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MEN AND MOIECULES by John F. Henahan Crown Publishers, Inc,, 1966

CHAPTER 5

THE WEB-BUILDING MACHINE

Seven days a week, at about 5:30 a.m., fifty female spiders in a Syracuse, New York, laboratory begin production of their own thirty-foot skeins of near-invisible thread. Each spider lives in a glass-enclosed aluminum frame about twenty inches square. By 6:00 a.m. she will do what she has to do, create a web that will serve as her home for the day.

Six out of seven days a scientist will remove the sliding glass windows from the aluminum frame, take the spider out and carry the web to a large black box. The web is sprayed carefully with white paint, then photographed. The scientist destroys the web, and the spider is replaced in her glass case to await the morning, when she will build another web.

The Syracuse spiders are sisters to thousands of others who have been weaving their compulsive webs day after day for more than fifteen years under the observant eyes of Dr. Peter N. Witt and his associates. Dr. Witt is an M.D. and pharmacologist at the Upstate Medical Center of the State University of New York. His scientific

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Fig. 12 The female of the species Araneus diadematus moving down the thread of a newly woven web. Peter Witt

charges—representing the females of the species Araneus diadematus—axe also known as cross spiders because of the typical identifying mark they wear on their backs.

As a pharmacologist. Dr. Witt’s main research interests center upon the effects of drugs on human beings. Unfortunately, human beings are not always the best subjects for accurate evaluation of a drug’s effects because of man’s variability, physiologically and psychologically. It is almost impossible to get a pure drug reaction from a human subject because its main effect may be masked by a clutter of subjective responses that have little to do with what the drug was supposed to accomplish.

On the other hand, the response of a spider is more consistent and unalloyed. Because she is instinctively driven to weaving the same type of web every day, any environmental fluctuation is mirrored by a change, ranging from mild to drastic, in the web the spider weaves. In a sense, a drug upsets the spider’s inner environment. It was in 1949 that Dr. Witt first considered the fe-

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male cross spider as a screen for drugs, but since then her webs have sent their spokes and spirals into many unexpected fields, revealing valuable insights into the chemistry of the brain, synthesis of protein in the body, behavioral psychology and even the clicking, whirring world of computer technology.

ASSORTED SPIDER LORE

Early in his spider studies, Dr. Witt found that the female cross spider’s web-building machinery is extremely susceptible to climate and season. (Male spiders are not good web builders at any time.) In the winter, when temperatures are low and days short, fewer webs are woven. To counteract these variables, Dr. Witt has programmed temperature and light conditions in his laboratory so that every day is a summer day for the lady Araneus diadematus.

As noted earlier, the spider unreels about thirty feet of silken thread for a web big enough to fill its roughly twenty-by-twenty-inch aluminum frame. The web thread is so fine that it weighs only about one ten-thousandth of a gram—six days out of seven, that is. For a long time Dr. Witt and his colleagues were puzzled by the webs woven on Monday morning; they were a little larger and heavier than webs woven on the six other days of the week. After considerable head-scratching, note-taking and careful observation of the spider’s habits, the answer was obvious. The scientists worked six days a week, but the spider worked seven. At the end of their normal workday, Dr. Witt or one of his associates always destroyed the spiders web after it was spray-painted and

THE WEB-BUILDING MACHINE    91

photographed. On Sunday night, however, no one came in to destroy the web, so the spider did it herself, by eating it. Apparently this gave her more starting material for Monday’s silk production than she had any other day of the week. The outcome of the finding was that Dr. Witt never uses Monday webs in his studies.

Because he employs so many cross spiders in his research, Dr. Witt has found that it is much easier to raise his own supply than to capture them in the great outdoors. In charge of this spider nursery for several months was Miss Ricarda Baum, then a young student in Syracuse. Miss Baum became so interested in the habits of the cross spider that she has contributed two well-received papers on the subject to the scientific literature.

Among other things, Miss Baum learned that a single egg cocoon yields about 200 minuscule cross spiders. Until they can build their own webs, the spiderlings are fed on fruit flies and water, but by the time they are six weeks old, they are building their own food catchers with the best of them, says Miss Baum.

