Representatives of the arachnid order can be found everywhere. These are predators that hunt insects. They catch their prey using a web. This is a flexible and durable fiber to which flies, bees, and mosquitoes stick. How a spider weaves a web is a question often asked when looking at an amazing catching net.
What is a web?
Spiders are one of the oldest inhabitants of the planet; due to their small size and specific appearance, they are mistakenly considered insects. In fact, these are representatives of the order of arthropods. The spider's body has eight legs and two sections:
- cephalothorax;
- abdomen.
Unlike insects, they do not have antennae and a neck separating the head from the chest. The abdomen of an arachnid is a kind of factory for the production of cobwebs. It contains glands that produce a secretion consisting of protein enriched with alanine, which gives strength, and glycine, which is responsible for elasticity. According to the chemical formula, cobwebs are close to insect silk. Inside the glands, the secretion is in a liquid state, but when exposed to air it hardens.
Information. The silk of silkworm caterpillars and spider webs have a similar composition - 50% is fibroin protein. Scientists have found that spider thread is much stronger than caterpillar secretion. This is due to the peculiarity of fiber formation
Where does a spider's web come from?
On the abdomen of the arthropod there are outgrowths - arachnoid warts. In their upper part, the channels of the arachnoid glands open, forming threads. There are 6 types of glands that produce silk for different purposes (moving, lowering, entangling prey, storing eggs). In one species, all these organs do not occur at the same time; usually an individual has 1-4 pairs of glands.
On the surface of warts there are up to 500 spinning tubes that supply protein secretion. The spider spins its web as follows:
- spider warts are pressed against the base (tree, grass, wall, etc.);
- a small amount of protein adheres to the selected location;
- the spider moves away, pulling the thread with its hind legs;
- for the main work, long and flexible front legs are used, with their help a frame is created from dry threads;
- The final stage of making the network is the formation of sticky spirals.
Thanks to the observations of scientists, it became known where the spider’s web comes from. It is produced by movable paired warts on the abdomen.
Interesting fact. The web is very light; the weight of a thread wrapping the Earth along the equator would be only 450 g.
Spider pulls thread from abdomen
How to build a fishing net
The wind is the spider's best assistant in construction. Having taken out a thin thread from the warts, the arachnid exposes it to an air flow, which carries the frozen silk over a considerable distance. This is the secret way a spider weaves a web between trees. The web easily clings to tree branches, using it as a rope, the arachnid moves from place to place.
A certain pattern can be traced in the structure of the web. Its basis is a frame of strong and thick threads arranged in the form of rays diverging from one point. Starting from the outer part, the spider creates circles, gradually moving towards the center. It is amazing that without any equipment it maintains the same distance between each circle. This part of the fibers is sticky and is where insects will get stuck.
Interesting fact. The spider eats its own web. Scientists offer two explanations for this fact - in this way, the loss of protein during the repair of the fishing net is replenished, or the spider simply drinks water hanging on the silk threads.
The complexity of the web pattern depends on the type of arachnid. Lower arthropods build simple networks, while higher ones build complex geometric patterns. It is estimated that it builds a trap of 39 radii and 39 spirals. In addition to smooth radial threads, auxiliary and catcher spirals, there are signal threads. These elements capture and transmit to the predator the vibrations of the caught prey. If a foreign object (a branch, a leaf) comes across, the little owner separates it and throws it away, then restores the net.
Large arboreal arachnids pull traps with a diameter of up to 1 m. Not only insects, but also small birds fall into them.
How long does it take a spider to weave a web?
A predator spends from half an hour to 2-3 hours to create an openwork trap for insects. Its operating time depends on weather conditions and the planned size of the network. Some species weave silk threads daily, doing it in the morning or evening, depending on their lifestyle. One of the factors determining how long it takes a spider to weave a web is its type – flat or voluminous. The flat one is the familiar version of radial threads and spirals, and the volumetric one is a trap made from a lump of fibers.
Purpose of the web
Fine nets are not only insect traps. The role of the web in the life of arachnids is much broader.
