The amazing toughness of spider silk
Spider silk strands are more uniform in diameter that most man-made artifacts. Per same diameter and weight, spider silk is 5 times stronger than steel and tougher than Kevlar.
It is one of the most elastic substances on earth. It does not break even if stretched to 4 times the original length.
Spider silk is extremely lightweight. The length of a silk strand weighing only 18 oz (500 grams) can circle the Earth.
Spider silk does not become brittle even at minus 40 degrees Celsius and it is water resistant.
How a spider produces silk
Spider silk is made of a protein called fibroin and is secreted from up to 7 glands in the spider’s abdomen.
The spider exerts abdominal pressure to force the silk out and varies the rate of flow by using muscles in the ducts and spigots at the extremities of the glands. Each gland produces a different type of silk intended for distinct purposes – wrapping prey, constructing the web, issuing sperm drops, and manufacturing the egg sac.
Spider silk production from 7 glands.
Img Structural Design in Nature by Professor M Neil James, Plymouth University.
Spider with strongest silk
The toughest biological material ever studied is the spider silk produced by the orb-weaver Darwin’s bark spider (Caerostris darwini – see the Bing images). Its silk fibers have a toughness of up 13956 Btu (IT)/foot³ (520 MJ/m3 [megajoule per cubic meter]). That is ten times tougher than a similarly-sized piece of Kevlar.
Note, there is a difference between strength and toughness. Spider silk is strong than steel but not as strong as Kevlar. It is, however, tougher than both.
The tiny Darwin’s bark spider – the females grow to only 0.9 in (20 mm) long, the males only a third of that – was discovered only in 2009 in Madagascar and is named after Charles Darwin, according to Wikipedia, which also reports:
The web of Darwin’s bark spider is remarkable in that it is not only the longest spanning web ever observed, but is among the largest orb webs ever seen, at an area of up to 30 sq ft (2.8 square metres).
Darwin’s bark spider. More on Encyclopedia of Life.
Spiders are not the only insects to produce silk. Centipedes, millipedes, and mites, among others, do it too.
The golden orb silk cape
Textile expert Simon Peers and American designer Nicholas Godley chose the golden orb spider (Nephila madagascariensis) of Madagascar to create a 13 foot (4 m) long spider silk cape. The golden orb was chosen because its silk is naturally gold in color.
It took dozens of worker three years to “milk” more than 1.2 million golden orb spiders, 24 at a time. At the end of each day’s milking, the spiders were returned to the wild.
The designers point out that it takes about 23,000 extractions to create 1 oz (28 g) of silk thread.
Synthetic spider silk
Imagine the possibilities if spider silk could be mass produced! However, one of the biggest problems for such a venture is that they eat each other. They have to be kept separated, an almost impossible and hugely expensive task.
Well, research on synthetic spider silk – “spiber technology” – is well underway, conducted by companies such as AMSilk in Germany, Araknitek, Bolt Threads and Kraig Labs in the United States, Spiber in Japan and Spiber Technologies in Sweden.
Spider silk production
Video: Godley explains the production process of the golden cape and scientists explain experiments with transgenics to produce spider-silk-like products.
OK, so now you know why Spiderman is so tough.
Edited from the original story by Sam Vaknin. For further interesting reading, also see Increasing silk fibre strength through heterogeneity of bundled fibrils.