Spider silk is a natural material produced by spiders through a complex biological process involving protein synthesis, liquid crystal formation, and mechanical spinning, resulting in a substance that is stronger than steel by weight, more extensible than most materials, and tougher than Kevlar, making it one of the most remarkable natural materials known to science.
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Spider Silk: Nature's Super-Material ExplainedAdded:
Spider silk is complicated.
Hello YouTube and welcome to one of the most difficult videos I've made so far.
For millennia, spiders have held a unique place in our minds. Many people might think that's because of their venom, but very few of them are significantly venomous. And lots of other creatures are venomous, too.
What sets spiders so distinctly apart, I think, is silk and the ways they use it.
They're not the only creatures that make silk, but they're the only ones that do such intricate things with it. And no other creature uses something like this at every stage of its life or for so many purposes. Spiders use silk for everything from getting around to catching food to bundling up eggs to flirting. The properties of this stuff are so incredible that it may as well be magical butt rope. Humanity has figured out how to get to the moon, how to split the atom, how to build machines that can calculate impossibly complex problems, and now are even capable of giving you spectacularly terrible advice. But we still haven't quite figured out exactly how a simple spider makes silk. It's not for lack of trying. I spent many days reading papers from the past 50 years trying to wrap my head around what scientists think is going on in spider butts. Most nights reaching a point where I just gave up and then quickly found out that if you want to vent frustrations by blowing things up in a video game, it helps if you're halfway good at that game.
>> Eventually, I ended up talking to people who actually understand the material.
>> Yeah, it's a very complicated topic actually. Oh, and actually the problem is that even the researcher community at some point is not completely in agreement how everything works. So that does make it easier.
>> It is way more complicated than people ever realized.
>> Now I don't feel so bad for having a tough time understanding it. Decades of research though have unlocked at least some of the secrets behind spider silk.
So today we can talk about its incredible properties, what it's actually made of, how spiders produce it, and why scientists created genetically engineered spider goats.
Yes, that is a real thing. We'll get there. Before I dive in, a quick thanks to the people who made this video possible. Dr. Katherine Scott, Dr. Sha McCann, Lesie Brunetta, Dr. Lisa Soyel, and of course, my wife who made the coherence of this script feel a little more like this instead of like this.
This video wouldn't be what it is without their kind help. So, a huge thank you to all of them. And now into it.
What's the big deal about spider silk?
Why has humanity shown so much interest in this stuff? The maddening paradox of spider silk is that it's delicate and easy for us to break whenever we want and also somehow strong enough that when we find it with our faces we panic like it's the cord of death itself.
That's because it is in fact incredibly strong just impossibly thin. So how strong is it you ask? Just like virtually everything else about spiders that's plotline of interstellar complicated. Is it stronger than steel like we hear people say so often? Yes, absolutely it is. Except for when it isn't because it depends. What kind of silk, what kind of steel? And what do we even mean by strength? There's tensile strength and then there's specific strength. And these are not the same thing. Let's start with tensile strength, which is the maximum amount of stress a material can withstand while being pulled or stretched before it breaks.
Obviously, a steel rod like this will be able to withstand more pulling force than a steel guitar string. So, we express tensile strength as how much force a given thickness or cross-section of the material can take before it breaks. And we measure it in megapascals.
What on earth is a megapascal? Many of you were saying a Pascal is a force of 1 Newton about the weight of a small banana or a tennis ball applied over an area of 1 square meter. A megapascal is 1 million of those and converts to about 145 lb per square in. So, a rod made of some hypothetical material with a cross-section of one square in and a tensile strength of 1 megapascal would break if you hung a weight from it that was more than about 145 lb.
Structural steel, the stuff we make construction beams from, has a tensile strength around 400 to 550 megapascals.
Steels specifically designed for high tensile strength reach up to over 2,000 megapascals.
Dragline silk, the stuff spiders use as a safety line and which orb weavers also use for the frame and radial threads of their orb webs, comes in at around 1,000 megapascals. Although this can vary pretty widely depending on the species of spider. So, if we had wires made of structural steel, spider dragline silk, and high tensile strength steel, and they were all the same thickness, the spider silk could hold about twice as much weight as the structural steel, but only about half as much as the high strength steel. Here's the real trick.
First, it should be kind of impressive that a rod made of spider silk with a one square in cross-section could suspend a weight of 145,000 lb, roughly the weight of an M1 Abrams tank. But on top of that, that same rod of spider silk would be 16th the weight of a steel rod the same thickness. And this is where we talk about specific strength instead of tensile strength. A cubic centimeter of steel weighs about 7.8 8 g. A cubic cm of spider silk weighs about 1.3 g. It would feel about as heavy as the plastic we make water bottles from. It's almost baffling to imagine something that light being stronger than structural steel and even half as strong as high-tech alloy steels. By the way, if you're looking for that 1.3 g per cubic cm number and you're having trouble finding where it came from, don't feel bad. When I was trying to find the density of spider silk, every paper that mentioned this figure just cited another paper, and sometimes the paper it cited didn't even mention it. I hit a lot of dead ends following the breadcrumb citation trail.
But I finally tracked it down to a paper from a US Army research lab in Massachusetts in 1968 by a JC Zlin.
Zlinan used a density gradient column, basically a vertical glass tube filled with two liquids mixed to create a steady increase in density as the depth increased to measure spider silk samples. By dropping them into the liquid, then observing where in the column they floated, it was possible to determine the density very reliably.
Specific strength is tensile strength over density. Basically, how strong is a material for its weight? Imagine we made really long wires or cables of different materials and hung them over the edge of an infinitely high cliff and kept making them longer until they broke under their own weight. Polyropylene, which is what we used to make a lot of threest strand rope, would break once it got to 3 or 4 km long, 2 to 2 1/2 miles. A wire made of incanel, which is a very strong modern steel alloy that machinists everywhere love working with, would break at about 15 km, around 9 m.
But a length of spider silk hung straight down would have to be a ridiculous 80 km, 50 m long before it broke under its own weight. So, while spider silk is only half as strong as high strength steel in terms of tensile strength, it's five or six times stronger than that same steel in terms of specific strength. And this is why you'll often hear the phrase pound-for-pound it's stronger than steel. That's referring to its strength to weight ratio, that specific strength.