Catching prey
All spiders are predators, killing their prey with poison. Moreover, some individuals have a fragile constitution and can themselves become victims of insects, for example, wasps. To hunt, they need shelter and a trap. Sticky fibers perform this function. They entangle the prey caught in the net in a cocoon of threads and leave it until the injected enzyme brings it into a liquid state.
Arachnid silk fibers are thinner than human hair, but their specific tensile strength is comparable to steel wire.
Reproduction
During the mating period, males attach their own threads to the female's web. By striking the silk fibers rhythmically, they communicate their intentions to a potential partner. The female receiving courtship descends onto the male’s territory to mate. In some species, the female initiates the search for a partner. She secretes a thread with pheromones, thanks to which the spider finds her.
Home for posterity
Cocoons for eggs are woven from the silky web secretion. Their number, depending on the type of arthropod, is 2-1000 pieces. The females hang the web sacs with eggs in a safe place. The cocoon shell is quite strong; it consists of several layers and is impregnated with liquid secretion.
In their burrow, arachnids weave webs around the walls. This helps create a favorable microclimate and serves as protection from bad weather and natural enemies.
Moving
One of the answers to why a spider weaves a web is that it uses threads as a vehicle. To move between trees and bushes, quickly understand and fall, it needs strong fibers. To fly over long distances, spiders climb to elevated heights, release a quickly hardening web, and then with a gust of wind they fly away for several kilometers. Most often, trips are made on warm, clear days of Indian summer.
Why doesn't the spider stick to its web?
To avoid falling into its own trap, the spider makes several dry threads for movement. I know my way around the intricacies of nets perfectly, and he safely approaches the stuck prey. Usually, a safe area remains in the center of the fishing net, where the predator waits for prey.
Scientists' interest in the interaction of arachnids with their hunting traps began more than 100 years ago. Initially, it was suggested that there was a special lubricant on their paws that prevented sticking. No confirmation of the theory was ever found. Filming with a special camera the movement of the spider's legs along fibers from the frozen secretion provided an explanation for the mechanism of contact.
A spider does not stick to its web for three reasons:
- many elastic hairs on its legs reduce the area of contact with the sticky spiral;
- the tips of the spider's legs are covered with an oily liquid;
- movement occurs in a special way.
What is the secret of the structure of the legs that helps arachnids avoid sticking? On each leg of the spider there are two supporting claws with which it clings to the surface, and one flexible claw. As it moves, it presses the threads against the flexible hairs on the foot. When the spider raises its leg, the claw straightens and the hairs push away the web.
Another explanation is the lack of direct contact between the arachnid's leg and the sticky droplets. They fall on the hairs of the foot, and then easily flow back onto the thread. Whatever theories zoologists consider, the fact remains unchanged that spiders do not become prisoners of their own sticky traps.
Other arachnids, such as mites and pseudoscorpions, can also weave webs. But their networks cannot be compared in strength and skillful weaving with the works of real masters - spiders. Modern science is not yet able to reproduce the web using a synthetic method. The technology for making spider silk remains one of the mysteries of nature.
Anyone can easily brush away cobwebs hanging between the branches of a tree or under the ceiling in the far corner of the room. But few people know that if the web had a diameter of 1 mm, it could withstand a load weighing approximately 200 kg. Steel wire of the same diameter can withstand significantly less: 30–100 kg, depending on the type of steel. Why does the web have such exceptional properties?
Some spiders spin up to seven types of threads, each of which has its own purpose. Threads can be used not only for catching prey, but also for building cocoons and parachuting (by taking off in the wind, spiders can escape from a sudden threat, and young spiders spread to new territories in this way). Each type of web is produced by special glands.
The web used to catch prey consists of several types of threads (Fig. 1): frame, radial, catcher and auxiliary. The greatest interest of scientists is the frame thread: it has both high strength and high elasticity - it is this combination of properties that is unique. Ultimate tensile strength of the spider's frame thread Araneus diadematus is 1.1–2.7. For comparison: the tensile strength of steel is 0.4–1.5 GPa, and that of human hair is 0.25 GPa. At the same time, the frame thread can stretch by 30–35%, and most metals can withstand deformation of no more than 10–20%.
