Yep, I used to keep silk worm larvae and feed the mulberry leaves from my Grandmother’s huge mulberry tree. (And, as an aside, I built wonderful treehouses in that very same tree and spent idyllic days there reading with the spring breezes rustling the new leaves). And as the tiny grubs munched up the mulberry leaves and spun their cocoons, I was fascinated but it kind of stopped there. Yes, I had a go at unwinding the silk but didn’t know all the techniques like boiling with the chrysalis still inside to avoid the fibres being cut by the emerging moth. But Prasad takes us on a journey that far surpasses the humble Bombyx mori...the common silk worm. She takes us to India, and Assam, and South America and the jungles of SE Asia to introduce us to a whole host of lepidoptera that produce silk cocoons. And to the people who researched them and promoted their use as alternative sources of silk.
Not content with confining herself to the fibres produce by the lepidoptera moths she studies the fibres produced by meter-high molluscs in deep water. There is a fascinating history here with all of these fibres. They were sufficiently rare and difficult to process that the articles produced from them were always luxury items; one-offs produced for kings and queens. And therein, lies the major difficulty that has faced all the would-be entrepreneurs; the raw material was just too rare, too difficult to collect and process that it would always be too difficult to generate economic scale operations.
The same problem bedevilled attempts to use spiders for the same end. Yes. Spider webs are extraordinary constructions and a single spider can extrude up to seven different types of silk thread. I was a little disappointed that Prasad did not go into the chemistry of silk a little more. Though I’ve consulted various of my Biochemistry text books and found that not much is included there about it. But the structures of the proteins laid down are quite complex;..anti-parallel (beta) sheets of fibroin protein linked up by short alanine and glycine side chains and by Hydrogen bonding between the pleated sheets. As I delved into the chemistry, I can see why Prasad avoided it. The truth is that it is very complex and not easily described. Here is an explanation from the European Protein data Base of spider silk:
“The spider silk fluid inside the spider's body is a liquid solution where the fibroin molecules retain a certain order, resulting in crystalline properties. It is believed that during their passage through the spinneret, the spider's silk-spinning organ, the fibroin molecules align, and partial crystallization occurs parallel to the fiber's axis. This is made possible through the self-assembly of the fibroin molecules, where their repetitive sequences contain polyalanine regions that cross-link together via hydrogen bonds to form pleated beta sheets, conferring the high strength of the silk. It is therefore not a coincidence that 50% of fibroin's amino acid content is alanine and glycine, as they are the smallest amino acids so are able to pack together tightly. The crystalline regions are also very hydrophobic, allowing the loss of water during the solidification of spider silk.”.......And that’s the clearest description I could find. And no mention there of the fact that the spider can extrude seven different kinds of silk. Diagrams help a bit but not that much. I really enjoyed reading the book and learned a lot. Especially about the large number of vey special people that did thinks like breeding spiders and placing them in little holders (how do you do this with a spider??) and then wound the thread off on a spool. And people experimenting with dying and weaving etc. really a fascinating tale. I’ve extracted some snippets below which caught my attention.
“At that time [1878] European manufacturers were discovering that there were more silks–ancient silks–than they had imagined, fabrics that had long been in local use in many parts of the world......What was more, silks were not just sourced from silk moths, either domesticated or wild, but from other organisms, too. Principal among them was an enormous mollusc that sat, immobile, on the floor of the Mediterranean Sea, from where it was harvested for its meat and its threads; as well as a startling type of spider, reports of which had begun flooding in from Africa, the Pacific and from the Americas. Its silken threads bore truly extraordinary biological properties that meant they would far surpass the strength of that of any other animal.
These products were commodities through which wealth could be accumulated, transported, and because of their value, monopolised, by emerging elites....In the early Chinese empires, silk was the most precious of all textiles. It could be exchanged for other items of high value,
What quickly became clear to me was that the knowledge and use of silk, in all its wonderful varieties, is a global story.
Part I – Moths
On 18 February 1668, almost exactly one year later, Malpighi’s new communication on the silkworm was read at the Royal Society. ‘The silkworm … is the most well-known insect among our countrymen’, it began, much as Merian had, ‘… in which so wonderful Metamorphoses happens,
Although there are now more than a thousand strains of Bombyx mori kept across the world, and this caterpillar is the creator of the vast majority of silk used today, not only was modern Bombyx mori not the only silkworm known to the Neolithic people of China–but for some part of the two thousand years during which the early Yangshao culture thrived it would not even have existed at all.
