Spiders make their webs from lots of different spider silk proteins. Some of them are called 'spidroins' - Spidroin 1 and Spidroin 2 and maybe some other spidroins.

They're in dragline silk, which is the silk that spiders dangle from and is also almost the same as the silk spokes in a spider's orb web. The capture-silk spiral in the orb web is much stretchier and not as strong as the dragline silk. My students and I did experiments with stretching silk and silk molecules, and a scientist working with me said our results looked like capture silk was a network of springs.

Dragline silk molecules pull apart piece-by-piece, sort of like pulling open a row of snaps. My student Emin discovered that by pulling on the molecules with an atomic force microscope [AFM].

Here's what I found by googling 'spider silk chemicals' - "The protein in dragline silk is fibroin (Mr 200,000-300,000) which is a combination of the proteins spidroin 1 and spidroin 2. The exact composition of these proteins depends on factors including species and diet. Fibroin consists of approximately 42% glycine and 25% alanine as the major amino acids."

Another article says spider silk is as strong as steel and as stretchy as rubber and tougher than Kevlar, but of course it's VERY thin.

I just read 2 news stories about spider silk. One says the spider's silk proteins are stored as blobs all packed together in its silk gland, and when the silk blobs squeeze out of the little hole in the silk gland, the squished blobs all get long, to make a strand of silk. The other news story says the silk spiral in the orb web gets stiffer and stiffer, out toward the edges of the spiral.

I like spiders and spider webs.