Information

How strong is spider silk?


Spider silk is pretty darn strong and all sorts of comparisons are made to steel. I'm more curious about the various moduli of spider silk and how it compares to other materials. What is the Young's modulus of spider silk? What is the bulk modulus of spider silk? What is the shear modulus of spider silk? In general how do those moduli describe the material properties of spider.

A simpler way to ask the question, what does it mean when it is said that spider silk is strong?


Wikipedia has a remarkably well-cited article on the subject of silks and their various biological isoforms and mechanical properties. With respect to tensile strength, spider's silk is as tough as high-grade steel.

Explcitly, dragline silk was measured by Pérez-Rigueiro at al. to be 600 ± 50 MPa with a comparison to silkworm silk.

Reference:

  • Pérez-Rigueiro J, Elices M, Llorca J, Viney C. 2001. Tensile properties ofArgiope trifasciata drag line silk obtained from the spider's web. Journal of Applied Polymer Science 82: 2245-2251 [pdf]

Spider Silk: The Biology Behind the Incredible Material

While many scientists are focused on finding novel ways to use this super strong silk, one researcher has focused her career on getting a better molecular understanding of exactly how and why these insects create their impressive silk.

Cheryl Hayashi, PhD, the curator in Invertebrate Zoology, professor in the Richard Gilder Graduate School, Leon Hess Director of Comparative Biology Research, and the director of the Sackler Institute for Comparative Genomics at the American Museum of Natural History, explained at the American Association for the Advancement of Science (AAAS) Annual meeting how important spider silk actually is for spiders.

“It is really absolutely essential for understanding almost all aspects of a spider’s life,” Hayashi said. “Spiders and their silks are ancient and incredibly diverse. If you look at the fossil record, spiders go back to well over 350 million years and a defining trait of spiders is the presence of spinnerets. That means every spider that has ever existed has been able to spin silk.”

Spiders are among the oldest and most diverse group of animals on the planet, with three different suborders—meosthelae, mygalomorphae and araneomorphae spiders.

Spiders use their silk in a number of ways, including for reproduction, protection, dispersal, making their homes and slowing down potential prey. In fact, some spiders no longer even use venom to hunt and kill prey, opting to suffocating their next meal with their silk.

Hayashi explained that each spider can produce several different types of silk and each spider web is made from multiple silk types.

“When you are looking at something like a spider web, what you’re looking at is the product of many kinds of silk,” she said. “To make the spider web we are talking about five different kinds of silk coming out of one animal.”

The key to spiders producing silk rests in the spinnerets, which contain glands of different sizes and shapes.

Hayashi explained how she studies the silk glands for many of the 35,000-plus different species of spiders known worldwide.

“Spinnerets are this pair of spinning organs,” Hayashi said. “If you look at each spinneret, there’s spigots on there and the spigot is where the silk actually comes out of. I would take a particular silk gland that I’m interested in and I would collect just those silk glands. I would use really fine forceps and I would collect those silk glands and make an expression library.”

Hayashi said the different glands of different spider species gives researchers a better molecular understanding of this silk producing process. Through genome sequencing, researchers have found unique protein clusters that are extremely large and repetitive to enable silk production.

“It is very clear that there is a very unique family of proteins called spidroins, these very large structural proteins that are found only in spiders and that’s the dominant protein in the silk glands,” she said.

Spider silk has a number of properties that make it popular for new technology in athletic gear, protective clothing and wearable technology. Scientists have long known that spider silk is incredibly strong, stretchy, immune-compatible and lightweight.


Is spider silk stronger than steel? Biologist disentangles fact from fiction on ‘Mythbusters Jr. ’

Spider silk, it is often said, is one of the strongest materials in nature.

But is it stronger than steel?

&ldquoMythbusters Jr.&rdquo host Adam Savage, left, and a junior cast member are seen here preparing to test the strength of spider silk.

To answer that question, the team at &ldquoMythbusters Jr.&rdquo &ndash a new TV series in which host Adam Savage and his crew of six &ldquojunior&rdquo scientists under the age of 16 put scientific myths and urban legends to the test &ndash turned to Dr. Todd Blackledge, a professor of biology here at The University of Akron.

The goal was to create a 2-foot &ldquorope&rdquo of spider silk and test its tensile strength &ndash the amount of tension it can endure, when bearing weight, before breaking &ndash against that of the material used to build skyscrapers, rollercoasters and bridges.

Together with students Angela Alicea-Serrano, integrated bioscience Ph.D., second year, expected graduation 2022 Luke Cramer, senior in biology, graduation spring 2019 and Ariel Onyak, junior in biology, graduation spring 2020, Blackledge spent two months collecting nearly 10 miles of silk from 40 golden silk orb-weaver spiders in his laboratory.

Rope from silk

Blackledge chose the golden silk orb-weaver, one of the largest orb-weaving spiders (Nephila clavipes), for its relatively robust, thick silk &ndash a strand of which is still about 50 times thinner than human hair. His students used a silk reeling device, custom-made in UA&rsquos Polymer Science Machine Shop, to gather 2-foot-long threads of silk, which they bundled into a rope.

UA students Luke Cramer, Ariel Onyak and Angela Alicea-Serrano helped collect nearly 10 miles of silk from 40 golden silk orb-weaver spiders for the on-screen experiment.

Once the rope was done, Blackledge gathered his luggage, silk and a few adult orb-weavers and flew to 32TEN Studios in San Rafael, Calif., for the episode&rsquos filming. During three long days of preparation, planning and filming, Blackledge put his biology expertise to work to make the myth a reality. The stakes were high &ndash with only enough silk rope for one try, there was no room for error.

&ldquoThere was only one chance to get the stunt right, and any mistake by me, the cast, or crew would have meant that the episode would be a failure,&rdquo Blackledge said.

Weights were attached to two cables of the same mass &ndash one a steel wire and the other 25,000 individual strands of spider silk &ndash to test the strength of each.

Behind the scenes

According to Blackledge, the human interaction seen on the show is authentic, most of it unscripted.

&ldquoAlmost all of the shots began with some general goal that the producers wanted, but the actual dialogue and actions were mostly ad lib,&rdquo Blackledge said. &ldquoThe goal was mostly to film natural interactions.&rdquo

Blackledge added that iconic host Adam Savage and his team of teen scientists are as curious and fun off-camera as during filming.

Dr. Todd Blackledge, far right, is pictured on set with the &ldquoMythbusters Jr.&rdquo cast, including host Adam Savage, second from left.

&ldquoAdam&rsquos on-camera persona is pretty genuine &ndash he really does carry that enthusiasm and curiosity off-camera too,&rdquo Blackledge said. &ldquoI was very impressed by his breadth of knowledge in design and building, which made him very helpful at troubleshooting some of the difficulties in the stunt design. And the kids were truly impressive &ndash they were fun-loving and goofy like any young teenagers, but they were also super smart and intensely curious and driven. They weren&rsquot afraid to try something and fail, which is exactly what I want to see in a future scientist.&rdquo

Those curious kids even got to handle some of the spiders, Blackledge added.

