“With time and patience the mulberry leaf becomes a silk gown”. An elegant Chinese proverb, though in practice with a few tons of mulberry leaves, a large number of silkworms and the right conditions, a kimono’s worth of raw silk can be produced in a couple of months. The queen of fabrics is admired for its beauty, lightness and strength, yet the story of silk cultivation (sericulture) is even more remarkable.
Although several insect species produce silk, the domesticated silk moth is the only one used for making textiles. A silk moth mates, produces eggs and dies within about a week. Once the eggs hatch after 2-3 weeks, the emerging caterpillars (which we call silkworms, though they are not really worms) are fed on fresh mulberry leaves. The silkworm has a voracious appetite, and in just a month it will increase its weight 10,000-fold and shed its skin four times, at which point it is ready to begin spinning a cocoon in preparation for becoming a chrysalis. Silkworms have to be protected from loud noises, temperature changes or strong smells, as these will affect their appetite and the quantity of silk produced.
The silkworm now climbs up a specially designed frame and finds a compartment in which to spin the cocoon around itself, which it does by moving its head rhythmically in a figure-of-eight pattern, secreting a sticky silk filament from two glands in its head. Within a few days, the silkworm spins enough silk to become completely encased in its cocoon.
The silkworms are then killed inside their cocoons by heat, with some being spared to metamorphose into moths in order to breed the next generation. Only perfectly shaped cocoons continue to the next step – reeling. A brush teases out the end of the very thin silk fibre, which is reeled through an eyelet together with several others to make a single thread, though still only as thick as a human hair. This photo of a silk factory (below, right) dates from the early 1900s, but modern silk reeling remains labour intensive despite today’s better technology.
An alternative method of silk cultivation allows silkworms to survive and emerge as moths, and the resulting product is labelled ‘peace’ or ‘cruelty-free’ silk. Allowing the moth to break out of its cocoon results in much shorter strands of silk and a different quality of fabric: it is spun rather than reeled, is softer and fluffier than the conventional shiny silk, it costs more and is slightly discoloured. Even ‘cruelty-free’ silk cultivation is not without ethical concerns, however, because the silkworm has been selectively bred to be totally dependent on humans for survival.
The silkworm and its cocoon have uses other than silk manufacture:
The total length of silk fibre that goes into the making of a top-quality silk kimono is unimaginably large. Each cocoon contains hundreds of metres of raw silk fibre, and thousands of cocoons are required. At the Yokohama Silk Museum we discovered that the number of cocoons needed to produce one kimono is around 9,000. So, although estimates vary widely, we can deduce that one traditional Japanese silk kimono requires at least 3,000 and possibly more than 5,000 miles of silk fibre!
Here are those 9,000 cocoons: