biology zoology blog spider web spiders arachneid


Arachno-Technology: Is there such a thing at all?

My grandfather, who was not a zoologist at all, but a tea merchant, always had a spider in a cage on his desk. Since most species of spiders in temperate countries do not live longer than a year or two, it was not always the same individual that entertained him (and me). Collectively, all these spiders had one thing in common: they all spun silk, which is why spiders are scientifically called Araneae (named after Arachne, who had challenged the goddess Athena to a weaving contest and promptly was turned into a spider as a punishment for such impertinence).

Typically an orb-weaving spider requires no more than 30-50 minutes to construct its web. The spiral sections perpendicular to the next radial line, in their entirety, results in a logarithmic spiral (that’s something for the math buffs), but this doesn’t mean each spider has to be a mathematical genius. It is the result of a genetically programmed simplest and shortest way of doing things and has been shown to work even under weightless conditions of a space shuttle flight, but it does not represent the greatest economy in material or a deliberate thought process. Should the web get damaged, the spider does not repair it, but as is usual for spiders, will ingest the remainder of the web and habitually start rebuilding an entirely new web the next day; ninety per cent of the web material is re-used in this fashion.

Spider silk is birefringent (an optical quality resulting in a double refraction of reflected light: that’s something for the physics buffs). It consists of polypeptides and has a variety of functions: eggs are wrapped in it, draglines are made from it, webs to trap prey are constructed with it, etc. Web fibres may be coated with some sticky material or, in the so-called cribellate spiders, consist of extremely fine fibres combined into wool-like strands without any glue-coating. Web fibres have a rupture tenacity which is higher than that of all natural fibres and higher even than that of man-made fibres. Spider silk combines great strength with a considerable amount of elasticity and tolerates elongations of up to 35%. Experiments with spiders, which were “silked” under laboratory conditions have yielded rupture tenacity figures of 1.8×1010 dynes/cm2 (no doubt that’s something for the materials scientists and technology buffs), which is roughly equivalent to a 0.5 cm thick wire carrying a weight of 16,000 kg. And what is further amazing: the tiny amount of silk-yielding liquid in the spider’s body can yield metre after metre after metre of silk, when you pull it out of the spider’s spinnerets. It’s like a magician pulling hundreds of silk handkerchiefs from his sleeve.

Being able to emulate spider silk properties and to copy the method by which spiders store the raw material in their body and allow it to turn into silk when exposed to air are goals not yet fully reached, but deemed achievable. However, folk-medicinally spider silk has for centuries found uses as a dressing for minor cuts, as earplugs or to stop nose-bleedings. Apparently, a Frenchman by the name of M. Bon in 1710 may even have been the first person to produce stockings and gloves made from the silk of spiders. Spider silk really is an amazing product – and consisting of protein it is even edible. So, the next time you try to clean away the cobwebs in your house and you are hungry, well…

© Dr V.B. Meyer-Rochow and, 2018.
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