This belly shot shows the spinneret, the organ used to spin its elaborate web. (It is right under the black marking in the middle of the abdomen.) If you look closely, you can see the silk coming from the opening. Argiopes are orb weavers that construct the beautiful webs with the spoke-like patterns. To see one of these webs bejeweled with dew in the early morning is utterly breathtaking.
Above is a closeup of the spinnerets. Each species of spider has between 2 to 8 spinnerets that are usually in pairs. The spinnerets are comprised of hundreds of glands that produce different types of silk. A spider will spin different types of silk depending on the job and can control each gland to produce silks of varying components. The silk is a liquid solution that is pushed through long ducts that lead to microscopic spigots. It can control these spigots to produce a silk with varying amounts of stickiness and strength. Also, each spigot has a valve that regulates the thickness of the silk and the speed it is deposited. The spinneret will wind the individual strands of silk fibers together to form the different types of silk.
Above is an amazing shot of the spigots from an electron microscope, magnified 1,500 times. This shot courtesy of MicroAngela. It show the multiple spigots that comprise the spinnerets. By examining the photo, one can somewhat understand how the spider spins silk with varying strengths and stickiness. In the same way that yarn is comprised of individual fibers that are wound together, the spider's silk is made by winding various strands of silk fibers together. If grandma wants to make a hat, she will choose various lengths, textures and colors of yarn that she will use to knit the hat. In the same way, the spider can take various silk fibers, some that are sticky, some that are stronger, some that might be thicker, to produce a product it can use for the task at hand. If it wants super strong silk for its egg case, it might use stronger, thicker fibers. If it needs super sticky fibers for the center of its web, it can produce those, as well.
If one spends a little time learning how awesome and amazing spiders really are, I think less people would be afraid of these small industrious creatures!