Spider Silk Is Nature's Miracle Fiber

Spider silk is one of the most miraculous natural substances on Earth. Most building materials are either strong or elastic, but spider silk is both. It's been described as stronger than steel (which is not quite accurate, but close), more impenetrable than Kevlar, and stretchier than nylon. It withstands a lot of strain before breaking, which is the very definition of a tough material. Spider silk also conducts heat and is known to have antibiotic properties.

All Spiders Produce Silk

All spiders produce silk, from the tiniest jumping spider to the biggest tarantula. A spider has special structures called spinnerets at the end of its abdomen. You've probably watched a spider constructing a web, or rappelling from a silk thread. The spider uses its hind legs to pull the strand of silk from its spinnerets, little by little.

Spider Silk Is Made From Protein

But what is spider silk, exactly? Spider silk is a fiber of protein, produced by a gland in the spider's abdomen. The gland stores silk protein in liquid form, which isn't particularly useful for building structures like webs. When the spider needs silk, the liquefied protein passes through a canal where it gets an acid bath. As the pH of the silk protein is lowered (as it's acidified), it changes the structure. The motion of pulling the silk from the spinnerets puts tension on the substance, which helps it harden into a solid as it emerges.

Structurally, silk consists of layers of amorphous and crystalline proteins. The firmer protein crystals give silk its strength, while the softer, shapeless protein provides elasticity. Protein is a naturally occurring polymer (in this case, a chain of amino acids). Spider silk, keratin, and collagen are all formed of protein.

Spiders will often recycle valuable silk proteins by eating their webs. Scientists have labeled silk proteins using radioactive markers and examined new silk to determine how efficiently spiders reprocess the silk. Remarkably, they've found spiders can consume and reuse silk proteins in 30 minutes. That's an amazing recycling system!

This versatile material could have limitless applications, but harvesting spider silk isn't very practical on a large scale. Producing a synthetic material with the properties of spider silk has long been the Holy Grail of scientific research. 

8 Ways Spiders Use Silk

Scientists have studied spider silk for centuries, and have learned quite a bit about how spider silk is made and used. Some spiders can actually produce 6 or 7 kinds of silk using different silk glands. When the spider weaves a silk thread, it can combine these varied kinds of silks to produce specialized fibers for different purposes. Sometimes the spider needs a stickier silk strand, and other times it needs a stronger one.

Read More

Why Spiders Don't Get Stuck In Their Own Webs

By Debbie Hadley

As you might imagine, spiders make good use of their silk-producing skills. When we think of spiders spinning silk, we usually think of them building webs. But spiders use silk for many purposes. 

1. Spiders Use Silk to Catch Prey

The best-known use of silk by spiders is for constructing webs, which they use to ensnare prey. Some spiders, like orb weavers, construct circular webs with sticky threads to snag flying insects. Purse web spiders use an innovative design. They spin an upright silk tube and hide inside it. When an insect lands on the outside of the tube, the purse web spider cuts the silk and pulls the insect inside. Most web-weaving spiders have poor eyesight, so they sense prey in the web by feeling for vibrations traveling across the silk strands. A recent study showed that spider silk can vibrate at a wide range of frequencies, allowing the spider to sense movements "as small as a hundred nanometers—1/1000 the width of a human hair."

But that's not the only way spiders use silks to catch meals. The bolas spider, for example, spins a sort of fishing line of silk – a long thread with a sticky ball at the end. When an insect passes by, the bolas spider flings the line at the prey and hauls in its catch. 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 and ensnares the prey.

2. Spiders User Silk to Subdue Prey

Some spiders, like cobweb spiders, use silk to subdue their prey completely. Have you ever watched a spider grab a fly or moth, and quickly wrap it in silk like a mummy? Cobweb spiders have special setae on their feet, which enable them to wind sticky silk tightly around a struggling insect. 

3. Spiders Use Silk to Travel

Anyone who read Charlotte's Web as a child will be familiar with this spider behavior, known as ballooning. Young spiders (called spiderlings) disperse soon after emerging from their egg sac. In some species, the spiderling will climb onto an exposed surface, raise its abdomen, and cast a silk thread into the wind. As the air current pulls on the silk strand, the spiderling becomes airborne and can be carried for miles.

4. Spiders Use Silk to Keep From Falling

Who hasn't been startled by a spider descending suddenly on a silk thread? Spiders habitually leave a trail of silk line, known as a dragline, behind them as they explore an area. The silk safety line helps the spider keep from falling unchecked. Spiders also use the dragline to descend in a controlled manner. If the spider finds trouble below, it can quickly ascend the line to safety.

5. Spiders Use Silk to Keep From Getting Lost

Spiders can also use the dragline to find their way home. Should a spider wander too far from its retreat or burrow, it can follow the silk line back to its home.

6. Spiders Use Silk to Take Shelter

Many spiders use silk to construct or reinforce a shelter or retreat. Both tarantulas and wolf spiders dig burrows in the ground and line their homes with silk. Some web-building spiders construct special retreats within or adjacent to their webs. Funnel weaver spiders, for example, spin a cone-shaped retreat in one side of their webs, where they can stay hidden from both prey and predators.

7. Spiders Use Silk to Mate

Before mating, a male spider must prepare and ready his sperm. Male spiders spin silk and construct small sperm webs, just for this purpose. He transfers sperm from his genital opening to the special web and then picks up the sperm with his pedipalps. With his sperm securely stored in his pedipalps, he can search for a receptive female.

8. Spiders Use Silk to Protect Their Offspring

Female spiders produce particularly tough silk to construct egg sacs. She then deposits her eggs inside the sac, where they will be protected from the weather and potential predators as they develop and hatch into tiny spiderlings. Most mother spiders secure the egg sac to a surface, often near her web. Wolf spiders don't take chances and carry the egg sac around until the offspring emerge.

_Sources:

• _{Borror and Delong's Introduction to the Study of Insects, 7th edition, by Charles A. Triplehorn and Norman F. Johnson.}
• _{Encyclopedia of Entomology, 2nd edition, edited by John L. Capinera.}
• _{ASU scientists unravel the mysteries of spider silk, Arizona State University, January 27, 2013.}
• _{Iowa State engineer discovers spider silk conducts heat as well as metals, Iowa State University, March 5, 2012.} 
• _{Lowering pH regulates spider’s silk production, Swedish University of Agricultural Sciences, May 12, 2010.}
• _{Stanford Researcher Sheds New Light on the Mysteries of Spider Silk, Stanford University, February 4, 2013.} 
• _{Bugs Rule! Introduction to the World of Insects, by Whitney Cranshaw and Richard Redak.}
• _{Spiders, Smithsonian National Museum of Natural History website.}
• _{Spiders Listen to Their Webs, by Carrie Arnold, National Geographic website, June 5, 2014.}
• _{Net-Casting Spiders, Australian Museum website.}
• _{Purseweb Spiders, University of Kentucky Entomology website.}