So, that's two ways in which spider silk is remarkable. It is both incredibly strong and incredibly light. But wait, there's more.
Spider Silk offers another exceptional quality, extensibility.
Five bucks says that's not the word you expected me to say just there. A lot of sources will use the term elasticity interchangeably with extensibility, but that would be basically wrong. And there's a thing we say here on this channel, say it with me now, less wronger is more better. Extensibility is how much we can stretch something in terms of percentage longer than its original length before it breaks. A steel wire normally breaks once it's been stretched to about 15% more than its original length. But this orb web frame silk typically can be stretched 25 to 35% before breaking. In this particular case, I was able to stretch it all the way from 1.08 to 1.66 in, which is actually about a 50% increase.
What is elasticity then? If we stretch a piece of drag line or frame silk to about 2% longer than its original length, then let go, the silk will return to its original length. This is elasticity. If we stretch it beyond that point, say to 10% longer than its original length, it won't break, but when we let go, it'll stay 10% longer.
The silk thread has actually deformed now and is permanently stretched longer.
But watch this.
That looked like a bit more than 2 to 4%, didn't it? For the most part so far, I've been talking about major ampulate silk, the silk that spiders use for their safety lines and the frames of orb webs. But the silk that's used to make the spiral part of an orb, called the capture spiral, is a different kind.
This is called fleella form silk, and it has different properties. While the frame silk can only be stretched to 25 to 35% of its length before breaking, this fleell form silk can be stretched to 270% of its original length before it breaks, sometimes more. And while the frame silk gets stuck at its stretch length beyond 2 to 4%, I was able to stretch this section of capture spiral silk by 66% and it snapped back to its original length. And this web was over a month old. So capture spiral silk has not just greater extensibility, it also has far far more elasticity than the major ampulate silk that the frame and radials are made of.
What's the point of this extra elastic silk? Why not just make the spiral out of the same stuff as the frame?
the the spiral catching silk in um orb webs is quite clearly uh a descendant of major ampulate silk.
You can see an actual amino acid chain change that would give rise to essentially a protein structure that kind of like kind of zippers in, zippers in and out.
Um, and like the advantage that that would give a spider if you have a very stiff web like this and you know if it's a slow fly it might you know it could get stuck but it what when you get fast flying insects which evolved later if it's a very stiff web they're just going to hit it and bounce off. So, if you have an elastic web, it absorbs a bunch of the energy and there's a chance for the glue to surround it and for it to get stuck.
There is a trade-off in strength. While it's still incredibly strong, it's only about half as strong as dragline silk.
But the combination of strength and extensibility gives us one more important material property, toughness.
In material science, we have something called a stress strain curve. This is a graph of how much a material stretches the strain relative to how much force you apply the stress. Most materials have a curve that looks something like this. And this shoulder here is the yield point, which is where the material stops being elastic and permanently stretches. The curve for dragline silk looks something like this. While the curve for capture spiral silk looks more like this. The area under the curve gives us the material's toughness. How much energy it takes to actually break it. Here it takes a lot of force but applied over a short distance. While here it takes less force but applied over a greater distance. And the toughness of these two silks ends up being pretty close to the same around 150 to 160 meg per cubic meter. Steel has a toughness between 50 and 200 megajoules per cubic meter depending on the type. So it's in the same range but is much heavier. Kevlar 49, not the body armor kind, but a kind of Kevlar used in cable and rope products, has a toughness of around 50 megajou per cubic meter, meaning it takes three times as much energy to break a strand of drag line or capture spiral silk as it does to break a strand of Kevlar 49.
And yet another type of silk, the asinopform silk of our Gaia trifasciata, had its toughness measured at 350 megajou per cubic meter, meaning it outperformed Kevlar 49 seven times over.
Ainopform silk is the stuff many spiders use to wrap up their prey, often when it's still kicking. So that toughness matters. The toughest silk we know of is the major ampuulate silk of the Darwin's bark spider, Kerostrus Darwini, which occurs in Madagascar.
In 2010, Ingi Agnerson, Madia Cutner, and Todd Blackedge collected some of them and found that major ampulet silk forcibly drawn from their spinettes had an average toughness of 354 megajou per cubic meter, but topped out at a whopping 520 megajou per cubic meter. This makes the spider silk the toughest biologically produced material known to humanity.
To ice the cake, spider silk, especially capture spiral silk, does a pretty cool thing when something hits it. Watch closely at what happens when I let this line snap back.
Rather than twanging like a rubber band, it snaps back relatively slowly. This is because of something called elastic hysteresis. This is basically the difference between the energy it takes to stretch a thing and the energy it releases when it springs back. When a flying insect hits a spiderweb, the silk lines stretch and absorb the energy of the impact. The silk converts about 65% of the energy into heat, dissipating it harmlessly, so that when the web snaps back, it does so gently. This helps the web actually stop the prey rather than bouncing the prey back out. All of this together is why scientists have been so interested in spider silk. This stuff outperforms basically every material humanity has ever produced. We thought we were hot stuff when we started adding carbon to iron to make steel. And we thought we were really clever when we dreamed up Kevlar and carbon fiber. But these little eight-legged freaks had us beat long before we even figured out how to make mud. So, how do they do it? What even is this stuff? What sorcery goes on in spider butts to produce this super material?
What is spider silk actually made of?
Spider silk is made up of proteins, which sounds kind of boring until you look into what proteins are and how they work. A very quick recap of how proteins are made in the body. It starts with an organism's genome, which is the whole set of sequences of DNA needed to produce every part of its body. Genes are sequences of nucleotides along the whole strand with identifiable start and end points and an enzyme comes along sort of unzips the gene reads the nucleotides and constructs a string of mRNA that mirrors the gene. That string then exits the nucleus of the cell which is a detail I got wrong in my feather-legged orb weaver video. So, thank you to the folks who corrected me in the comments. And then a little molecular machine called a ribosome reads that string of RNA nucleotides and grabs corresponding amino acids out of the cellular soup creating a chain. That chain then folds itself up into a particular shape depending on various factors. That is a protein. The shape of the protein determines its function and it can react to different stimuli like temperature, the presence of certain substances or stresses. Proteins can do all kinds of things. For instance, many of the toxins in venom are proteins. The proteins that make up spider silk are called spidroins. And as proteins go, they're huge. In 2007, Nadia Aub and a team in California obtained the complete gene sequence for two of the main proteins in black widow dragline silk, which we call major ampulate bidin 1 and major ampulates bidroin 2, abbreviated like this.
