The Web Crawler

April 30, 2009 at 10:55 am | Posted in itchy mouth | Leave a comment
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Itchyfingers have not seen this in the forest for a very long time. This was the first time I saw it in the mangrove. It could be we didn’t look carefully enough, though we often see many other species of spiders, many even smaller than this one. It is one of the beautiful spiders found in Singapore, with a most interesting name – the Saint Andrew’s Cross Spider (Argiope mangal)

cross
Do the outstretched legs remind you of a cross?

The Saint Andrew’s Cross Spiders get their name for the way their hold their eight legs in pairs to form an X shape. The X is called the St. Andrew’s cross because it is believed that the saint was martyred on a cross of this shape rather than the conventional + shape. Besides their standard orb-web, Argiope spiders build additional white opaque zig zag lines on their webs, called stabilimentumSometimes the zig-zag lines match their leg positions, which some people suggest that this helps give the appearance of longer legs. 

The purpose of these zig zag lines has a few possible explanation. At first thought to strengthen or “stabilise” the web, more recent ideas associate it with capturing prey or avoiding predators. They warn larger animals in the same way that safety strips on glass doors warn people from walking into them. Thus the web is protected from damage by flying birds. Research has shown that the ribbon-like silk in the stabilimentum reflects ultraviolet well, unlike the silk used in the rest of the web. Such light is attractive to flying insects, which use it to locate food sources like flowers and to navigate through openings in the vegetation. If the stabilimentum silk attracts insects it may increase the web’s prey catching efficiency.

Like many other spiders, the male is half to one-third the size of the females (body size around 5mm). So I think the one shown here should be a female with a freshly spun web, looking at the small amount of stabilimentum. We didn’t find the male though. :p

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