What Makes A Spider Web Sticky?

Scientists Untangled Spider Web Stickiness

By Marlene Cimons 12 November 2010

This Behind the Scenes article was provided to LiveScience in partnership with the National Science Foundation.

Ali Dhinojwala and Vasav Sahni consider themselves materials scientists, not biologists. They study surfaces, friction and adhesion. Nevertheless, they have discovered that understanding how nature makes things stick sometimes means getting up close and personal with the creatures responsible.

When they recognized, for example, the stickiness of spider silk, «we thought there’d be nothing sexier than working in this area,» Sahni said. «Little did I realize that working with spider silk meant working with spiders too. Big, scary spiders.»

Making fresh samples «involved working with newly-spun spider webs in which the spider would be waiting for its prey,» he added. «Then I was informed that the spiders I am working with are non-poisonous, which calmed me down a little.»

Anyone who comes into direct contact with a spider web knows how sticky it is, the result of a glue-like substance the spider produces from one of the glands in its stomach. But, until recently, scientists did not understand how the glue behaved.

Dhinojwala, a professor and chair of the department of polymer science at the University of Akron in Ohio, and Sahni, a doctoral candidate there, joined with Todd Blackledge, professor of biology, to try to figure out the properties of the microscopic substance that orb-weaving spiders deposit along the round rings of silk they spin as part of their webs. Those droplets — three times thinner than the diameter of a single hair — capture the flies and other insects that spiders eat.

«It’s not just the stickiness,» Dhinojwala said. «We wanted to better understand the adhesion — how elastic is it? How stretchy is it. The objective was not to determine what it was made up of, but how it behaves and why is it so sticky?”

The drops are composed of highly entangled polymers, which are physically or chemically cross-linked and transmit forces very efficiently. Under a microscope, the researchers pulled on individual glue drops while measuring their force-extension behavior — not easy to do using a tiny probe.

They found the material to be both viscous and elastic, valuable properties for catching fast-flying incoming insects — and in keeping the victims trapped long enough for the spider to subdue, and devour, them.

The material’s consistency is not quite liquid, nor like honey, nor even like silly putty. «It feels like chewing gum,» Dhinojwala said. «It just keeps stretching and stretching.»

It is also water resistant, a useful feature since spiders work in humid conditions, including rain. In fact, the material loses its stickiness without moisture, «unlike scotch tape, which isn’t sticky anymore once you put water on it,» Dhinojwala said. «This glue needs water to be sticky.»

The researchers hope the data will have important practical applications in developing new bio-adhesives, particularly in bandages and other products that must retain their stickiness when in contact with water. «Sometimes you want your bandages to work under water,» Dhinojwala said. «Also, there are quite a number of times we want to attach things under water. Water is always a problem with adhesives. But this can hold under water.»

The researchers studied only orb-weaving spiders, which are commonly found in trees and grasses. As their name suggests, they spin an orb-like web — that is, a web in the shape of a circle, with spokes and rings.

The spiders use different glands in their stomachs to secrete proteins that make up the web. The thread of the spokes — which provides the web’s strength — come from a gland known as the major ampullate. Each spider has two of these.

«That thread is well-known for its strength,» Dhinojwala said. «It supports a lot of weight. By weight, that silk is stronger than steel.»

Sahni recalls the day the researchers tried to find something synthetic that could compare to the properties of spider silk. «Needless to say, we failed,» he said.

The circles — where the glue is deposited — come from the minor ampullate gland. Each spider has two of these as well.

«The material is called spiral silk and its purpose is to catch insects, so it is sticky,» Dhinojwala said. «If you look at spiral silk under a microscope, you will see these little drops — the glue.» The drops come from yet another gland, known as the aggregate gland. Each spider has four of these.

Once Sahni overcame his fear, he went off on field trips to hunt spiders for the experiments. «Field trips to hunt spiders to bring to our lab, going to nature preserves, etc. was something which I, a non-biologist, was never exposed to, and hence, enjoyed it a lot,» he said.

«When Vasav came here he had no clue he would be working with spiders,» Dhinojwala added. «He came to work with polymers. He was really scared of spiders — he’d never touched one or handled one. His instinct was to run away. Now he goes under the bridge and catches them. He’s a curious guy, and his curiosity overtook his fear.»