Now, in animals, the average protein is around 400 amino acids long. One of the proteins Iub's team identified was over 3,100 amino acids long and the other nearly 3,800. And the proteins contain certain sequences of amino acids that were repeated in the chain hundreds of times in a row. Different sections of the protein can fold up in different ways. And it turns out that's critical to spider silk. Way back in the 1950s, Richard Marsh and a team in California decided it would be fun, I mean decided it would be valuable from a scientific perspective to shoot some X-rays through spider silk and see what kind of pattern was generated. This is a technique called X-ray defraction, which has been around since 1912. And the pattern they saw indicated that at least parts of the silk were in crystal form, regularly spaced molecules rigidly arranged in a consistent pattern. From that we learned that parts of the protein chain doubled back on themselves to form a zigzaggy panel called a beta pleated sheet. And when those sheets stack on top of each other, the very regular arrangement of atoms forms regions of solid crystal.
Kind of like stacking egg trays back when regular folk could afford eggs.
Those were good days.
Other parts of the protein folded into less organized patterns like alpha helyses, spiral structures that are much looser. Ultimately, the finished silk is a matrix of these loose spirals and helyses which act almost like springs with all these chunks of solid crystal embedded in it which add extraordinary strength. In trying to understand all of this, I spoke with Dr. Lisa at the University of Broit in Germany who is the lead author on a paper examining our current understanding of how spiders actually produce silk. So you actually have sections within a single protein molecule where some sections are crystallin and other sections are not.
>> Yes, exactly. That is the whole reason why spiders has those tremendously great characteristics of this high elasticity while being mechanically incredibly stable.
>> And the longer the chain of amino acids, or in other words, the bigger the protein molecule, the stronger the silk can be. These proteins are produced in silk glands in the spider's abdomen. And at this point, they're dissolved in a liquid solution called silk dope. By the time they exit the spider, they've transformed into this incredibly strong, tough, surprisingly elastic fiber. So, what's happening in between? How does this bizarre mixture go from room temperature soup here in the abdomen to super tough and stretchy bum bungee cord here?
The ability to spin silk organically is already impressive and mysterious to us.
But there are a few factors that make it particularly remarkable. First, the silk in the glands uses water as a solvent to remain liquid. But water does not dissolve finished silk. Meaning something is happening to take the stuff from soluble in water to not. Second, the whole process happens at ambient temperature. It would be easy to think of spider silk like it's hot glue coming out of a glue gun, a substance that solidifies as it cools, like literally everything does. But there's no temperature change taking place. Third, this silk is somehow stored as a liquid, then converted to an incredibly strong and tough fiber on demand at incredible rates. A jumping spider literally spins its drag line midair as it's jumping.
So, the production of this silk is less like hot glue from a glue gun and more like a two-part epoxy, which cures with chemical processes, except it happens in milliseconds and it's not done by mixing different substances. So, what's going on inside these little creatures to make this happen? That's a challenging question.
>> You know, it's it's difficult to work with with spiders in general and especially spider sick mechanism. is is at a at a dimension that is crazy hard to to even investigate at all.
>> There are at least seven or eight different kinds of spider silk, but one particular type of silk called major ampulate silk would be particularly useful to humanity if we could produce enough of it. So that's the one we know the most about which does have a downside as Leslie Brunetta, one of the authors of this book explains.
But unfortunately it means that you know a lot of the research very basic research is like focused on that one silk where to me at least the really interesting thing is the whole body of silks. The question is whether people have had funding to do that >> right >> because it's really almost a pure biology and science question. Most of the silks, you know, really, except for maybe fleellopform, maybe the glue and major ampulate silk doesn't have any sort of at least that we can think of now like potential commercial promise.
While it sort of makes sense to put the research dollars toward work that we think might have practical applications, we also have no way of knowing what we might be missing by not studying types of silk we can't see practical uses for.
Back in the 1880s, two doctors took the pancreas out of a dog because they wanted to understand its role in digestion. They were sort of just fooling around and finding out because they wanted to know stuff. But down the line that resulted in our discovery of insulin which has saved countless lives.
This is why public funding for scientific research matters. So many important breakthroughs have been made when someone was looking at something else entirely.
Also because I want to know is already by itself a valid reason to study and research a thing. But so far our research on silk production has focused on the silk from the major ampulate gland which looks something like this.
This section is called the tail and that's where the proteins are actually produced. This larger space here is called the ampula and it seems to function mostly as a storage tank for the liquid silk dope. When the spider needs some silk, the dope enters this funnel, then progresses through this S-shaped duct, then passing through a structure called the valve, then out the spigot on the spinet as a solid thread.
Our understanding of the transformation that occurs throughout that process has had a couple of notable developments over the past few decades. In 1999, David Knight and Fritz Volwrath removed the major ampulet glands from some orb weeding spiders and examined the silk dope inside the glands with a polarizing microscope. The silk dope in the gland in the duct produced repeating optical patterns indicating that there was some sort of organization to the arrangement of the protein molecules even though they were in a liquid state. This indicated the presence of liquid crystals.
Liquid crystals can be created when the molecules all align in the same orientation but are free to move relative to each other. It's like when you learned line dancing in middle school gym class. Everyone's pointing in the same direction. Everyone's moving but everyone's afraid to touch each other. Meaning the molecules can still flow like a liquid while retaining crystallin properties. It was theorized that this allowed the proteins to reach high concentrations without solidifying, but it didn't fully explain how the spidroins remained soluble at such high concentrations and no one could replicate it in the lab. In 2003, Young Jun Jinn and David Kaplan examined the silk dope in the glands of Bombix Morai, the silk worm, which produces silk in much the same way spiders do. They found that different parts of the protein chain called domains had varying levels of attraction or repulsion to water. And this could cause them to fold and arrange themselves into little spherical groups with domains that loved water on the outside and domains that hated water beneath those. The paper didn't say anything about domains that liked water just as a friend. This resulted in a little sphere called a myel that could float around in the water but also contain a bit of that water in its middle. And those myels would group together into globules. This is something called liquid liquid phase separation or LLPS.
