Biology and Applications of Spider Silk

Web-building spiders utilise distinct strategies to capture prey, reflected in the evolutionary divergence between cribellate and ecribellate silk. Primitive cribellate spiders produce dry, multi-stranded capture threads by combing ultrafine fibrils over thicker axial lines using a specialised leg structure. Adhesion occurs primarily through physical van der Waals forces and hygroscopic nanofibre tangling. Conversely, modern ecribellate spiders coat single silk strands with viscous, aqueous droplets containing glycoproteins and hygroscopic salts. Although both types effectively immobilise insects, aqueous droplets require ambient humidity to retain adhesion, whereas dry cribellate silk functions consistently across a broader range of environmental conditions.

Replicating the physical properties of natural spider silk in laboratory settings has long challenged bioengineers. Although researchers have successfully inserted spidroin genes into host organisms such as bacteria, yeast, and transgenic plants, mass-producing functional fibres remains difficult. The native assembly process in a spider's gland involves precise gradients of pH, ion exchange, and shear stress, which guide the proteins from a liquid crystal dope into solid filaments. Artificial extrusion systems often struggle to replicate these exact microfluidic conditions, yielding synthetic fibres with irregular molecular alignment and inferior toughness compared to their biological counterparts.

Constructing an orb web requires a considerable expenditure of metabolic energy and protein reserves. To offset this nutritional investment, many orb-weaving species regularly dismantle their damaged webs and ingest the discarded silk before spinning a new structure. The ingested silk is rapidly degraded by proteolytic enzymes in the digestive tract, allowing the spider to reclaim amino acids with minimal waste. Radiolabelling experiments indicate that a substantial fraction of these reclaimed nutrients is reincorporated into freshly secreted silk within several hours. This internal recycling loop represents an efficient evolutionary adaptation that maintains high web-building frequency while conserving finite metabolic resources.

The diving bell spider spends virtually its entire lifecycle submerged underwater, an ecological niche made possible solely by specialised silk. The spider constructs an underwater dome anchored to aquatic vegetation and manually transports air bubbles from the surface on its abdomen to fill the structure. The silk lattice not only holds the air pocket stable against water currents but also acts as an artificial gill. Because the silk membrane permits gas exchange with the surrounding water, dissolved oxygen diffuses inward while carbon dioxide diffuses outward, allowing the spider to remain submerged for extended durations without frequent surface visits.