Essentially, the spiders spun their webs in a box in the lab «and we collected the samples,» Dhinojwala said. «We put the spider web in a glass plate, and used a tiny probe to poke it and measure how much force was required to pull it off. We tested the strength and the elasticity — not just its sticking power, but how elastic and stretchy it was, which is critical for stickiness, and the major crux of understanding the adhesion.»

See also:  What'S A Brown Recluse Spider?

The National Science Foundation funded the work and the findings appeared recently in the journal Nature Communications.

Dhinojwala and his colleagues have long been interested in how nature produces its own adhesives. He has studied how the gecko lizard can stick to surfaces without any glue-like substance, and currently is creating synthetic material inspired by his gecko research. «We designed tapes without glue based on what we learned from the geckos,» he said.

«What the spider does is evolution at its finest,» he added. «They have survived by using nature effectively. The more we learn of how nature uses these materials, the better position we will be in to take advantage of this and design things based on what we learn.»

Sahni agrees. «We, non-biologists, get totally excited even now when we see a spider spinning a web, or when we see it catching its prey,» he said. «This interest and fascination with this field prompts us to ask the whys and hows to just about everything.»

Read more about the project and watch an audio slide show about the work here.

Editor’s Note: This research was supported by the National Science Foundation (NSF), the federal agency charged with funding basic research and education across all fields of science and engineering. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author and do not necessarily reflect the views of the National Science Foundation. See the Behind the Scenes Archive.

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Spiders Spin Electrically Charged Silk To Make It Sticky

The garden center spider doesn’t put sticky glue on its web; it uses a complex spinning process to build prey-snaring silk threads

Scientists and engineers love spider silk. The unique material is a major target for efforts to mimic nature’s inventiveness because it is so strong, lightweight, biologically compatible and disposable — all properties that make it attractive for creating smart materials that could be used to make bullet-proof clothing, strong rope, bandages, artificial tendons and more. We’ve created goats that secrete spider silk in their milk and listened in to the messages encoded in vibrating webs.

Now researchers from Oxford University have investigated spider webs’ stickiness. In a paper published in Biology Letters, they looked at a strategy employed by a spider found in British garden centers (it’s able to survive in hot, humid greenhouses) that differs a bit from most spiders’ method of snagging prey.

Sticky webs spun by the more common orb weavers, for example, are studded with a glue-like substance created in glands on the spider’s belly. Typically, spiders also create silk that is several micrometers thick, but the garden center spider, also called the feather-legged lace weaver and Uloborus plumipes, spins silk threads so fine they are measured on the nano-scale. Still, these filaments are very sticky.

The spider creates this unique silk in an organ called the cribellum, which consists of «one or two plates densely covered in tiny silk outlet nozzles,» according to a press statement. The organ funnels raw silk through very long, narrow ducts before spitting them out the tiny nozzles. Then, using special hairs growing on its hind legs, the spider combs the newly formed silk threads. The combing and a «violent pulling,» or hackling, on the many gossamer filaments emerging from the nozzles actually adds an electrostatic charge to the threads and creates «regularly spaced, wool-like ‘puffs’ covering the capture threads,» one of the study’s authors, Fritz Vollrath, says in the statement. The thinness of the silk and the electric charge culminate to make the puffs very sticky.

The micrographs and close-up photographs of the spider’s silk-generating structures and the silk itself are stunning.

The discovery points toward a new way of making polymers, reports Arielle Duhaime-Ross for the Verge. «It might even help scientists come up with their own version of the super sticky nano-scale threads,» she writes. It’s yet another spider secret we’ve learned and a step closer to those sci-fi sounding applications we hope to achieve with super strong, sticky silk.

About Marissa Fessenden

Marissa Fessenden is a freelance science writer and artist who appreciates small things and wide open spaces.

www.smithsonianmag.com

Everyday Mysteries

Answer

Spiders are able to spin sticky and non-sticky silk. They avoid walking on the sticky silk. In addition, spiders have moveable claws on their feet that grip and release the web’s threads as they walk.

Golden Orb Weaver. Bandelier National Monument, 2010. National Park Service, NP Digital Asset Management System

Spiders are invertebrate creatures in the araneae order of the class arachnida in the phylum arthropoda. A spider has up to eight eyes, eight legs and seven silk-producing glands in its abdomen. These glands secrete proteins that are extruded through spinnerets to produce different kinds of silk. Many spiders, particularly orb, funnel, sheet and cob-weaving spiders, use this silk to build webs with which to catch prey.

