IRIDSCENCE IN NATURE — ©Marc A. Spataro
This is a photo of a BOELEN PYTHON - Whether you know it or not, you have likely been familiar with iridescence since you were a kid. You probably marveled at it in soap bubbles. Light first passes through the top layer of the bubble, where some of it is reflected, while some light continues through to the bottom layer, where again some of it is reflected.
Rather than having just the constructive interference from the top and bottom layer that you have in a bubble, the many, equally spaced layers of butterfly wings or snake scales create multiple instances of refraction.
When light hits the different layers of the wing or scales, it is reflected numerous times, and the combination of all these reflections causes the very intense colors that you see in many species. See the snake above without the iridescent sheen here
Changes in intensity are often particularly noticeable, as iridescent colours usually appear brilliant and saturated at optimal viewingangles . When the viewing angle changes, however, the iridescence can disappear entirely, leaving visible only the colour produced by underlying pigments, which are often black [as in the snake above].
A benefit of beneficial angles showing or hiding iridescence is that they might allow animals to be obvious to their intended signal receivers (ie. other snakes) while remaining relatively inconspicuous to potential predators
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