Posts Tagged ‘stabilimenta’

When I was walking in the meadow last week, looking at boneset, I noticed this spider. It’s a Banded Argiope (Argiope trifasciata), a common orb weaver spider. They’re quite large, more than an inch long, and build webs up to a couple of feet across, strung between plant stalks in fields and gardens.

The first photograph shows the spider’s upper surface, while the second shows the underside of an Argiope. The second Argiope had caught a moth. After I spotted the first spider, I started watching for webs, and sure enough, I saw quite a few of them. It’s a great example of how we so often only see what we are looking for. I find that the more I know about nature, the more I see when I go walking. And the more I see, the more I learn.

This Argiope had captured a small dragonfly that she was wrapping up with silk. When she noticed me standing near the web, she scurried back up to one of the flower heads that the web was attached to.

Not only was she less visible there, she was also safer should a big, dumb mammal such as myself blunder blindly into her web and rip it down.

In the photo above you can see the silk web decoration often featured in argiope webs. This example consists of several thick, zigzagging lines. It’s called a stabilimentum. There is some debate as to its exact purpose. It was originally thought to stabilize the web, thus the name, but this idea has been largely dismissed. Here are some of the proposed explanations for the stabilimentum. It attracts prey by reflecting ultraviolet light, which is attractive to insects. It makes the web more visible to birds and other larger creatures that might accidentally tear the web down. It may have a function in alerting male spiders when the female is ready to reproduce.

It is said that EB White was inspired to write Charlotte’s Web after observing stabilimenta in spiders’ webs (Wikipedia). I’m sure you will recall how brilliant Charlotte saves Wilbur by writing “SOME PIG!” across her web.

Here is one final spider. I found her on a boneset plant I stopped to look at. Unlike most of the webs I saw, which stretched across an open space between two plants, this one was set into stems of one plant. She was well-disguised and blended in well with her surroundings.

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