We’ll focus on orb-weavers because their webs are the most recognizable. Their webs are complex nets of strong dragline threads (frame, spokes) radiating out from the center; and elastic, sticky catching threads spiraling into the center. An orb-weaver begins its web with radial and framework threads using dragline silk, providing a foundation upon which to spiral the sticky catching threads. The spiders then create an auxiliary spiral to help the radial threads support the spider’s weight as it builds. Next, the spider uses, and subsequently destroys, the auxiliary spiral as a guide to create the catching spiral, which it dots with glue. What is perhaps the most amazing part of this hour-long process is that orb-weaving spiders often have poor eyesight and weave using only their sense of touch.

See also:  What Is The Scientific Name Of A Spider?

Orb-weaving spider (araneus). Oregon Coast National Wildlife Refuge. Peter Pearsall, USFWS photographer, 2010. U.S. Fish and Wildlife Service National Digital Library

The sticky, complex nets of silk used for the catching spiral are effective hunting tools, but have often made people wonder how the spiders themselves avoid entangling themselves in their own webs. Many people believe that spiders have special oils that repel the stickiness of their threads. This, however, has never been proven. Scientists are still not entirely certain how most spiders manage to avoid ending up ensnared in their own trap, but there are a few accepted theories. Spiders can spin different kinds of silk, and not all of their silk is sticky. In fact, in a spider web only the silk used for the intricate catching spirals are dotted with glue, so spiders know which threads to avoid. In addition to producing different kinds of silk, web-spinning spiders also have an extra set of claws on their feet. All spiders have two claws on their feet; web-spinning ones have three. These claws are used to grasp threads and provide traction as the spider moves along.

Spider silk itself is interesting to scientists because of the irreversible transformation it makes from a water soluble liquid inside the spider, to a non-water soluble thread outside of the body. The reaction has nothing to do with the thread’s exposure to air once it exits the spider; rather scientists believe it has to do with the act of pulling on the thread that realigns the molecules into a solid form.

A spider web in a forest. An unidentified spider is visible near the center of the web. Randolph Femmer, USGS photographer, 2007. USGS Science Explorer Multimedia Gallery

Scientists are interested in spider silk for manufacturing purposes, specifically the viscid (sticky for catching prey) and dragline (strong for stiff radials and framework) threads. The viscid thread is comparable to rubber in elasticity, but has more strength. The dragline thread is comparable to steel and Kevlar® (bulletproof material) in stiffness, but is more elastic and able to absorb higher impact.

What makes spiders truly unique in their silk-producing abilities is that they are the only animals that use this silk for multiple purposes. Their multiple silk glands each produce different kinds of silk to aid in mating rituals, create shields for protection from predators, encase their eggs and, of course, weave webs.

Black and yellow garden spider on web (Argiope aurantia). West Virginia, Ryan Hagerty, USFWS photographer, 2017. U.S. Fish and Wildlife Service National Digital Library

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Spiderweb stickiness secret

Living creatures have a wide variety of ingenious ways of sticking to things, 1 which we have written about in this magazine. These include: the fine hairs on gecko 2 and spider 3 feet that exploit fine chemical forces, and have inspired self-cleaning adhesive tape, 4 the mechanical and hydraulic machinery of ant and bee feet 5 and mussels that secrete special proteins that can even stick to “non-stick” frying pans. 6

One of the best-known sticky things in nature is the spider’s web. We have written before on the amazing strength of the fibres—they are stronger than any man-made fibre of the same thickness, including Kevlar and steel, 7 and are heat resistant as well. 8 However, strength is not enough to trap insects—spiders also deposit tiny droplets of glue over the fibres, about 20 per mm of length. How this worked was a mystery—until biologists at the University of Akron, Ohio, USA, discovered its secret. 9

Most glue is uni-functional: its one function is to stick things together. But the spider glue is multi-functional—a ‘smart material’. 10 It is composed of polymers—long molecules composed of small molecules joined together—called glycoproteins, where the small molecules are amino acids and sugars. These are cross-linked, which means that forces can be transmitted efficiently—as one of the researchers said, “The success of an adhesive, however, depends on how efficiently the force is transmitted through the adhesive.” 11 The crosslinking makes the droplets a hundred times stickier.

