Spiders possess a remarkable ability: the production of silk. Every spider species creates silk, even those that do not spin webs. This natural material is central to a spider’s survival, serving numerous functions throughout its life cycle. Its unique characteristics allow spiders to thrive in diverse environments.
The Anatomy of Silk Production
Spiders produce silk within specialized internal organs called silk glands, located in their abdomen. These glands synthesize and store silk proteins as a highly concentrated liquid solution, which remains soluble inside the spider’s body. When a spider needs to spin silk, this solution travels through narrow ducts. As it moves, changes in pH and shear forces cause the proteins to align and solidify into a thread.
The solidified silk is then extruded through external appendages called spinnerets, located on the spider’s underside. Most spiders possess multiple spinnerets, typically ranging from two to eight, which can move independently or in coordination. Each spinneret contains numerous microscopic spigots, with each producing a single filament for the final silk thread. Different silk glands produce distinct types of silk, each suited for specific purposes.
The Remarkable Properties of Spider Silk
Spider silk is primarily composed of large, complex proteins called spidroins. These proteins consist of long chains of amino acids, predominantly glycine and alanine, arranged in repetitive sequences. This molecular structure, with its combination of crystalline and amorphous regions, gives spider silk its unique physical characteristics.
One notable property is its exceptional strength. By weight, spider silk is stronger than steel, making it one of the toughest natural materials. For instance, dragline silk, used for structural support, has a tensile strength of approximately 1.1 GPa, surpassing that of silkworm silk. Furthermore, spider silk exhibits remarkable elasticity, with some types able to stretch up to two to four times their original length without breaking. This combination of high strength and significant elasticity allows silk fibers to absorb substantial energy before fracturing.
The Many Purposes of Spider Silk
Spiders use their silk for a diverse array of functions. The most recognized use is the construction of webs, which act as adhesive traps to capture prey. Different parts of a web are made from different silks, such as strong, non-sticky dragline silk for the frame and spokes, and sticky, elastic silk for the capture spiral.
Silk also serves as a safety line, allowing spiders to drop quickly from heights or retreat from predators while remaining anchored. Many species use silk to build protective egg sacs, shielding offspring from predators and environmental hazards. These sacs vary in appearance and can contain dozens to hundreds of eggs.
Silk also plays a role in spider mobility through “ballooning.” Smaller spiders, especially spiderlings, release fine silk threads into the air, allowing wind currents or static electric fields to carry them over considerable distances for dispersal. Additionally, silk is used to line burrows, wrap captured prey to immobilize them, and in courtship and mating rituals. Some spiders even consume their own silk to recycle proteins, particularly when rebuilding webs.