In nature, the color blue is unique and rare. While animals come in a variety of colors, blue seems to be the rarest of them all. Why is this so? The answer lies in mysterious processes of evolution, chemistry, and physics. In this article, I will explain why animals have colors, how butterflies provide fascinating insights into colors, and how the color blue is created in nature through microscopic structures.
The role of colors in nature
Colors play an important role in the animal world. Butterflies are an excellent example as they have evolved to be active during the day, giving them a communicative advantage through the use of light. Their wings display diverse patterns and colors that convey vital information, such as toxicity or the territory of males. However, not all butterfly colors are created equal.
The secrets of the color blue
Butterflies of the Blue Morpho genus, known for their extraordinary beauty, possess a remarkable blue color on their wings. Surprisingly, this is not due to pigmentation. When we examine them under a microscope, we notice that the wings of these butterflies have microscopic ridges resembling tiny Christmas trees. These structures are responsible for the blue color. When light hits these structures, part of it reflects from the upper surface, and part of it passes through the layer and reflects from the lower surface. For blue light, the waves reflecting from the top and bottom are synchronized, making only the blue color visible to our eyes. This fascinating structure acts like a hall of mirrors, allowing only blue light to escape. Additionally, there is a pigment at the base of the wing that enhances the blue color by absorbing scattered red and green light.
Not just butterflies
The color blue in nature is not limited to butterflies. Other animals also create this color through intriguing mechanisms. For example, the blue feather of the Blue Jay disappears when viewed through it because it contains microscopic balls that eliminate all colors except blue. Peacock feathers also obtain their blue color through structures that reflect light in a more ordered manner. Even blue eyes, including our own, are colored by structures rather than pigments.
Evolutionary puzzle
Why is it that most blue colors in nature are created by structures rather than pigments? Scientists have been asking this question for a long time, and one theory suggests that birds and butterflies evolved the ability to produce pigments but accidentally “swallowed a bacterium” that possessed blue structures. Since then, birds and butterflies had the ability to create structures but were unable to produce blue pigments. Evolution, therefore, found a way to create the color blue through microscopic structures instead of pigments.
Sources:
- Prum, R. O., & Torres, R. H. (2003). Structural colouration of avian skin: convergent evolution of coherently scattering dermal collagen arrays. Journal of Experimental Biology, 206(14), 2409-2429.
- Prum, R. O., Quinn, T., & Torres, R. H. (2006). Anatomically diverse butterfly scales all produce structural colours by coherent scattering. Journal of Experimental Biology, 209(4), 748-765.
- Vukusic, P., & Sambles, J. R. (2003). Photonic structures in biology. Nature, 424(6950), 852-855.
- Stavenga, D. G., Leertouwer, H. L., & Marshall, N. J. (2011). Colouration principles of nymphaline butterflies—thin films, melanin, ommochromes and wing scale stacking. Journal of Experimental Biology, 214(2), 215-227.
