Wednesday, September 19, 2007

Spider Web colours

Thie picture of light reflected from spider webs, looking on a direction towards the Sun, with 2-stop underexposure and the camera out of focus. Note the fact that, although the web strand is out of focus in the direction at right angles to the strand, the colour bands are sharp in a direction along the strand.

4 comments:

Ágnes Kiricsi said...

Yes, this is very similar indeed to the question raised by the 12th September post of the thistle seed. Les then wrote in his comment: "some colours of the banded variety occur even when the hairs or web are microscopically devoid of small droplets. Spider webs are sophisticated structures, some silk threads have droplets, some do not." I've been thinking about it. Spiders have different types of glands, producing different threads (there are 7 known types). Can we say, however, that even if the thread is not the sticky one with the droplets, the material that comes out of the spider's spinners is absolutely smooth on the micron (or even sub-micron) level? Something must scatter the rays here as well, causing interference.

Les said...

The light scattering is not necessarily from surface features. The internal structure of spider silks is complex with periodic structures capable of scattering.

Les

Noli said...

Spider silk contains some special amino acids, and the sequence of them gives the elastic character of the silk. Might these amino acid sequences have different ability to scatter, do you mean this by internal structures?

Dieter Z. said...

The colours seen are due to interference of the light waves scattered from adjacent spots along the thread which, because of the defocusing, are superposed on the same spot on the film or sensor. Silk has a wrinkled surface, responsible for its "silky" shimmer.

I have discussed these effects on my pages on spider webs
which show some more colourful pictures.

Dieter