Spider's silk is made up of chains of amino acids. In other words, it is simply a protein (see How Food Works for details on amino acids and proteins). The two primary amino acids are glycine and alanine.

Spider silk is extremely strong -- it is about five times stronger than steel and twice as strong as Kevlar of the same weight. Spider silk also has the ability to stretch about 30-percent longer than its original length without breaking, which makes it very resilient.

Here are some interesting links:

• Fiber Engineers, Meet Thy Master
• Spider Web Exhibit
• The study of arachnids: Silk & Webs
• Bioengineered Spider Silk
• Biomolecular Self-Assembling Materials - Pretty deep article; figure 6 shows the structure of glycine and alanine in spider's silk.
• Kevlar