"The cycle of silk production begins with a small number of cocoons that are not processed so that adult moths can emerge. These domesticated insects cannot fly and die soon after mating to produce a new batch of eggs. Each female moth produces about 400 tiny eggs and these remain in a dormant state until a sharp rise in temperate triggers hatching. The new generation of silk worms must be kept at the egg stage until spring when the fresh leaf-growth of the mulberry crop allows the cultivation of a new batch of larvae. For five months the eggs are allowed to develop in a warm environment (24 degrees), then, to suspend their lifecycle, they are transferred to a cool storeroom (5 degrees) for a further five months. The entire life-cycle is a delicate process and temperate fluctuations, or even strong odours, can interrupt the incubation period or affect the appetite of the pupa. Complete batches of silk worms can die if they hatch too early when their required food is not in season.
In spring, under the care and supervision of Chinese grandmothers, wives and daughters, the silk worms were hatched from minute grey eggs that were the size of a pinhead. The eggs were encouraged to hatch by being placed in a humid environment while the temperature was gradually increased back to 24 degrees. The miniscule hatchlings weighed half a milligram, but five weeks of constant feeding increased their weight 10,000 times. During the pupa stage the grubs needed a warm environment, so they were kept indoors in trays and baskets well-stocked with fresh leaves cut from mulberry trees several times a day. Each pupa could potentially eat its entire body-weight of leaves in one day.
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Five to six weeks after hatching, the caterpillars are up to 3 inches long and ready to enter the larval stage of their development. Each caterpillar unravels a single strand of delicate raw silk from its salivary glands and wraps the minute thread thousands of times around its body in a figure of eight pattern. It takes four days for the insect to wind the soft elastic thread around its form. As this is occurring the silkworms are attached to racks or false tree branches so that the cocoon is suspended and forms into a perfect cylindrical shape. The thread then hardens into a large protective cocoon. Each cocoon is formed from a single thread several thousand feet long, but over 2,000 of these cocoons are required to make a single pound of silk.
To process the cocoons, they are immersed in scalding water to kill the pupae. This must be done before the pupa can destroy the silk strands by secreting a fluid called ‘coconase’ that will degrade the fibre permitting the emerging moth to chew through the chrysalis. The cocoons are floated and stirred in steaming hot water to dissolve a gummy protein known as ‘sericin’ that holds the silk strands together. Dexterity is required to pull apart the chrysalis, locate the end of a strand and unravel the cocoon into a fine, lustrous filament of strong, lightweight thread.
This was a skillful and time-consuming process with each cocoon yielding a single filament that was half a mile (800 metres) long. After reeling, the delicate filaments were twisted, spun and spliced together into a thread containing up to fourteen strands. These threads could be woven into cloth or gathered into yarn that was ‘thrown’ into loops and coiled into skeins."
(The Roman Empire and the Silk Routes)