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August 31, 2007

Charlotte's Web Revisited

Tim Gibb, Insect Diagnostician, Department of Entomology, Purdue University

"What spider is this and will it poison me?" is a question that frequently comes into our laboratory during the late summer and fall.  When large, ornate and beautifully colored spiders hang in elaborate webs in gardens or window sills they always call for closer (but not too close) examination.  If webs are constructed between bushes or buildings where unsuspecting persons walk face first into the web, they demand attention, and of course and answer to the question “what spider is this and will it poison me?”

Many spiders make webs but one of the most remarkable groups of web making spiders is called Argiopes or "garden spiders".  These spiders may become quite large and are always beautifully colored but are not venomous and do not bite people.  They have poor vision and so rely on webs to catch their prey.  The garden spider makes a large orb web and hangs, head down, in the hub of the web.  When an insect enters the web, the spider can sense the vibrations and tension on the various threads and immediately rushes to the exact spot that the insect has fallen into.  It quickly and efficiently wraps the captive up using silk and carries it back to the center of the web where it is eaten.

The female spider is much larger that the male and can often be seen making egg sacs and either hanging them in the web or attaching them nearby to herbs or other objects.

Garden spiders not only create very large orb webs, but these are the spiders that sometimes weave interesting patterns into their webs, patterns that someone might even mistake as written words.  If you really use your imagination the words might read, “I am a friendly garden spider and I am not poisonous.”

Click image to enlarge

Argiopes spider

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