Let's imagine a flying insect that hits a stretched web. In this case, the thread of the web must stretch so that the kinetic energy of the flying insect is converted into heat. If the web stored the received energy in the form of elastic deformation energy, then the insect would bounce off the web like from a trampoline. An important property of the web is that it releases a very large amount of heat during rapid stretching and subsequent contraction: the energy released per unit volume is more than 150 MJ/m 3 (steel releases 6 MJ/m 3). This allows the web to effectively dissipate the impact energy and not stretch too much when a victim is caught in it. Spider web or polymers with similar properties could be ideal materials for lightweight body armor.
In folk medicine there is such a recipe: to stop the bleeding, you can apply a cobweb to a wound or abrasion, carefully clearing it of insects and small twigs stuck in it. It turns out that spider webs have a hemostatic effect and accelerate the healing of damaged skin. Surgeons and transplantologists could use it as a material for suturing, strengthening implants, and even as a blank for artificial organs. Using spider webs, the mechanical properties of many materials currently used in medicine can be significantly improved.
So, spider web is an unusual and very promising material. What molecular mechanisms are responsible for its exceptional properties?
We are accustomed to the fact that molecules are extremely small objects. However, this is not always the case: polymers are widespread around us, which have long molecules consisting of identical or similar units. Everyone knows that the genetic information of a living organism is recorded in long DNA molecules. Everyone was holding plastic bags in their hands, consisting of long intertwined polyethylene molecules. Polymer molecules can reach enormous sizes.
For example, the mass of one human DNA molecule is about 1.9·10 12 amu. (however, this is approximately one hundred billion times more than the mass of a water molecule), the length of each molecule is several centimeters, and the total length of all human DNA molecules reaches 10 11 km.
The most important class of natural polymers are proteins; they consist of units called amino acids. Different proteins perform extremely different functions in living organisms: they control chemical reactions, are used as building materials, for protection, etc.
The scaffolding thread of the web consists of two proteins, which are called spidroins 1 and 2 (from English spider- spider). Spidroins are long molecules with masses ranging from 120,000 to 720,000 amu. The amino acid sequences of spidroins may differ from spider to spider, but all spidroins have common features. If you mentally stretch out a long spidroin molecule in a straight line and look at the sequence of amino acids, it turns out that it consists of repeating sections that are similar to each other (Fig. 2). Two types of regions alternate in the molecule: relatively hydrophilic (those that are energetically favorable to contact with water molecules) and relatively hydrophobic (those that avoid contact with water). At the ends of each molecule there are two non-repetitive hydrophilic regions, and the hydrophobic regions consist of many repeats of an amino acid called alanine.
A long molecule (eg, protein, DNA, synthetic polymer) can be thought of as a crumpled, tangled rope. Stretching it is not difficult, because the loops inside the molecule can straighten out, requiring relatively little effort. Some polymers (such as rubber) can stretch up to 500% of their original length. So the ability of spider webs (a material made up of long molecules) to deform more than metals is not surprising.
Where does the strength of the web come from?
To understand this, it is important to follow the process of thread formation. Inside the spider gland, spidroins accumulate in the form of a concentrated solution. When the filament is formed, this solution leaves the gland through a narrow channel, this helps to stretch the molecules and orient them along the direction of the stretch, and the corresponding chemical changes cause the molecules to stick together. Fragments of molecules consisting of alanines join together and form an ordered structure, similar to a crystal (Fig. 3). Inside such a structure, the fragments are laid parallel to each other and linked to each other by hydrogen bonds. It is these areas, interlocked with each other, that provide the strength of the fiber. The typical size of such densely packed regions of molecules is several nanometers. The hydrophilic areas located around them turn out to be randomly coiled, similar to crumpled ropes; they can straighten out and thereby ensure the stretching of the web.