Kind of like oil droplets forming in water. a drop of liquid within another liquid, enabling the proteins to reach high concentrations within the water while remaining essentially soluble and liquid instead of crystallizing into a solid then and there.
Turns out spider silk dope does basically the same thing silkworm dope does as the spidroin moves from the tail into the ampula. When the spidoins are first produced, they exist at very high concentrations which would normally cause them to bond together. But the pH and salt in the water stops that from happening.
>> So we have the sodium chloride which interrupts coalent hydrogen the hydrogen bonds um and that makes the protein in itself soluble at this high concentration. We have concentrations of up to I think 50% of the spittering.
>> This is in the lab. This is nearly impossible to produce. So, this was also something research just didn't get their mind around for quite a while.
>> Turns out the proteins remaining dissolved is pretty important.
>> But they're not solidifying at that point.
>> No, no, no. That that would be very bad for a spider. Actually, >> I'm not positive on this, but I'm pretty sure that would be about the equivalent of a kidney stone. If it happened, the spider would have to pass something solid through a channel intended for something liquid. And I've heard that virtually never goes well. As the proteins in this salt solution move through the ampula, things start to happen. At that point, we have a diner, right? We have the normal spitrine. We have a N terminal side on one side. Then we have a large hydrophobic >> Yeah.
>> block. And then we have the C terminal end.
>> Okay.
Um in the storage conditions the basically the part when it comes out of the tail into the ampula um the C terminal domains are as are are present as dimes and that way we have basically this is what we draw right um such a structure they we have one side that is connected and the other side is free and what is important is that those even though they are bonded together right at the this terminal end. They are highly flexible at that point. They do not have any intrinsic structure. They are intrinsically disordered proteins and this is quite important for them to actually undergo all the process that follows. So they're very very flexible.
They can move in any direction. They can bend. They can turn. They can form coils. Everything.
These are the little units that form these little structures called myels.
And that arrangement is largely driven by how attracted to or repelled by water the different parts of the unit are. You have hydrophilic domains and you have hydrophobic domains. And the second you have that somehow a self assembly occurs where you form structures globular structures that have hydrophilic uh outside and a hydrophobic inside.
>> Right? And this is what actually happens.
>> Those myels then group together into larger roughly spherical globules as they move across the ampula and toward the funnel. This is liquid liquid phase separation. Although the proteins are grouping together like this, they're not solidifying.
This is all driven by weak interactions between the molecules. But these globules are still very flexible.
They're still essentially kind of a liquid at this point.
Yes, we call it liquidlike condensates.
Only from the liquid like condensate uh state the fiber can be drawn. The solid like condensates cannot be drawn into a fiber.
So this is very important that it stays in this liquidlike state.
>> As the whole mixture moves from one side of the ampula to the other, a lot is happening. The salt concentration is dropping and so is the pH. And then a funny thing happens. The myels themselves elongate while the larger globule seems to more or less keep its shape. In 2018, Lucas Parent and a team of researchers observed this directly in silk glands dissected from black widows.
Using cryotansmission electron microscopes, they were able to see these clumps of my cells dissolved in water.
Then they vigorously microipipeted some dope mimicking the extrusion process that occurs in the spinning duct. Then looked at it with the electron microscope. a second time. They could see that the myels had transformed from flake-like shapes into long narrow fibbrals but remained in place in the larger globule. In 2024, Michael Landry and a team in Sweden proposed that as these myels elongate and begin to interact with each other, they arrange into the liquid crystal phase that Volwrath and Knight had seen evidence of 25 years earlier. And at this point there are some structural changes happening in the terminal ends especially in these C terminal ends that make the myellular structures open up a little bit. So the these spitrines then get into a more elongated fibrous state but inside a bigger globular state and that is where we have the pneumatic face starting >> the repeating sections of the proteins in the interior of the myel start to align in a way that sort of puts the right parts of each protein chain next to each other preparing them to form those beta pleated sheets. We are still not at solid silk yet. And already the spider has needed controlled salt concentrations, acidity regulation, myel formation and aggregation and now pneumatic liquid crystal arrangement in order to be halfway to finished useful hiney twine. Finally, this silk dope heads through the funnel into the spinning duct. So what part of this is spinning? What is rotating or turning in this whole process? No part actually.
Humanity in our hubris just called it that because we needed to build a machine with rotating parts to make something even remotely resembling spider silk and even then it was nowhere close. Anyway, what happens in the duct here? The larger globules are starting to sort of get squished and elongated and the proteins are getting more and more compacted.
there's more and more elongation happening and the due to a narrowing of the duct those globers come into more contact to each other and then we have um those intra and intramolecular interactions start to actually be happening right and this is what is happening throughout the spinning duct and while it gets longer and longer and they align even more and um this way the the amino acid residues come into closer contact and they can actually interact with each other. But this is the point where we are yet not 100% sure which amino acid has which impact.
>> Even this is not as simple as it sounds.
Throughout this entire process, we need to be aware of the effect of sheer forces which are forces that occur in a fluid when you push or pull it through a pipe. The fluid against the walls of the pipe moves more slowly than the fluid in the middle of the pipe due to friction.
Meaning the stuff in the middle has to kind of slide past the stuff at the edges, shearing the liquid. This creates internal friction within the liquid.
That is sheer force. It's ultimately shear forces that transform the liquid silk dope into solid silk fiber. Meaning that shear forces need to be kept low until the right time.
>> And if it occurs too soon, then well, the spider will not be happy about that.
>> No.
>> And we can then we have a solid fiber inside the spider. That would be bad.
>> There's some mystical math wizardry involved here. If you send a volume of liquid through a pipe that gets narrower, that volume of liquid has to get longer. And if the pipe narrows at a constant linear rate, the rate at which the fluid elongates speeds up dramatically as it goes through the taper, which creates big shear forces.
To keep shear forces low, you need that rate of elongation to be constant. And you can make that happen if you shape the pipe like a hyperola instead of a cone. Remember hyperolas from high school? We all loved those, right?
Knight and Volwrath back in 1999 measured the diameters of the spinning ducts of a couple of different species of orbw weavers along their length. And well, guess what?
Yep, they narrowed at more or less that hyperbolic rate. So, this spinning duct is engineered to keep those shear forces low. Enough shear force to orient the proteins, but not enough to stretch them.
