Forbidden colours: backlight spiderwebs (part 2) and more surprising finds

To prove my claim that the colours in a spiderweb can indeed be created with the sun as backlighting, I took photos of spiderwebs high in a tree, with my camera pointed dangerously close to the sun. And a new surprise finding.

[1927] Original picture (scaled to 900x600 pixels).

All of the following spiderwebs are backlight pictures high in a Juneberry (Amerikaans krentenboompje, Amelanchier lamarckii ). Because they are so high in the tree, I could not identify the spider, but presumably it is also a Garden Cross Spider (kruisspin, Araneus diadematus).

[1902]. back-lighted spiderweb. overview. contrast enhanced

[1938] Spiderweb, backlight, contrast enhanced.

 

The background is dark because the contrast in the photo was increased afterwards, making the colours stand out better. Originally, the background was very light: it is a backlit photo; the sun was dangerously close to the spiderweb.

Here is a unedited photo which looks to me like an impressionistic painting: 

[1864] Out of focus results in an impressionistic painting!

 

[1864] detail. contrast slightly enhanced

Surprising finds

The typically feathery pappus of a ripe thistle flower is known as thistle-down. The feathers make the seed airborne with the slightest breeze. The feathers are lightweight and thin by design: they are supposed to be blown by the wind. I found somewhere that the individual hairs can produce colours, and indeed that's what I found too. They look very similar to the colours of spiderwebs! 

 

[5586]. Seed with feathers.

 

[5580]. Same object. Note colour patterns similar to spiderwebs!
Slightly post-exposure enhanced contrast.

Artificial objects

 

[5559]. Snap Ball Tea Strainer (without sunshine)

 

[5573] Same object with sunshine (detail)
Out-of-focus enhances the effects.
No post-exposure editing.

[5573] Unexpected black concentric circles! (detail)
No post-exposure editing.

[5576]. image 2x magnified.
Surprise: 5 black concentric circles! Wow!

 

[5573] Detail. some look like parts of spiderwebs?

 

So, artificial and natural objects exhibit at least some comparable patterns. Does this invalidate my hypothesis that spiderweb threads have an internal banded structure? and that everything has to be explained by the laws of optics? Are they visual illusions? However, are the colour patterns really similar enough? 

We can safely assume that the artificial metal objects have no internal crossbands. So, the optical phenomena are not caused by internal structures of the metal. They must be optical effects. But spiderwebs and the feathers of seeds are composed of proteins and possibly other biological compounds. Could that make a difference? These questions are far outside my own expertise and technical capabilities. I wonder if physicists recognize these patterns, especially those black concentric circles? I included them in my blog because they are so wonderful.

 

 

Technical details

Spiderwebs: SONY RX10-iv. 

Macro (Snap Ball Tea Strainer; seed): SONY A6700/90mm macro. Sunlight.

 

Previous blog

• Spiderweb colours violate the rainbow rule 28 July 2026

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Solar eclipse 12 August 2026 in The Netherlands captured with digital camera equipped with Neutral-density filters

SONY RX10-iv 600mm ISO200 f/4 1/15 sec. time 20:02
that is about 8 minutes before maximum
Dimensions of the sun on this image: 780x725 pixels
Original image: 5472x3648 pixels.

The solar eclipse 2026 was a total eclipse in Iceland and Spain, and partial in The Netherlands. The weather was perfect, completely cloudless, but a littlle bit too hot at first. The maximum was around 20:10 in the evening, with 90% coverage. Because the sun was low on the horizon, a location was required with a good view to the West without trees or buildings, in this case a nature reserve (Westbroekse Zodden). The last contact was around 21:03 and sunset at 21:10.

At a previous solar eclipse I used an improvised method to photograph the eclipse. This time I used photographic HOYA PROND EX - ND500 filters. These are Neutral-density filters (ND filters) which reduce the intensity of all wavelengths of light equally, giving no changes in hue of color rendition. The filters can be combined. To ensure that the camera sensor would not be damaged, I used two of them on top of each other (1) and on top of the standard UV filter. Still, I didn't dare photograph the beginning of the eclipse and waited until the maximum. 

