Thursday, February 6, 2020

Featured Artifact: Silkworm Cocoons

Today I'd like to feature one item from the Benton County Historical Museum's Horner Collection. At the time the Horner Museum began, one of its goals was to assemble a large collection of natural history artifacts which would be of use to students in a number of disciplines. However useful they may have been to students, some of these items do not display well.  Many of the shells are very small and would be hard to see in an exhibit space, for example.  So it's nice to be able to feature one item from the collection here.

The items in the photograph above are silkworm cocoons from Thailand. These cocoons are the source of the fibers used to make silk fabrics.  The silkworm moth (Bombyx mori) lays eggs which hatch after about 14 days.  The larvae then feed on their preferred food-- the leaves of the white mulberry.  They eat continuously for about 42 days and enter the pupal phase by spinning a cocoon of fibers produced by their salivary glands. If humans do not intervene, the silk moth develops within, produces an enzyme which eats a hole in the cocoon, enabling the moth to emerge.

Humans began cultivating the silkworms in China about 5,000 years ago.  They provide the mulberry leaves and collect the cocoons.  Before the moth can emerge, humans would immerse the cocoon in hot water to kill the pupa within and to soften the cocoon. Then, the filament which makes up the cocoon is unraveled.  The individual thread is incredibly fine (.0004 inch in diameter) and stretches an amazing 1,000 to 3,000 feet long!

The filaments are so fine that several must be twisted together to create silk thread which can then be woven into silk fabric.  The sheen or shimmer characteristic of silk results from the prism-like structures of the filaments. It takes about 2,500 cocoons to make one pound of silk!

The production of silk began in China and eventually spread to Japan and westward, eventually reaching Italy and France.  Disease and the development of synthetic fabrics brought an end to silkworm cultivation in Europe. Today, China is the leading producer of silk; India is the second largest. Thailand, where these cocoons come from, is the fourth largest producer. 

By Martha Fraundorf, Volunteer for Benton County Historical Society, Philomath, Oregon