The walls of the duct are made of special cells that act as a dialysis membrane, removing water, lowering the pH further and pulling sodium chloride ions out. And remember, those sodium chloride ions were preventing hydrogen bonds back in the ampula. By the end of the duct, they're out of the way. The proteins are aligned and we're ready for the final step.
shortly before you draw it where the share forces increase very strongly and then you have the remaining water removed. Um then only then the better sheets form and these better sheets stabilize the crystal structure.
>> Everything up until this point has been a matter of arranging things correctly on a literally molecular level such that one very simple action then makes something amazing happen. At the end of the spinning duct, we have something called the draw down taper. Here, the diameter of the duct narrows suddenly as the silk is being pulled out. That sudden restriction creates very high sheer forces within the liquid dope. As the proteins slide past each other, the right regions of the proteins come in contact with each other and grab on, locking together. The proteins are now interlocked chains that have both solid, highly structured crystal regions as well as more disordered helical regions.
This is where the silk finally and very suddenly becomes a solid and this process cannot be reversed. The spider now has a solid thread. But that thread is still inside the spinette at this point and it now passes through a structure surrounded by muscles called the valve, which is kind of like a clamp or brake that allows spiders to stop on a drag line or even orient themselves during a jump. It's also thought that this valve may act as a ratchet or pump if the thread is broken inside the spinterette to restart the spinning mechanism. Past the valve is the lips of the spigot itself, which strip away the last of the water and add a bit more tension to the thread. And just like that, the spider has this magical bum bungee cord that it can use for a ton of different things.
It's important to note here that as near as we can tell, the spider does not push the silk out. She pulls it out. Watch this black widow throw silk over a cricket. She can't spray it at the prey.
She needs to pull it out with her hind legs. When orb weavers wrap prey, you can see them doing the same thing. Most spiders leave a drag line behind them when they walk, anchored to the ground somewhere, and it's drawn out of the speres as they move away from that anchor point. What this means is that if Spider-Man's web spinners worked like actual silk glands, apprehending a bad guy would look less like this and more like this.
Two crazy things about everything I just took the last 10 minutes to explain.
One, what I just gave you was essentially the Kohl's notes version because it's even way more complicated than this. Two, this entire process happens in milliseconds, which is even less time than the 1 second it would take you to click the like button and help me continue to be able to make these videos. It really helps out, so I appreciate it. Anyway, the fact that jumping spiders spin this silk midflight under tension the whole way gives you some idea just how quickly this entire process gets completed.
>> Yeah, you can see why nobody's successfully replicated this yet. It's incredibly complicated.
>> And this is all based on what we know about only one kind of silk from one type of silk gland. This really is just the tip of the iceberg.
There are actually at least eight different kinds of spider silk we can talk about all produced by different kinds of glands in the abdomen.
Naturally, they have sciency sounding names. Major ampulate silk, minor ampulate silk, fleellopform silk, ainopform silk, purform silk, aggregate silk, griellar silk, and tubularform silk. sometimes called cylindrical silk.
Why, you may ask, "Does a spider need so many different kinds of silk?" I'm going to bet many of you have spouses that ask questions like, "Why do you need so many shoes?" or "What do you need another fishing rod for?" The answer is the same there as it is for spiders. They all do different things and serve different purposes. The best known, the kind I've mostly been talking about here, is major ampulet silk. This stuff has a very high tensile strength but lower elasticity than some other silks. In orb webs, the outer frame, the anchor lines, and the radials are all made of this relatively stiff, strong silk. In cobwebs, most of the tangle sheet and the gumoot lines are made of it. And spiders use major ampulate silk for the drag lines they leave behind them. The evolution of major ampulet silk is probably what allowed spiders to move beyond burrows in the ground and start climbing on things because they now had a safety line like major ampulate silk. Probably the biggest benefit that that gave it for a long long time was just being able to drop out of predators reach.
>> Mhm. Okay.
>> You know before probably before it became useful in prey catching. Of course, a safety line is only useful if it's anchored to something. And for that, spiders use what's called purform silk. Puroform silk contains different proteins than major ampulet silk, but they still have that structure of repeating sequences, and it becomes a system of nano fibbrals embedded in a cement-like matrix.
You can watch this false widow here glue down her drag line to this piece of acrylic before carrying on. And she does it again here. When she gets to the edge at high magnification, here's what that attachment disc looks like. And you can see the drag line coming from it, securely anchored to the surface.
Ainopform silk is the toughest kind of silk we know of. It was the asinform silk of the banded garden spider that outperformed kevlar by seven times. Its primary use is for wrapping up prey.
This is a crucial function for many spiders and many actually begin wrapping prey before they actually bite and inject the venom. So this stuff comes into play while prey is still very much alive and kicking and in many cases very much a real threat to the spider which is why the spiders sort of throw it over the prey with the back legs. The tough silk immobilizes the prey to the point where it can't injure the spider. And then the spider gets its face in there.
And you know, minor ampulate silk isn't quite as strong as major ampulet silk, but it's more elastic, making it a bit tougher.
And orb weavers use it to build the auxiliary spiral, which stabilizes their orb web during construction.
Fleellopform silk is used by orb weavers for that capture spiral. It lacks the tensile strength of the major ampulet silk that makes up the frame of the orb web, but it is far far more extensible and elastic. This is the stuff that stops flying insects in their tracks, absorbs most of the energy and converts much of it to heat and keeps them stuck there until the spider can come unal alive them. If we look closely at that fleellopform capture spiral, we notice little droplets on it. These are made from their own kind of silk known as aggregate silk, which is the glue that the capture spiral gets coated in to snatch away any last little bit of hope that fly might have had. The glue itself is a form of silk. And there are a couple of really wild things about it.
One, the adhesion of this glue, its stickiness varies with humidity. And in 2015, Garav Amarpuri and a team discovered that the glue of different species maximized its stickiness at very different humidity levels. But those different levels corresponded exactly to the different species natural foraging habitats. So the spiders are actually tuning their glue to their environment to make it more effective.
Second, in 2010, Basavsani and a team found that the glue droplets functioned as a visco elastic material. Once something is stuck in a droplet, if it pulls away quickly, the glue acts like a very thick liquid like honey and doesn't let go. This is sheer forces at play.