Crew gets &lsquohands-on &rsquo with spiders

&ldquoI brought live Nephila with me, so everyone on the cast and crew got to handle the spiders and see how they produced silk closeup,&rdquo he said, adding that this &ldquohands-on&rdquo approach is the best way to do science.

&ldquo&lsquoMythbusters&rsquo has always taken the approach of &lsquolet&rsquos find out for ourselves,&rsquo which is exactly how science works,&rdquo he said. &ldquo&lsquoMythbusters&rsquo is really good at conveying the fun of discovery.&rdquo

So, was the &ldquomyth&rdquo proven or busted?

You can watch the &ldquoBug Special&rdquo Season 1, Episode 8, for yourself to see what was revealed. Simply sign in on the Science Channel website with your cable/streaming provider info to access the episode.


Contents

Uses Edit

All spiders produce silks, and a single spider can produce up to seven different types of silk for different uses. [4] This is in contrast to insect silks, where an individual usually only produces one type of silk. [5] Spider silks may be used in many different ecological ways, each with properties to match the silk's function. As spiders have evolved, so has their silks' complexity and diverse uses, for example from primitive tube webs 300–400 million years ago to complex orb webs 110 million years ago. [6]

Use Example Reference
Prey capture The orb webs produced by the Araneidae (typical orb-weavers) tube webs tangle webs sheet webs lace webs, dome webs single thread used by the Bolas spiders for "fishing". [4] [6]
Prey immobilisation Silk used as "swathing bands" to wrap up prey. Often combined with immobilising prey using a venom. In species of Scytodes the silk is combined with venom and squirted from the chelicerae. [4]
Reproduction Male spiders may produce sperm webs spider eggs are covered in silk cocoons. [4] [7]
Dispersal "Ballooning" or "kiting" used by smaller spiders to float through the air, for instance for dispersal. [8]
Source of food The kleptoparasitic Argyrodes eating the silk of host spider webs. Some daily weavers of temporary webs also eat their own unused silk daily, thus mitigating a heavy metabolic expense. [1] [9]
Nest lining and nest construction Tube webs used by "primitive" spiders such as the European tube web spider (Segestria florentina). Threads radiate out of nest to provide a sensory link to the outside. Silk is a component of the lids of spiders that use "trapdoors", such as members of the family Ctenizidae, and the "water" or "diving bell" spider Argyroneta aquatica builds its diving bell of silk. [6]
Guide lines Some spiders that venture from shelter will leave a trail of silk by which to find their way home again. [9]
Drop lines and anchor lines Many spiders, such as the Salticidae, that venture from shelter and leave a trail of silk, use that as an emergency line in case of falling from inverted or vertical surfaces. Many others, even web dwellers, will deliberately drop from a web when alarmed, using a silken thread as a drop line by which they can return in due course. Some, such as species of Paramystaria, also will hang from a drop line when feeding. [9]
Alarm lines Some spiders that do not spin actual trap webs do lay out alarm webs that the feet of their prey (such as ants) can disturb, cueing the spider to rush out and secure the meal if it is small enough, or to avoid contact if the intruder seems too formidable. [9]
Pheromonal trails Some wandering spiders will leave a largely continuous trail of silk impregnated with pheromones that the opposite sex can follow to find a mate. [9]

Types Edit

Meeting the specification for all these ecological uses requires different types of silk suited to different broad properties, as either a fibre, a structure of fibres, or a silk-globule. These types include glues and fibres. Some types of fibres are used for structural support, others for constructing protective structures. Some can absorb energy effectively, whereas others transmit vibration efficiently. In a spider, these silk types are produced in different glands so the silk from a particular gland can be linked to its use by the spider.

Gland Silk Use
Ampullate (major) Dragline silk – used for the web's outer rim and spokes, also for the lifeline and for ballooning.
Ampullate (minor) Used for temporary scaffolding during web construction.
Flagelliform Capture-spiral silk – used for the capturing lines of the web.
Tubuliform Egg cocoon silk – used for protective egg sacs.
Aciniform Used to wrap and secure freshly captured prey used in the male sperm webs used in stabilimenta.
Aggregate A silk glue of sticky globules.
Piriform Used to form bonds between separate threads for attachment points.

Mechanical properties Edit

Each spider and each type of silk has a set of mechanical properties optimised for their biological function.

Most silks, in particular dragline silk, have exceptional mechanical properties. They exhibit a unique combination of high tensile strength and extensibility (ductility). This enables a silk fibre to absorb a large amount of energy before breaking (toughness, the area under a stress-strain curve).

A frequent mistake made in the mainstream media is to confuse strength and toughness, when comparing silk to other materials. [ citation needed ] Weight for weight, silk is stronger than steel, but not as strong as Kevlar. Silk is, however, tougher than both.

The variability of mechanical properties of spider silk fibres may be important and it is related to their degree of molecular alignment. [10] Mechanical properties depend strongly on the ambient conditions, i.e. humidity and temperature. [11]

Strength Edit

A dragline silk's tensile strength is comparable to that of high-grade alloy steel (450−2000 MPa), [12] [13] and about half as strong as aramid filaments, such as Twaron or Kevlar (3000 MPa). [14]

Density Edit

Consisting of mainly protein, silks are about a sixth of the density of steel (1.3 g/cm 3 ). As a result, a strand long enough to circle the Earth would weigh less than 500 grams (18 oz). (Spider dragline silk has a tensile strength of roughly 1.3 GPa. The tensile strength listed for steel might be slightly higher – e.g. 1.65 GPa, [15] [16] but spider silk is a much less dense material, so that a given weight of spider silk is five times as strong as the same weight of steel.)

Energy density Edit

The energy density of dragline spider silk is roughly 1.2 × 10 8 J/m 3 . [17]

Extensibility Edit

Silks are also extremely ductile, with some able to stretch up to five times their relaxed length without breaking.

