: Dr John Kershaw Author
: The Story of Silk
: Dolman Scott Publishing
: 9781911412489
: 1
: CHF 6.00
:
: Einzelne Wirtschaftszweige, Branchen
: English
: 298
: DRM
: PC/MAC/eReader/Tablet
: ePUB

My interest in silk dates from 1990. Since then I have bred my own silkworms and found something of interest about silk in all five continents. It all began 400 million years ago when ancestors of spiders crawled out of the sea onto dry land and used silk to prevent their eggs from drying out and make trap lines to detect prey. Many animals make silk: among them spiders reign supreme, but the silk industry depends on a moth, Bombyx mori, that has been bred in captivity over thousands of years and long since lost the power of flight to become the only insect to be completely domesticated.
We look at animals that make silk and how they use it, describe its composition, structure and properties, examine the silkmoth and its life history and see how its silk is extracted and processed. We find some of the world's earliest sites of silk production, accompany merchants conveying it along ancient trade routes across Asia from China to the Mediterranean, and follow the expansion of the silk industry into Europe in the mid 16th century, eventually reaching the Americas.
Though our story has its end, it is not the end of the silk story. Recent discoveries briefly mentioned in our closing paragraphs, including its use in reconstruction of human tissues, and the fact that silk forms the basis of the strongest fibre of any type ever recorded point the way to a whole new chapter. But exciting though it is, that will be for others to write.

2

Silk in Nature

2:1 Dew covered spider’s webs on my garden hedge.

In summer 2003 a four millimetre (1/6 inch) long thread with droplets of glue spaced along it was found near Jazzine in southern Lebanon. It looked as though it had come from the web of a modern orb web spider, but it was in a blob of tree resin that had solidified to amber 130-135 million years ago, according to popular legend at the time when the dinosaurs ruled the world. One of the plant eating forms may even have fed on the leaves of the tree. It is the oldest silk known. Its sticky droplets separated out then, as they do now, when the spider disturbed the viscous coating of glue on the thread by tweaking it with its hind leg.

Silk is one of the most amazing products of nature. Many insects, spiders, mites, centipedes, millipedes and even some marine shrimp-like animals (all, you will note, animals with jointed legs and no backbones) depend on it for survival at least some time in their lives. They may use it in their young stages, on special occasions, or daily, and they use it for a wide variety of purposes.

2:2 A hand-sized tarantula wandering from its lair in Peru.

As I mentioned earlier silk first made its appearance when spineless sea creatures started to invade the land. Among them were the ancestors of our spiders, and after 400 million years of development and innovation spiders have become the most familiar silk producers. They originally used their silk to wrap up their eggs and stop them drying out, a vital measure to ensure their survival on land. Later they used it to line their burrows and make trip wires to detect possible prey. Silk-lined burrows still feature in the lives of some descendants of these early ground-dwellers, including trapdoor spiders and this 13 cm (5 inch) legspan pink-toed tarantulaAvicularia that I encountered in the Amazonian jungle. Since those early days animals have come to use silk in a wide variety of ways related to food gathering, self preservation, reproduction and dispersal.

2:3 A lacewing takes a rest after laying a batch of eggs on a plant.

Many creatures rely on silk for protection from their enemies.Latrodectus hesperus, a close relative of the notorious American Black Widow spiderLatrodectus mactans repels mice and other unwelcome intruders into its territory by smearing sticky silk on their heads. Unprotected eggs are especially at risk and we see a variety of ways for keeping them safe from predators.3 Lacewings for example, as shown here (Fig. 2:3) lay their eggs on the ends of long stalks made of a relatively inflexible silk where they are beyond the reach of many potential foe, while the common garden Wolf SpiderPardosa hunts with its eggs concealed in a silk sack attached to the rear of its abdomen. Nursery-web spiders of the family Pisauridae also carry their egg sacks around while hunting, clasping them beneath their bodies between their fangs and palps (Fig. 2:4). When the female detects the vibrations that tell her that her young are about to hatch out she puts the sack in a silken mesh over which she stands guard until her offspring can fend for themselves.

2:4 The Nursery-web spider Pisaura mirabiliswith her silken egg sac.

2:5 Guarding her newly hatched brood in their web – she can just be seen to the right of the silk mesh.

2:6 Moth caterpillars feeding communally in their nest, Ancona, Lake Maggiore, Italy.