But if it pulls away slowly, the glue now acts like a rubber band, allowing for some stretch but returning to its original form. So, this glue actually behaves differently depending on how force is applied, maximizing its effectiveness. It's way more advanced than just sticky goo. It's sticky, elastic, liquid, solid something. It turns out there's more than one way to make stuff stick to your web, though.
Some spiders can produce kribellar silk, which is extremely fine and woolly. They actually have to comb it out with a line of hairs on their hind legs called a calamist.
Some of these spiders make orb webs and they cover the capture spiral not with that sticky glue but with this fine dry fluffy silk. This cribellar silk works in two ways. One, it can function sort of like velcro untangling rough structures on insects unlucky enough to fall on it. And two, the fibers are so small that intermolecular forces called Vanderwal's forces can actually make it adhere even to perfectly smooth and dry surfaces. It's effectively sticky without actually being sticky. Many female spiders can produce tubularform silk or cylindrical silk, which is the primary component of the egg sacks. All spiders lay eggs, and they all wrap them in silk, even if it's just a few threads. In fact, we think this may have been silk's first purpose. Egg sacks can take many different forms. From these hangy teardrop things that our guy makes to these golf ball looking things that dodites carry around to the egg sacks of parson spiders which look ironically kind of like fried eggs. Most of these egg sacks are very tough with the inner layers of silk being quite soft and fluffy but the outer layers being densely woven becoming almost paperlike.
The egg sack usually needs to protect against parasites, predators, and even fungi, all while maintaining an ideal humidity level inside. So, they're essentially waterproof. And many spiders add some asinopform silk to them, making them extremely tough.
All of these kinds of silks come from the six spinetses, which have a whole bunch of tiny nozzles called spiggots on them that are all connected to the different silk glands. Here on the anterior pair of spinteretses, you can see what look like tiny hairs. Those are actually purform silk spiggots, and the spider needs a lot of them to make that attachment disc. These same spinets have the spigots for that major ampulate dragline silk, but only one spigot each for a total of two. In orb weavers, these posterior lateral spinets contain the triads. Each spinnerette has a spigot for fleellopform silk to make the capture spiral flanked on either side by spiggots for aggregate silk that visco elastic glue. So the capture spiral is coated with glue as it comes out. These smaller spinets tucked in the middle usually produce the asinophform silk for prey wrapping and in females the tibuloform silk for egg sacks.
Silk though is not a one silk onepurpose phenomenon. In 2008, Kobe Lamatina and a team in California found that black widows use a combination of a synopform and minor ampulet silk to wrap up prey.
And in 2019, Jonas Wolf found that orb weavers, who make their drag lines out of only major ampulate silk, are the exception, not the rule. Most other spiders were adding minor ambulance silk to their drag lines, and a few were adding some asinform in there, too. This is a part of what makes spider silk so maddeningly difficult to study. There's basically an infinite number of combinations. It's sort of like asking what's the recipe for Italian food.
These different silks seem to have driven the evolution of different web styles, different hunting styles, and different morphologies in spiders. It might surprise you to know that the cobweb, as messy and random as it seems, is actually a more recent development than the aesthetically pleasing, tidy, organized orb web. It's believed the cobwebs are actually a more advanced version of the orb. To our eyes, this looks like progress about as much as the Windows 11 rollout does. But there's a method to the madness of the cobweb, which I explained in my Black Widow video. What's interesting though is that these other styles of web, the vertical orb web, the horizontal orb web, the sheet web, the funnel web, all of these kinds of webs are still around and work just fine for their respective spiders.
And this is a poignant demonstration that there isn't really one ideal way of being.
>> And I think, you know, the way that we understand it often is it's like this knockout tournament.
And that's just not that's not it. The orb weavers are still here. It's not like the cobwebs have knocked out the orb webs, >> right?
>> So there's no like end point to all of this really. Evolution like spiders are like the microcosm of everything else.
It's a story of this spreading. It's not a story of this >> coming to some acme.
>> There's no fixed ideal. There's just variety.
>> There's just variety.
And I've barely scratched the surface of this variety. Nephosids have a specialized pair of long cylindrical spinteretses and actually use a modified form of purform silk normally used for attachment discs to subdue prey.
Deonopids use silk to make a net they actually throw over flying prey. And skytoies, the spitting spiders, have silk glands in their heads as well as in their butts and spray venomladen silk out of their fangs to immobilize and paralyze prey. We could go for days talking about this because the language of evolution was written to express a beautiful and endless diversity that we can hardly even begin to imagine.
Not with our own butts, no. But by other means, maybe. In fact, it's happening as we speak. And we've been trying a long time. Creating a synthetic material with the properties of spider silk, particularly that strong, tough, light major ampulet silk, is sort of the holy grail of materials engineering. Humanity has been using spider silk for ages. The ancient Greeks would bundle up spider silk for use as a wound dressing. In Australia, Aboriginals used spider silk as a fishing line. And in New Guinea, natives used it to make fishing nets and bags. Over the centuries, people have tried making fabrics out of spider silk.
The first written record of anyone doing this comes from 1710 when Francois Xavier Bon wrote a discourse on the usefulness of the silk of spiders, which is a much more entertaining document than you might expect. In all, it's just over 14 pages of text. The first four of which are nothing but Monserbon explaining why studying nature isn't really a complete waste of time.
The best part comes on page nine where he writes about the abdomen of a spider.
It contains the back, belly, parts of generations, and the anus. I shall apply myself more particularly to the description of the anus as being the part from whence the spiders draw their silk. It is certain that all spiders spin their thread from the anus about which there are five pilli or small nipples which at first sight one would take for so many spindles that serve to form the thread.
I have found these pilli to be muscular and furnished with a sphincter.
Nobody tells you how much fun it is to read science texts from the 1700s.
Anyway, this guy collected a ton of spider egg sacks, mostly by promising to pay people the price of actual silk for them, then boiled them, carted them like wool, and spun them into threads, from which he then made a pair of stockings and a pair of gloves. Bon was convinced that silkworms could be replaced with spiders. That was apparently before he encountered the difficulty of breeding and housing really large numbers of them in small spaces because they invariably eat each other, which history shows is the major limiting factor in using spider silk for anything. The most recent example of something made from genuine spider silk is the cape made by Simon Piers and Nicholas Godley. It's woven entirely from the gold tinted silk of tricana spiders from Madagascar. And it took them years to create. They collected 24 spiders at a time, put them in little harnesses, extracted silk, and wo it into threads, then released the spiders back into the wild at the end of each day, which is nice. I guess it took 1.2 million spiders to get enough silk to make this thing. So clearly using natural spider silk to make fabrics isn't really viable unless you're selling a hoodie for the price of a Boeing 747.