Manual focus required (∞). I used diaphragm f/4,0 because higher settings didn't work well. I used the SONY RX10-iv with maximum zoom 600mm, see pictures. I succeeded in making a few sharply focused photos but I stopped at the moment the sensor seem to produce distorted images. Luckily, it turned out afterwards that the sensor was not damaged! 

©A.B.

Subjectively speaking, the eclipse at the moment of the maximum coverage of 90% was somewhat disappointing; it didn't get really dark. However, the colors in the landscape did fade noticeably, and it became less warm. The human side: people came together from all over to admire the eclipse at the hospot I had chosen. It was a social happening. There was a cheerful and friendly atmosphere.

©A.B

Next solar eclipse: 2 Aug 2027 (49%).

 

Notes 

1. Warning: don't tighten the filters too much! I couldn't get mine apart anymore! I eventually managed to get mine loose again after all. One ND500 filter equals 9 stops down. Two of them equals 18 stops down! So I have used more than recommended ND100.000 (16.6 stops) and coud have easily made pictures of the start of the eclipse. See for table ND filters and stops: Fotograferen met filters and Zonsverduistering fotograferen: de complete gids voor 12 augustus 2026. I only found this website after the eclips.

 

Previous blogs

• Zonsverduistering fotograferen met een gewone digitale camera? Het kan! (29 maart 2025) Solar eclipse with standard digital camera. 31 Maart 2025
• Maansverduistering Maandag 21 januari 2019. Lunar eclipse.  21 Jan 2019
• Totale maansverduistering maandag 28 september 2015 groot succes ondanks slechte weersvoorspellingen. 28 Sep 2015

Spiderweb colors violate the rainbow rule

Spiderweb (overview). Backlight [1]

According to the laws of physics, rainbows caused by sunlight always appear in the section of sky directly opposite the sun [2]. Here I show that spiderwebs violate this rule by pictures of spiderwebs with backlight resulting in rainbow-like colors as well.

Kruisspin / Garden Cross Spider / Araneus diadematus 

Detail. length ~ 1 cm / 0,4 inches

Straight white lines demarcate a sector of the spiderweb circle
that lights up selectively. The rest is faintly visible and colorless.
The lines meet at the center of the web,
and seem to point towards the sun.

detail of previous picture. Click to enlarge.

So the part of the spider web circle that lights up seems to be a segment which points to the sun [3]. Furthermore, as shown in the previous blog, the threads of the web consist of many small segments with different colors. Contrary to the previous blog, these pictures are taken towards the sun. The fact that colors are seen at all contradict the physical rules for the formation of a rainbow by the sun. A possible explanation could be that the spider web threads are not made up of water droplets but of proteins...   

Garden Cross Spider
This little spider had nothing to eat for a week.
Finally she caught a fly! Enjoy your meal!
Note the difference in size!

An adult Garden Cross Spider
built its web on the window of the barn door.
Fortunately we could still use the door!
By the way: this location is perfect to investigate the effect
of different directions of the sunlight
because you can move the door without damaging the web!
Addtionally you can photograph the web from both directions!

 

Notes

1. The main light source, the sun, is behind the spider, facing the camera and photographer. Note: in Dutch this is called 'een tegenlicht opname'.
2. Thanks Rolie Barth and Matt Young for pointing this out. See for example wikipedia article Rainbow.  
3. However, I did not investigate this effect systematically!

Previous blogs

• Accidental discovery of the ultra finestructure of the web of the Garden Cross Spider [+additional pictures].  29 June 2026
• Araneus diadematus. Panda's Thumb Photography Contest. July 27, 2026

Links

• Spider web colorations on Youtube (high quality photographs, much better than mine!)
• Glistening spider silk with beautiful pictures of Dietrich Zawischa

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Accidental discovery of the ultra finestructure of the web of the Garden Cross Spider [+additional pictures]

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.  