Toughness Edit

The combination of strength and ductility gives dragline silks a very high toughness (or work to fracture), which "equals that of commercial polyaramid (aromatic nylon) filaments, which themselves are benchmarks of modern polymer fibre technology". [18] [19]

Temperature Edit

While unlikely to be relevant in nature, dragline silks can hold their strength below -40 °C (-40 °F) and up to 220 °C (428 °F). [20] As occurs in many materials, spider silk fibres undergo a glass transition. The glass-transition temperature depends on the humidity, as water is a plasticiser for the silk. [11]

Supercontraction Edit

When exposed to water, dragline silks undergo supercontraction, shrinking up to 50% in length and behaving like a weak rubber under tension. [11] Many hypotheses have been suggested as to its use in nature, with the most popular being to automatically tension webs built in the night using the morning dew. [ citation needed ]

Highest-performance Edit

The toughest known spider silk is produced by the species Darwin's bark spider (Caerostris darwini): "The toughness of forcibly silked fibers averages 350 MJ/m 3 , with some samples reaching 520 MJ/m 3 . Thus, C. darwini silk is more than twice as tough as any previously described silk, and over 10 times tougher than Kevlar". [21]

Adhesive properties Edit

Silk fibre is a two-compound pyriform secretion, spun into patterns (called "attachment discs") that are employed to adhere silk threads to various surfaces using a minimum of silk substrate. [22] The pyriform threads polymerise under ambient conditions, become functional immediately, and are usable indefinitely, remaining biodegradable, versatile and compatible with numerous other materials in the environment. [22] The adhesive and durability properties of the attachment disc are controlled by functions within the spinnerets. [23] Some adhesive properties of the silk resemble glue, consisting of microfibrils and lipid enclosures. [22]

Types of silk Edit

Many species of spiders have different glands to produce silk with different properties for different purposes, including housing, web construction, defence, capturing and detaining prey, egg protection, and mobility (fine "gossamer" thread for ballooning, or for a strand allowing the spider to drop down as silk is extruded). Different specialised silks have evolved with properties suitable for different uses. For example, Argiope argentata has five different types of silk, each used for a different purpose: [24] [25]

Silk Use
major-ampullate (dragline) silk Used for the web's outer rim and spokes and also for the lifeline. Can be as strong per unit weight as steel, but much tougher.
capture-spiral (flagelliform) silk Used for the capturing lines of the web. Sticky, extremely stretchy and tough. The capture spiral is sticky due to droplets of aggregate (a spider glue) that is placed on the spiral. The elasticity of flagelliform allows for enough time for the aggregate to adhere to the aerial prey flying into the web.
tubiliform (a.k.a. cylindriform) silk Used for protective egg sacs. Stiffest silk.
aciniform silk Used to wrap and secure freshly captured prey. Two to three times as tough as the other silks, including dragline.
minor-ampullate silk Used for temporary scaffolding during web construction.
Piriform (pyriform) Piriform serves as the attachment disk to dragline silk. Piriform is used in attaching spider silks together to construct a stable web.

Macroscopic structure down to protein hierarchy Edit

Silks, like many other biomaterials, have a hierarchical structure. The primary structure is the amino acid sequence of its proteins (spidroin), mainly consisting of highly repetitive glycine and alanine blocks, [26] [27] which is why silks are often referred to as a block co-polymer. On a secondary structure level, the short side chained alanine is mainly found in the crystalline domains (beta sheets) of the nanofibril, glycine is mostly found in the so-called amorphous matrix consisting of helical and beta turn structures. [27] [28] It is the interplay between the hard crystalline segments, and the strained elastic semi-amorphous regions, that gives spider silk its extraordinary properties. [29] [30] Various compounds other than protein are used to enhance the fibre's properties. Pyrrolidine has hygroscopic properties which keeps the silk moist while also warding off ant invasion. It occurs in especially high concentration in glue threads. Potassium hydrogen phosphate releases hydrogen ions in aqueous solution, resulting in a pH of about 4, making the silk acidic and thus protecting it from fungi and bacteria that would otherwise digest the protein. Potassium nitrate is believed to prevent the protein from denaturing in the acidic milieu. [31]

This first very basic model of silk was introduced by Termonia in 1994 [32] who suggested crystallites embedded in an amorphous matrix interlinked with hydrogen bonds. This model has refined over the years: semi-crystalline regions were found [27] as well as a fibrillar skin core model suggested for spider silk, [33] later visualised by AFM and TEM. [34] Sizes of the nanofibrillar structure and the crystalline and semi-crystalline regions were revealed by neutron scattering. [35]

It has been possible to relate microstructural information and macroscopic mechanical properties of the fibres. [36] The results show that ordered regions (i) mainly reorient by deformation for low-stretched fibres and (ii) the fraction of ordered regions increases progressively for higher stretching of the fibres.

Schematic of the spider's orb web, structural modules, and spider silk structure. [37] On the left is shown a schematic drawing of an orb web. The red lines represent the dragline, radial line, and frame lines, the blue lines represent the spiral line, and the centre of the orb web is called the “hub”. Sticky balls drawn in blue are made at equal intervals on the spiral line with viscous material secreted from the aggregate gland. Attachment cement secreted from the piriform gland is used to connect and fix different lines. Microscopically, the spider silk secondary structure is formed of spidroin and is said to have the structure shown on the right side. In the dragline and radial line, a crystalline β-sheet and an amorphous helical structure are interwoven. The large amount of β-spiral structure gives elastic properties to the capture part of the orb web. In the structural modules diagram, a microscopic structure of dragline and radial lines is shown, composed mainly of two proteins of MaSp1 and MaSp2, as shown in the upper central part. In the spiral line, there is no crystalline β-sheet region.

Non-protein composition Edit

Various compounds other than protein are found in spider silks, such as sugars, lipids, ions, and pigments that might affect the aggregation behaviour and act as a protection layer in the final fibre. [17]

The production of silks, including spider silk, differs in an important aspect from the production of most other fibrous biological materials: rather than being continuously grown as keratin in hair, cellulose in the cell walls of plants, or even the fibres formed from the compacted faecal matter of beetles [17] it is "spun" on demand from liquid silk precursor out of specialised glands. [38]

The spinning process occurs when a fibre is pulled away from the body of a spider, whether by the spider's legs, by the spider's falling under its own weight, or by any other method including being pulled by humans. The term "spinning" is misleading because no rotation of any component occurs, but rather comes from analogy to the textile spinning wheels. Silk production is a pultrusion, [39] similar to extrusion, with the subtlety that the force is induced by pulling at the finished fibre rather than being squeezed out of a reservoir. The unspun silk fibre is pulled through silk glands of which there may be both numerous duplicates and different types of gland on any one spider species. [38]

Silk gland Edit

The gland's visible, or external, part is termed the spinneret. Depending on the complexity of the species, spiders will have two to eight spinnerets, usually in pairs. There exist highly different specialised glands in different spiders, ranging from simply a sac with an opening at one end, to the complex, multiple-section major ampullate glands of the golden silk orb-weavers. [53]

Behind each spinneret visible on the surface of the spider lies a gland, a generalised form of which is shown in the figure to the right, "Schematic of a generalised gland".

