Sangeetha Pulapaka
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Technically, a web is not just anything a spider makes out of silk; it is a silk structure made to catch prey. Only about half of the known spider species catch prey by means of webs. Others actively hunt for prey (including members of the wolf spider, jumping spider, ground spider, sac spider, lynx spider, and other spider families), or sit and wait for prey to come to them (trap door spiders, crab spiders, and others).

Hunting spiders use their silk for the dragline (the single thread all spiders leave behind them when they walk), the egg sac, and in some species, the retreat (a little silk "house" the spider rests in), all shown below, but do not make true webs.

 Here are some pictures of hunting spiders


Various species of spiders use silk extruded from spinnerets to build webs. Spinnerets are the organs through which a spider produces silk threads. They’re located at the rear of the abdomen, on the underside. Spiders normally have three pairs, but some species have only one pair and others as many as four. Seven types of silk glands have been identified, but no spider has all seven. The spinnerets move independently but in a coordinated way.


Silk glands produce proteins and other organic molecules which flow in liquid form through microscopic tubes to the spinnerets. As the mixture moves along, a process occurs which removes water from the proteins and adds hydrogen. The result is an acidic fiber which solidifies as it exits into the air through the spinnerets.

Each silk gland produces silk used for a different purpose: attachment silk; dragline and web frame silk; silk for wrapping, sperm web, and egg cocoons; and sticky silk. Spiders can use the threads singly or in combination. Silk threads are about one-millionth of an inch thick, but spiders can use muscles and valves in the necks of their spinnerets, singly or in combination, to thicken them.

Spiders use their silk in many ways, and different spiders use silk for different purposes. Not all spiders build webs, but all spiders do produce silk and use it for draglines. All males use silk to spin a sperm web before mating, and all females spin a silk cocoon around their eggs. Some spiders use silk to build shelters. Spiders are thrifty with their silk. Webs begin to degrade after a few days, so often spiders eat them and re-use the protein.

Spider silk is stronger than steel on a weight basis. If you made a steel rod and compared it to a rod of silk of the same weight, the silk rod would be stronger. Silk is amazingly elastic, too, able to stretch up to many times its original length. The thread of the orb-weaver spider Stegodyphus sarasinorum, an Asian species, is said to stretch up to 20 times its original length.

Orb-weavers spin their webs at night. From a suitable starting point, such as the branch of a tree, they release a thread of strong silk from a spinneret into the wind. If it doesn’t snag on something, the spider may pull it back and eat it to recycle the protein it contains before trying again. 

Once it catches on something, the spider pulls the thread tight and anchors it. Then, it walks back and forth, reinforcing the line by adding more threads. Called the bridge line; it will support the weight of the entire web. Here is a little more info on this

https://io9.gizmodo.com/how-does-a-spider-decide-where-to-build-its-web-1643527688