Silkworm farms can only be built and tended by those that have won a rank-2 Beetle Garden competition as part of the The Test of Khefre's Children.
Silkworms generate raw silk when fed the proper thistle.
There are 3 parts to a silkworm's lifecycle:
Raw silk output ranges from about 1 - 1.2 raw silk per thistle. (It takes 50 raw silk to make one silk cloth.)
Thistle Requests are listed here.