  1. The first section of the gland labelled 1 on Figure 1 is the secretory or tail section of the gland. The walls of this section are lined with cells that secrete proteins Spidroin I and Spidroin II, the main components of this spider's dragline. These proteins are found in the form of droplets that gradually elongate to form long channels along the length of the final fibre, hypothesised to assist in preventing crack formation or even self-healing of the fibre. [56]
  2. The second section is the storage sac. This stores and maintains the gel-like unspun silk dope until it is required by the spider. In addition to storing the unspun silk gel, it secretes proteins that coat the surface of the final fibre. [18]
  3. The funnel rapidly reduces the large diameter of the storage sac to the small diameter of the tapering duct.
  4. The final length is the tapering duct, the site of most of the fibre formation. This consists of a tapering tube with several tight about turns, a valve almost at the end (mentioned in detail at point No. 5 below) ending in a spigot from which the solid silk fibre emerges. The tube here tapers hyperbolically, therefore the unspun silk is under constant elongational shear stress, which is an important factor in fibre formation. This section of the duct is lined with cells that exchange ions, reduce the dope pH from neutral to acidic, and remove water from the fibre. [57] Collectively, the shear stress and the ion and pH changes induce the liquid silk dope to undergo a phase transition and condense into a solid protein fibre with high molecular organisation. The spigot at the end has lips that clamp around the fibre, controlling fibre diameter and further retaining water.
  5. Almost at the end of the tapering duct is a valve, approximate position marked "5" on figure 1. Though discovered some time ago, the precise purpose of this valve is still under discussion. It is believed to assist in restarting and rejoining broken fibres, [58] acting much in the way of a helical pump, regulating the thickness of the fibre, [39] and/or clamping the fibre as a spider falls upon it. [58][59] There is some discussion of the similarity of the silk worm's silk press and the roles each of these valves play in the production of silk in these two organisms.

Throughout the process the unspun silk appears to have a nematic texture, [60] in a similar manner to a liquid crystal, arising in part due to the extremely high protein concentration of silk dope (around 30% in terms of weight per volume). [61] This allows the unspun silk to flow through the duct as a liquid but maintain a molecular order.

As an example of a complex spinning field, the spinneret apparatus of an adult Araneus diadematus (garden cross spider) consists of the glands shown below. [31] Similar multiple gland architecture exists in the black widow spider. [62]

  • 500 pyriform glands for attachment points
  • 4 ampullate glands for the web frame
  • about 300 aciniform glands for the outer lining of egg sacs, and for ensnaring prey
  • 4 tubuliform glands for egg sac silk
  • 4 aggregate glands for adhesive functions
  • 2 coronate glands for the thread of adhesion lines

To artificially synthesise spider silk into fibres, there are two broad areas that must be covered. These are synthesis of the feedstock (the unspun silk dope in spiders), and synthesis of the spinning conditions (the funnel, valve, tapering duct, and spigot). There have been a number of different approaches but few of these methods have produced silk that can efficiently be synthesised into fibres.

Feedstock Edit

The molecular structure of unspun silk is both complex and extremely long. Though this endows the silk fibres with their desirable properties, it also makes replication of the fibre somewhat of a challenge. Various organisms have been used as a basis for attempts to replicate some components or all of some or all of the proteins involved. These proteins must then be extracted, purified and then spun before their properties can be tested.

Geometry Edit

Spider silks with comparatively simple molecular structure need complex ducts to be able to spin an effective fibre. There have been a number of methods used to produce fibres, of which the main types are briefly discussed below.

Syringe and needle Edit

Feedstock is simply forced through a hollow needle using a syringe. This method has been shown to make fibres successfully on multiple occasions. [71] [72]

Although very cheap and easy to produce, the shape and conditions of the gland are very loosely approximated. Fibres created using this method may need encouragement to change from liquid to solid by removing the water from the fibre with such chemicals as the environmentally undesirable methanol [73] or acetone, [72] and also may require post-stretching of the fibre to attain fibres with desirable properties. [74] [71]

Microfluidics Edit

As the field of microfluidics matures, it is likely that more attempts to spin fibres will be made using microfluidics. These have the advantage of being very controllable and able to test spin very small volumes of unspun fibre [75] [76] but setup and development costs are likely to be high. A patent has been granted in this area for spinning fibres in a method mimicking the process found in nature, and fibres are successfully being continuously spun by a commercial company. [77]

Electrospinning Edit

Electrospinning is a very old technique whereby a fluid is held in a container in a manner such that it is able to flow out through capillary action. A conducting substrate is positioned below, and a large difference in electrical potential is applied between the fluid and the substrate. The fluid is attracted to the substrate, and tiny fibres jump almost instantly from their point of emission, the Taylor cone, to the substrate, drying as they travel. This method has been shown to create nano-scale fibres from both silk dissected from organisms and regenerated silk fibroin.

Other artificial shapes formed from silk Edit

Silk can be formed into other shapes and sizes such as spherical capsules for drug delivery, cell scaffolds and wound healing, textiles, cosmetics, coatings, and many others. [78] [79] Spider silk proteins can also self-assemble on superhydrophobic surfaces to generate nanowires, as well as micron-sized circular sheets. [79] It has recently been shown that recombinant spider silk proteins can self-assemble at the liquid air interface of a standing solution to form protein permeable, super strong, and super flexible membranes that support cell proliferation. Suggested applications include skin transplants, and supportive membranes in organ-on-a-chip. [80]

Due to spider silk being a scientific research field with a long and rich history, there can be unfortunate occurrences of researchers independently rediscovering previously published findings. What follows is a table of the discoveries made in each of the constituent areas, acknowledged by the scientific community as being relevant and significant by using the metric of scientific acceptance, citations. Thus, only papers with 50 or more citations are included.