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

[4684-detail] original positions. GK.

[4669-detail] main thread. GK.

[4658-detail] original positions. GK

[4657-detail] original positions. GK

 

[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

• Optical effects on spider webs by Dietrich Zawischa (beautiful pictures with explanations)
• Accidental Observations by Dietrich Zawischa is a collection of remarkable optical effects in everyday life. (With thanks to Matt Young) (22 July 2026)
• Wikipedia: Orb web spiders, Orb web construction

Are there biological facts that the theory of evolution does not explain and does not need to explain?

The theory of evolution is the overarching unifying theory in biology. Are there biological facts that the theory of evolution does not need to explain? Or does the theory of evolution have to explain every fact about life? According to the theory of evolution every species and every individual of a species is the result of evolution. That would imply that every feature of an organism must somehow be explained by the theory of evolution. 

Aerodynamic forces on a bird (Videler, 2012)

Even at the time when I was a student and attended evolutionary biology courses and did lab experiments on evolution, I had the vague idea that the theory of evolution was incomplete, although at the time I couldn't say why, or what exactly was missing (here). There is so much to explain, and "A change in gene frequencies over time" and "Differential reproduction of heritable variation" seem far too simple for the task. Yes, there was a Second and Third Evolutionary Synthesis, but still a lot was missing. Obviously, the planetary, geological and cosmological context of evolution is often missing in the textbooks. Last year I blogged about the fact that evolution textbooks are suffocating: very low levels of Oxygen!  My list of top 20 evolution books (blog) reflects my preoccupation with the question of what is missing. Furthermore, physicist Rolie Barth pointed out physical factors and constraints in evolution (blog) [1]. At the other end of the spectrum: is evolution supposed to explain human behaviour, intelligence, consciousness, psychology, language, culture, civilization, war? What is the scope of the theory? Where does it end?

A few days ago I had an interesting discussion with google-AI about the question: Are there biological facts that the theory of evolution does not need to explain?  The initial answers seemed incorrect and incomplete. So, I demanded better answers and google-AI came with surprisingly insightful answers:

1. What evolution does NOT need to explain: The physics of how cells physically move, stick together, or split. For example, when a sheet of cells bends into a tube, it follows basic laws of fluid mechanics and surface tension.
2. What evolution DOES need to explain: Why the cells bend into a tube at that exact moment, in that specific location, to form a spinal cord. The timing, the instructions, and the genetic switches that trigger those physical movements are entirely shaped by natural selection.
3. What evolution does NOT explain: The electromagnetic forces that allow a hydrogen bond to form between Adenine and Thymine. That is pure physics and chemistry.
4. What evolution DOES explain: Why a specific three-letter sequence (like UUU) maps to a specific amino acid (like Phenylalanine), and why this map is nearly universal across all life.
5. Evolution does NOT explain: Why a hydrogen bond forms at all, why the universe is made of matter instead of antimatter, or the laws of thermodynamics that govern energy conversion.
6. Evolution DOES explain: How life hijacked those inescapable physical realities and organized them into the intricate, Mendelian, metabolic, developmental masterpiece we call biology.

Additionally:

• Lipid Bilayers: Amphiphilic lipid molecules automatically assemble into complex, spherical, semi-permeable cell membranes when exposed to water, driven entirely by hydrophobic physical forces.
• Membraneless Organelles: Inside the cell, proteins and RNA's undergo liquid-liquid phase separation—similar to droplets of oil separating in water. This thermodynamic behaviour spontaneously forms highly organized, functional compartments (such as the nucleolus) without needing an explicit genetic blueprint directing every coordinate.

These examples can be expanded with:

Microtubules: the self-assembly of microtubules. The proteins themselves are inherited, but they self-assemble into microtubules. 

Biochemistry: See also the primacy of biochemistry as opposed to genetic determinism [2].

