Question

why is it necessary to kill the pupae by boiling

Answer 1

Yes, it is necessary to boil the cocoon and kill pupa. This is because to make a continues thread of silk otherwise pupa grows and break the cocoon and we will not get a continues thread.......

hope it helps you :)

Answer 2

The sorted cocoons after which moth cuts the cocoon and flues out is sorted and immersed in boiling water.

This is done so to kill insect inside them.
The cocoons are given a series of hot and cold immersions. This makes the silk-gum soft.

Hence, to get silk without any insect corporation we need to have to give it a hot immersions.