Table of significant papers (50 or more citations)
Area of contribution Year Main researchers [Ref] Title of paper Contribution to the field
Chemical Basis 1960 Fischer, F. & Brander, J. [81] "Eine Analyse der Gespinste der Kreuzspinne" (Amino acid composition analysis of spider silk)
1960 Lucas, F. & et al. [82] [83] "The Composition of Arthropod Silk Fibroins Comparative studies of fibroins"
Gene Sequence 1990 Xu, M. & Lewis, R. V. [84] "Structure of a Protein Superfiber − Spider Dragline Silk"
Mechanical Properties 1964 Lucas, F. [85] "Spiders and their silks" First time compared mechanical properties of spider silk with other materials in a scientific paper.
1989 Vollrath, F. & Edmonds, D. T. [86] "Modulation of the Mechanical Properties of Spider Silk by Coating with Water" First important paper suggesting the water interplay with spider silk fibroin modulating the properties of silk.
2001 Vollrath, F. & Shao, Z.Z. [87] "The effect of spinning conditions on the mechanics of a spider's dragline silk"
2006 Plaza, G.R., Guinea, G.V., Pérez-Rigueiro, J. & Elices, M. [11] "Thermo-hygro-mechanical behavior of spider dragline silk: Glassy and rubbery states" Combined effect of humidity and temperature on the mechanical properties. Glass-transition temperature dependence on humidity.
Structural Characterisation 1992 Hinman, M.B. & Lewis, R. V [26] "Isolation of a clone encoding a second dragline silk fibroin. Nephila clavipes dragline silk is a two-protein fiber"
1994 Simmons, A. & et al. [88] "Solid-State C-13 Nmr of Nephila-Clavipes Dragline Silk Establishes Structure and Identity of Crystalline Regions" First NMR study of spider silk.
1999 Shao, Z., Vollrath, F. & et al. [89] "Analysis of spider silk in native and supercontracted states using Raman spectroscopy" First Raman study of spider silk.
1999 Riekel, C., Muller, M.& et al. [90] "Aspects of X-ray diffraction on single spider fibers" First X-ray on single spider silk fibres.
2000 Knight, D.P., Vollrath, F. & et al. [91] "Beta transition and stress-induced phase separation in the spinning of spider dragline silk" Secondary structural transition confirmation during spinning.
2001 Riekel, C. & Vollrath, F. [92] "Spider silk fibre extrusion: combined wide- and small-angle X- ray microdiffraction experiments" First X-ray on spider silk dope.
2002 Van Beek, J. D. & et al. [28] "The molecular structure of spider dragline silk: Folding and orientation of the protein backbone"
Structure-Property Relationship 1986 Gosline, G.M. & et al. [93] "The structure and properties of spider silk" First attempt to link structure with properties of spider silk
1994 Termonia, Y [32] "Molecular Modeling of Spider Silk Elasticity" X-ray evidence presented in this paper simple model of crystallites embedded in amorphous regions.
1996 Simmons, A. & et al. [27] "Molecular orientation and two-component nature of the crystalline fraction of spider dragline silk" Two types of alanine-rich crystalline regions were defined.
2006 Vollrath, F. & Porter, D. [94] "Spider silk as an archetypal protein elastomer" New insight and model to spider silk based on Group Interaction Modelling.
Native Spinning 1991 Kerkam, K., Kaplan, D. & et al. [95] "Liquid Crystallinity of Natural Silk Secretions"
1999 Knight, D.P. & Vollrath, F. [96] "Liquid crystals and flow elongation in a spider's silk production line"
2001 Vollrath, F. & Knight, D.P. [17] "Liquid crystalline spinning of spider silk" The most cited paper on spider silk
2005 Guinea, G.V., Elices, M., Pérez-Rigueiro, J. & Plaza, G.R. [10] "Stretching of supercontracted fibers: a link between spinning and the variability of spider silk" Explanation of the variability of mechanical properties.
Reconstituted /Synthetic Spider Silk and Artificial Spinning 1995 Prince, J. T., Kaplan, D. L. & et al. [97] "Construction, Cloning, and Expression of Synthetic Genes Encoding Spider Dragline Silk" First successful synthesis of Spider silk by E. coli.
1998 Arcidiacono, S., Kaplan, D.L. & et al. [98] "Purification and characterization of recombinant spider silk expressed in Escherichia coli"
1998 Seidel, A., Jelinski, L.W. & et al. [99] "Artificial Spinning of Spider Silk" First controlled wet-spinning of reconstituted spider silk.

Peasants in the southern Carpathian Mountains used to cut up tubes built by Atypus and cover wounds with the inner lining. It reportedly facilitated healing, and even connected with the skin. This is believed to be due to antiseptic properties of spider silk [101] and because the silk is rich in vitamin K, which can be effective in clotting blood. [102] [ verify ] Due to the difficulties in extracting and processing substantial amounts of spider silk, the largest known piece of cloth made of spider silk is an 11-by-4-foot (3.4 by 1.2 m) textile with a golden tint made in Madagascar in 2009. [103] Eighty-two people worked for four years to collect over one million golden orb spiders and extract silk from them. [104]

The silk of Nephila clavipes was used in research concerning mammalian neuronal regeneration. [105]

Spider silk has been used as a thread for crosshairs in optical instruments such as telescopes, microscopes, [106] and telescopic rifle sights. [107] In 2011, spider silk fibres were used in the field of optics to generate very fine diffraction patterns over N-slit interferometric signals used in optical communications. [108] In 2012, spider silk fibres were used to create a set of violin strings. [109]

Development of methods to mass-produce spider silk has led to manufacturing of military, medical and consumer goods, such as ballistics armour, athletic footwear, personal care products, breast implant and catheter coatings, mechanical insulin pumps, fashion clothing, and outerwear. [110]

Spider silk is used to suspend inertial confinement fusion targets during laser ignition, as it remains considerably elastic and has a high energy to break at temperatures as low as 10–20 K. In addition, it is made from "light" atomic number elements that won't emit x-rays during irradiation that could preheat the target so that the pressure differential required for fusion is not achieved. [111]

Spider silk has been used to create biolenses that could be used in conjunction with lasers to create high-resolution images of the inside of the human body.[1]

Replicating the complex conditions required to produce fibres that are comparable to spider silk has proven difficult in research and early-stage manufacturing. Through genetic engineering, Escherichia coli bacteria, yeasts, plants, silkworms, and animals other than silkworms have been used to produce spider silk proteins, which have different, simpler characteristics than those from a spider. [110] Extrusion of protein fibres in an aqueous environment is known as "wet-spinning". This process has so far produced silk fibres of diameters ranging from 10 to 60 μm, compared to diameters of 2.5–4 μm for natural spider silk. Artificial spider silks have fewer and simpler proteins than natural dragline silk, and are consequently half the diameter, strength, and flexibility of natural dragline silk. [110]


If scaled up, could we use silk to hold people?

This question is difficult to answer, because we can’t actually make big ropes out of spider silk yet. In order to be spun at the optimal strength, the chemical conditions of any silk produced outside of the animal’s body have to be perfect. We’re not quite at large-scale production yet, although we may be getting closer.

Regardless, it helps to have a comparison of some sort. Climbing ropes are made out of stretchy nylon, and a strand the strongest spider silk on record is 18 times stronger in proportion. Silkworm silk, which is produced in mass quantity, is about 6 times stronger in proportion. We’ve been mass-producing caterpillar silk for thousands of years, so this is a pretty good model.

It should be mentioned that the above information is comparing individually spun threads with a commercially prepared climbing rope. Preparation methods, humidity, the way the fabric is woven, and even things like dyes can effect the strength of commercially prepared products. While an individual strand of silk, either spider or caterpillar, is about as strong as an individual strand of nylon used in climbing rope…I’m not particularly happy with this comparison.

I feel like the only way properly answer this question is by looking at commercially prepared products designed to hold people. This is where aerial silk comes back in.

