Sunday, December 9, 2007

St. Andrews Cross spider

The Argiope group of spiders often make special patterns in their webs, like stripes, crosses, or spirals. I just read about some researchers that wanted to see if the webs without crosses and the ones with crosses had different success in capturing prey. So they filmed over 120 different Argiope webs in Taiwan for 700 hours with video cameras, and then counted the number of caught insects in the web on the movies. The result? That if you had a cross in your web you got more prey - maybe bees are attracted to symmetric patterns. But if you have a cross in your web, predators like birds, are also more likely to come and snatch your prey out of your hands. So it is a trade off, more food and less food at the same time. I thought it was a neat field study of ecology in action.

The photo is the St. Andrews cross spider (image from Wikipedia).

In our garden we have another Argiope spider found by EH a few years ago. It is called the Yellow and black garden spider or Writing Spider, which is beautiful with black and yellow patterns on its body. It is trying to make sure that it won't get eaten by looking like a wasp. And in Europe you have the Wasp spider in the same genus. Their love life is dramatic too with this going on in our back yard and garden:

"The males roam in search of a female, building a small web near or actually in the female's web, then court the females by plucking strands on her web. Often, when the male approaches the female, he has a safety drop line ready, in case she attacks him. After mating, the male dies, and is sometimes then eaten by the female." (read more on Wikipedia)

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