Many composite materials, such as reinforced plastics, are constructed on the same principle as the scaffolding thread: in a relatively soft and flexible matrix, which allows deformation, there are small hard areas that make the material strong. Although materials scientists have been working with similar systems for a long time, man-made composites are only beginning to approach spider webs in their properties.
Interestingly, when the web gets wet, it contracts greatly (this phenomenon is called supercontraction). This occurs because water molecules penetrate the fiber and make the disordered hydrophilic regions more mobile. If the web has stretched and sagged due to insects, then on a humid or rainy day it contracts and at the same time restores its shape.
Let us also note an interesting feature of the formation of the thread. The spider extends the web under the influence of its own weight, but the resulting web (thread diameter approximately 1–10 μm) can usually support a mass six times that of the spider itself. If you increase the weight of the spider by rotating it in a centrifuge, it begins to secrete a thicker and more durable, but less rigid web.
When it comes to using spider webs, the question arises of how to obtain it in industrial quantities. There are installations in the world for “milking” spiders, which pull out threads and wind them on special spools. However, this method is ineffective: to accumulate 500 g of web, 27 thousand medium-sized spiders are needed. And here bioengineering comes to the aid of researchers. Modern technologies make it possible to introduce genes encoding spider web proteins into various living organisms, such as bacteria or yeast. These genetically modified organisms become sources of artificial webs. Proteins produced by genetic engineering are called recombinant. Note that usually recombinant spidroins are much smaller than natural ones, but the structure of the molecule (alternating hydrophilic and hydrophobic regions) remains unchanged.
There is confidence that artificial web will not be inferior in properties to natural ones and will find its practical application as a durable and environmentally friendly material. In Russia, several scientific groups from various institutes are jointly studying the properties of the web. The production of recombinant spider web is carried out at the State Research Institute of Genetics and Selection of Industrial Microorganisms; the physical and chemical properties of proteins are studied at the Department of Bioengineering, Faculty of Biology, Moscow State University. M.V. Lomonosov, products from spider web proteins are formed at the Institute of Bioorganic Chemistry of the Russian Academy of Sciences, and their medical applications are studied at the Institute of Transplantology and Artificial Organs.
Probably every person quite clearly understands what a web is. There is hardly anyone who has not encountered similar “laces” in the forest or in their own home. However, in everyday life, people usually think little about how spiders do it. And the goals of creating networks are usually presented by people in a very truncated version. At the same time, the web can be considered one of the most amazing and mysterious natural phenomena.
What is a web and how is it made?
Spiders are the only creatures that have special glands that are capable of secreting a liquid of incredible composition. It hardens almost instantly upon contact with air - the spider is not given much time to weave a web from it. Moreover, the secreted secret is of two types. One is the so-called dry one - the base of the “lace” is created from it. The second has increased stickiness - the spider uses it to treat its creation so that the insect that touches it cannot escape from the trap.
What are networks for?
Having understood what a web is, let’s figure out the purposes for which it is created. Contrary to general misconceptions, spider “laces” are not used only for hunting, although this is a predominant task. However, there are others.
- Cocoons are woven from the web into which the spider lays her eggs.
- The loot is wrapped in it for storage in reserve.
- Wintering shelters are constructed from nets; those spiders that wait out the cold in earthen burrows make a very ingenious door-lid to cover the entrance.
- The female, who has entered the mating season, signals this to potential partners and points the way to herself with the help of a thread soaked in pheromones.
- Young individuals of certain species move to new hunting grounds on a long thread carried by the wind.
So the web is a very important and multifunctional part of the life of arachnids.
Curious facts
The web has not yet been fully studied by scientists. And modern science is not yet able to repeat this natural phenomenon.
- The spider's web is simply amazingly strong. If you weave a net the size of a football field from such threads, it will be able to stop a flying Boeing. In South America, there are spider bridges on which monkeys cross gorges and use spider nets to catch fish.
- Spider "lace" has electrostatic properties, which allows its threads to rush towards prey flying by.
- Many spiders eat their old webs.
- Spider web is considered to be almost the lightest material in the world: if stretched along the entire equator, it would weigh only 340 grams.
