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.