Bio-electricity: "Without bioelectricity, your cells couldn't communicate, your muscles couldn't move, and your heart wouldn't beat." [3]:

• The Cellular Battery: Membrane Potential
• Nervous System Communication
• Muscle Contractions (Powering Movement and the Heart)
• Wound Healing and Tissue Regeneration
• Specialized Biological Superpowers (Electroreception, Electrogenesis)

Quantum effects: photosynthesis. 

Mechanical forces: Venus flytrap [4].

Van der Waals forces that hold molecules together (Gecko).

Hydrogen bonds (DNA bases).

Aerodynamics (birds, bats, insects), hydrodynamics (fishes, dolphins, sharks, blood flow).

Gravity: Effect on body size (scaling laws).

Geomagnetic field: is used by pigeons for navigation

Ultrasound navigation (bats)

etc. 

 

It seems very reasonable that evolutionary theory doesn't need to explain physical and chemical phenomena, because it is a biological theory. Physics and chemistry do explain physical and chemical phenomena. A biological theory can take them for granted, isn't it?

However, there is a problem. For a full scientific explanation of the evolution of life on earth, one cannot do without additional non-biological explanations. But organisms are undivided wholes. They can't be subdivided into biological, chemical and physical parts. So, must we conclude that the theory of evolution, as a biological theory, by definition is incomplete? [5]. Could it be that the theory only has to explain how biological things have evolved, and not all the details of how they work precisely? Would it be enough to demonstrate which genes and which mutations are involved in creating a specific trait and how it contributes to fitness? Does the theory need to include aerodynamics to explain the origin and evolution of flight? Finally, if new scientific discoveries are made on a daily basis, how can the theory of evolution ever be complete? I am afraid that the question of the scope and completeness of the theory of evolution is a rather complex and elusive question. Maybe, several quite different questions. Anyway, the question is too wide-ranging and too tricky to settle in one blog post. 

Notes

1. See also this blog where Rolie Barth explains that "Protein evolution can draw from a reservoir of a limited number of physically possible structures".
2. Nick Lane say about the primacy of biochemistry contra genetic determinism: Genes evolved simply to stabilize and optimize these already functioning biochemical pathways, rather than starting from scratch to build the cell. Also: The electrical origins of life!  
3. According to https://gemini.google.com 
4. Fast cell wall softening causes Venus flytrap closure, Science, 11 Jun 2026
5. Note: Could that be the cause of my gut feelings about the incompleteness of the theory of evolution half a century ago? 

Preliminary Conclusions

17-19 June 2026

• The Theory Of Evolution is a high level abstract paradigm that generates research strategies to investigate the details of structure and function of species.
• The Theory Of Evolution can be so compact because all the details are supplied by the biological subdisciplines, chemistry, physics and so on.
• Another reason why the Theory of Evolution is so compact is that it does not predict 'the brute facts of life': the existence of Kangaroos, Penguins, Anteaters, Hummingbirds, Bats, Octopuse, Sundew, Ocean sunfish, Platypus, Eukaryotes, Sex, Genetic Code, Split genes, the structure of DNA, etc. (historical contingency).
• The two hardest problems of The Theory Of Evolution are the origin of life and the origin of consciousness.
• Common descent predicts deep similarities of all life, and indeed this has been found on the genetic, biochemical, developmental and anatomical level, although the extent and specifics of similarities cannot be predicted in advance and often have surprised scientists.

Read more...

Autonome wereld en theodicee bij Taede Smedes (3)

