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Kruisspin / Garden Cross Spider / Araneus diadematus ©GK
One radial line is visible.
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Yesterday my attention was drawn by an orange coloured spider illuminated by the
sun. I was forced to underexpose the photo by 2 stops to get the right
exposure of the spider. It appeared to be the common Garden Cross Spider
(Kruisspin). But what me surprised the most was one thread (fiber) of the
web:
Here is a detail of the thread (cut into two parts). A remarkable pattern of very fine stripes with all the colours of the rainbow emerged. I've never seen such a pattern. I expected a continuous thread. Furthermore, lengthwise along the thread, I see 3 dark lines. That would imply that the thread is not one thread, but a combination several (four?) threads.
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| detail, 2x zoom, high contrast, b&w. |
Why
in heaven's name this very detailed structure? What is going on? How
does the spider manage to create this pattern? And what is its function
(if it has a function at all)?
Afterwards I realized that I have been extremely lucky. First, the sun must illuminate the web at the right angle to make the thread and the pattern visible. Spider webs are supposed to be invisible to be effective! In the shadow, you see absolutely nothing. I was also lucky that a thread was nearly parallel to the camera sensor, which keeps it in focus over a sufficient length of the thread. Secondly, I underexposed the photo to get the spider right. As a side effect the pattern appeared. I almost never underexpose a photo. Normal or overexposure make the fine details disappear. Thirdly, I was lucky there was no annoying wind that could move the web. Because web threads are so thin, the slightest breeze brings them out of focus. Wind is the enemy of macrophotography. Finally, it was a clean and fresh web in the garden, so no house dust attached.
The science behind it
I know that scientists have analysed the chemical composition of the threads. The threads are made of Spidroins proteins that form the majority of spider silk fibers.
Major Ampullate Spidroin Structure.
The repetitive domains of major ampullate (dragline) silk consists of
alternating regions of polyalanine and glycine-rich sequences. These repetitive
domains are important for the strong and elastic features of the dragline silk
fibers (
Xu and Lewis,1990). (Synthetic Spider Silk Production)
It seems very unlikely that what we are seeing here are alternating regions of Alanine and Glycine (Amino Acids) rich regions in the proteins. More likely we see crystalline and non-crystalline regions in the threads? Maybe different spidroins? I have really no idea. There is a lot to explore...
Surprisingly, I did not find similar pictures of the fine structure of spider web threads in the relevant Wikipedia pages, Spidroins, Spider silk and Spider web.
June 30 / July 1: some edits in the text, +1 picture.
Additional pictures
8 July 2026
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| [4684-detail] original positions. GK. |
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| [4669-detail] main thread. GK. |
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| [4658-detail] original positions. GK |
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| [4657-detail] original positions. GK |
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| [4654-detail] original positions. GK. |
All pictures with a factor -2 to -3 stops under-exposure. Kruisspin / Garden Cross Spider. They are not enlarged. Macrolens Sony 90mm. Threads have direct sunlight from behind the photographer. No artificial light source. All threads except one [4669] are connecting threads. See here for the anatomy of a spider web.
What stands out is that no threads are the same. Can all this be explained by pure optics??? That is: no internal structure of the threads???
9 July: Meanwhile, I have made pictures with the sun in front of the camera ('tegenlicht'). They also show the usual patterns depending on the angle of the sun's rays. Direct sunlight is necessary. The sun must not be wholly or partially covered by clouds. Also, the cross bands are never visible across the entire web at the same time. This can be interpreted either as differences in the structure of the threads themselves or as a difference in the angle at which the sunbeams strike the web. The fact that the visibility of structures highly depend on sunlight is in no way an argument against the existence of structures. In biology structures are always made visible by chemical or optical techniques. For example, chromosome bands are only visible when stained, but are absolutely real.
Further Reading
