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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.
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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.
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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
