Outdoors spider spin a web known as the orb, a masterpiece of symmetry that takes on a beautiful aspect when spangled with morning dew. Using abdominal pressure, the female spider forces silk to flow outwards, initially attaching one end of the first strand, the bridge, to an object, stem leaves, etc. Dropping the strand, she run across the ground to another high spot, pulls the strand tight and attaches it firmly in place with a spit of sticky glue from another gland.
Once the first horizontal strand is fixed, the spider drops two plumb lines of silk, one at either end and construct a second bridge lower down to form a framework. Within the framework, she spins a series of radii with a hub at the center. Only the outer radius is coated with sticky globules of a substance produced by a specialist organ called the amputate gland. Once she is done, she’ll deposit more sticky globules an interval on the other radii, leaving spaces to step between.
As a final touch, she spins a warning strand of silk between the nest and the radius closest to the hub of the web, so when something lands, the strand vibrates. She then hurries to the center of the web along the untreated warning strand.
Spider has poor eyesight, so they need to rely on other senses to determine the size and strength of the prey. If the victim is unmanageable, say a deadly, poisonous insect; the strand may be cut off. If it’s large, like a wasp or hornet, inedible, the spider will squirt silk at it from a safe distance. Then the spider can make its’ approach slowly via the built-in stepping stone on the web strands. If she accidentally step on a sticky globule, her body will produce an oily secretion that acts as chemical thinner, enabling her to free herself.

P.S : the guinness book of why - donald mcfarlan and ian bishop 101 things you don't know about science and no one else does either - james trefil

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