Spider silk is very strong, elastic and sticky. Studies have shown that spiders attract specific types of prey through their manipulation of silk colors and patterns. All insect silks are made of the same proteins. The concentrations of these proteins in the silk -- alanine, glycene and serine -- vary with the type of silk. Some scientists believe that more advanced spiders diverged from primitive spiders by developing superior silk-producing glands.
Spider webs are made of silk and do not fossilize. Researchers theorize that ancient spider webs probably looked different from those seen today, because spiders must have adapted and started producing better silk while weaving webs that keep them farther away from predators and help catch their prey. Scientists say that a link exists between spider evolution and web function. Over time, many spiders began to produce dryer and stickier silk. These spiders also began spinning flat aerial sheet webs instead of orb webs, and many of them abandoned webs altogether, preferring to live in silk-lined burrows or on the ground.
The venom of spiders is a mixture of toxins used primarily to immobilize their prey. From spider to spider, the composition and the toxicity of venom varies greatly. Studies of an enzyme unique to the venom of the brown recluse spider found that it is a chemical that causes skin lesion and systemic reactions -- skin rotting -- in bitten humans. Scientists then found this same enzyme in the venom of a close relative of the brown recluse. When both gene sets were compared, it was found that both spiders had inherited their venom from a common ancestor.
Spiders live in every habitat except for the polar regions and the oceans. Spider species found in multiple regions traveled there originally by ballooning -- putting out silk threads that are caught by the wind, carrying spider for a few to a few hundred miles away. Some spiders evolved in specialized habitats like caves or even underwater. A water spider lives at the edge of the water and can survive underwater for several months using the same pocket of air. Surviving on small fish and insects, this spider mates underwater and lays its eggs underwater in order to avoid its predators, which live on land. The fisher spider is another type of water spider that feeds on tiny fish and can float on the surface of the water.