A spider web is a complex and beautiful thing. It is also functional. Spider webs have evolved through natural selection. That means that random changes in genes have been passed on to later generations. Spiders, like all animals and adaptations,  have evolved over millions of years and spider webs have existed for at least 100 million years (based on examples found in amber specimens).

Not all spiders build webs to catch prey. Some do not build webs at all. “Spider web” is what we say referring to a web that is in use (or seems to be) and “cobweb” refers to abandoned (dusty) webs. (There are some three-dimensional webs from spiders of the theridiidae family which are known as the tangle-web spiders, cobweb spiders and comb-footed spiders.)

The book, Spider Silk: Evolution and 400 Million Years of Spinning, Waiting, Snagging, and Mating, is what got me thinking about webs. It covers spiders found on the ground, in the air, and even under water. Authors Leslie Brunetta and Catherine Craig’s book answers the question that every kid asks when seeing a spider create line of silk: How do they do that?

The orb web is the name for the wheel-shaped web that we are used to seeing. It contains at least four different silk proteins, each performing a different function. Together they make a superior tool for catching other insects.

 

Spider webs turn up in literature and culture. Just about every American kid knows Charlotte’s Web, a book that has turned many a child from anti-spider to the pro-spider side.

There are also the many versions of the comic book superhero Spiderman Spiderman. If you read about the incredible strength of a spider’s silk web, you may think that Spiderman is not so farfetched and that he would be truly an “Amazing Spiderman.”

Some spiders are more like Spiderman and don’t build webs, but chase their prey or make sticky nets which they throw over their prey when it gets close enough.

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.

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.

It was once thought that this was caused by a reaction from the thread’s exposure to air once it exits the spider.Now, the belief is that it has to do with the act of pulling on the thread that realigns the molecules into a solid form.

Their multiple silk glands each produce different kinds of silk. Besides weaving webs, they have silk used for mating rituals, to create shields for protection from predators and encase their eggs.

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.

 

 


Spider Silk: Evolution and 400 Million Years of Spinning, Waiting, Snagging, and Mating

Leslie Brunetta spoke at Google (watch the talk) about the spider silk and her book Spider Silk.

 

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