Re: How do silk worms make silk?

Silk worms are the caterpillars of silk moths, which are in the family 
Bombycidae. Silk is produced by two modified salivary glands,which are 
long, complexly-folded tubes that run along the digestive tract, and may be 
up to seven times the length of the caterpillar itself! The two glands come 
together in a spinneret organ in the caterpillar's mouth. The hind part of 
the spinneret has muscles which contract, forcing silk into the tube-like 
front part of the spinneret. When the tube is touched to something, the 
silk sticks. The caterpillar then moves its head to draw more silk outward. 

The silk itself is a double-stranded ribbon, since it comes from two 
separate glands. It's made of a tough, elastic protein called fibroin.