Small amounts of silk have proven useful though. The thickest spider silk fibers are only 5 to 10 microns in diameter while the average human hair is 50. So it worked well for crosshairs in optical instruments including rifle scopes as it was the only material thin enough and strong enough to withstand the recoil.
As late as the 1990s, some military facilities actually kept a black widow around to provide silk to repair the crosshairs in old instruments.
But today, the possible uses of spider silk are vast. Sure, you may have heard talk of it being used to create lighter, more flexible body armor, as it's stronger and tougher than Kevlar. But believe it or not, there are non-military uses for this stuff. Who'd have thought that? There's been a lot of interest in using it to make better sutures for closing up wounds. Why would we do this? Well, again, spider silk being exceptionally strong while exceptionally thin is reason number one.
Reason number two is biocompatibility.
Spider silk appears to have no negative interactions with living tissue and degrades naturally and harmlessly in the body over time. I found a couple of papers stating that the first recorded use of spider silk as a surgical suture was in the 18th century. Thing is, none of those papers pointed to a primary source. I threw this at consensus, which is an AI assisted search engine trained on academic papers to see what it came up with. And consensus also indicated that it could find papers making the claim, but none that pointed to a primary source. So, internet sleuths, if anyone can find an actual primary source from the 18th century documenting this, drop it in the comments. In 2011, Yorn Kubir and a team in Germany tried creating a micro suture out of spider silk, one that would be fine enough for micro surgery, the kind of surgery that repairs things like nerves.
They demonstrated that spider silk sutures were much stronger than conventional nylon sutures of the same thickness and their braided surfaces provided a good medium for cells to adhere to, suggesting that this was an idea we should probably try out. Five years earlier, Christina Alang and a team that had a few of the same people from the suture study successfully used spider silk as a scaffold on which to grow nerve cells, ultimately producing artificial nerve grafts.
This was a step forward in the field of tissue engineering, the effort to grow artificial tissues and structures for medical applications. And Dr. Soyel is continuing that work.
>> I'm working in voluometric printing of spider silk. So I'm doing 3D printing with uh the sick proteins. They were trying to use this preassembly mechanisms. I'm printing in a with a lightbased process.
So uh I have to modify the silk to make it photochemically active and then I try to cross link it into bigger 3D constructs to make tissues for various applications. tissue engineering, tissue regeneration, disease models.
>> So, there are lots of reasons for us to try to figure out how to make this stuff on our own. Spider silk can be collected directly from actual spiders, but it's a slow, difficult process, and it takes a huge amount of effort to collect even a minuscule amount of silk. Making spider silk, though, is a complicated problem because it's really a two-part problem.
We don't only need the substance itself, an artificial silk dope, but we also need the biio machinery to transform it from liquid protein into solid fiber.
And both problems are really challenging.
First, creating the silk dope. This isn't a matter of just pouring the right ingredients into a test tube. You need living cells with the right DNA to assemble a chain of amino acids into the finished protein. So, you need a living thing to do it for you. And if you want any useful quantity of the protein, you need a lot of those living things. And you need them to not be spiders because when you try to farm spiders, they just keep eating each other. So you take the genes that produce those proteins out of the spider and stick them into something less cannibalistic. The idea is that the cells of the new organism will just read the instructions in the gene you slipped in and make the protein without really questioning it. This is sort of like if you really want an alpaca, but your spouse does not want an alpaca, you just quietly add buy an alpaca to their calendar and hope they just carry out that task without really thinking about whether it's a good idea or not. And scientists have actually done this the gene thing, not the alpaca thing.
Scientists are able to cut strands of existing DNA into little pieces and stick them together to create the gene they want. and they can then insert that gene into something else like a bacteria. This is called recombinant DNA since they've recombined bits and pieces of genes from more than one source. Back in the mid 1990s, Randy Lewis and a team from the universities of Wyoming and Massachusetts artificially constructed a gene that contained the repeat sequence of major ampulate spidroin 2, then stuck it into E.coli bacteria. The cellular machinery of the bacteria did what it does. It read the artificial gene and expressed the protein. It bought the alpaca. The thing is, their gene only had 16 of the repeat sequences. And E.coli seemed to only be able to produce small, relatively short proteins. A year later, Steven Fannisttock and Laura Bedzik at Dupant did similar work, but this time with yeast and were able to produce larger, longer proteins. All of these proteins, though, weren't really soluble. They clumped together instead of dissolving into a dope that could be artificially spun into a fiber. In 2002, Anthula Lazarus and a team at a Canadian company called Nexia Biotechnologies managed to insert engineered genes that contained the repeat sequences from major ampulate spidins into mammal cells. These proteins were more soluble and Nexia managed to actually spin decent fibers out of them by extruding the solution through a tiny hole. kind of like the draw down taper of a spinette.
But Nexia Biotechnologies sort of had a moment of fame for the next step in their research. Transgenic spider goats.
What's meant by transgenic? Basically, when you take a gene from one organism and stick it into the actual genome of another and grow the whole organism, that's a transgenic organism. Nexia had gone beyond just modifying clumps of cells and modified goat embryos to produce a whole goat. One that produced spider silk proteins in its milk. So when you hear about money being spent to research transgenic organisms, this is the kind of thing that's being talked about. Just in case that needed clarification, it worked, but the spider goats only produced low concentrations of the protein which still had to be purified and spun. In 2004, Jurgen Sheller and Udo Conrad in Germany modified tobacco and potato plants to express the proteins. In 2005, Young and Mayo and a team in Japan managed to get silkworm cells to express a protein based on fleellopform silk using a technique that sounds much more terrifying than it actually is.
Basically, they engineered a virus called a bulo virus. stuck the gene for the silk in the virus, then infected the insect cells with the virus. The virus kind of sneaks into the insect cells and delivers this DNA payload. Silkworms were ideal because they actually already produce silk, just a kind of silk that isn't as strong or tough as spider silk.
