Technically, a web is not just anything a spider makes out of silk; it is a silk structure made to catch prey, although, only about half of the known spider species catch prey with a web. Others actively hunt for prey, or sit and wait for prey to come to them.
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, which is a little silk “house” the spider rests in.
About 320 million years ago arthropod’s known as arachnida began making silk to protect their bodies and their eggs. They gradually learned to use that same silk for hunting purposes, first as guide lines and signal lines, then as ground or bush webs, and eventually as the aerial webs that are familiar today.
Spider silk is a protein fibre spun by spiders, who use their silk to make webs or other structures. In some cases these webs function as sticky nets to catch other animals, or as nests or cocoons to protect their offspring. In some cases spiders use silk to wrap up prey. They can also use their silk to suspend themselves, to float through the air, or to glide away from predators. Most spiders vary the thickness and stickiness of their silk for different uses.
Silk is produced from a spiders spinneret glands, located at the tip of their abdomen. Most spiders have three pairs of spinnerets, each having its own function. Each gland produces a thread for a special purpose – for example: a trailed safety line, a sticky silk for trapping prey or fine silk for wrapping it. Different gland types are used to produce different silks, and some spiders are capable of producing up to 8 different silks during their lifetime.
Finer than a human hair, spider silk is almost as strong as Kevlar. Its tensile strength is greater than the same gauge of steel and has much greater elasticity. Its microstructure is under investigation for potential applications in industry, including bullet-proof vests and artificial tendons. Researchers have used genetically modified mammals to produce the proteins needed to make this material.
Throughout history, humans have found uses for spider silk. Peasants in the southern Carpathian Mountains of central and eastern Europe used to cut up silk tubes built by Atypus (the purse web spider) and cover wounds with the inner lining. It reportedly facilitated healing, and even made a connection with the skin. This is believed to be due to an antiseptic property of spider silk which is rich in vitamin K. It can also be effective in clotting blood.
Fishermen on coasts of the indopacific ocean remove Nephila webs and form them into a ball, which is thrown into the water. There it unfolds and is used to catch bait fish.
Nephila silk is an excellent scaffold material thanks to its biocompatibility, mechanical strengths, and its property to promote cell adhesion and proliferation and the silk of Nephila clavipes has recently been used to help in mammalian neuronal regeneration.
At one time, it was common to use spider silk as a thread for crosshairs in optical instruments such as telescopes, microscopes, and telescopic rifle sights.
Due to the difficulties in extracting and processing substantial amounts of spider silk, the largest known piece of cloth made of spider silk is an 11-by-4-foot textile with a golden tint made in Madagascar in 2009. To do this, eighty-two people worked for four years to collect over one million golden orb spiders and extract silk from them.