Spiders belong to the oldest inhabitants of the Earth: traces of the first arachnids were found in rocks that are 340–450 million years old. Spiders are about 200–300 million years older than dinosaurs and more than 400 million years older than the first mammals. Nature has had enough time to not only increase the number of spider species (about 60 thousand are known), but also to equip many of these eight-legged predators with an amazing means of hunting - a web. The pattern of the web can be different not only among different species, but also among one spider in the presence of certain chemicals, such as explosives or narcotics. Spiders were even going to be launched into space to study the effect of microgravity on the web pattern. However, the substance that makes up the web hid the most mysteries.
The web, like our hair, animal fur, and silkworm threads, consists mainly of proteins. But the polypeptide chains in each spider thread are intertwined in such an unusual way that they have acquired almost record strength. A single thread produced by a spider is as strong as a steel wire of equal diameter. A rope woven from a web, only about the thickness of a pencil, could hold a bulldozer, a tank, and even such a powerful airbus as a Boeing 747 in place. But the density of steel is six times greater than that of spider webs.
It is known how high the strength of silk threads is. A classic example is an observation made by an Arizona doctor back in 1881. In front of this doctor, a shootout took place in which one of the shooters was killed. Two bullets hit the chest and went right through. At the same time, pieces of a silk handkerchief stuck out from the back of each wound. The bullets passed through clothing, muscles and bones, but were unable to tear the silk that got in their way.
Why is it that steel structures are used in technology, and not lighter and more elastic ones - made of material similar to spider webs? Why aren't silk parachutes replaced with the same material? The answer is simple: try to make the kind of material that spiders easily produce every day - it won’t work!
Scientists from around the world have long studied the chemical composition of the web of eight-legged weavers, and today the picture of its structure has been revealed more or less fully. The web strand has an inner core of a protein called fibroin, and surrounding this core are concentric layers of glycoprotein nanofibers. Fibroin makes up approximately 2/3 of the mass of the web (as well as, by the way, natural silk fiber). It is a viscous, syrupy liquid that polymerizes and hardens in air.
Glycoprotein fibers, the diameter of which can be only a few nanometers, can be located parallel to the axis of the fibroin thread or form spirals around the thread. Glycoproteins - complex proteins that contain carbohydrates and have a molecular weight from 15,000 to 1,000,000 amu - are present not only in spiders, but also in all tissues of animals, plants and microorganisms (some proteins in blood plasma, muscle tissues, cell membranes, etc.).
During the formation of a web, glycoprotein fibers are connected to each other due to hydrogen bonds, as well as bonds between CO and NH groups, and a significant proportion of bonds are formed in the arachnoid glands of arachnids. Glycoprotein molecules can form liquid crystals with rod-shaped fragments that stack parallel to each other, giving the structure the strength of a solid while maintaining the ability to flow like a liquid.
The main components of the web are the simplest amino acids: glycine H 2 NCH 2 COOH and alanine CH 3 CHNH 2 COOH. The web also contains inorganic substances - potassium hydrogen phosphate and potassium nitrate. Their functions are reduced to protecting the web from fungi and bacteria and, probably, creating conditions for the formation of the thread itself in the glands.
A distinctive feature of the web is its environmental friendliness. It consists of substances that are easily absorbed by the natural environment and does not harm this environment. In this regard, the web has no analogues created by human hands.
A spider can produce up to seven threads of different structure and properties: some for catching “nets”, others for its own movement, others for signaling, etc. Almost all of these threads could find wide application in industry and everyday life, if It would be possible to establish their widespread production. However, it is hardly possible to “tame” spiders, like silkworms, or to organize unique spider farms: the aggressive habits of spiders and the individual-farming traits in their character are unlikely to allow this to be done. And to produce just 1 m of web fabric, the “work” of more than 400 spiders is required.
