Spider silk mystery

While watching the roosting birds come in as the sun gradually descended down to the level of the hills at Parkgate, I became aware of all these lines that had appeared in the grass of the marsh – apparently long strands of spider silk lit up by the very low sunlight behind them. The more I looked, the more the grass seemed to be covered in lots of long strands of spider silk. So I took a photograph.

You can see the left-right yellowish line clearly in the photograph. Now, what puzzles me is, how can a single strand of spider silk appear so thick on a photograph?

Analysis

According to earthlife, the diameter of a typical garden spider silk thread is 0.003mm.

Assume my photo, taken at zoom, is the picture of a width of around 1m, and I know the dimension of the original image is just under 5000px, so 1 px on the photo covers about 0.2mm of real ground. So the actual silk thread is nearly two orders of magnitude thinner than a pixel. Why does it show up?

I look at the original image and the width of the bright line is around 15px, which simply increases the discrepancy.

Explanations

• Obviously, this phenomenon is something to do with the backlighting sun and its angle, and maybe its refraction through the silk, as the threads are not normally visible.
• Possibly at that time of day, the addition of settling dew could be a factor.
• Maybe the thread was moving about in the wind, although I do not recall its being particularly windy, and it does hug the ground. (Shutter speed 1/125 sec, f/6.4).

Any ideas?

Spider silk is the strongest of all fibres, natural and man-made – see the above link.

2 thoughts on “Spider silk mystery”

1. Reflection from a radial surface might be the answer. But the moisture probably also expands the radius. And the angle, the orange tint of longer wavelengths of light (blue might not reflect or penetrated nearly as well).

Nice. Did you take a more expansive photo?

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2. Sorry, I didn’t do any better photos, although the one posted is 50% reduced. It was a bit of an afterthought, as a short eared owl appeared around that time. There were lots of web lines and I clearly could have done more. Sod’s Law says if I go there again the phenomenon will not recur, due to different angle of Sun, different humidity etc.
I’m sure you’re right that the wavelength of the light is a significant factor.

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