The spider’s web

StoryImage( ‘/Images/Story//Auto-img-114548110415082.jpg’, ‘Photo by Dr. Robert A. Hedeen’, ‘The spider's web is much stronger than it looks.’);

Many people classify all creepy crawly animals, including spiders, as insects. Spiders are in a different class of jointed-legged arthropods called the Arachnida. Insects have three divisions of the body where arachnids have only two, and bugs have three pairs of legs while spiders have four pair. No spider has wings. Only a small number of insects are able to produce silk, whereas all spiders have a special silk-manufacturing apparatus within their bodies. The silk is used to construct the web and for other purposes.

In most of our households we become aware of the presence of spiders when we notice cobwebs gathering in out-of-the-way places. Actually, a cobweb is a spider web that has collected dust particles and becomes more visible.

The silk of spiders is secreted by several internal glands. These glands open to the outside via fingerlike projections called spinnerets. There are several different types of silk glands, and they manufacture silk of different qualities; each of which may be used for a specific purpose such as parts of the web, the egg cocoon, and so on. When the silk is exuded from the spinnerets, it is liquid, but once in the air it hardens quickly.

Spider silk, for its size, is among the strongest materials known. It will stretch one-fifth its length before breaking, and its tensile strength exceeds that of steel. One can easily see how large flies and other prey animals are held firmly by spider webs that appear dainty and fragile. The webs of some tropical spiders may be up to 6 feet in diameter and strong enough to hold birds. Natives in Australia sometimes use these large webs as nets, which may hold as much as 3 pounds of fish. But, we must not suppose that the use of spider silk is limited to primitive people. Even today, spider silk is used for the cross hairs and lines of reference in various kinds of optical instruments such as levels, telescopes, and surveying transits. In recent years, however, fine platinum wires and etchings on glass have replaced spider silk to a large extent.

Many of us have seen spiders launch themselves into space and float slowly downward suspended by a thin strand of silk that is attached to the spot from which the jump was made (maybe this antic gave us the idea of bungee jumping).The silk strand is called the dragline. As spiders gallivant from place to place, they play out the dragline from the spinnerets. If the spider scrambles back up the dragline, it catches the strand on one of its legs and rolls it into a ball as it climbs. When it arrives at a safe perch, the balled up dragline may be discarded, or, if the spider is conservative, it may be eaten.

Many years ago, a Frenchman had the brilliant idea that spider silk could be used to make fancy clothing, and in 1710 he made a pair of stockings from spider silk. This so intrigued the Paris Academy of Science that it commissioned the famous French biologist Rene Antoine Ferchaualt de Reaumur to investigate the possibility of using spider silk on a large scale.

Visions of independence of the silk from the orient quickly faded as Reaumur’s investigations proceeded. He found the spiders to be cannibalistic, having a definite fondness for their brothers and sisters. Consequently, spiders used in the experiments had to be isolated in individual holding cages. He found much of the silk produced was not usable, and thousands of spiders were required to produce a single pound of silk. When he presented his findings to the Academy, it was wisely concluded that the amount of labor and expense was too great, so the project was abandoned.

It is has been said that, in general, the female is the more deadly of the species, and this is certainly applicable to spiders. At mating time, the female spider constructs a web and lures a male into it. After mating, the female routinely kills the male and enjoys him for dinner.

All spiders have venom glands attached to two fangs with which they dispatch their prey. Fortunately for us, there are only two species of spiders in the United States whose venom is dangerous to humans. These are the black widow spider and the brown recluse spider or fiddle back spider, and they are quite rare in northern Illinois.

Many have an inborn fear of spiders, and this sometimes develops into a pathological condition known as arachnophobia—as with Miss Muffet eating her curds and whey, when along came a spider and sat down beside her and scared Miss Muffet away.

From the April 19-25, 2006, issue

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