Saturday, August 18, 2012

Black and Yellow Argiope (Argiope aurantia)

A large, robust spider, the female Black and Yellow Argiope can attain a length of about 25 mm, the considerably smaller males, as is often typical among spiders, are only about 5 mm long. To date, a Cicada or Dogday Harvestfly is the largest prey I have ever seen one of these spiders take down.

The white zigzag pattern in many orb weaver's webs is called a stabilimentum, so called because at one time it was thought to stabilize the web. But experiments have shown that the stabilimentum – and the spider itself – reflect ultraviolet light. Since many insect's eyes are sensitive to the UV spectrum and flowers often reflect patterns visible in UV to attract insect pollinators, the current theory in vogue is that the stabilimentum and spider may act as lures to entice insects into the web. However, as adult Cicadas don't eat it's not likely this one was tricked into flying in the web – it was unlucky and simply blundered in.

A couple more views of this harmless, attractive arachnid.