This remarkable orb spider web is courtesy of reader Matt:
This individual was in my garden, and the colors of the web caught my eye. I don't think I've ever noted something like this before, and was quite surprised it showed on the photo. The outer edge of the nickel sized web pattern is iridescent blue, the inside fades into a purplish-magenta. No colors are visible when shaded.
How did the spider make a color gradient in its web? I'm really not sure. Although spiderweb can refract or diffract light quite spectacularly, the result is not as organized as this - it's more of a rainbow effect (see here)
Matt wonders if it could be an example of chromoskedasic color - color created by the differential scattering of light from particles in a colorless material. This is similar to the process behind a clear blue sky (or a vibrant red sunset): selective scattering of light from molecules (or dust) in the air contributes to the brilliance of the color. Chromoskedasic painting or print development, pioneered by Dominic Lam, is a technique in which emulsions of silver particles of various sizes are used to create the illusion of colored pigments on black and white photo paper. Lam's collaborator Bryant Rossiter coined the term "chromoskedasic" in 1989 (Lam and Rossiter, Scientific American, 1991). If differently sized particles are at work, then I guess the different regions of the web must be made from chemically distinct types of silk!
So is this refraction, chromoskedasic color, or something else entirely? Any optics types want to weigh in on what's happening here? And has anyone else seen this phenomenon before?
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Any way you can put up a higher res version? rb
Done - at bottom of post. This is the highest res version Matt gave me.
Thanks. I've never seen anything like it, even without the color. I await an 'optics type' for an answer. Ah, nickel sized, I missed that. Perhaps it's the spacing between the individual fibers. Geez, I hope someone who knows sees this. rb
I don't really have an answer, but maybe I have a possible explanation:
When I was cutting ultra-thin sections for transmission electron microscopy work, I could gauge their thickness by their apparent color as they floated in a drop of water. Thicker sections were redder, through blue (following the rainbow) and then on to almost a metallic silver, then gold color. Once I had the silver/gold, they were thin enough.
The thickness of the material reflected back the color of light where the wavelength matched the thickness of the slice. Those were really thin slices, but maybe something similar is happening here. Here is a pic of ultramicrotome slices. The big amber colored thing at the top of the image is a ~0.5 cm diameter polymer plug that the sample is embedded in; so the whole picture is about 0.7-ish cm across.
I see a lot of orb webs every fall, but have never seen anything like that. We usually have at least two resident orb weavers around our porch come *spider season*.
I have no idea about the color, though MikeG's thickness argument sounds good. My first thought was that perhaps the color was caused by some chemical or something in her diet or system, and that it ran out as she worked her way outwards. Then I realized that this is probably a ridiculous idea.
As for the spider, I would almost certainly guess that it's an Argiope web. I have lot's around my house (usually big and bright yellow spiders). They usually have a single zig-zag down the center of their web, but the juveniles often make spirals in the center instead (the hypothesis is that this serves as a warning for birds so they don't fly into it).
Actually, I just remembered that I have a really good picture of an Argiope on my blog (not trying to spam here - it really is relevant :) - the post is "Spiders and Insects Around the House")
Hey, I found this article on the topic, hope it to be usefull. http://news.nationalgeographic.com/news/2008/06/080612-spider-webs.html
Thanks Camilo! The article was quite good.
The observations about uv light would fit pretty well with what I saw, since the colors did not appear in indirect light or camera flash illumination.
I wondered after reading the replies if it was a juvenile Argiope, but sadly, it's moved on. Maybe I'll spot the little guy/gal webbing in the cucumbers next.
--Matt
Dan - don't be so shy! Here's the link to your Argiope post.
Thanks for that article, Camilio. It's an interesting idea - it's quite possible the different regions of the web reflect different UV light (as flowers do). But could that be what we are seeing in Matt's photo? Wouldn't we need a special setup to photograph that? And if the spider is making an invisible UV pattern, that would also require some unknown way to change the filament size or composition or arrangement to make that pattern appear. . .