Spiders silk comes out of the butt region. The spinneret, the visible part of the silk gland, emits the silk strand when the spider needs it.
Spider silk is a protein fiber spun by spiders. Spiders use their silk to make webs or other structures, which function as nets to catch other animals, or as nests or cocoons for protection for their offspring. They can also suspend themselves using their silk.
Many small spiders use silk threads for ballooning, the popular, though technically inaccurate, scientific term for the dynamic kiting spiderlings (mostly) use for dispersal. They extrude several threads into the air and let themselves be carried away by winds. Although most rides will end a few yards later, it seems to be a common way for spiders to invade islands. Many sailors have reported that spiders have been caught in their ship's sails, even when far from land. The extremely fine silk used by spiders for ballooning is known as gossamer.
A spider web, spiderweb, spider's web, or cobweb (from the obsolete word coppe, meaning "spider") is a device created by a spider out of proteinaceous spider silk extruded from its spinnerets.
Spider webs have existed for at least 100 million years, as witnessed in a rare find of Early Cretaceous amber from Sussex, southern England. Insects can get trapped in spider webs, providing nutrition to the spider; however, not all spiders build webs to catch prey, and some do not build webs at all. "Spider web" is typically used to refer to a web that is apparently still in use (i.e. clean), whereas "cobweb" refers to abandoned (i.e. dusty) webs. However, "cobweb" is used to describe the tangled three-dimensional web of some spiders of the theridiidae family. Whilst this large family is also known as the tangle-web spiders, cobweb spiders and comb-footed spiders, they actually have a huge range of web architectures.
The anatomy of spiders includes many characteristics shared with other arachnids. These characteristics include bodies divided into two segments, eight jointed legs, no wings or antennae, the presence of chelicerae and pedipalps, simple eyes, and an exoskeleton, which is periodically shed.
Spiders also have several adaptations that distinguish them from other arachnids. All spiders are capable of producing silk of various types, which many species use to build webs to ensnare prey. Most spiders possess venom, which is injected into prey (or defensively, when the spider feels threatened) through the fangs of the chelicerae. Male spiders have specialized pedipalps that are used to transfer sperm to the female during mating. Many species of spiders exhibit a great deal of sexual dimorphism.