of hunting spiders, which are communicate with each other about more sharp-eyed than web-builders, the claiming territory and attacking male dances before the female. She ap- prey .29,32 pears to watch as he zigzags across her Some spiders have adopted a chame- field of vision, displaying his brightly leon-like survival tactic, according to colored body markings and waving his Zahl. Some members of the 3,0W spe- Iegs.zg In other species, the male rushes cies of crab spiders change color to pink, up to the female and strokes her legs white, or yellow to match the flowers

242 they sit in to wait for prey. The camou- hausted. It was important to play the flage prevents the spiders from being right tune for the victim. Otherwise, it seen by btrds or other predators. When was believed, the symptoms could wors- prey comes near, the spiders snap their en. Alf that remains today of the taran- legs shut on it and inject an extra-potent tati is the lively dance, the tarantella, venom. These smalf spiders attack wasps and an old German saying, “bitten by and bumblebees that are large by com- tarantula,” meaning crazy.~ parison.B Since the time of the tarantati, the cul- Probably the most famous spider of all prit has been found to be not the taran- is the tarantula. In North America, what tula, but the black widow spider, Latro- is commonly called the tarantula be- dectus.~ Black widows get their name longs to the family Theraphosidae. It has from the habit of females of consuming a leg span of up to five inches. It lives males after mating. The ten or so species longer than most spiders—sometimes up of black widow inhabit warm to moder- to 30 years—and takes nearly a decade ate climates throughout the world. The to grow to full size. Its bhe is rarely venom of a mature female, drop for worse than a wasp or bee sting, and it drop, is 14 times as potent as rattlesnake shies away from humans, usually biting venom. Venom from males is weak by only if provoked. Many species live in comparison, and poses no serious the dry, sun-baked regions of the Ameri- danger to humans.~,J5 can Southwest and Mexico.6 Herbert E. Longenecker and col- South American tarantulas live in the leagues, Rockefeller University, New temperate and tropical zones of that York, found that female black widow continent. Their bodies alone can be up venom makes the body’s nerve endings to six inches long, and they can catch release their supply of neurotransmit- and eat smalf birds.J3 ters, the chemicals that carry messages The European tarantula, about an across the spaces between nerves.~ inch long, belongs to the family Lycosi- Resulting symptoms are those exhibited dae and lives in the regions surrounding by the tarantati. the Mediterranean. It is also known as Mareti& and Lebez say that intense the wolf spider. It has been studied by pain is the most prominent feature. In- Zvonimir MaretiE and Drago Lebez, terestingly enough, the pain is somewhat University of Ljubljana, Yugoslavia. alleviated by physical exertion. A They have found that the European 23-year-old farmer, bitten in a field in tarantula’s bite is usually no worse than a Yugoslavia, bicycled nearly 12 and a half bee sting. In sensitive persons, however, miles over bad roads in severe heat to it can cause redness, swelling, and the the nearest hospital. He reported that eventual death of large patches of tissue the pain lessened when he cycled, but surrounding the bite.% whenever he stopped to rest, it flared up Mareti6 and Lebez found that in the quickly. Three hours after he was bitten, fifteenth to seventeenth centuries, this he was diagnosed as in good condhion. species was believed responsible for In another case, a victim who was inac- epidemics of spider bites in towns tive could not even stand up three hours throughout southern Europe. Bitten after the bite.~ people ran through towns, alternately Bite victims usually have a flushed laughhg and crying, and performing face; swollen, tearful eyes; and a look of unusual, sometimes vulgar, acts. The apprehension and pain.ss Though wri- “tarantati,” as they came to be called, OUS, bites are rarely fatal, Zahl reports. suffered pain, sweating, convulsions, Hospitals use antivenoms to treat vic- paralysis, delirium, and death.% tims. Only four or five of the 1,000 The cure was dancing. Victims Americans bhten each year dle.8 danced to lively tunes, sometimes for MaretiE and Lebez list four species of days, until they fell to the ground, ex- black widow as common to the Ameri-