But this might be a problem when the spider wants to remove a trapped insect from the web. The solution is a variable-strength glue: much stronger at high speeds than at low speeds. Thus it can stick strongly to a flying insect, but when the insect struggles, with slower movements than flight, then the glue behaves more like a rubber band. When the insect stops moving, the spider can remove it fairly easily because the sticky force is lower still.

As usual, the researchers pay a fact-free homage to evolution, although it was irrelevant to their research. Take out such vacuous nonsense, and the researchers’ comments provide powerful evidence for design:

“Nature has evolved a myriad of well-designed adhesives that assist in locomotion, self-defence and prey capture”.

Then they list some examples in the first paragraphs. 9

©istockphoto.com/stphillips

“Existence of similar adhesion strategies in distantly related species of animals suggests a common design principle in the evolution of natural adhesives.” 11

To highlight the reality of design, human designers are now trying to learn from the spider’s secrets. One researcher said:

“This finding should significantly benefit the development of synthetic adhesives for biomedical, orthopedics and wound-healing applications. The understanding of how spiders use this unique glue will allow scientists to develop reversible adhesives that work in the presence of water.” 11

This is hardly the only example of humans learning from the Master Designer 12 —in reality, “Nothing in biology makes sense except in the light of design.” 13

See also:  What Spiders Can Bite In The Uk?

The only remaining question is, why would God create something used to entangle insects? First, this is irrelevant to the fact of design. Second, maybe they originally entangled something else before the Fall. Even today, some baby spiders catch pollen for food, 14 and there is even a vegetarian spider. 15 Third, insects are likely not biblical life (Hebrew nephesh chayyah), since they were not Ark passengers—the Flood was to wipe out land creatures that breathed through nostrils (Genesis 7:22).

Related Articles

  • God’s webspinners give chemists free lessons
  • Spectacular spider stickiness
  • Hot spider silk
  • Copying God’s design:

Further Reading

References and notes

  1. See Sarfati, J., By Design, chapter 7, CBP, 2008. Return to text.
  2. Great gecko glue?Creation23(1):54–55, 2000. Return to text.
  3. Spectacular spider stickiness, Creation27(4):54–55, 2005. Return to text.
  4. Gecko foot design—could it lead to a real ‘spiderman’?Creation26(1):22–23, 2003. Return to text.
  5. Startling stickiness, Creation24(2):37, 2002. Return to text.
  6. Mussel muscle, Creation22(4):7, 2000. Return to text.
  7. God’s webspinners give chemists free lessons, Creation23(2):20–21, 2001. Return to text.
  8. Hot spider silk, Creation27(3):9, 2005. Return to text.
  9. Sahni, V., Blackledge, T.A., and Dhinojwala, A., Viscoelastic solids explain spider web stickiness, Nature Communications1(19):1–4, 17 May 2010 | doi:10.1038/ncomms1019. Return to text.
  10. Lee, H., Biomaterials: Intelligent glue, Nature465:298–299, 19 May 2010 | doi:10.1038/465298a. Return to text.
  11. Researchers discover spider webs’ true ‘sticking power’, physorg.com, 17 May 2010. Return to text.
  12. See Expert engineer eschews “evolutionary design”: Philip Bell interviews creationist and Professor of Engineering Design, Stuart Burgess, Creation32(1): 35–37, 2010; creation.com/biomimetics. Return to text.
  13. Turning around the cliché from famous evolutionist Theodosius Dobzhansky (1900–1975), by substituting ‘design’ where he had ‘evolution’ . Return to text.
  14. Pollen-eating spiders, Creation22(3):5, 2000; White, T., Pollen-eating spiders, Nature Australia26(7):5, Summer 1999–2000. Return to text.
  15. Catchpoole, D., Vegetarian spider, Creation31(4):46, 2009. Return to text.

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Readers’ comments

Dear Dr Sarfati

This is a very interesting article. Isn’t the world absolutely fantastic? Who can fail to be amazed?

However, I always find articles like these merely tickle the fancy and leave me hungry for more. I wonder if you can recommend a few books that describe in detail how all these wonderful things have developed since the Fall? A crash course in baraminology perhaps?

PS: I’m sure you’ve just forgotten that Spiders are not insects.

I haven’t forgotten that spiders are arachnids, and never said otherwise. The last paragraph was referring to the insects as the spider’s prey as not nephesh chayyah. In general, invertebrates are not nephesh chayyah, so would apply to the spiders too.

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