Spider silk is a protein fibre 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 to protect their offspring. They can also use their silk to suspend themselves.

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 that spiders use for ballooning is known as gossamer. They use silk as a drag-line to help them escape from predators

In detail a drag-line silk's tensile strength is comparable to that of high-grade alloy steel, and about half as strong as aramid filaments, such as Twaron or Kevlar (3000 MPa)

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