[This was written by Fran Siebrits and published online by Wild Magazine http://www.wildcard.co.za/, 2011]
Orb-weaving spiders do not construct silky patterns only to catch their prey, but also as a means of reacting to web damage.
The intricate webs of the Argiope species of orb-weaving spiders are something to
behold. Skilfully woven to capture flying insects, some webs also incorporate detailed crosses in the centre. This behaviour has been observed for over a century. But it was not until recent studies were done that scientists could shed some light on the mystery.
Orb-weaving spiders position their webs in the flight path of insects – but sometimes larger animals blunder into them too, causing damage to the intricate trapping device.
When this happens, the spiders repair the damaged web by building big silk crosses. "It's much like we mark glass windows with tape to prevent people walking into them," explains Professor Mark Elgar from the University of Melbourne's Department of Zoology. This ingenious move by orb-weaving spiders has resulted in the evolution of successful web protection.
What is of even more interest, though, is that the spiders only fix their web if there has been severe damage. They do not seem to bother if the web has only been mildly damaged. Not worth all that effort, I suppose. Or is there a more logical explanation?
By adding extra silky strands to repair damage, the web becomes more visible to passing animals. And if it is more visible, there is less chance for accidental damage. But this also means that the web is more visible to prey, so the spider has to weigh up damage control and food.
Tough decision for these orb-weaving spiders, but a beautiful result nonetheless!
Source:
André Walter, Mark A. Elgar. Signals for damage control: web decorations in Argiope keyserlingi (Araneae: Araneidae). Behavioral Ecology and Sociobiology, 2011; DOI: 10.1007/s00265-011-1200-8
Viewed online [http://www.sciencedaily.com/releases/2011/05/31/110531102249.htm]
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