Silkworm city

    On the surprisingly short list of animals that humans have figured out how to domesticate over the last 20,000 years, there are two insects.

    One is the honeybee, and the other is this little guy, the silkworm. Honeybees have certainly been manipulated by man, most recently by the trend to artificially enlarge larval cells to produce bigger adult bees than would occur in nature. But the honeybee is much closer to its original condition than the silkworm.

    Humans have been domesticating the silkworm for such a long time that it has become a distinct species from its wild forebear- akin to the way dogs are descended from wolves. This little creature has been engineered for qualities valued in the production of silk to such a degree that it can no longer survive without human intervention. After thousands of years of selective breeding, the adult moth has lost the ability to fly. The caterpillar is sluggish to the point that it can’t move more than a few inches in its entire life, and has no defense mechanism against predators. Its life cycle has become accelerated as well; if fed mulberry leaves constantly the silkworm can go from egg to cocoon in a matter of weeks.

    To make silk, a cocoon is unspooled in one continuous filament- a mile of fiber that must be twisted with hundreds of other filaments to make even the thinnest silk thread.

    Much of the history of the silkworm, as well as the production of silk (known as sericulture), has taken place in China, but interestingly Northwest Philadelphia was once the site of the largest experimental silk industry in America. Encouraged by the federal government which was looking to increase exports, in 1838 and 1839 numerous cocooneries were established around Germantown. The most sophisticated of these operations consisted of 400,000 mulberry trees and 1,000,000 silkworms, with the intention of growing the operation to 5,000,000 worms within a year.

    Unfortunately the entire enterprise was speculative, and when the bottom fell out of the silkworm market in 1840 all the many people that had invested in the industry lost their money. The cocooneries were abandoned, and silk manufacturing never recovered in the United States. Today, the only vestige of what historical texts refer to as “the great silkworm craze” is the large number of white mulberry trees, descendents of the ones planted in the 1830s, which are still growing all over the city.

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