A young spider weaves a very complex web. As if trying to show off her skills, she packs the web area with tightly spaced spirals running across fine but sturdy radial spokes. As the spider gets older, its web becomes less dazzling, but only slightly less efficient. A great number of thin spirals are replaced by fewer, thick spirals. Because the open areas of the web are wider, only large flies will be caught; but the older web, for all. its structural inadequacies, is better than no web at all.

Dr. Witt believes that the older spiders weave a thicker web because they “feel heavier” and need stronger threads to support their own weight. Strong backing for his belief derives from a series of experiments in which

Fig. 13 Web built by a young cross spider. Peter Witt

he placed small weights on the backs of young spiders. Slowed by the added weight, the young spiders soon fell into the energy-conserving habits of their elders; they wove webs with fewer, thicker strands.

The cross spider sits in the center of her web waiting patiently for an insect to blunder into her gauzelike trap. Because her eyesight is very poor, she must rely on other senses to tell her that her meal has arrived. When the fly thuds against the web, the spider is instantly alert. As the fly struggles to get free, the spider extends her two front legs and tugs at the radial threads to determine which part of the web is vibrating. Then she almost scampers toward the frantic fly, embraces it, and injects a lethal poison with her pincer jaws. In seconds, the fly is dead. With a few deft movements, like a clerk wrapping a package, the spider enshrouds the hapless fly with loops of silk, then carries it back to web center where she can feed at leisure.

So sensitive is the spider to any vibration that she

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nui/.zicallv probes the air with her front legs in response to the sound of a tuning fork. In fact, if the tuning fork touches the web, the spider moves toward the shimmering tine as if it were a real catch. This phenomenon! was first observed in 1880 by the zoologist C. W. Boys. In 1962, a young man with the similar-sounding name of S. M. Bays carried the tuning fork study a little further. While working with Dr. Witt, Bays proved that a tuning fork could be used to teach or condition the spider to respond to different stimuli in different ways. Previously most researchers had suspected that spiders just were not very teachable.

Young Bays placed “sweet” flies that had been treated with sugar in the spider web, then touched the web with a fork vibrating at a given frequency (Ch). As if it were a special delicacy, all spiders bit into the sweetened fly immediately. When Bays placed “bitter” flies, treated with quinine, in the web and then touched the web with a fork that vibrated at a different frequency (C), the reaction was different. The spiders either discarded the fly or wrapped it in a silken package, but in no case did they bite into it as they had done with the sweetened fly.

After the spiders had become throughly familiar with the routine (sweet fly, Q vibration; bitter fly, C vibration) Bays then placed a small glass bead in the web, and touched the web alternately with the two tuning forks. With the Ci fork the spider was so conditioned that she bit into the glass bead, expecting that the familiar vibration meant a tasty fly. With the sounding of the C fork, the spider again did what it had learned to do, discard or enwrap the bead, just as it had done with the bitter flies.

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MEN AND MOLECULES DHUC STUDIES

Soon after he began working with spiders, Dr. Witt realized that the web builders were uncovering subtle aspects of drug action that were not obvious when they were given to man. The drug studies included sedatives, tranquilizers, stimulants and so-called hallucinogenic drugs, among others.

In some cases. Dr. Witt compared normal webs with those built by the same spider when drugged. In others he compared webs built by a large number of drugged spiders. Although the effects were often gross enough to be seen by casual observation, Dr. Witt was not too interested in these qualitative effects. To probe the less obvious effects of drug action, he drew up a set of mathematical measurements which can be applied to enlarged photographs of the various spider webs. Carefully recorded on long data sheets are the angles between the threads that jut out from the hub of the web, thread length, distance between the spirals, overall web size, shape and regularity—the beginnings of a sophisticated computer program set up later on.

The. hallucinogenic drugs have received considerable study inside pharmacological laboratories and great notoriety outside the lab walls because of their dramatically bizarre effects. These range from wild, almost psychotic hallucinations, through visions of monsters, pleasantly technicolored impressions of the surrounding world, new appreciation of paintings and music, to a feeling of being one with God. Otherwise little is known of their specific biochemical effects in the body.

