Spider silk is one of Nature’s most miraculous natural substances. Both strong and more elastic than nylon, it is relatively impenetrable. It actually can conduct heat, and is known to have antibiotic properties. All spiders produce silk from special structures called spinnerets at the end of their abdomens. Hind legs are used to pull the strand of silk from the spinnerets.
Spider silk is made up of silk protein in liquid form coming from a gland in the spider's abdomen. The protein is a natural polymer chain of amino acids and is stored until needed to form solid silk. When needed, it passes through an exit canal where it undergoes chemical changes. The act of pulling the silk from the hind-leg spinnerets puts tension on the silk causing it to form a solid strand.
Spider silk has been studied for centuries, and is known to consist of layers of both soft and harder crystal proteins. The protein crystals give silk its strength, while softer proteins give it stretch and make it sticky. Spiders produce the differing types of silk such as sticky for capturing prey, or stronger for web building. The exact protein arrangement determines how strong and stretchy the silk becomes. Spider silk is less than one thousandth of an inch in diameter and consists of a bundle of protein fibers within a shell.
Spiders can recycle their silk by consuming their webs when damaged or web relocation is desired. Some rebuild every day to maintain a fresh web. Scientists have studied silk recycling using radioactive markers and discovered that recycled silk can occur in a web in thirty minutes. The most common use of spider silk is for webs to catch prey. These often are elaborate circular webs with sticky threads. These webs have amazing geometry. Most web spiders sense the presence of a captured insect from web movement created by struggling insects. I actually played a trick on my big yellow garden spider by vibrating the edge of her web which caused her to come investigate thinking I was a struggling insect.
"Purse" web spiders spin an upright silk tube and hide inside waiting for an insect to land on the outside so the spider can pull it into the tube. Another spider called the "Bola", uses long threads with sticky balls at the ends, flinging them after victims. "Net-casting" spiders spin a small web shaped like a tiny net and hold it between their feet. When an insect comes near, the spider throws its silk net over the insect. "Cobweb spiders", use silk to quickly wrap victims like a mummy before ingesting them. These spiders have special hair-like structures on their feet enabling them to tightly wind sticky silk around a struggling victim. Who knew there were such varied and creative ways that spiders use their silk to capture victims?
Spiders also use their silk strands for purposes other than building a web. Some use silk to travel. Young spiderlings need to disperse soon after emerging from their egg sac. Some climb onto an exposed surface, raise their abdomen, and cast a silk thread into the wind becoming airborne traveling for long distances. Spiders always leave a silk line trail, known as a dragline, behind them as they travel or explore. Should a spider find trouble, it quickly can climb the line to safety or the silk line can be used as a safety line to prevent hazardous free falling. Many spiders use silk to build or reinforce a shelter. Both wolf spiders and tarantulas dig burrows in the ground and line them with silk. Some web-building spiders build special "retreats" within or adjacent to their webs. "Funnel weaver" spiders spin a cone-shaped retreat to one side of their web where they hide while waiting for prey.
Before mating, a male spider must prepare for storing his sperm by spinning small silk sperm webs just for this purpose. The male then carries it with his second pair of legs called pedipalps that are attached near his head. With his sperm securely stored, he then can search for a receptive female. Female spiders produce particularly tough silk to construct egg sacs. My previous article about the big female yellow garden spider that lived in my garden contained a photograph of her brown silk egg sac that was near her web. I watched her firmly attach it to the building with her silk it was protected from the weather and potential predators. "Wolf" spiders actually carry their egg sac around until the offspring emerge.
Spiders are beneficial arachnids (not insects, since they have eight not six legs). Unfortunately their association with Halloween and ghoulish imagery inspires fear and revulsion for many people. This is a real disservice for the spiders leading to unnecessary death for many harmless beneficial spiders. Please think about thid the next time you encounter a spider.
