Monday, September 1, 2008

Golden Garden Spiders

A female Argiope aurantia, the golden garden spider, hangs upside down as it finishes wrapping its prey in a gauze straight jacket. The heavy zig-zag stitching on the web (called stabilimento) is believed to warn birds that might otherwise wreck the web. The yellow flowers supporting the web are brown-eyed Susans 'Goldsturm.'
© Dave Spier photo # D050779 [resolution reduced for web use]

Golden Garden Spiders
© Dave Spier

The small patch of Brown-eyed Susans 'Goldsturm' has grown over the years and it now spreads along the entire east side of our patio. Sheltered from north and west winds, it catches the morning sun that burns off the dew. Yesterday I was leaving the house and just walking past when a new visitor caught my attention. A great, circular web stretched through a gap between several of the taller plants. A white, zig-zag stitching reinforced the center and there, hanging head down, was a huge multi-colored spider wrapping her prey. The eight black and pink legs easily spanned two inches. The egg-shaped abdomen was black with bright yellow markings. This was a Golden Garden Spider, Argiope aurantia, also known as the Black-and-yellow Orb Weaver.

I've also found these spiders in shrubs, tall grass and fields of wildflowers. They build their elastic webs by first throwing a "bridge" thread (a loose strand of silk) carried on air currents to a second support. From the center of the bridge, they drop down with an anchor thread to form a tripod. A box frame is built around the intended area and more radial spokes are added. Then a few quick spirals of non-stickly thread allow the spider to walk anywhere on the web. Finally, a tight pattern of sticky spirals completes the trap and the spider waits for its victim. They ignore the high-frequency vibrations of dangerous prey such as wasps, but quickly dash out and wrap more delectable goodies such as grasshoppers and other juicy insects. With its potential meal in a gauze straight jacket, the spider bites with fangs and injects a paralyzing venom. Then digestive enzymes are pumped in to liquify the soft body tissues, turning them into a soup that the spider sucks out. All that's left is the insect's exoskeleton.

By the end of the day, the sticky threads are too dry to be effective, so the spider eats the web and spins a new one. The silk, produced by spinnerets under the tip of the abdomen, is a liquid protein that hardens when it contacts the air. Besides the two types used to make webs, their is a third silk used to wrap prey and then another silk to wrap and protect the spider's eggs. Silk can also be used for "ballooning," sort of a magic carpet ride on the air. The heavy, zig-zag stitching, called stabilimento, across the central hub of the web is believed to warn birds that might otherwise blunder through the web. This saves the spider time, energy and material in prematurely rebuilding the web.

Late summer is spider season. Look out across any field just after sunrise and notice all of the dew-soaked webs catching the morning light. Each of these is both home and kitchen to a spider.

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(This copyrighted article and photo first appeared in the Times of Wayne County, September 1, 2008. All rights reserved.)

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