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Marbled Orb Weaver, araneus marmoreus - Araneus marmoreus - female

Marbled Orb Weaver, araneus marmoreus - Araneus marmoreus - Female
Ivydale (Big Otter), West Virginia, USA
October 25, 2014
Size: body, 1/2 inch
This is the first time I've ever seen this beautiful spider. Browsing has led me to believe it's a Marbled Orb Weaver, and I would like to confirm that and share the image. I assume it's a female because of the size. While focusing I noted that the round protruberances on her back were pulsating. Are these respiratory?

Moved from ID Request.
The pulsing is likely from the spider's heart beating.

Yes! You are correct. And I can see why you are excited. I find these very cool due to there coloration. This is a beautiful specimen. Excellent work! :)
I've noticed the pulsating as well. I believe it is a defense mechanism. Yes, I know I sound like Spider man, lol, but that's the impression I get.
When these spiders spot me, they start pulsating. It could be that they are trying to produce silk so that they can 'web' away from me.
But as I origionally said, I think it's just a defense mechanism. Perhaps to make them look larger to predators.

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