Cobweb on glass, with spider foot for scale

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rjlittlefield
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Cobweb on glass, with spider foot for scale

Post by rjlittlefield »

The "False Black Widow" cobweb spider that I show HERE spent long enough in a small glass cage to create some interesting bits of silk.

In this stereo pair (crossed-eye, with the glass plane at the back), you can see three pads made of many small strands attached to the glass, with some thicker strands of normal cobweb stretching out into open space.

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The above is almost a whole frame of Canon T1i at 20X, so just a bit over 1 mm of subject, top to bottom.

Here's a closer view.

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For comparative scale, here is the silk digitally overlaid on an image of the spider foot that was made at the same scale. For more about the foot, see HERE.

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121 frames at 0.002 mm focus step, stereo at +-5 degrees off axis (about +-3%, in this portrait orientation).

--Rik

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Re: Cobweb on glass, with spider foot for scale

Post by MarkSturtevant »

Perhaps the concentrated spots are where it attaches web directly to the glass with its spinnerets.
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Re: Cobweb on glass, with spider foot for scale

Post by rjlittlefield »

MarkSturtevant wrote:
Mon Dec 28, 2020 8:07 pm
Perhaps the concentrated spots are where it attaches web directly to the glass with its spinnerets.
Yes, I believe that's correct. Pads like that are the only places where the web seems actually attached to the glass.

I did a brief search for more detailed information on this aspect, but not much turned up. Foelix's "Biology of Spiders" has quite a lot about webs in general, but all I could find about attachment points was this snippet (Second Edition, page 116):
The silk thread that exits from the ampullate gland serves as a dragline. In many spiders such a dragline is continually left behind as the spider walks around. It is anchored at intervals to the substrate by the actin of the piriform glands. This results in distinct "attachment discs" (fig. 98) which are barely perceptible as tiny white dots. Aside from draglines the ampullate glands also provide the material for the frame threads of orb webs and for the gossamer threads of young spiderlings.

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In the latest version of "Biology of Spiders", this same paragraph appears on page 144. Clearly a lot of material has been added.

I do not know whether the spider in the cage was trying to spin a prey-capturing web, or whether it was just wandering around in a small space leaving bits of dragline. Recall that I found this spider walking across my kitchen floor, so clearly it was in wandering-around mode when I found it.

--Rik

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Re: Cobweb on glass, with spider foot for scale

Post by MarkSturtevant »

In web building spiders, its the females that seem to be stay-at-homes in their webs while males are seen either a-wandering, or living dangerously in the web of a female or in a small satellite web next to the females' web (that is seen in garden spiders. Its an interesting behavior). I don't know much about males of web building spiders. How do they get prey? Heck if I know.
I have the Biology of Spiders book somewhere upstairs. Older edition I am sure.
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Re: Cobweb on glass, with spider foot for scale

Post by rjlittlefield »

MarkSturtevant wrote:
Tue Dec 29, 2020 3:46 pm
In web building spiders, its the females that seem to be stay-at-homes in their webs while males are seen either a-wandering, or living dangerously in the web of a female or in a small satellite web next to the females' web (that is seen in garden spiders. Its an interesting behavior). I don't know much about males of web building spiders. How do they get prey? Heck if I know.
I have the Biology of Spiders book somewhere upstairs. Older edition I am sure.
In the Second Edition, page 176, it is written that
In contrast to females, most male spiders change their habits after their last molt. They leave their retreats or webs, and become vagabonds; often they no longer even catch prey.
I'm guessing that this male spent its growing-up time in a web in my garage or nearby outdoors, happily catching and eating prey like we'd expect for a cobweb spider. During that time I would have never noticed it. Only when it got the urge and took to wandering, would it suddenly become highly visible crossing my off-white floor.

--Rik

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Re: Cobweb on glass, with spider foot for scale

Post by micro_pix »

Very impressive stereo!

Dave

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