The Spiders Web
Part I
by Bill Amos, Vermont, US
Once there was a maiden of ancient Greece, Arachne, who wove a tapestry of such compelling beauty that the goddess Athene, who fancied herself superior to any mortal girl, became furious and so intimidated the unfortunate young woman she attempted to hang herself in repentance. But the rope broke and became a silken thread, while Arachne turned into a spider (an arachnid) and forever after has spun her glistening webs. Many centuries later in Old English, the word to spin was "spinnan," while a person who spun was a "spinder." Subsequently in Middle English the word evolved into "spithre," and the final jump from there to "spider" was easy.
Now that winter is over, Arachne is busy again and fresh spider webs are beginning to appear. Are their makers rushing the season? No, because a few small moths are already fluttering about. It's time to get on with spring and the pursuits of summer.
Spiders are among the world's most fascinating creatures and some of the most familiar. Even if we shun the leggy animals themselves, we are drawn to the geometric precision and dew-frosted beauty of their webs on a sunlit morning. Before long our hillside will be decorated with sparkling gossamer threads woven into the meadow grass and I'll remember, as I always do at this time of year, a bewitching production of Midsummer Night's Dream seen long ago. There is real magic in such a field. There is also the reality of life and sudden death down at the spider's level.
Spiders established their own web sites millions of years before we created analogs with computers. In early amber-encased spider fossils I have seen spinnerets, little nozzles from which threads are spun. No doubt each prehistoric spider species had its own distinct and inherited pattern of web-building as do our spiders today.
Every spider produces silk in several different kinds of glands, each gland responsible for its own protein chemistry. In the arachnid world there are a half-dozen types of spinning glands, not all found in all spiders. The glands are never depleted, because even when web-building is at fever pitch, new proteins (fibroins) are constantly being made. Researchers have found that some spiders can produce up to 2,000 feet of thread continuously, and a mere thousand feet is no big deal for many others. While still in the gland the secretion is a water soluble viscous fluid, but upon being drawn through spinnerets, its molecular arrangement changes and becomes insoluble and ten times more dense than the fluid state. The faster a thread is drawn out, the tighter its molecules cling together and the stronger the strand. Despite being a very fine filament, spider silk is so enormously strong scientists have calculated a strand would have to be fifty miles long before it would break under its own weight. A thread of spider silk has greater tensile strength than steel of the same diameter, at the same time being so elastic it can stretch more than twenty-five percent of its normal length before breaking. (Not every arachnid species produces webbing with such features: some spider silk is more elastic, some less, and the same is true with strength.)
Without thinking much about spider silk, we nevertheless are aware of some of its remarkable properties. It never dries out, doesn't decay from bacterial action, and won't become covered with mold. Under sheltered conditions, a web may last a lot longer than the spider itself. We know that some threads are sticky, others are not. They can be fine and delicate, or very strong and even quite thick. Each type is important to a spider 's needs.
It's easy to think of spinnerets as simple nozzles, which they may have been in ancestral spiders, but they are much more than that today. Modern spiders possess complicated valves and muscles and interior plumbing. Certain species have such long spinnerets they almost seem like appendages. I used to keep large tarantulas and whenever they moved, their spinnerets waved about, more or less coordinated with their leg movements. Even the smallest spiders have muscles that direct spinnerets to one side or another, up or down, separately or all together. If you study a spider as it spins a complicated web, you will see that the animal doesn't have to reposition its body in order for silk to come out at an angle. Its spinnerets busily point this way and that, sometimes coordinated, sometimes working independently, all with a common purpose.
Silk is not ejected under pressure, but must be drawn out by external means by a force such as wind or gravity. A drag line, for example, is first attached to a surface, then the spider walks or jumps away, or drops into the air where it dangles on its life-line. It may further lower itself, regulating speed and distance, and can be made to plummet all the way to the ground if you disturb its mid-air reverie. Or it may turn around and scramble back to its former perch, gathering in silk and consuming it as it goes. Spiders recycle this valuable protein product and may eat webbing under a variety of conditions. Arachnologists have found that digestion is so quick, the molecular building blocks are ready for new silk production in half an hour.
Is spider silk the same as the silk from moths that has such great commercial value? Yes and no. Chemists have found that its fibroin composition is similar, but not identical to moth larva fibroin. Spider silk tends to swell and curl, is more water-repellent, and varies in thickness and composition (depending not only upon different spiders, but upon what a spider is doing at a given moment), so its use to us is negligible. Furthermore, raising spiders for silk production is out of the question. Spiders are predators and cannibals, and not only would have to be fed multitudes of living insects, but would have to be kept separated from one another. Not much profit for an entrepreneur in that business! Moth silk, on the other hand is homogeneous in chemistry and thickness, and the larvae spinning it can be crowded together in trays and fed cultivated mulberry leaves. The Chinese discovered this thousands of years ago when the silk industry was born.
If not used for fabric, spider silk has been important to indigenous people of the Pacific world, Asia, and Australia. Natives have used webbing for personal ornamentation, have woven water-shedding rain gear and constructed kites, while others may make nets and fishing line out of spider silk. Before modern technology in the Western World allowed manufacture of extremely fine metallic and synthetic threads possessing both strength and durability, spider silk was used for centering cross hairs and measuring reticles in optical instruments. If you have such an instrument from the last century, there is a good chance the lines you see suspended are spider silk. Surveyors of the past were glad of this, for if something happened to their transit cross hairs, all they had to do was seek the nearest spider web, select a few strands, and install them in their instruments.
Five minutes ago a familiar spider descended from the ceiling and dangled in front of my computer screen. Since she was heading for the keyboard, I deflected the thread to where she could fall gently to the floor. She keeps her part of my study cleaner than I do at my level and I appreciate her efforts. And now with spring here at last, I look forward to admiring once again those shimmering webs that grace the landscape.
Comments to the author Bill Amos welcomed.
© William H. Amos 1998
Author's note: This essay was written in the spring two years ago. For readers who wish to learn more about authoritative published sources from which some of the above information was gleaned, contact the author I will be glad to send a short bibliography of important publications.
Editor's note: Bill Amos' earlier Micscape articles on spiders are -
Part II of 'The Spiders Web' will be published in December 1998 Micscape.
Published in November 1998 Micscape Magazine.
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