Eight Striking Facts about Spider Silk Fiber

Spider silk is one of the most unique natural fibers in the world. It is a smooth material produced by various sources, such as silkworms. However, spider silk is quite different from silkworm silk. Most spider species produce silk because it is essential to their survival. They use it for shelter, transportation, and mating purposes. It is also a necessary tool for catching the prey a spider eats. 

This article explores eight exciting facts about spider silk. We will discuss how spider silk is five times stronger than steel and 1,000 times thinner than human hair. We will also discuss how spiders produce spider silk and what makes spider silk different from other natural fibers. 

What makes spider silk unique?

1. By weight, spider silk is stronger than steel.

Spider silk is five times stronger than steel. Scientists figured this out by analyzing the silk from venomous brown recluse spiders with an atomic force microscope. Each strand of spider silk is 1000 times thinner than human hair as it consists of thousands of parallel Nano strands⁶.

Spider silk is a strong and versatile material for such a thin material. It explains how spider webs hold up in strong winds and rain and withstand the force of struggling insects trapped inside. Spider silk doesn’t have the stiffness of steel, but it has a higher strength-to-density ratio and similar tensile strength. 

Tensile strength is the stress a substance can endure before it breaks. Spider silk is as strong as Kevlar, the strongest artificial polymer. Spider silk’s tensile strength measures 0.45 - 2.0 GPa, while a dragline is about 1.1 GPa. The golden orb-weaving spider’s dragline silk is the toughest silk among all spider species.

The elasticity of spider silk is also something to write home about. It can stretch up to four times its original length without breaking, making it better than rubber, silk, or nylon. Also, it can maintain its strength below -40 degrees Celsius and above 200 degrees Celsius—the structure of the spider silk breaks under conditions above 300 degrees Celsius⁴.

2. Spiders have seven silk glands that produce silk.

Spiders produce seven types of silk. They don’t produce all silk types from the same silk gland. There are different silk glands to various kinds of silk, and a spider can produce up to 4 types of silk. For example, common orb-web spiders produce four types of silk glands, and Darwin’s bark spiders have all seven glands. 

Most types of spiders have at least three silk glands (dragline, attachment, and swathing silk glands)  unless it is a female spiders. Female spiders have at least four because they produce egg sac silk. These silk glands are in the lower side of the spider’s abdomen. The glands can occupy a lot of space in a spider’s body, depending on the quantity.

The seven silk glands that spiders use are: 

• Achniform: Achniform glands produce swathing silk that captures and envelops a spider’s prey.
• Aggregate: Aggregate silk glands are common to araneid spiders, and they produce the spider glue on the surface of sticky silk. 
• Ampullate: there are two groups of Ampullate silk glands: major and minor ampullate glands. Ampullate Major produces non-sticky dragline silk used to connect the spider to its web. Non-sticky dragline silk is a safety line as spiders can move or fall out of their webs. It is usually the strongest part of a spider web because it supports the weight of a spider.  

The silk from the ampullate minor gland isn’t as strong as non-sticky draglines. However, it is more elastic, and web-building spiders use it to build webs and trap prey. Newly hatched spiderlings and jumping spiders use ampullate major silk to disperse, like an elevator. 

• Cylindriform: this gland produces stiff silk used as egg sacs. The stiffness helps protect spider eggs from harm. 
• Flagelliform: It works hand in hand with the aggregate gland to create the core fibers of sticky silk. It produces the stretchy center of a web’s capturing lines. The spider glue from the aggregate gland coats the lines, and their elastic properties give the glue enough time to catch prey before it escapes. 
• Pyriform: produces the threads that form the attachment disks that anchor a silk thread to a surface or another silk thread. 

3. Spider silk forms from a fluid, spinning dope, and spider silk proteins known as spidroins.

Spider silk forms from the proteinous liquid in the silk glands and the spinneret.  Spiders produce silk from fluid with proteins arranged in a liquid crystalline solution. The liquid is formed in the silk glands, and it moves via the little tubes in the glands into the spinneret. 

Fluids from all the silk glands often lead to the same spinneret, where the proteins align and solidify. The spinneret helps the spider make silk for specific tasks. The spidroins can be up to 350 kDA per monomer. They share a primary structure pattern containing a large central core of repeated modular units, which account for 90% of the protein's amino acids. Also, non-repetitive domains accompany the primary structure.

The terminal domains are necessary for protein storage and fiber formation in the silk glands and spinneret because that is where spiders trigger the assembly of proteins according to environmental changes. 

Spider silk isn't just made from proteins. It also requires the mechanical properties only spiders possess. Humans have tried to recreate spider silk from spidroins, but the fibers spun were not similar to spider silk. This shows that the spider’s spinning process is essential to creating spider silk⁷.

4. Spider silks conduct heat better than most materials.  

A professor of mechanical engineering at the Iowa State University, Xinwei Wang became curious about the capabilities of spider webs in 2012. His study focused on the ability of materials to conduct heat. Throughout his career, he looked for natural materials, like copper and aluminum, that could conduct heat.

Some speculated that spider silk could conduct heat, but no one tested the possibility until Xinwei Wang came along. With the help of the Army Research Office, National Science Foundation, Xiaopeng Huang, a mechanical postdoctoral research associate, and Growing Liu, a mechanical engineering doctoral student, Wang tested dragline silk. 

The lab experiments showed that spider silk, especially dragline silks, conducts heat better than most materials, such as silicon, copper, pure iron, and aluminum. Spider silks also conduct heat 1,000 times better than silkworm silk and 800 times better than other natural tissues.

