Cobwebs, the delicate, dusty strands often seen in undisturbed corners, might seem like simple indicators of neglect. However, they represent a fascinating intersection of natural engineering and biological complexity. Understanding them involves examining the remarkable material they are made from and the intricate biological processes spiders use to create them.
Distinguishing Cobwebs from Fresh Webs
A cobweb is an older, abandoned spider web that has collected dust and debris. Unlike a fresh web, which a spider actively maintains for hunting, a cobweb no longer serves its original function. These dusty remnants are frequently found in quiet, undisturbed areas like ceiling corners, attics, basements, and behind furniture.
Dust and airborne particles accumulate on cobwebs because the silk threads, particularly those coated with a glue-like substance for prey capture, become sticky and efficiently trap these materials. This dusty appearance differentiates a cobweb from a new, often glistening, web. While any abandoned web can become a cobweb, they are often associated with the irregular, tangled webs built by certain house spiders, especially those from the Theridiidae family.
The Remarkable Material: Spider Silk
Cobwebs are made of spider silk, a protein-based fiber with extraordinary properties. Spider silk is composed primarily of large proteins called spidroins, which consist mainly of nonpolar and hydrophobic amino acids like glycine and alanine. These amino acids contribute to the silk’s unique combination of strength and flexibility.
Spider silk’s mechanical properties include high tensile strength and remarkable elasticity. Some types of silk have a tensile strength comparable to steel, yet are nearly as elastic as rubber, stretching significantly without breaking. This combination of strength and stretchiness allows silk to absorb a large amount of energy before failing, a property known as toughness, surpassing synthetic fibers like Kevlar on a weight-for-weight basis. Spider silk is also inherently biodegradable, breaking down naturally due to its protein composition.
Spider Silk Production and Its Variety
Spiders produce silk within specialized glands in their abdomen. The silk begins as a liquid protein solution and solidifies as it is extruded. This transformation occurs as the spider pulls the liquid silk through narrow ducts, where water is removed, and proteins align to form a solid thread.
Extrusion occurs through spinnerets, silk-spinning organs typically found on the underside of a spider’s abdomen. Most spiders possess multiple spinnerets, each with numerous microscopic spigots. These spigots connect to different silk glands, allowing spiders to produce various types of silk, each optimized for specific functions. For instance, dragline silk, used for the web’s structural framework and as a safety line, is exceptionally strong. Capture silk, found in the sticky spiral of a web, is highly elastic to ensnare prey. Other silks include those for wrapping prey, constructing egg sacs, or creating specialized attachment discs. This versatility allows spiders to construct diverse web structures, even those that eventually become cobwebs.