"Het blog over Autonome Wereld bij Taede Smedes (2) is een van mijn meest bekeken blogs. En er kwamen soms vreemde reacties. Iemand die je een Taede Smedes-kenner zou kunnen noemen, schreef dat Taede Smedes nooit over het probleem van het kwaad had geschreven. Dat vond ik een vreemde bewering.
In een vorig blog (1) schreef ik over het probleem van het kwaad zoals beschreven in het boek God en Darwin van theoloog-godsdienstfilosoof Taede Smedes. Het probleem werd in dat boek maar heel kort aangestipt omdat het boek over een ander onderwerp ging. Toch werden er in dat boek zeer belangrijke en revolutionaire uitspraken gedaan. Sommigen (2) beweerden dat Taede Smedes nooit iets over het probleem van het kwaad had geschreven, en daaruit volgde op de een of andere manier dat ik het helemaal mis had. Of zo iets. Onzin! Onwetendheid! Smedes heeft wel degelijk over het probleem van het kwaad geschreven in zijn boek God en de Menselijke Maat (2006). Met name in Hoofdstuk 11 (toelichting, literatuurlijstje) (bewijst ook dat hij zich met de literatuur heeft beziggehouden)." 

Tot zover een draft blog dat ik nooit heb afgemaakt. Ik publiceer het nu ongewijzigd zoals het sinds 2011 als draft is blijven staan. De aanleiding is een blog van Taede Smedes: Lieke Marsman – Een oproep tot leven, 4 juni 2026. Dat blog opent met de woorden:

"Ik heb het feit dat kanker bestaat altijd gezien als een van de belangrijkste argumenten tegen het bestaan van een bovennatuurlijke God. ... Dat kanker bestaat, toont voor mij aan dat een bovennatuurlijke Schepper-God – zoals voorgesteld in het christendom – niet kan bestaan. Zo’n God is voor mij dan ook een illusie."

Je kunt in ieder geval vaststellen dat Smedes in de loop der jaren consistent is gebleven in dat opzicht [3].

Noten

1. Autonome wereld en theodicee bij Taede Smedes (2) Het probleem van het kwaad, 28 november 2011. 
2. Uitgerekend filosoof Jan Riemersma heeft vele malen gezegd dat je vooral Taede Smedes moest lezen. Overigens is het helemaal niet relevant of Smedes 'nooit over het probleem van het kwaad' geschreven heeft. Het gaat er om wat hij wel geschreven heeft. Daar doe ik het mee.
3. Dit blog van Smedes over hetzelfde onderwerp had ik nog niet eerder gezien: Sluit zinloos lijden het bestaan van God uit? 17 mei 2010.

A likely breeding case of the Common Hoopoe in the Netherlands

Common Hoopoe / Hop / Upupa epops ©GertKorthof

The Hoopoe is a rare and unique bird in The Netherlands. It has an unusual combination of a movable crest like that of a cockatoo, and a long beak curved slightly downwards like that of an Eurasian Curlew (wulp). The plumage is a combination of an inconspicuous brown and a striking black-and-white pattern. The food-seeking behavior is mostly on grasslands and clearings in the forest, but it breeds in tree cavities like a woodpecker.

©GertKorthof

Recently, I was fortunate enough to watch this beautiful bird in the wild in The Netherlands. It landed on a bare spot in the forest about 20 meters (65 Feet) away from where I was walking. From my position, I could observe, photograph, and film it perfectly. After a few minutes, it flew away. I was able to make a short video:

A short video clearly shows the hurried way of foraging.

Evidence for a breeding case

The bird is very busy gathering food for short moments during most of the day on different locations and returning again and again. It has been observed that the birds repeatedly fly with food in their beaks in the same direction. They are usually very relaxed, but this bird was very busy. I have seen pictures made by another birder that clearly show a Hoopoe flying away with an insect in its beak. That is the best, albeit indirect, proof of a nest with young. This is not the same as fledging, the stage that the young leave the nest. Only then can it be called a success.

I have submitted my observation to waarneming.nl. The image recognition system (ObsIdentify) resulted in a 100% certain identification. Not really a surprise for an easily recognizable bird. This observation appeared to be under embargo and is only visible to myself and authorized persons. So, I can't see how many observations have been submitted. My observation was automatically approved. This shows that manually approved observations of the bird on the same location must have existed already at that moment. Despite its rareness, there are a lot of Hoopoe observations visible in waarneming.nl at many locations in The Netherlands, but these aren't breeding cases.

How rare is the Hoopoe in the Netherlands?