In a find dated to 3500 BCE, around 5,500 thousand years ago [some silk] was found instead to have been the creation of another silk moth......The scientific name it would be given was Rondotia menciana......In China, its silk must already have been in use by the time it began being farmed. The most likely origin of Bombyx mori seems to have been
A Chinese variant of a wild moth found across Asia, in Korea and Japan. [The transition to the modern moth] was initiated around 7,500 years ago
Domestication led to the cocoon shell of Bombyx mori becoming ten times heavier than that of Bombyx mandarina, and creating a silken thread that would reach up to a kilometre or more from a single cocoon. This genetic engineering, started by Neolithic Chinese farmers, and the technology that would be developed by their descendants, made the new silk not just easier to control and harvest but to spin and to dye into vibrant colours,
The stifling or heating of the pupal stage of the domesticated silk moth so that it could not break apart the cocoon had been an age-old Chinese innovation; that, and the use of an alkali to strip the silk’s fibroin protein of its gummy sericin glue, was what had given the fabrics they created their coruscant, fluid-like gloss. It was also what made the silk more able to take, and hold, the dyes......The silkworm itself reached Iran rather later than its silk, starting, it seems, in the sixth century, up along the borders of the Caspian Sea. Four hundred years later, it had spread across most of the regions of the Iranian Plateau....Come the seventh century, the Islamic Empire would see the establishment of silkworm rearing across North Africa and all the way to Spain, which, later, in 1530, the conquistadors would take to Mexico.
Not until the thirteenth century would the breeding of silkworms be established in Malpighi’s Bologna, at roughly the same time as it also began, if more modestly, in France.
Across the globe were other animals creating other tantalizing threads......
......fabrics made from the giant cocoons of the Saturniidae–wonderful cloths of wild silks–had been in use in very ancient times, too.......[ in another Indus city were found] forty or fifty strands of silk that some fine-fingered artisan had, sometime between 2450 and 2000 BCE, twisted together in order to string them.........These silks were not those of the famed domestic silkworm. Instead, they had been extracted ...from the large, wonderfully coloured wild Saturniidae family. Those threads suggested that silk had never been an exclusively Chinese invention.
Roxburgh ....But by] April 1798.. penned a letter to Joseph Banks to let him know that he had finally ‘completed an account of the Tasseh silk worm’.....It was not to be the only silk moth that would be rediscovered by the new wave of naturalists from the West who made India their laboratory.....Silk from the Antheraea assama had indeed been produced since time immemorial.......Among those was an astonishing, delicate cocoon of bright yellow silk, by the caterpillars of Cricula trifenestrata.....Far earlier than Roman trade records, muga would appear among the silks described in the Arthaśāstra, a Sanskrit text on domestic politics and foreign affairs probably dating to between 321 and 297 BCE,
The cloths made from the silks of all of these moths were valued not just for their beauty, but because their colours did not fade, but improved with use and with age
.....Because of the irregular way in which naturally brown tasar took up dyes, his and others’ attempts were ultimately abandoned.. .....None of that wild silk had been used since. William Morris......The struggles with the use of tasar in Europe, Wardle had found, had resulted from the structure of its threads to which others who worked silk had paid no attention....His patient observations of the structure and the chemistry of tasar was what helped him to do what no one else had yet done: to break tasar’s resistance to dyes and create his gem-coloured wild silks.
Part II – Silken Shells, Golden Orbs
Pinna nobilis, with its byssus. The noble pen is an enormous marine mollusc, reaching over a metre at its zenith. It narrows to a sharp point at its base and fans out into a semi-oval above, like a gigantic quill penAt its sharp-pointed base is a shock of long, fine filaments disturbingly like auburn locks of human hair, but up to three times finer. They spill from its ‘foot’,.....Pinna nobilis is not unique among its relatives in having anchoring threads. There are many mussels that live in the sea, or in bodies of freshwater, that create hair-like strands of protein...... Sea silk is sometimes called byssus. And Pinna nobilis is not its only source.......other Pinna,....Pinna carnea, and Pinna rudis also produce the fibres....Byssus is the biological term for the filaments, the ‘beards’, of all of these mussels, whether woven or not.
What is truly remarkable is that the anchoring threads of Pinna nobilis are still used in Sulcis. It is the last place in the Mediterranean where the knowledge of weaving textiles from sea silk is being kept alive.
Alinari wrote of the beautiful effect produced by the Pinna nobilis silk. It was ‘of a beautiful metallic colour that approaches copper’....though they have suffered recently from an infection: ......What is more, the mycobacterium thought to be killing them was also found in Pinna nobilis and Pinna rudis that were living quite healthily in the sea.....These parasitic infections are not working alone.....They are linked with changes in the opportunities that pathogens have to interact with a number of animals, including people.....
Their loss represents more than that of a legendary animal of the Mediterranean Sea. It is the loss of an ecosystem.
Silk from spiders:.....‘by reason of spiders bags, in respect of their lightness, afford much more silk than the others, as proof of which, thirteen ounces yield near four ounces of clean silk; three ounces of which will make a pair of stockings for the largest-sized man.’
by the end of his trials [around 1709] Bon had made not just textiles from his spiders’ silk, he had also distilled a large quantity of spirit and a volatile salt from it, .....changes had shown the by-products of his extracts of spider silk to be not just ‘very active’, but so much more so than the extracts of Bombyx mori cocoons,
It was high time that the ‘despicable’ and ‘common’ spider ceased to be overlooked..... Réaumur [some 7 years later] confirmed Bon’s observation that spiders in fact appeared to have many different silks, of varied thicknesses, some with which they made their webs, and others for the egg cases that his predecessor had so coveted. But Réaumur tested the strength of these silks.......To produce one pound of silk would need some 55,296 spiders, In the end, Réaumur did not close the possibility of spider silk entirely. His suggestion was to look elsewhere, to different sorts of spiders, and in particular to the Americas.
