I knew silkworms in captivity had a hard life, I just wasn't prepared to see actual footage of the process. After dining on leaves and sleeping for a month, they then spin their wormy hearts out to create silk fiber for their cocoon. When not in captivity, this outer casing will protect them during the pupal stage. In captivity, this is when they are boiled or steamed alive so that the silk can be retrieved. According to this video, these boiled pupa are then stir-fried with kaffir lime leaves or used in traditional medicine.
Lotus silk is a vegan alternative, though it's time consuming to harvest which makes it 10 times more expensive than regular silk.