Hop Upupa epops. breeding 2021-2023 SOVON

Hop Upupa epops. Non-breeding 1989-2014 SOVON

See for more data:  SOVON [3]

 

Fun facts

Peterson, Mountfort, Hollom, Kist 1964 [2]

My first serious bird guide, at the time it was referred to as 'De Kist', now 62 years old, has a Hoopoe on the cover! How charming! They placed a very rare breeding bird on the cover! Field characteristics of the Hoopoe:

"Searches for food mainly on open ground. Nests in tree cavities and the like. Very rare breeding bird of open woodland. Reappeared for the first time since 1943, after 30 years. Rare migrant from mid-August to late October and in spring in April and May." (page 195)

The map in this bird guide shows that the Netherlands lie above the northern border of the breeding area. Birds showing up in The Netherlands could be called pioneers venturing into unknown territory. This could explain why the number of birds fluctuates from year to year. I imagine that after a good breeding season in southern countries, young birds migrate north. Their usual food grasshoppers and lizards are relatively rare in our country, so the pioneer birds must adapt to other prey [1]. They must be flexible.

A bird encyclopedia published between 1770 and 1829 DE NEDERLANDSCHE VOGELEN: [4]

De Nederlandsche Vogelen. (Grutto op omslag)
Compare with a modern bird guide.

 

3 pages about the 'UPUPA' or HOPPE. [4]

 

The illustration is of high quality and is absolutely sufficient to identify the bird. The author describes the bird as a rare breeding bird. It was difficult to locate the nest of the bird. Between 1747 and 1778 it has not been seen. This shows how irregular the presence of the bird was at the time. However, the most striking fact in modern eyes is the fact that the author received a (dead!) breeding pair of Hoopoes complete with eggs and part of the 'nest' that had been captured (?) shot(?) from the wild! Fun fact: the author mentions that the famous philosopher Aristotle already knew the bird [5].

 

Title plate of book III clearly showing a Hoopoe..

Finally, the Hoopoe is present in the holy book of Christians, The Bible: " It is mentioned in the Old Testament as one of the birds that the Israelites were forbidden to eat under the dietary laws of the Mosaic Law." [6],[7].

 

Notes

1. R.M. Teixeira (1979) Atlas van Nederlandse broedvogels. page 212-213. 
2. Dutch translation of: Peterson, Mountfort, Hollom 1964) A Field Guide to the Birds of Britain and Europe. Translated and adapted by Mr. J. Kist.
3. SOVON, (Stichting Ornithologisch Veldonderzoek Nederland, Sovon Dutch Centre for Field Ornithology) is the most reliable source of the numbers of bird species in The Netherlands. The most recent report is Broedvogels in Nederland 2024. The Hoopoe is described on this page with an estimated number of 5-7 breeding cases. (information from Klaas van Dijk 2 Jun 2026).
4. DE NEDERLANDSCHE VOGELEN free online edition. 'Hoppe' is the old name of the Hop.
5. I checked it, and indeed: THE HISTORY OF ANIMALS by Ari" target="_blank">on this pagele, tr with an estimated number of 5-7 breeding cases. nslated by D'Arcy Wentworth Thompson, Book VI.
6. It is mentioned in the Old Testament as one of the birds that the Israelites were forbidden to eat under the dietary laws of the Mosaic Law. Leviticus 11:19, Deuteronomy 14:18. Unclean for consumption: the Hoopoe is grouped with other "unclean" and detestable birds (like vultures and bats). It is indeed repeatedly mentioned in the literature that droppings accumulate in the nest and are not cleaned up. Understandable that it is an 'unclean bird'. However, it is possible that this fact has been endlessly copied without first-hand observations! Most birds keep their nests clean due to the risk of infection. [added: 2 Jun 2026]
7. Vogels in de Bijbel geeft 21 vogels, waaronder de Hop, maar ook de Struisvogel! Dat kan natuurlijk niet, want de Struisvogel komt alleen in Afrika voor. [4 juni 2026]

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