Spider webs are remarkable feats of natural engineering, designed to capture prey. Their success stems from specialized silk properties and intricate architectural design. The stickiness of a spider web involves distinct components working in concert to ensnare unsuspecting insects.
The Silk’s Unique Structure
Not all parts of a spider web are sticky. The primary structural elements, such as the radial spokes and outer frame, are made of non-sticky dragline silk. This silk provides the web’s strength and acts as the spider’s lifeline.
Dragline silk has tensile strength comparable to high-grade steel, yet is lighter. It also possesses elasticity, allowing it to stretch and absorb the impact of a struggling insect without breaking. This non-adhesive framework supports the web and transmits vibrations to the spider, signaling a capture.
The Adhesive Glue
The true stickiness of a spider web comes from specialized capture spiral silk, coated with an adhesive substance. This “glue” forms tiny, viscous droplets along the silk strands, resembling beads on a string.
Chemically, spider glue is a mixture of glycoproteins (proteins with sugar groups), hygroscopic compounds, and water. Hygroscopic compounds are water-attracting, maintaining the glue’s softness and tackiness by absorbing moisture from the atmosphere. This allows the glue to remain effective across a range of humidity conditions. Glycoproteins act as binding agents, forming connections with anything that touches the web.
How the Web’s Design Enhances Stickiness
The web’s physical layout, especially the sticky capture spiral, works with the adhesive glue to maximize trapping efficiency. The capture silk’s elasticity allows the web to stretch significantly upon impact, sometimes up to five times its original length, absorbing the prey’s kinetic energy.
This stretching prevents insects from bouncing off or tearing through the web. Precisely spaced glue droplets, combined with silk tension, create a wide surface area for contact and adhesion. When prey hits, droplets deform and spread, increasing contact and ensnaring the insect more effectively. This combination of elastic silk and strategically placed adhesive allows the web to capture a broad range of prey sizes.
Spider’s Sticky Solution
How do spiders avoid becoming entangled in their own sticky traps? Spiders have evolved several mechanisms to navigate their webs safely. They primarily walk on the non-sticky radial spokes and frame threads.
Spiders also possess specialized leg features, such as dense arrays of branched hairs called setae, which minimize contact with the adhesive. These hairs allow sticky droplets to slide off easily. Some spiders have a non-stick chemical coating on their legs that reduces adhesion. Spiders also employ careful movement patterns, minimizing adhesive forces during web construction and movement. They can also groom themselves to remove any accidental adhesive.