The Araneae have made silk for some 380 million years........While it is only the larvae of insects that are able to produce silk and not their adults, spiders retain that ability throughout their lives......Many insects produce silk, but each one only of one type, while a single spider might make as many as seven different types of silk thread,
Termeyer caught the end of the silk, and attached it to a little reel precisely four and a half inches in diameter, equipped with cylindrical glass arms that he slowly turned, winding onto the reel perfect strands of thread......Termeyer died not long after 1814, by which time he had induced his reluctant spiders to produce for him items not so dissimilar to those made with such pride by Bon just over a hundred years earlier......There were the stockings made of Aranea diadema silk sent to grace the royal legs of King Charles III.....And he would even produce a shawl for Napoleon’s first empress, Josephine, which was put on show in Milan.
The various silk glands of the females and males of spiders like these [black widows] appeared to produce some fifty proteins creating at least three major types of silk, as well as others related to the formation of silk,
Camboué then put away his studies with the wild silk moths, quickly, he moved on to working with the threads of spiders instead. ......And Cambour set out to attempt breeding with the giant Nephilia.....Camboué . And by spinning these threads he developed a machine so efficient that it generated 200,000 metres of twelve-strand silken skeins every year......It was from these threads that an enormous bed canopy, were made and sent from the Indian Ocean to the 1900 Paris Exposition Universelle.......But as the journalists marvelled, the passing visitors simply walked by, and noticed nothing much at all.
Part III – Reinvention
In Chicago, [a Polish priest invented], and submitted the first patent for, a bulletproof vest of silk, armour that was to be acquired by the kind of men who brought a glint to the eyes of assassins......raw silk had the technical capacity to resist the puncture of a fast-travelling missile designed to kill, so long as it was correctly woven and thick enough.
In the wondrous metamorphosis of Bombyx mori.......by the time they craft their cocoons, they will have produced ten kinds of silk. These have distinct strengths and qualities.
are particular sequences and complexes of tiny building blocks that coalesce to build the chains of its fibroin protein......Fibroin strands are the primary source of such strength and ability to stretch that allowed even the finest of woven silks to avert arrows, and then bullets–strands at a scale a thousand times smaller than a millimetre, at least four times smaller than the human eye is able to see.
On 18 January 2002, a group of scientists published a study in which they had sought to mimic the process of spider silk production.....The mammary cells of cows were selected......and also the kidney cells of baby hamsters,....Using only a partial sequence of the MaSpI and MaSpII spidroin genes, rather than the full run utilized by an actual spider, white goats selected to be modified......The idea was that those quantities would also include the spider proteins the goats’ genes had been modified to carry, from which the strongest fibres of spider silk were formed, which could then be easily harvested when the animals were milked. The end result was that the mechanical properties of the silk they got out of it were very similar to those of the dragline silk of the spider. But–the silk itself.... was only ‘30–40% spider silk and roughly 60% silkworm silk’.
But,....as history has shown only too well, ‘until you can produce it cheap enough, it’s not gonna do the job’........Alternative formats like films and adhesives were anticipated, so that a variety of materials with numerous technological applications might be moulded, printed or formulated...... except for using the fibres, really inexpensive production of any other applications is still not possible yet.
Spider silk, however, does not have sericin......‘out of studying a strange silk in a spider you come up with a new class of material. And that has all sorts of potential applications for microtechnology for soft robotics.
For Fritz Vollrath it has a future both in biomedical and in smart materials.’....An artificial, implanted silk cornea would also need to be porous enough to allow our own cells to enter it to allow it to regrow by using the shape of the silk as a scaffold, or mould......It was found that silk film had a near-perfect transparency–superior to anything made of glass, or indeed any synthetic material available.
David Kaplan had....decided If he could get hold of the silk fluid itself, he could mould it into whatever shape he needed..... with possible replacements for cartilage, and bone; packages for safely delivering medications deep into the body; artificial blood vessels made of silk for the repair of the heart and other organs; and dissolvable nuts, gears and bolts that could be implanted in the body for surgical repair.
Omenetto’s lab has also developed a soft-tissue filler based on silk fibroin protein. That is in clinical trials for cosmetic use, to fill wrinkles. But it is already approved for the treatment of vocal cord paralysis,
Another group of researchers, co-developed in 2022 a silk-based replacement for a type of
Another positive is that if you have a million tonnes, roughly the annual production of raw silk cocoons–that’s a lot of carbon that is bound for a very long time.’
So what's my overall take on the book? I'm very impressed. She covers a lot of ground. Maybe I would have liked to understand the chemistry a little better and maybe that could be placed in an appendix. But an easy five stars from me.