Uses

Spiders use silk for a variety of functions:

• Swathing silk for the wrapping and immobilisation of prey.

• Webs for catching prey using sticky silk - it is elastic to prevent the prey from rebounding off the web.

• Draglines which are used to connect the spider to the web, as safety lines in case a spider should fall and as the non-sticky spokes of the web.  Dragline silk is the strongest kind of silk because it must support the weight of the spider.

• Parachuting or ballooning which is used to aid the dispersal of young and to find new areas as a food source.  Silk is released and is caught by the wind to lift the spider up into the air - flying spiders!

• Shelters such as burrows or nests

• Egg-sacs

• Mating: male spiders weave sperm webs on which they deposit sperm and subsequently transfer it to their front palps, ready for placing on a females genital organs.  Some species make a web and coat it with sex pheromones to attract a mate.

The spider, after spinning its web, will then wait on or near the web for a prey animal to become trapped. The spider senses the impact and struggle of a prey animal by vibrations transmitted along the web lines.

Spiders do not usually adhere to their own webs. However, they are not immune to their own glue. Some of the strands of the web are sticky, and others are not. For example, if a spider has chosen to wait along the outer edges of its web, it may spin a non-sticky prey or signal line to the web hub to monitor web movement. Spiders have to be careful to climb only on the non-sticky strands of their webs.

A spider positioned in the middle of the web makes for a highly visible prey for birds and other predators, even without web decorations. Many day-hunting orb-web spinners reduce this risk by hiding at the edge of the web with one foot on a signal line from the hub or by appearing to be inedible or unappetizing.

Some species of spiders do not use webs for capturing prey directly, instead pouncing from concealment (e.g. Trapdoor spiders) or running them down in open chase (e.g. Wolf spiders). The Net-casting spider balances the two methods of running and web spinning in its feeding habits. This spider weaves a small net which it attaches to its front legs. It then lurks in wait for potential prey and, when such prey arrives, lunges forward to wrap its victim in the net, bite and paralyze it. Hence, this spider expends less energy catching prey than a primitive hunter such as the Wolf spider. It also avoids the energy loss of weaving a large orb web.

Some spiders manage to use the signaling-snare technique of a web without spinning a web at all. Several types of water-dwelling spiders will rest their feet on the water's surface in much the same manner as an orb-web user. When an insect falls onto the water and is ensnared by surface tension, the spider can detect the vibrations and run out to capture the prey.

In traditional European medicine, cobwebs are used on wounds and cuts and seem to help healing and reduce bleeding.

Cobweb paintings, which began during the 16th century in a remote valley of the Austrian Tyrolean Alps, were created on fabrics consisting of layered and wound cobwebs, stretched over cardboard to make a mat, and strengthened by brushing with milk diluted in water. A small brush was then used to apply watercolor to the cobwebs, or custom tools to create engravings. Fewer than a hundred cobweb paintings survive today, mostly in private collections.

Commonly, webs are about 20 times larger than the spider building it. Spider webs are rich in vitamin K, which can be effective in clotting blood. Webs were used several hundred years ago as gause pads to stop an injured person's bleeding.