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Kruisspin / Garden Cross Spider / Araneus diadematus ©GK One radial line is visible. |
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.
Hi Gert, nice photos. Spider webs keep fascinating us.
ReplyDeleteAs far as I know, these different colors are optical effects of light refracted under different angles for each color (wavelength).
For more background see:
https://farbeinf.de/static_html/spiderweb.html
or
https://share.google/lMtpW32A4Ez78aZVo
I made a mistake: "refracted" should be "diffracted", of course.
DeleteRefraction: light rays change direction when passing for example the surface of water or glass, coming from air.
Diffraction: light rays are bended in different directions depending on the wavelength and the angle of incidence.
Thank you, Rolie Barth for your valuable comment. You wrote: "these different colors are optical effects of light ". In this blog I was not interested in optical effects and colors in itself, but what it tells us about the STRUCTURE of the threads. The website you refer seems to have an exclusive physical point of view. If I am not mistaken it suggests that those optical effects and colors are optical illusions similar to Moiré effects. To me the pictures above unmistakingly show a structure. How could the pattern in my photo originate without an internal structure of cross lines? Spider silk contains multiple threads. Each thread consists of specific silk proteins, called spidroins. (see: https://www.goldbio.com/blogs/articles/synthetic-spider-silk-production-finding-the-biofactory). It seems to me that Dietrich Zawischa completely ignores the internal structure of the thread.
ReplyDeleteDiffraction, refraction or something else: the only thing a biologist could ask is how do flying insect perceive these 'artificial' of 'illusionary' colours? do they see them or not? If they do see them that is a disadvantage for the spider because insects could quickly turn around to avoid flying in the web. It seems rather difficult for the spider to make a web, that is strong, flexible and invisible at the same time. The spider could adapt to make its web in the shadows?
ReplyDeleteThe spiderweb seems a good example of where biology (the theory of evolution) must be supplemented with physics (optics) and chemistry (sticky, flexible molecules) to have a complete explanation of an adaptation.
Gert, I don't know whether insects can see a diffraction pattern formed by the threads of a spiderweb. Probably not, since they don't have camera-type eyes.
ReplyDeleteOptical patterns can indeed arise from the periodic characteristics of a thread, but also from optical effects interacting with a patternless metal thread.
The pattern you see, cannot be traced directly back to a physical pattern. Think of a rainbow. There is no physical pattern in the clouds, only tiny droplets moving around randomly and still you see a huge bow.
for this: also from optical effects interacting with a patternless metal thread
ReplyDeleteread:
also from optical effects OF LIGHT interacting with a patternless metal thread.
Dear Rolie Barth, I am not convinced by your arguments. So, we have two hypotheses:
ReplyDelete1) there is an internal structure in the threads which is shown by a pattern of different colours.
2) there is no internal structure, the thread is homogeneous, and what we see is an optical effect, an 'optical illusion'.
How can we decide which is true? If hypothesis 2 predicts a rainbow pattern, then it is falsified because the order of colours in the threads is not a rainbow pattern, although all individual colours seem to be present. In the threads we see repeating blocks of the same colours, contradicting the strict colour sequence of a rainbow. If this is not what your hypothesis predicts, then what does it predict?
I will add later a few more pictures.
Gert, to answer your questions we need to know more about the structure of the spiderweb threads and the setup used to take the photos. Optical patterns depend on the angles at which light enters and is reflected by the treads. But the small diameter of these threads can result in optical patterns (not necessarily a rainbow pattern), without any doubt.
ReplyDeleteRolie, have you seen the additional 5 pictures? You asked about the structure. Here is information about the structure:
ReplyDeletehttps://en.wikipedia.org/wiki/Spidroin#Structure
however the information is about the structure on protein and amino acid level, NOT on a macroscopic level (higher than proteins) such as in my pictures. Unfortunately, there is a lack of information of that level. More research is needed. Anybody???
As I wrote, the sunlight is from behind me, but I don't know the angle...
Further, I tried to photograph the spiderweb in the shadow with a rather powerful led lamp. Indeed, there are some faint structures visible, but without colour and not nearly as beautiful and detailed as in the sunlight.
I will try pictures with sunlight but with sunglasses, Polaroid glasses, UV-filters, etc. Does it make sense to you? Would it help to solve the mystery?
Gert, new photos with polaroid may give new information, try with glasses in two orientations, perpendicular to each other (so turn the polaroid glass in front of the lens over 90 degr.
ReplyDelete