Why call it 'spider silk' instead of 'silkworm silk', though? Silkworms (1.) never have long hairy legs; (2.) never have the name Shelob; (3.) never crawl under

Why call it 'spider silk' instead of 'silkworm silk', though? Silkworms (1.) never have long hairy legs; (2.) never have the name Shelob; (3.) never crawl under your bedsheets at night and bite you.