Among the best-known hallucinogenic drugs are mescaline (found in the sacred cactus raised by the Peyote

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Indians of the American Southwest) and psilocybin (derived from certain mushrooms). In human beings their effects seem to be generally the same. The hallucinations are clear evidence that the drugs are affecting the brain, but because many subjects report a feeling of heaviness after taking the drugs, some pharmacologists suspect that they are also hitting other physiological centers that control the motor functions (muscle action, breathing, heartbeat, etc.). However, when the same two drugs are fed to spiders, the webs tell Dr. Witt that the drugs are probably not pharmacological equals at all.

With mescaline, the spiders build smaller webs with less regularity in the spacing of the spirals: a strong indication that the spider’s motor activity has been affected.

It just does not move as efficiently as it might.

When Araneus diadematus was fed psilocybin, the webs were shorter, but the thread was normal width. This could mean that the drug had somehow interfered with the spider’s silk-making glands, which other experiments have shown may be linked to brain activity. Because mescaline apparently had no such effect, its influence on the spider’s chemical machinery must be significantly different, according to Dr. Witt.

Caffeine, found in coffee, and amphetamine, the chief constituent of many weight-reducing drugs, are both stimulants, but their pharmacological effects in spiders show interesting variations. A spider fed a low dose of amphetamine is inspired to build larger webs more frequently than she does when not taking the stimulant. With low doses of caffeine, she weaves her webs on a normal schedule but they come out smaller and much less regular than normal. With larger doses of amphetamine, the stimulant upsets the spider’s web-building drive

Fig. 15 Web of the female cross spider after a dose of the stimulant drug amphetamine. Peter Witt

so drastically that the usually delicately wrought web becomes a chaotic cross patch of misplaced spirals and gaping holes. As a food catcher, the web is utterly useless.

When the cross spider is fed one of the stronger barbiturate sedatives, she drowsily cuts down on web size. It becomes misshapen; spirals and radii are abnormally placed. The tranquilizer chlorpromazine, which normally calms a human being without causing sleepiness, appears to dull the spiders incentive to build webs. Some tran-quilized days, when her usual instincts would prod her to build her web, she ignores the signal. Other days, ön the same drug, she builds, and the web is completely normal.

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Tin«; CIIFMISTUY OF WF.B BUILDING

After more than fifteen years of web watching, Dr. Witt finds himself more and more enmeshed in the biochemical, physiological and behavioral riddles that underlie the daily constructions of Araneus diadematus. How is the silk produced? Is there a molecular signal that tells a spider to start or stop building her web?

Some answers were relatively easy to come by. Several years ago, Dr. Witt found that if the spider does not get her normal intake of flies, she continues to build her daily webs, nudged on by the same instinctive urge found in all other female cross spiders. As the unfed spider builds, she resorts to structural shortcuts to conserve her dwindling thread supply. Gradually the threads thin out, and each new web becomes a little smaller than the last. In the process, the spider loses weight at such a rate that it seems as if she uses her own body constituents to make thread for the web.

Since 1963, Dr. David Peakall, a physical chemist, has been working with Dr. Witt to clarify some of the more sophisticated mysteries of silk production in the spider. Other chemists have shown that the spider’s thread is a fairly simple protein, composed of smaller amino acid building blocks. Of these, alanine is the most prevalent. Although it was obvious that the spider must get the bulk of her alanine supply from her diet, it was not clear how long it took to build the alanine into the protein of the web itself.

Borrowing a technique from nuclear chemistry, Dr. Peakall fed the spider small amounts of alanine tagged with a radioactive carbon atom, the assumption being that the “hot” alanine would eventually be built into

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the thread protein. Using a radiation detector on the silk of the final web, the chemist learned that it took only twelve hours for the alanine to make the complete route from meal to web.

