Here, you will discover 10 new ideas on the curious optics of spider webs. Five might be right. This site is evolving as we gain more knowledge about the technology hidden within the beautiful web. 

Did you know a single spider will capture 200 insects a year? Worldwide, they capture 400 million tons of insects. Additionally, there are fewer than three deaths per year from spider bites, but approximately 60 from dog bites and 60 from bee stings. The spider is your friend.

Be kind to our spider friends and appreciate the beauty of webs!

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Capturing colors,
a web waving in the breeze

The glints of light on the web draw my attention to a large spider web outside the kitchen window. Such glints are common. The window is open, no screen. The glints are bright, colorful, and at eye level, demanding attention! With no plan to explain anything, my goal is simple: to capture the attractive glints of the spiderweb.

Computer editing changes the grey background to black, revealing that the glints are blue, red, and green. Each colored spot is unique, yet they are organized in a direction. It was late in the evening when the beauty was recognized. By the next afternoon, Marie had cleaned the window, and the beautiful spiderweb was gone.   

Fortunately, there were more spiderwebs in the backyard. It was fun photographing beautiful spiderwebs. Most photos were captured in my yard using a standard Canon Rebel 2Ti. 

Only later did I realize that color creation was a complex technology. I had not recorded the camera detail, sun position, and the type of web. My apologies to those wishing for a truly scientific document. 

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Introducing Technical Features

The primary features of the spiderweb discussions are introduced in one image, Figure 4. In the upper right of the photo, there are tiny threads with bright spots. This is the thread that the spider creates. The spots are gluedrops that capture prey. In mid-image, going from right to left, notice the slender line of “ghost spheres.” The bright, colorful central feature emerges and attracts the most attention. The color pattern is beautiful.

How are all these features related?

As you continue reading, you will understand each of these features. These three technical features are the focus of this website: gluedrops, interference, and refraction.

Gluedrops

The figure 8 photograph is unique. It deserves special attention. Cool.

The spheres seen in figure 8, called gluedrops, originate as a viscous fluid from the spider and surface tension collapses them into spheres. In the central zone of the photo, the thread and glue drop appear to be in sharp focus, although the true thread is too small to see with the naked eye or even with conventional camera practice.

Focus on Gluedrops

The camera’s plane of focus is a slice through the divergent light from the threads. As the distance increases, the focus shifts away from the thread and the gluedrops appear larger. The pinpoints of light expand until they overlap the adjacent points. The expansion and overlap of images fuel the technical focus of this discussion.

Figure 9 shows an optical microscope image of some gluedrops.

Fascinating optical features

Two things are interesting here, maybe they’re important in figure 10.
They are curious.

1. The circles on the upper thread have variations of brightness across the diameter. This is diffraction of an aperture, a feature that limits camera resolution.
2. Many of the spheres also have a smaller “parasite sphere.”

There is no explanation here. Curious? Keep reading!

Diffraction and Interference

Diffraction and interference are technical words to explain the interaction of light as waves. When two waves mix, they result in dark and light interference bands. Figure 12 shows what this light interaction looks like:

• The first illustration shows the diffraction pattern of two sources.
• The second picture shows interference pattern of light waves.
• The third picture is a detail crop one of the spectra from a light wave in my yard.

When spectroscopy experts examine this detail, they refer to it as a diffraction pattern. In reality, it is an interference pattern. This document will switch words back and forth.

Looking in detail at web color patterns

The color that we have seen on webs come in many patterns. Some are more artistically pleasing colors than other. In figure 13 we see odd colors that are a little unpleasant to look at.

Figure 14 is a good  illustration of diffraction.  This is caused by the edges of the aperture like camera diffraction. The important part of this image is the ends of each line have an irregularity like the top of a bedpost.  It is diffraction seen differently.  It is like the diffraction limit of a camera.  

Comparing Colors on Radial and Spiral Spider Web

There are different kinds of spider web. In figure 16, we see color patters on both radial and spiral web. We continue to look at more curious and interesting photos of colorful webs.

Still curious? Keep reading!

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Field Observations

Much can be learned about the spiderweb by studying it its natural environment.  People commonly see the bright glint from the web.  It is not the total web but glint from a small zone.  

Exploring angles and perspective

Do you notice how that it’s possible to walk along a horizontal web and the bright zone will move too?  Try standing at one position outside, moving your head up and down, and see if the glint is stationary.  Conversely, when looking at a vertical web, the up-down movement causes the glint to shift while it is stationary to a horizontal motion.  

In figure 24 we see a magnified look at gluedrops and in figure 25, a 3D illustration.  It is necessary to map all 360° with relationship to the sun and the web.

Tabletop testing with a laser

It would be nice to have a controlled piece of sunlight for experiments in the lab.  

A laser is a bright light source that can be controlled in a lab, so we used that.  The test arrangement below uses:

• A laser pointer.
• A thread on a wire holder in the middle.
• A paper fence around to display the light effect.

The laser pointer is located in an opening in the paper fence. 

 The vertical spiderweb is at the center of the circle and the laser beam, spread by the web, is on the paper fence.  

It is a very revealing test but it needs explanation.  While collecting web samples, it was difficult to capture a single thread.  It turns out that this multiple-strand sample was the most instructive of all samples.  The spider web is held in a vertical position at the center of the table. There is a cluster of threads that create a bright horizontal band.  There is a single vertical thread that creates the small horizontal line below the cluster. Sarah Stellwagen properlley points out that tension is important and we didn’t pay attention to that.

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Pretty Entertaining Things

We appriciated the photos of Cindy Skeie.

More laser fun

This series of photos below illustrates how the incident angle causes the refracted pattern to form a circle.

Top left, we took photos showing a vertical glass rod (spiderweb) and laser pointer (horizontal line) going straight at the cylinder.
In the other photos, we angle the glass rod slightly, so that we obtain the first curve, and further tipping leads to the sphere.

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