Wednesday, September 21, 2011

The Web She Weaves

The golden silk orb-weavers (genus Nephila) are a genus of araneomorph spiders noted for the impressive webs they weave. Nephila consists of numerous individual species found around the world. They are also commonly called golden orb-weavers, giant wood spiders, or banana spiders. Golden silk orb-weavers are widespread in warmer regions throughout the world, with species in Australia, Asia, Africa (including Madagascar), and America. One species, N. clavipes, occurs in the United States of America, where it ranges throughout the coastal southeast and inland, from North Carolina to Texas. Nephila spiders are the oldest surviving genus of spiders, with a fossilized specimen known from 165 million years ago.

Spiders produce silken thread using several paired spinneret glands located at the tip of their abdomen. Each gland produces a thread for a special purpose. The last Nephila web I saw was here. It was built vertically, but they need not always be like that. The Nephila also weaves horizontal webs (sheet webs) that I am showing you today, but you really have to strain your eyes to see it.

The circular-orb portion of a mature N. clavipes web can be more than 1 meter across, with support strands extending perhaps many more feet away. In relation to the ground, the webs of adults may be woven anywhere from eye-level upwards high into the tree canopy.

During the process of making an orb web, the spider will use its own body for measurements. Many webs span gaps between objects which the spider could not cross by crawling. This is done by letting out a first fine adhesive thread to drift on the faintest breeze across a gap. When it sticks to a suitable surface at the far end, the spider will carefully walk along it and strengthen it with a second thread. This process is repeated until the thread is strong enough to support the rest of the web.

After strengthening the first thread, the spider will continue to make a Y-shaped netting. The first three radials of the web are now constructed. More radials are added, making sure that the distance between each radial is small enough to cross. This means that the number of radials in a web directly depends on the size of the spider plus the size of the web.

After the radials are complete, the spider will fortify the center of the web with about five circular threads. Then a spiral of non-sticky, widely spaced threads is made for the spider to easily move around its own web during construction, working from the inside out. Then, beginning from the outside in, the spider will methodically replace this spiral with another, more closely spaced one of adhesive threads. It will utilize the initial radiating lines as well as the non-sticky spirals as guide lines. The spaces between each spiral will be directly proportional to the distance from the tip of its back legs to its spinners. This is one way the spider will use its own body as a measuring/spacing device. While the sticky spirals are formed, the non-adhesive spirals are removed (actually, eaten and recycle the protein they lost during the construction) as there is no need for them anymore.

To take this photo, I had to lay flat on the ground,looking up into the zenith. This lady spider is quite large but she is so high I can't get a better shot without special camera and lens. You can't see much of the orb web, but it's there to support her in mid air. Not sure if she is ready to eat, or to mate. Looking at this though, I am mesmerized and can't help to think of old and exciting legends. In Japanese folklore, Jorōgumo, a type of yōkai, is thought to be a Nephila (Jorō spider) which can change its appearance into a seductive woman. If that is the case, should I just lay here underneath this web to wait and witness the metamorphosis, or I'd better get out of here fast? What do you think is better?
Spider Lady

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