Throughout Dr. Witt’s studies on the effects of drugs on web-building behavior, abundant evidence has accumulated that there must be a link between brain chemistry and the spider’s ability to make more thread protein after it has exhausted its daily supply. Although much of the evidence is circumstantial, Dr. Witt knows that some drugs that stimulate important chemical reactions in the brain induce the spider to build bigger webs containing more protein than usual. Other drugs that inhibit the same aspects of brain chemistry appear to suppress the production of thread protein.

Although there are still many loose ends to be tied together, Drs. Witt and Peakall now suspect that their work points to two biochemical messages that tell .the empty gland to start making protein again: one signal probably emanates from the brain, and the other may be more localized, residing in the silk gland itself.

The spider’s silk gland is a saclike cavity surrounded by a wall of tissue in which the thread protein is synthesized. After emptying the gland, which he can do quickly by reeling the thread onto a small spool, Dr. Peakall finds that tiny globules of protein begin to accumulate in the gland wall, then empty into the gland sac.

As mentioned above, this process can be speeded up or decelerated by certain mental drugs. However, when Dr. Peakall removed the gland from the spider and treated the dissected organ with the same drugs, it reacted as if it were still attached to the spider; some drugs

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made protein move from the gland wall to the gland sac, while others blocked that movement.

Earlier in this chapter it was noted that Dr. Witt compares one web with another by measuring a number of radial angles and other important architectural characteristics of the webs. Since the average weh has about twenty radial spokes crossing thirty spiral turns, the web is composed of 600 smaller sections, any one of which can vary from one web to another. Multiply those 600 measurements by the number of webs woven each day and it is clear that it would take a large staff of technicians and scientists days, or even weeks, just to tabulate the measurements. Interpretation of the results would take even longer.

Although his first fourteen years of web work produced hundreds of pages of useful information about pharmacology and spider behavior, the project took a dramatic leap forward in 1963 when Dr. Witt joined forces with Dr. Charles F. Reed, associate professor of psychology at Temple University. Considerably impressed by the enormous amount of paper work that went into the evaluation of even a single web, Dr. Reed suggested that the project might be streamlined with the help of the IBM computer then making its debut at the Upstate Medical Center. According to Dr. Reed’s plan, certain essential web dimensions (far less than the theoretical 600) would be coded on punch cards, then fed into the computers brain, and stored there for future evaluation. Although he knew little about computer technology at the time. Dr. Witt agreed to give it a try, whereupon the cross spider stepped into the world of automation.

In the beginning, Drs. Witt and Reed were faced with the problem of translating the constituents of a many-

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faceted spider web into the language of the computer. As a model against which all other webs could be judged, Dr. Reed concocted a stripped-down, fictionalized master web that reflected the basic qualities of any real web that the computer would ever encounter.

With this master web lodged firmly in its electronic memory, the computer is ready to be confronted with the structural ingredients of real webs punched neatly on cards: about sixty cards for each web. Almost instantaneously, the machine can now riffle through its memory and spot differences in webs of the same spiders built before and after it has been fed a drug. It can also compare a large number of webs built by many different spiders on the same drug, or note structural abnormalities resulting from injuries to the spider, e.g., the loss of a leg.

As a remote and perhaps ultimate objective of their work, Drs. Witt and Reed hope that some day the computer’s memory will hold a complete record of every variable-physiological, psychological, anatomical, etc.—that goes into the production of the ideal cross spider web. When that day arrives, the scientists expect that the machine will figuratively be in the same condition that a spider is each morning before she‘makes her first movement toward building a web. Primed with all the pertinent information that its memory can hold, the computer will then be asked to do electronically what Araneus diadematus does by instinct. With a push of a button, this properly programmed computer will begin to feed out a catalog of data, radial angles, thread length, distances between spirals, etc., until the dimensions of this machine-made web are all recorded. At that point, scientific, mathematical substance will be accorded an

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ability that previously had been the unique silken reflection of one animals chief function in life.

That ultimate computer web could also be the electronic answer to a question first posed nearly four hundred .years ago by the philosopher Michel de Montaigne:

“Why doth the spider spin her artificial web,

Thick in one place, thin in another,

And now useth one and then another knot,

Except she had an imaginary kind of Deliberate forethought and conclusion?”