Spider silk: biology, properties, and human applications

Composition and production

Silk threads are made from large structural proteins called spidroins that are synthesized in specialised silk glands in the spider's abdomen. Each gland produces a distinct silk type. Liquid protein dope is extruded through spinnerets and converted into a solid fibre by a controlled process of dehydration, pH change and mechanical shear. This biological spinning gives silk its characteristic microstructure and performance.

Types and biological functions

Different glands yield functionally distinct silks. Common types include:

• Dragline (major ampullate) – strong structural threads used as lifelines and web frames.
• Capture spiral (flagelliform and aggregate) – elastic, often coated with sticky glue for trapping prey.
• Tubiliform – used to construct egg sacs and protect offspring.
• Aciniform and others – used for wrapping prey, lining retreats or anchoring silk structures.

Mechanical properties and distinctions

Spider silk combines high tensile strength with extensibility, giving it high toughness. In popular descriptions it is often said to be "tougher than steel on a per-weight basis," which reflects the fibre's notable energy absorption relative to its mass. Mechanical performance varies by silk type and species. Unlike the continuous filament silk produced by silk worms and harvested in sericulture, spider silk is spun by individual animals and historically has been difficult to collect in large quantities.

Human interest and applications

Because of its biodegradability and mechanical traits, spider silk is studied for medical sutures, tissue engineering scaffolds, high-performance fibres and advanced composites. Direct farming of spiders is impractical—many species are solitary or cannibalistic—so research has focused on producing spidroin proteins recombinantly in bacteria, yeast, plants or transgenic animals, and on biomimetic spinning techniques to replicate natural fibre properties.

Notable facts and conservation

Spider silk illustrates how evolution can produce multifunctional materials at ambient temperatures. While it cannot yet compete with industrial fibres in bulk production, advances in biotechnology aim to bridge that gap. For further reading on spiders, silk production, and ongoing synthetic efforts see resources linked here: silkworms and comparative sericulture, and additional scientific overviews at relevant repositories.