This is a dance performed on nylon fabric, which means I can compare the breaking strength of this fabric to commercially prepared silk fabric. Aerial silk fabric (again, made of nylon) can hold a little over 1100 kg. Surah, on the other hand, has a breaking strength of 30 kg. This is well below anything I’d ever support myself with. Ropes or aerial silks need to be able to hold at least 10 times your weight in order to be safely used.

There are applications of silk which have been used to hold people, but shortages and trade agreements after WWII changed silk from a fabric used to make these sorts of protective equipment to clothing. The way silk is prepared can drastically change its strength, so things made of silk may not be stronger than things made of nylon even though the individual threads may be stronger.


Spin me a web

Spiber's approach is the latter. The company's process involves decoding the gene responsible for the production of fibroin in spiders and then bioengineering bacteria with recombinant DNA to produce the protein, which they then spin into their artificial silk.

Spiber says it will manufacture ten tons of silk in 2015 (Photo: Spiber)

While interest in artificial silk is high and competition is tough, Spiber says it has the advantage of speed: apparently, it can engineer a new type of silk in as little as 10 days, and has already created 250 prototypes with characteristics to suit specific applications.

Spyber starts by tweaking the aminoacid sequences and gene arrangements in its computer models to create artificial proteins that try to maximize strength, flexibility and thermal stability in the final product.

Then, the company synthesizes a fibroin-producing gene, modifying it in such a way that it will produce that specific molecule. The company adopts its own system of gene synthesis, which can produce large quantities of DNA for the fibroin gene in only three days.

Microbes are then modified with the fibroin gene to produce the candidate molecule, which is turned into a fine powder and then spun. The bacteria feed on sugar, salt and other micronutrients and can reproduce in just 20 minutes. A single gram of the protein produces about 5.6 miles (9 km) of artificial silk.

The artificial protein derived from fibroin has been named QMONOS, from the Japanese word for spider. The substance can be turned into fiber, film, gel, sponge, powder, and nanofiber form to suit a number of different needs.

Spibers says it is building a trial manufacturing research plant, aiming to produce 100 kg (220 lb) of QMONOS fiber per month by November. The pilot plant will be ready by 2015, by which time the company aims to produce 10 metric tons (22,000 lb) of silk per year.

The video below introduces the attractive features of the silk and some of its possible applications.


4 Answers 4

Spider silk is amazingly strong (something like 17 times more tensile strength than steel per unit weight), so the idea of making body armour out of silk isn't strange at all. The only difficulty is to scale up production to meet the requirements of a large scale force, and in our world genetic engineering is being used to do unlikely things like coding for spider silk proteins to be expressed in goats milk!

Keratin is the protein used for skin, nails and hair. Very strong materials can be made from this, but it isn't nearly as tough as some of the shells of various molluscs, which turn out to be a composite of ceramic like calcium compounds in a matrix of a more flexible protein, which provides strength without being brittle.

"Wet" bone in living creatures shares some of the same properties bone under a microscope looks a bit like a sponge with calcium particles suspended in the matrix (yes there is a lot more to bone than that), but since the scale of the particles and the matrix is much larger than in shells, bone is actually not as strong or "tough". The need for bone to be "wet" (i.e. living tissue) in order to remain strong will also be an issue if you want to use it for armour.

Bone, silk and keratin are strong materials in their own right but I wouldn't use them for high value foot soldiers. As you said, there are better materials, use them for the elites.

Use these cheaper materials to make cannon fodder shock troops. For any kind of invasion, you need lots of them. Make zerglings or hormagaunts in the millions.

Ranged weapons take extra resources so just give the shock troops melee weapons. If enough of them survive to melee range, whatever weaponry the enemy has won't do them any good.

You should consider that while spider silk, keratin, and bone are each strong in different ways they did not evolve to function as armor. While this means that they may not be ideal as armor, it opens up the possibility that other organic materials that were designed to function as armor could be orders of magnitude more effective. If your aliens are sufficiently advanced I see no reason why they would be limited to using existing biological materials to make armor for their soldiers. They could engineer something far, far stronger. Imagine an armored skin composed of a single molecule of layered and interwoven spider silk filaments, or even carbon nanotubes. Engineered organic armor could be vastly stronger than any known material. Potentially any organic molecule you can think of could be synthesized by engineered enzymatic processes.

As to your question of what sort of weapons might be effective, it depends on the exact nature of the armor. If it is brittle and hard then kinetic weapons like bullets may be able to crack it if they can deliver enough force to a small enough point, but the armor will be resistant to shockwaves as it won't propagate the force to the interior. If the armor is elastic and flexible bullets will have difficulty penetrating, but the shockwave of hits and particularly explosions could still be transferred through the armor to cause internal damage. If the armor is well-made and layered to be both hard and elastic, well, you are just going to have to shoot them a lot. Or try fire! Organic things tend to burn and sufficient heat could break the molecular bonds holding the armor together. Also maybe very strong armor is not very good at allowing a creature to cool off. Cook them in their own super-armor oven.


New protein found in strongest spider web material

Credit: CC0 Public Domain

A team of researchers affiliated with several institutions in the U.S. and Slovenia has found a previously unknown protein in the strongest known spider web material. In their paper published in the journal Communications Biology, the group describes their study of Darwin's bark spider silk and the glands that produce it.

Humans have been impressed by the silk made from spiders for thousands of years—so much so that a lot of effort has been put into harvesting it from spiders for use in making clothing—and in reproducing it in a lab to create new strong materials. In this new effort, the researchers focused their efforts on Darwin's bark spiders, their silk-producing glands and the silk that is produced.

Darwin's bark spiders are a type of orb spider, which means they make their spider webs in the shape of a spoked wheel. They make the largest known orb webs of any spider, which they spin above the surfaces of streams. Prior research has shown that the spider actually makes seven different kinds of silk for use in different parts of its web. One of those silk types, called dragline, is used to build the spokes that give the wheel its strength. Prior research has shown it to be the strongest spider silk in existence. In this new effort, the researchers took a closer look at the dragline silk and the gland that produces it.

The researchers found two familiar types of spindroins—types of repetitive proteins—called MaSp1 and MaSp2, which are found in many spider silks. But in the dragline from Darwin's bark spiders, they found another spindroin, which they named MaSp4a. Study of this protein revealed that contained high quanitities of an amino acid called proline, which prior research has shown is generally associated with elasticity. The protein also had less of some of the other components found in MaSp1 and MaSp2, which made it quite unique.

The researchers also found that the gland that produces the silk—the ampullae—is longer than in other spiders, perhaps providing another clue to the strength of the silk that is produced.


8 Answers 8

Cloth armor - specifically, linen armor - was a thing, historically. It was used, tested, and could be quite effective. it was lighter and, reportedly, more comfortable and/or maneuverable than other armors, for the tradeoff of being also not quite as effective. Silk was more expensive, so there don't seem to be as much evidence for cloth armor made of silk - but on a cloth-for-cloth basis, there doesn't seem to be any reason the same kinds of techniques shouldn't work, if you have enough of the silk to make it cost-effective.

