Cultivated silk is the life's work of a specific species of silkworm, Bombyx mori. These silkworms have been domesticated for centuries, carefully bred to produce the highest quality, brightest white, most heartbreakingly beautiful silk possible.
As you might expect after centuries of inbreeding, the moth of the Bombyx mori resembles no other. It is fat. Its stubby little vestiges of wings could never lift it into flight. It lives its entire life cycle in pure dedication to the production of silk. Most silkworms will go into the Big Sleep while still in the cocoon. Those who do emerge from their cocoons live out their adult-moth lives in sensual revelling, dedicated to making future generations of silk producers.
In any part of its life cycle, Bombyx mori depends on the presence of human servants, hovering and eager to provide it with anything it requires.
This is where the trees come into the story.
The silkworms hatch from tiny eggs and come into life with a voracious appetite. They depend on their humans to bring them the one and only thing they will deign to eat: fresh mulberry leaves.
The worms eat quickly, digest thoroughly, expect their human servants to keep their rooms tidy -- and most importantly, to bring more fresh leaves. The worms rapidly increase in size, splitting their skins to make room for their expanding, healthy, happy, hungry girth -- and to make it easier to eat even more leaves. And that's the daily rhythm: more and more and more, right up to the point where it's time to spin a cocoon.
Mulberry trees and sericulture go hand in hand, and have for as long as the Bombyx mori silkworms have been kept by humans.
A spindle that's the right weight for spinning silk and made from the wood of mulberry trees is a perfect spindle, indeed. :-)
To read an in-depth personal account of silk rearing, accompanied by detailed and beautiful photos, check out Michael Cook's excellent website wormspit.com.