Spider silk’s heat conduction is at 416 watts per meter Kelvin. It is 15 watts higher than copper, which is 401 watts per meter. Xinwei Wang also learned that the silk’s conductivity increases by 20% when stretched to its 20% limit¹.

Wang's discovery opens up the world to a lot more possibilities. For example, we can create flexible, heat-conducting parts for electronics and bandages that don't trap heat. We need more research into the heat-conducting abilities of spider silk to utilize its full potential. 

5. Spider silk is a versatile material that spiders use in various ways. 

Spiders use their silk in various ways, including shelter, transportation, and catching prey. One method of transportation is ballooning, in which spiders make silk sails to travel long distances. Newly hatched spiderlings use this method to disperse from their birthplace. Some adult spider species also use ballooning to transport themselves.

Orb-weaving spiders use their silk like a slingshot to catapult themselves over short distances. They rely on the silk’s elastic recoil to move quickly. The arachnids also use silk to make trapdoors, tubes, and funnels. They create unique webs like spiral and sheet webs. 

Semi-aquatic spiders, like the diving spell spider, use their silk to make submarines. As seen in the video above, it is the only spider that spends almost its entire life underwater. It uses silk to create a bubble around itself underwater and leaves open an air chamber to get oxygen and catch prey. 

The diving bell spider creates a bell-shaped web that hangs on underwater plants, with silk lines that extend to the surface. It uses these lines to reach the surface and collect air bubbles into the spider web. The bell-shaped web can also absorb dissolved oxygen from the water.

Spiders produce silk to wrap up and immobilize their prey. It is pretty difficult for insects to escape a spider’s web. They also use their silk to make protective egg cocoons, molting nests, spiderling nurseries, courting, and reproduction activities. Male spiders use their silk to wrap food items as a gift for females to woo them. 

They practice mate binding or bridal veil during courtship. They tie females with silk to connect their sensory hairs with the male’s pheromone silk. It makes them a lot more receptive to mating. Furthermore, male spiders can tie females up during mating to prevent cannibalism.

6. The feather-legged lace weaver has the most unique silk that produces electrostatic charge.   

The feather-legged lace weaver, also known as the Uloborus plumipes or the garden center spider, has a unique method of catching their prey. According to a paper published in Biology Letters on January 27, 2015, by Katrin Kronenberger and Fritz Vollrath, the process is complex.

The garden center spider produces a silk fluid from the cribellum into a silk thread. It has the world’s smallest spigots, tiny and hollow hairs at the tip of the spinneret.  It also comes out with thousands of tiny filaments by combing the hair on its hind legs. The violent movements spin an electrostatic web that attracts insects. 

Combing the thread as it solidifies makes the web look like cotton fiber. However, it gives the web a little electrostatic charge. Scientists are excited about this discovery because of its implications for nanotechnology⁵. 

The research co-author, Fritz Vollrath, says conducting more studies on the feather-legged lace weaver spider will help us learn how to create nano-scale filaments, and we could produce a new kind of polymer processing technology.

7. Spiders use their silk to communicate with each other.

Spiders listen to their environment through the vibrations from their web. Many spiders know that prey has been caught in their web through the vibrations on the spider silk. However, it is more challenging than it sounds. 

Spider silk can produce a wide range of frequencies when plucked like a guitar string. Most spiders see poorly and rely on the sensory information from the vibration of the silk in their web. The sounds from the silk strings can tell the spider the type of prey caught in its web and the quality of a potential mate.

Also, spiders can determine the condition of their web by listening to the sounds of plucking the silk threads. Scientists studied this process using ultra-high-speed cameras to film the threads as they reacted to being hit by bullets. They also used lasers to measure the littlest vibrations.

Furthermore, the researchers learned that spiders receive these vibrations with slit sensillae, an organ on each of their legs. They believe the ability of silk to transfer delicate information will make a significant impact in the field of light-weight engineering².

8. Spider silk inspired the production of synthetic spider silk. 

The impressive qualities of spider silk inspired the production of artificial spider silk. Material scientists have been trying to recreate spider silk for decades. Unfortunately, they have been unsuccessful because of the complexity and evolution of their process.

Recently, a group of researchers at the University of Oxford created a new material that is as stretchy and absorbs as much energy as spider silk³. The material is from hydrogel, a substance that is 98% water and 2% silica and cellulose. It also contains cucurbituril molecules, which act as a binder for the silica and the cellulose.

They remove the silica and cellulose fiber from the hydrogel, and the water evaporates in about 30 seconds, leaving behind a stretchy and tough thread. The fiber is strong but less firm than spider silk's natural fiber. 

Synthetic spider silk has massive potential because it is biodegradable and easily affordable. After all, it is made from accessible materials. Also, production doesn’t require chemical solvents because we can produce them at room temperature. Producing it won’t need as much energy as making other synthetic fibers that require incredibly high temperatures, like nylon.

We can use synthetic fiber to make protective fabrics, sail clothes, hot air balloons, helmets, and parachutes. It is also biocompatible, meaning we can use it in medical procedures inside the human body.  

Conclusion  

As you can already tell, spiders are cool arthropods capable of producing one of the strongest materials in the world. Spider silk is an exceptional bio-material formed from a fluid with many proteins in an organ in the spider’s abdomen. 

The spider silk has sticky and non-sticky parts, and spiders use sticky silk to trap prey. It has extraordinary mechanical properties that cannot compare to steel, aluminum, and pure iron. Spider silk also gets bonus points because it is hypoallergenic and has antimicrobial activity.