A Greek style armor called linothorax was reconstructed through using a lamination technique to transform linen cloth into stiff plates - essentially using multiple layers brushed with glue. This reconstruction was tested against arrows, and a thickness of 12mm supposedly would have been enough against any arrow the wearer was likely to encounter for about a 400 year period (see link for original tests).

Quilted Gambesons or Padded Jacks were sometimes used under other armor, but also sometimes used as a standalone. they were made from many layers, perhaps as many as thirty, of cloth quilted together - Linen was a popular choice as it was available, lightweight, and fairly effective (though some incorporated cotton, wool, or leather for extra effect). Testing of a reconstruction showed that such all-linen gambesons were an imperfect, but effective armor - the armor blunted some shots and reduced others to what would be lesser injuries from many of the arrows (though not all, depending on the arrowheads, see link for original tests), and proved somewhat effective even against spear or sword.

As for silk, I've vaguely heard of quilted silk armor being used (like the gambeson, up to thirty layers quilted together) among the Japanese and Koreans historically - and even in modern times, since this kind of armor may be bullet resistant, depending on caliber. However, I don't have nearly as good historical references, or testing information, about this kind of armor. Xplodotron's previous answer mentioned the use of a layer of silk and air pressure could deflect most (70%) of the arrows fired at it, which seems to indicate silk resists penetration pretty well as a single layer (compared to linen which I could not find used as a single layer for armor), and suggest that a layered silk version, like the linen armors, would be quite effective.

So your basic choices might be quilted silk, using many layers to resist the penetration of arrows, spears or swords or else a laminated silk, where the layers are stiffened with glue to form a kind of plate mail. The first is going to be a lot more flexible, and probably easier to make, adjust, or work with, with the tradeoff of somewhat lower protection (arrows and the like might still penetrate, but much less than without the armor - and it does much less to protect against blunt force). The second is a lot more tricky to work with (and you'd need the glue, though a relatively low quality rabbit glue was well used) - and each piece of each armor must be separately laminated and fitted (it will resist tools as much as weapons), making it more labor-intensive but also a better protection.

Of course, since you plan for an abundance of spider-silk, maybe you could use both, either/or depending on the warrior and their role in fighting, or a hybrid with reinforced plates over vital areas, but quilted armor over other areas for more maneuverability.

I don't think you could make a visor out of it - you might get enough transparency to get away with a single sheer or gauzy layer, but you would get very little protection from it, and it would reduce visibility. At most you might deny your opponents an aiming point (faceless! aah!) if you used that single layer in conjunction with other silk armor, like a laminated silk helmet that does cover the rest of the face, but still allows openings like knights' helmets had for seeing through and such.


Spider Silk Is Stronger Than Steel. It Also Assembles Itself.

Scientists are figuring out the chemical triggers that turn the liquid stored in silk glands into a solid that’s tougher than Kevlar.

Pound for pound, spider silk is stronger than steel and tougher than Kevlar. But it doesn’t start out that way.

The silk starts out in a liquid form called dope (literally, dope). But in fractions of a second, this goopy, liquid slurry of proteins is transformed. And it doesn’t just turn into a solid. On their way out of a spider’s bottom, the protein building blocks in silk, called spidroins, fold themselves and interlace, creating a highly organized structure without guidance from any outside force.

This remarkable process of self-assembly is about as strange as a garden hose spitting out a stream of perfect snowflakes. Scientists have spent years trying to mimic it in the hopes that it will someday revolutionize the construction of ultra-strong, sustainable materials.

“You can really generate materials with unique properties by exploiting this self-assembly process,” said Ali Malay, a structural biologist and biochemist at the Riken Center for Sustainable Resource Science in Japan.

Dr. Malay doesn’t yet have the entire process figured out. Neither does anyone else. But in a paper published Wednesday in Science Advances, he and his colleagues lay out a new way to tackle the spider silk puzzle, mimicking its orderly exit from the spinneret with chemical tools in the lab.

A crucial part of spinning, the researchers found, requires the spidroins to separate themselves from the watery buffer that swaddles them inside silk glands — a step that hyper-concentrates the proteins. An influx of acid then prompts the proteins to securely interlock.

The paper uses a simplified laboratory model in place of real spiders. But the research is remarkable for providing a glimpse into the sausage-making behind silk spinning, “from liquid dope to fiber,” said Angela Alicea-Serrano, a spider silk researcher at the University of Akron who wasn’t involved in the study. “We’ve seen a lot of the beginning of this process and the end, but not the in-between.”

The metamorphosis spider silk must undergo as it exits an arachnid cannot be overstated, said Anna Rising, a spider silk expert at the Karolinska Institute in Sweden who was not involved in the study. While still in the gland, spidroins have to stay suspended in a liquid form at “really extreme concentrations,” Dr. Rising said. “It’s viscous, almost like a toothpaste.”

If the silk hardens too soon, it could clog the spider’s glands with a nightmarishly webby form of constipation. Too late, and the arachnid might spew only shapeless liquid. That makes both timing and efficiency central to the silk-spinning process.

Luckily for spiders, millenniums of evolution have made spidroins versatile. The proteins, Dr. Rising explained, are structured like barbells: a long, disorderly string capped on each end by a bolt-like blob. In the silk glands, these barbells are thought to naturally pair up at one end, creating V-shaped duos that slosh around in the dope.

To form the more stable architecture required of solid silk, the spidroins need to link up in chains, using the other ends of the barbells. That seems to happen under the influence of a couple of chemical cues, said Jessica Garb, a spider silk researcher at the University of Massachusetts, Lowell who was not involved in the study. As the spidroin slurry is extruded through a labyrinth of increasingly narrow ducts, the spider cells pump acid into the mixture, making the free ends of the barbells stick together. The journey through these tapering tubes also tugs and squeezes the silk into its final form.

Dr. Malay and his colleagues found that this sculpting and self-assembly could not happen if the liquidy spidroins weren’t dehydrated as they moved through the spider’s anatomy.

Further experiments showed salts made the proteins rapidly distance themselves from the liquid surrounding them, like oil and vinegar in a salad dressing. This allows the spidroins to more easily interact, said Cheryl Hayashi, a spider silk researcher at the American Museum of Natural History who wasn’t involved in the study. Freshly thickened, the stew of spidroins then shapes itself into an increasingly stringy structure.

The silk extrusion pipeline might sound a bit cumbersome. From an engineer’s perspective, though, it’s extraordinarily elegant, said Keiji Numata, a Riken scientist who led the study. Scientists can build superstrong polymers in the lab through brute force, coercing materials to come together in ways they otherwise wouldn’t. But given the right ingredients, under the right conditions, the recipe that is spider silk essentially cooks itself.

