The home of a spider. A spider has the ability to extrude silk through glands known as spinerettes, it will use this silk to create a net between two or more fixed objects in order to catch it's prey. They are often beautiful and delicate.

 

You could balance a spider's brain on a needletip.

Each species of spider is able to spin a certain type of web — be it funnel, sheet, or orb. The force of an insect hitting the center of an orb web is comparable to that of an airplane hitting a tennis net1. That the web doesn't explode in a sparkling shower of fibroin is thanks to the aerodynamics of the individual strings.




Chemistry

The web silk does not become fibroin until it leaves the spider's body. Before then, it's a protein with a molecular mass of roughly 30,000 Dalton. Upon being ejected by the spinners, it polymerizes into the substance we know as fibroin, a new protein whose molecular mass has increased tenfold. To this day, polymerization of web silk is a mystery.

Bacteria and fungi love protein. Decomposition is the work of mycelia and flagellates. Spider web is a protein, but it doesn't decay. There are cobwebs thousands of years old — fibroin ages well.

Spider silk is full of pyrolidin, potassium hydrogen phosphate and potassium nitrate. Pyrolidins bind water (the adjective is "hygroscopic"), preventing the web from drying out — you can also find them in plant poisons and natural dyes. It's more concentrated in the sticky catching threads. The potassium hydrogen phosphate makes the web acidic and resistant to fungal and bacterial growth. The low pH of acids causes the denaturation of proteins, a phenomenon you've observed firsthand if you've ever opened a carton of sour milk. This is where the potassium nitrate comes in: it acts like salt.

Steel is one of the strongest metals we have: it stretches by 8% before breaking. Nylon is a bit more elastic--it'll go about 20%. The web of an orb-weaver is good for 30-40%. The thread of the Stegodyphus sarasinorum is constructed in a weave and will stretch to twenty times its original length.

2,000%.




Biology

Different spiders have different glands for the production of web proteins. Across the vast tapestry that is spider, there are seven common glands. Some spiders have more than others; none have all seven.

A typical spider has three pairs of spinners; a typical spinner contains thousands of tubes, all connected to the protein-secreting glands. The appropriate measurements are tenths and hundreds of micrometers. The thinnest strand of spider silk ever measured came in at roughly .02µm. We see spider web only because it shines in the light.

The glands are a varied and complex bunch:

Tubiliformes make thread for cocoons;
Aciniformes make thread for bundling up prey;
Ampulleceae (major and minor) make non-adhesive walking thread;
Aggregata make sticky material for the threads;
Pyriformes make outer anchoring threads;
Coronatae make the core of the adhesive threads, which are coated in the secretions of the aggregata.


The bodily strain of building a home from secretions is large. Orb-weavers eat their own webs to conserve resources, ingesting the night's ragged ends to be recycled for the next morning's refinishing.




Architecture

The subtleties of spiderweb construction are comparable to those of human homes.

Virtually all spiderwebs fall into one of three categories: orb, sheet, spatial.

Big, prototypical yarn webs you buy at the party store are imitations of orb webs: the concentric mesh sheet with the spiral.

Sheet webs are a rarer phenomenon. Three-foot ladder webs in the rainforest bounce prey off and deposit them in silk reservoirs for later consumption.

The spatial web is the work of a disorganized spider: a tangle of thread anchored to corners. Black widows like these.

Of course, there are exceptions. The trapdoor spider fits the top of an earth hollow with a flat rock and attaches a trip wire.

The construction of suspended webs is a cavalier process. In orb and sheet webs, the spider finds two upright structures from which to hang the top thread. Instead of depositing a strand at one structure and walking to the other, she throws the web. This done, she reinforces the line with thicker thread and descends from its center, creating a Y shape from which the remainder of the web radiates. Non-adhesive and adhesive strands are deposited accordingly: usually the mesh structure is non-adhesive walking rope while the spiral holds prey in place.




Human uses

I loved playing with spider's web as a kid--the invisible pull between fingers, the tiny sounds of threads popping under tension.

But more practically:

Fishermen casing the waters off the coast of French Polynesia use the gold-colored thread of the Nephila as a fishing line.

During the Second World War, Americans used the thread of the black widow as hairs in telescopic gun sights.

At the beginning of the eighteenth century, Frenchman Bon de Saint-Hilaire made gloves from fabric refined from spider's web. In this process he found that one cannot possibly refine spider-silk profitably: he calculated that he'd need over a million egg cases to produce a single kilogram of fabric.

 


1 From ABC — fourth source.


Sources

Conservation Biology
http://www.conservation.unibas.ch.team/zschokke/spidergallery.html

Ed Nieuwenhuys, "The Spider Web and Thread."
http://www.xsforall.nl/~ednieuw/Spiders/InfoNed/webthread.html

Knowledge Adventure, Inc.
http://www.nides.bc.ca/Assignments/Insects/Spiderwebs/htm

ABC
http://www.abc.net.au/science/k2/moments/s37273.htm

 

Spi"der web" (?), ∨ Spi"der's web". Zool.

The silken web which is formed by most kinds of spiders, particularly the web spun to entrap their prey. See Geometric spider, Triangle spider, under Geometric, and Triangle.

<-- = cobweb -->

 

© Webster 1913.

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