I found myself unsure of some silk terms, so I went to the library. Most, but not all, of this information is taken from The Silkworker's Notebook by Cheryl Kolander. When it emerges, it eats through one end of the cocoon, cutting most of the fibers in to much shorter lengths.
Most silk is cultivated, and produces a very fine white product.
Silk can be made from certain varieties of spider cocoons, but they are much more difficult to farm than the silkworm moth cocoon. The oldest silks found are from China, dated to 1500 BC, although the word for silk in Chinese is known to be older than that. The establishment of the Silk Road sometime between 140-60 BC marks the beginning of silk use in the West. It was still rather rare, but when the Crusaders began returning from the mideast with silk, demand developed and better trade routes to Europe were established. Venice, Lucca and Florence became renowed centers of silk weaving starting in the fourteenth century.