There's a lot of effort going into just that, though there are some stumbling blocks researchers are still working their way through before we start seeing production scaled up.
http://news.discovery.com/tech/spider-silk-silkworms-genetic...
http://news.discovery.com/tech/spider-silk-silkworms-genetic...
[ed: insert dystopian sci-fi plot of scattered survivors of the nano apocalypse growing bullet proof vests from silk worms found in old industrial (nano)waste sites...]
Where do you think "natural silk" comes from?
[ed: I probably should've written "normal" silk, not natural silk...]