So, just getting silkworm cells to produce the protein was very promising.
We need to go back and talk about the goats for a second, though. It was actually very difficult to get solid information on the origins of spider goats. It seems Nexia never actually published about their work on this. The paper that's usually cited is the one describing their work with mammal cells, not whole goats. They were working to develop a material they called bioel which was basically a spider silk fabric but they were never able to produce it in commercial quantities and they went bankrupt in 2009. at which point the goats were sold to the Canada Agriculture Museum and put on display.
This made headlines in 2012 when a woman went to the museum with her kids, decided to visit the Central Experimental Farm, saw these goats, and was absolutely horrified by the fact that one, anyone had done this, and two, that the museum had put the goats on display.
I'm not sure what kind of thing she expected to find when she visited something called the central experimental farm. It already sounds like something out of a dystopian novel.
Anyway, the collapse of Nexia Biotechnologies was not the end of transgenic spider goats. Professor Randy Lewis, the guy who originally stuck the gene into E.coli coli back in the mid '90s continued this work at Utah State University and in 2012 he had a herd of about 30 happy transgenic spider goats.
In 2018 Lewis's student Richard Decker did a poster presentation at Utah State entitled Spidergoats 2.0 creating better transgenic goats.
I love that title so much. Decker went on to write his entire PhD thesis on better spider goats. So there have been advances on that front. But around the same time Nexia started working with mammal cells, someone was working on a different approach. In 2006, Kim Thompson had founded Craig Biocraft Laboratories and was working with silkworms instead of goats, thinking that it might be better to work with an animal that already had the equipment to actually turn the proteins into silk instead of having to do that part ourselves. The University of Wyoming held the rights to the gene sequences Nexia had been using in their goats.
When Nexia went belly up in 2009, the university granted Thompson exclusive rights to those sequences. The lead scientist at Wyoming, who had worked with Nexia, had a whole list of reasons why those sequences would never ever, not in a million years, work in silkworms. But Thompson was working with Dr. Malcolm J. Fraser, a geneticist at Notre Dame in Indiana, who had done a lot of the pioneering work with something called the piggyback transposon.
A transposon is basically a DNA sequence in a gene that can get up and leave, then come back in a different spot. And one kind of these was seen to ride along or piggyback on a bula virus. Remember the kind of virus that was used to insert DNA into insect cells? See what they did there? Piggyback bacular virus paper doesn't say, but I bet these guys were dads. This turned out to be the way to get these gene sequences into silkworms.
Around 2010, Florence Tulie and a team of researchers in Wyoming, Indiana, and China, which included people from Craig Biocraft, as well as Randy Lewis, the spider goat guy, managed to insert an engineered silk gene, the combined parts of the regular silkworm gene with elements of spidroin gene into silkworms using piggyback vectors. These now transgenic silkworms carrying this chimeic silk gene were not only able to produce the protein in their bodies but also convert it into silk fiber because they were you know silkworms. They just happened to have the machinery to do that. And these fibers were actually pretty good, much tougher than silkworm silk and about as tough as actual spider dragline silk.
It's a bit difficult to get the details on where things have gone from there because unlike most of the research that I present in these videos, the research and development that Craig Biocraft has been doing ever since is not public.
It's private proprietary product development at this point. This might be kind of annoying to curious internet people like us, but they've done the work, so I guess they get to keep their secrets. Imagine what could be done if universities had more public funding for research. But now, in fact, last month being April of 2026, as I film this, history in the field of magical spider buttropppe was made. Craig Biocraft announced early in April that in the previous month alone, they had successfully produced 1.3 metric tons of recombinant spider silk in the form of cocoons made by these transgenic silk worms. Never before has synthetic spider silk been produced at this kind of scale. And this makes this incredible material suddenly a viable option for actually making stuff. This is major news in the field of material science.
Don't be surprised if you start seeing spider silk apparel in the next couple of years because I could see this stuff being a bigger deal than Goreex. I'd bet it won't be cheap, but it'll probably be there. Humanity has been chasing this for hundreds of years, and we may finally have it in our hands.
There's something kind of poetic about the fact that after all of this, hundreds of years of study and experimentation, millions of dollars spent, we still need to get a caterpillar to make this stuff for us because we're not quite smart enough to figure out how to do it ourselves.
That's not so much a dig at humanity, though, as a testament to just how miraculous spider silk really is. Few natural substances on Earth have captured our attention and fascination as much as silk has. Its incredible strength, resilience, versatility, and sheer beauty are unmatched by virtually anything in the natural world. It's easy when we see that dusty cobweb in the corner of the living room to brush it away without a second thought. But within those dusty strands is an elaborate mystery of attraction and repulsion, of locks and keys on a scale we cannot see. A delicate process that happens at unthinkable speed in the tiny bodies of creatures we so often look right past. And this unbelievable material may give us the means to create finer sutures, artificial tendons, regrown nerves, and a million other things we haven't even thought of yet.
There are other creatures that have eight legs, that have fangs, that have venom, but only spiders make silk this strong and use it in so many different ways through all stages of life. And for that, spiders take their unique and uncontested place in our minds and imaginations.
If you enjoyed this video or found it helpful, give it a like. It really helps out. And if you want more spidery goodness like this, subscribe and help me get to that 100,000 mark. If you want to support this channel, check out my Patreon page where I post additional research notes, random spider encounters from my own life, and other spider stuff that doesn't make it into these videos.
There's behind the-scenes details about the making of these videos, sometimes explanations of some of the equipment I use, and additional details about some of my collaborative work with other spider researchers. Patreon is the very best way to support my work here on the channel, and I deeply appreciate the support my patrons give me. It really does keep this channel going. So, a huge thank you to all of them. Also, you can head over to my Shopify store for some channel merch. If you're wondering what the stupid cheese stuff is about, go back and watch my video on the Yellow Sack Spider. It will all make sense after you've seen that. And these mugs and shirts are relevant in virtually all situations. In the classroom, in the boardroom, in the courtroom, in the kitchen with your significant other, and that helps support the channel as well.
Of course, just watching this video helps out. So, I deeply appreciate anyone who got this far. I know this was a long one. So, to all of you, thank you so much for watching. I hope you've learned something about the incredible nature of spider silk. And I hope to see you next time. Cheers.
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