Once the worms happily eat their way to 10,000 times their weight at hatching time, which only takes them about a month, they have enough energy to spin their cocoon ... Then the cocoons are steamed or heated to a higher temperature to kill the worms inside them ... great care is taken to ensure the worm does not hatch into a moth because then the long silk thread filament that the worm have made its cocoon out of will get broken.
A silk sari then involves the boiling alive of hundreds of thousands of worms. This is very ironic, because silk plays a part in many Hindu ceremonies. The best Indian silk is made in Varanasi and Kanchipuram, both cities with very active temple cultures. Some Hindu temples forbid people from bringing in leather purses. But none, as far as I know, forbids silk saris.
The next time I see a holier-than-thou vegetarian wearing a silk sari (or even a silk tie), I will have a nice factoid to mention.