Is it possible to reproduce the chemical processes that take place in the body of spiders and copy natural material? Scientists and engineers have long ago developed the technology of Kevlar - aramid fiber:
produced on an industrial scale and approaching the properties of spider webs. Kevlar fibers are five times weaker than spider webs, but are still so strong that they are used to make lightweight bulletproof vests, hard hats, gloves, ropes, etc. But Kevlar is produced in hot sulfuric acid solutions, while spiders require regular temperature. Chemists do not yet know how to approach such conditions.
However, biochemists have come closer to solving the materials science problem. First, spider genes were identified and deciphered, programming the formation of threads of one or another structure. Today this applies to 14 species of spiders. Then American specialists from several research centers (each group independently) introduced these genes into bacteria, trying to obtain the necessary proteins in solution.
Scientists at the Canadian biotechnology company Nexia introduced such genes into mice, then switched to goats, and the goats began to produce milk with the same protein that forms the thread of the web. In the summer of 1999, two African pygmy bucks, Peter and Webster, were genetically programmed to produce goats whose milk contained this protein. This breed is good because the offspring become adults at the age of three months. The company is still silent on how to make threads from milk, but has already registered the name of the new material it created - “BioSteel”. An article on the properties of “biosteel” was published in the journal “Science” (“Science”, 2002, vol. 295, p. 427).
German specialists from Gatersleben took a different path: they introduced spider-like genes into plants - potatoes and tobacco. They managed to obtain up to 2% soluble proteins in potato tubers and tobacco leaves, consisting mainly of spidroin (the main fibroin of spiders). It is expected that when the quantities of spidroin produced become significant, it will first be used to make medical bandages.
Milk obtained from genetically modified goats can hardly be distinguished by taste from natural milk. Genetically modified potatoes are similar to regular ones: in principle, they can also be boiled and fried.
The abdomen of spiders contains numerous arachnoid glands. Their ducts open into tiny spinning tubes, which are located at the ends of six arachnoid warts on the spider's abdomen. The cross spider, for example, has about 500-550 such tubes. The arachnoid glands produce a liquid, viscous secretion consisting of protein. This secret has the ability to instantly harden in air. Therefore, when the protein secretion of the arachnoid glands is secreted through the spinning tubes, it hardens in the form of thin threads.
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1. Cross spider (with an open abdominal cavity)
2. Spider arachnoid warts
The spider begins to spin its web like this: it presses the web warts to the substrate; at the same time, a small portion of the released secretion, solidifies, sticks to it. The spider then continues to pull out the viscous secretion from the web tubes using its hind legs. When it moves away from the attachment site, the rest of the secretion simply stretches into quickly hardening threads.
Spiders use webs for a variety of purposes. In the web shelter, the spider finds a favorable microclimate, where it also takes refuge from enemies and bad weather. Some spiders weave webs around the walls of their burrows. The spider weaves sticky trapping nets from its web to capture prey. Egg cocoons, in which eggs and young spiders develop, are also made from cobwebs. The web is also used by spiders for travel - small Tarzans use it to weave safety threads that protect them from falling when jumping. Depending on the purpose of use, the spider can secrete sticky or dry thread of a certain thickness.
In terms of chemical composition and physical properties, cobwebs are close to the silk of silkworms and caterpillars, only it is much stronger and more elastic: if the breaking load for caterpillar silk is 33-43 kg per 1 mm 2, then for cobwebs it is from 40 to 261 kg per mm 2 (depending on the type)!
Other arachnids, such as spider mites and pseudoscorpions, can also produce webs. However, it was spiders who achieved true mastery in weaving webs. After all, it is important not only to be able to make a web, but also to produce it in large quantities. In addition, the “loom” should be located in a place where it is more convenient to use. In pseudoscorpions and spider mites, the raw material base of the web is located... in the head, and the weaving apparatus is located on the oral appendages. In conditions of the struggle for existence, animals whose heads are weighed down with brains, and not with cobwebs, gain an advantage. That's what spiders are. The spider's abdomen is a real web factory, and the spinning devices - arachnoid warts - are formed from atrophied abdominal legs on the underside of the abdomen. And the spiders’ limbs are simply “golden” - they spin so deftly that any lacemaker would envy them.