243 cas. The most venomous and wide- extracts.~ While the side effects of the spread is L. mactuns, which has a black venom must be treated along with the body with a red hourglass shape on the original ailments, these encouraging re- underside of its abdomen. It hangs up- sults may soon be surpassed as methods side down in silk nests in low bushes and of collecting and purifying black widow grass, and can be found in trash heaps venom improve .38-@ and outhouses. Its relative, L. variolus, Although some spiders are harmful, looks similar, but builds its webs in trees. they are greatly outnumbered by the It lives mostly in the western areas of thousands of species that, directfy or in- North America. Black with a gray or directly, benefit mankind. Spiders are brown abdomen, L. geometn”cus lives in increasingly recognized as a valuable tropical cities. And a native to the scrub natural means of controlling caterpil- pine of Florida, L. bishopi, has an lars, aphids, mites, and grasshoppers in orange-red body and legs.s’f apple and peach orchards; in soybean, The brown recluse spider, Loxosce[es cotton, and alfalfa fields; and in avocado reclusa, is another spider native to North and citrus groves.qt M. Nyffeler and America whose bite is harmful to hu- G. Benz, Swiss Federal Institute of mans. In a letter to Science in 1957, J.A. Technology, Zurich, report that spiders Atkins, C.W. Wingo, and W.A. Sode- have been introduced into rice fields in man, University of Missouri, Columbia, the Peopfe’s Republic of China and first described the symptoms of the Lox- other Asian countries to help control the osceles bite: the skin surrounding the more than 800 species of rice pests,qz bite becomes painful, raised, and And around the world, spiders quietly scabrous; turns black and dry; and even- and consistently keep insect populations tually sloughs off.sT A scar remains that in balance—annually destroying 100 takes several weeks to heaLsG South times their number in insects. 17 American species cause larger and more There are about 800 arachnologists in painful lesions than other vaneties.ss the world, according to Jonathan Reis- Ironically, the spider survival tactic kind, Department of Zoology, Univer- that people fear most may provide a way sity of Florida, Gainesville, Florida to enhance human life. Black widow 32601, president of the American venom is being used in laboratory ani- Arachnological Association. His address mals to study the effects of botulism and is also the present address of the associa- progressive muscular dystrophy. One tion, which publishes the Journal of characteristic of both afflictions is that Arachno[ogy.qs nerve endings are prevented from releas- Reiskind’s figure includes amateur ing neurotransmitters, resulting in paral- arachnologists, who contribute a great ysis. This is exactly the opposite effect of deal to the field, but excludes acarolo- black widow venom, which forces gists, who study mites and ticks.qo The nerves to release neurotransmitters. number of professional arachnologists P. Stem and K. Valjevac, University of worldwide “is probably 300 to 400 at Sarajevo, Yugoslavia, and S. Gomez, most, ” says Herbert W. Levi, Harvard National Hospital, Institute of Neurol- University Museum of Comparative Zo- ogy, London, England, have found that ology.~ Furthermore, many arachnolo- rats with botulism live longer when gists combine their study with other treated with extracts from black widow fields, such as biochemistry, ecology, or spider glands. If they survive, they physiology,’ls recover more quickly with the treat- Arachnologists are sometimes ento- ment.38,39 mologists as well, or are closely associat- Rats with progressive muscufar dys- ed with them. Many belong to entomo- trophy, Stem and Valjevac found, retain logical societies such as the Entomologi- muscle control longer and recover much cal Society of America, 4603 Calvert more quickly when treated with gland Road, College Park, Maryland 20740,

244 which publishes the Annals of the Ento- remote part of the world living examples mological Society of A merica. Arachno- of the fittle animals that spin from their logical work appears often in entomol- bodies threads of silk of different ogy journals. kinds.. and with these threads construct The British Arachnological Society, snares of surprising regularity for trap- 42 Lakeland Park, Keswick, Cumbria ping their prey, the presence of such CA12 4AT, England, publishes the Bul- marvelous animals would attract gener- letin of the British Amchnologica[ Soci- al attention, and we would make long ety. And most arachnologists belong to journeys to see them.”ls the Centre International de Documenta- Perhaps there is too much in the mod- tion Arachnologique (CIDA), Labora- em world to distract us from nature’s ev- toire de Zoologie (arthropods), 61 rue eryday marvels. But whether you are fas- Buffon, F-75005 Pans, France. cinated by spiders or simply afraid of ISF covers the Annals of the Ento- them for no apparent reason at all, re- mological Society of A men”ca both in member that they are indeed relevant. If Current Contents@’/Life Sciences and the aesthetic value of understanding Current Contents/Agriculture, Biology spiders does not appeal to your sense of & Environmental Sciences (C@/ practicality, remember that some little AB&ES). The Journal of Amchno[ogy is known research in arachnology might covered in CC/AB&ES, as are the Jour- one day open up an important pathway nal of the New York Entomological So- to solving many practical human prob- ciety and the Florida Entomologist. All lems. of these journals are covered in Science Citation Index@ and in Automatic Sub- ject Citation Alert (ASCA” ). ***** Naturalist John Henry Comstock noted in 1912, “If spiders did not occur My thanks to Linda Cooper and Len’ in our fauna, and if the keepers of a zoo- Perkins for their he[p in the prepamtion logical garden were to bring from some of this essay. ~’rm1s1

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