Web Design

The artwork of web design shows everything but accidental evolution.   Orb web weaving spiders create an amazing design of strength, efficiency and beauty.  The spider begins by producing a light weight web that is easily caught by the wind and is carried until it anchors itself on an object.  Then the spider follows this guide web and spins a strong, thick support thread that will be the corner stone of its web.  Then she lays the foundation strands followed by supporting strands for the orb.  The orb is then weaved with intricate detail. 

A product of evolutionary chance?  The faith it takes to believe this is a product of random evolution is even further challenged by the production of the web itself.  Lets look at the creation of the strand produced by the spider.

 
These are the spinnerets magnified under the electron microscope.  Each spinneret contains a hollow tube connected to the gland.  Spider webs are pound for pound stronger than steel yet is incredibly flexible.  One study concluded the strength of a spider web in this way, if a web was produced the width of a pencil, it would have the strength to stop a 747 at full speed.  The strength material is measured by a unit called dernier. 1 dernier = 1 g per 9000 m.  A spider thread has a value between 5 - 8. This means that the thread will break under its own weight at a length of 45 - 72 km. Steel has a value of approximately 3.

One of the more descriptive commentaries on spider webs I read on a biochemical research company that is actively seeking how to engineer this amazing technology.  Here is what they have to say:
Spider silk shows great promise for technological applications and is of tremendous
economical value due to its following extraordinary mechanical properties:

• High tensile strength stronger than steel,
• High extensibility comparable to rubber,
• High capability of water uptake comparable to wool.
  
  The mechanical properties of the dragline  from the orb weaver (Nephila clavipes)
  is even superior even to the high performance fiber “Kevlar” that is used for bullet-proof vests.

What makes this amazing material?  There are seven types of web glands.  No spider has all seven.  Most spiders have a combination of these glands.

Glandula aggregata produces the sticky material.
Ampulleceae major and minor for the production of the walking threads
Pyriformes for the attaching threads
Aciniformes produces silk for the encapsulation of the prey
Tubiliformes for the silk of the egg-sac
Coronatae threads for the axis of the sticking threads.
Cribellar glands are only found in the cribellate spiders.

Spider silk's main components are specialized proteins.  Not any ole protein would produce this mastery.  Three main proteins are found in spider silk.  
Pyrolidin - very hygroscopic (water retenative).  Pyrodidin prevents the web from drying out.
Potasium hydrogen phosphate - very acidic and acts as a deterrent to bacteria and fungi.
Potassium nitrate - prevents the low pH from causing the proteins to become insoluble.

The proteins are also salted to prevent decay from bacteria and fungi.

Inside the gland of the spider, the protein has a molecular mass of 30,000 Dalton.  Once outside the gland, the web polymerizes to a molecule called fibroin and expands to a mass of approximately 300,000 Dalton.  Scientist do not understand what activates the polymerization process.  The web then takes on its elasticity properties and can be stretched up to 40% before it breaks.  Compare this to steel which breaks at 8% and nylon (used in stockings) which breaks at 20%.

Because of the nutrients lost by spinning webs, the orb weaver eats her web to recycle the protein before re-creating her web.