Researchers still don’t know enough about this process to fully recreate it. There are also many ways to spin spider silk, which varies between species, and even within the same spider, Dr. Garb said. Although silks might be best known for their roles in web-building, they can also be used to lure mates, protect eggs or even help wayfaring spiders hitch a ride on a passing breeze.

This study focused on the proteins found in dragline silk, which serves as a sort of bungee cord for spiders dangling from their webs or ceilings. “But there’s still a lot more that nature has figured out that we don’t know about,” Dr. Hayashi said.


The Biology of . . . Spider Silk

Up on the roof of the zoology building, Fritz Vollrath pushes open the door of a small greenhouse and walks in. Tupperware containers full of maggots and decomposing fruit are scattered on every available surface, and the thick and sickly smell of rot fills Vollrath's nostrils. But he ignores these signs that all is well: "It's too hot," he says. Not for the palm by the door or the tall cactus, but for the distinguished architects who are hanging out in the upper corners. Most of them are a species of Nephila, the golden silk spider. The species has an inch-long abdomen, greenish-black with yellow markings, and eight long, delicate legs. Nephila are orb weavers, and the silk orbs they have woven in Vollrath's "spider house" are thick with the flies he intended for them. But the spiders themselves are looking a bit sluggish. Vollrath opens a window to cool things off. Right next to the window there is a web, and Vollrath brushes its owner into a little plastic jar. Come nightfall it will get a bit too chilly in that spot, and anyway he needs a spider to take to the synchrotron in Grenoble.

Vollrath is a handsome, muscular man with shaggy gray hair, a very slight German accent, and a face that broadens readily into a pleased grin when he sees he's amazing you with facts about spider silk. It is pretty amazing stuff. Nephila silk has a tensile strength almost as great as steel's per unit volume and far greater than steel's per unit weight. Kevlar is three times harder to break than Nephila silk, but the spider silk is five times more elastic. Kevlar stops bullets by brute force Nephila silk stops flies by stretching without breaking. As is so often the case, human engineers trail the elegant solutions of nature.

Lately though, the humans have been trying hard to catch up. Spider silk not only has wonderful mechanical properties it is made of biodegradable proteins, using water as a solvent, rather than nasty organic chemicals. Thus there are strong economic and environmental incentives for finding a way to make spider silk artificially. (You can't farm spiders as you would silkworms, because they eat each other.) Fragments of genes for a few spider-silk proteins have been cloned and inserted in goats, which secrete the proteins in their milk, and just this year in tobacco and potato plants, which secrete them in their leaves. Nexia Biotechnologies, the company that keeps the goats on a farm in upstate New York, has even announced the creation of a product called BioSteel— though all the company really seems to have at the moment are artificial proteins, not threads of artificial silk. "There is a lot of optimistic hype in this field," Vollrath says.

Vollrath began studying spiders in 1974 and concentrated on silk a decade ago. He soon found, he says, that "it was an extremely interesting material and far more complex than people gave it credit for." There are more than 34,000 known species of spider, each of which makes its own silk and some of which make different silks for different purposes. The toughest kind is called dragline silk: It forms the framework of the spider web, and it's also what the spider spins at frantic speeds of up to a meter per second when it jumps off a tree or house to escape a bird.

More research has been done on the dragline silk of Nephila than on any other kind. But it is a long way from being understood. A single thread of that silk is perhaps three to five micrometers across. When Vollrath started looking into it, people thought dragline silk was a relatively simple composite material, like fiberglass, consisting of stiff sheets of crystallized protein floating in an elastic rubbery matrix. But that, Vollrath has found, is not the structure of the whole thread it's the structure of a single filament inside the thread— and there may be thousands of such filaments, each only a few nanometers across, too small to be seen with a typical microscope, and perhaps bundled in some way that has yet to be discerned.

"That's what gives it this incredible tensile strength, this whole microstructure," Vollrath says. "If you're jumping off a bridge, would you prefer I gave you a single rubber band or a thousand rubber bands with the same total diameter? It's intuitive— if you have a thousand, a few can snap and there are still enough to hold you." The spider's dragline is made even more snap-resistant, Vollrath thinks, by long, fluid-filled channels that are interspersed among the tightly packed filaments. Those channels may help distribute the tensile forces and so stop a nascent crack from ripping right across the thread.

Of course, some of the strength of the silk must come from the protein molecules that make it up. Earlier this year, John Gatesy and Cheryl Hayashi of the University of California at Riverside and their colleagues reported that in all of the orb-weaving spiders they have studied, the long chain of amino acids that constitutes a silk protein is dominated by certain repetitive sequences— long stretches consisting only of the amino acid alanine, for example. Natural selection has apparently kept those repetitive sequences intact over the 120 million years since the orb weavers diverged into different species, which suggests the sequences are important. Alanine chains, for instance, are very good at binding to other alanine chains, allowing protein molecules to link up side by side like logs in a raft, forming the stiff sheet crystals that are the heart of each silk filament. "Silks with polyalanine regions are the strongest tested thus far," Hayashi says.

A garden spider's silk, seen through a magnifying glass (top) and a microscope (middle and bottom), is coated in amino acids that attract water. As the water gathers in beads it reels in the line, keeping it taut. Photograph courtesy of Fritz Vollrath

But strong proteins alone don't make strong silk, any more than good logs alone make a good raft: It has to be assembled well. "Silk is not a self-assembling material," says Vollrath. "It has extraordinary properties because it is spun in a very sophisticated device." The proteins that will become dragline silk are secreted by cells on the walls of a long, saclike gland, from which they are funneled as a watery solution into a long, looping duct. The protein molecules line up with the direction of flow, as logs do in a river— and they become a liquid crystal. In the tapering duct this dope is stretched long and thin and bathed in acid water is extracted from it and recycled and the proteins bind and solidify. Vollrath and his colleague David Knight have applied for a patent on a device, whose secrets they won't divulge, that reproduces part of this process. But Vollrath is the first to admit that no one understands in full detail how the complex structure of a spider thread emerges from a spider's abdominal machinery.

That's why he takes a nephila to the synchrotron in Grenoble every now and then. There he straps the spider to a little platform and gives her milk to keep her happy as she is manhandled. He then proceeds to pull silk from her bottom with a tiny reel, sometimes for eight hours at a stretch. By varying the speed of the reel he can vary the speed at which she spins, and by heating or cooling her platform he can vary the temperature. The synchrotron produces high-energy X rays that allow Vollrath to see how those and other variables affect the internal structure of the silk— the overall idea being to perfect a way of producing artificial spider silk before someone else beats him to it.

"It's a race now," Vollrath says. "People have tried before and given up, because they've used standard industrial technology scaled down. You can do a lot worse than copying the spider."