Why is Blue So Rare in Nature?

Blue tigers do not exist. Neither blue bats, blue squirrels, nor blue dogs. Even blue whales are not as blue as one might think. Animals come in a wide range of colors, but blue appears to be the most uncommon. However, it is fascinating when we do come across a blue animal, as they have a captivating appearance.

Nature does not compromise when it comes to the color blue. To comprehend this phenomenon, we will delve into the realms of evolution, chemistry, and fascinating physics. Before we embark on this journey, it is essential to grasp why animals exhibit various colors. To achieve this, let us observe some butterflies, as they are truly remarkable creatures. If you disagree, you are mistaken. Meet individual is Bob Robbins, the curator of Lepidoptera at the National Museum of Natural History in Washington D.C. It is undeniable that butterflies are truly magnificent. They belong to a group of moths that have adapted to be active during the daytime. This adaptation provides them with a significant advantage: the ability to utilize light for communication.

You may already be aware of this fact, but it is worth noting that among all insects, butterflies exhibit the most vibrant and intricate patterns. This phenomenon can be attributed to a significant reason: the colors present in butterfly wings serve as a means of communication, conveying messages such as "I am toxic" or "This is my territory, I am a male." However, it is important to acknowledge that not all butterfly colors are equal in terms of their creation. Upon closer examination of a butterfly wing, we can observe that the colors originate from minuscule scales. In fact, this is how moths and butterflies acquire their scientific names. These scales encompass a range of hues including oranges, reds, yellows, and browns, each containing pigments which are organic molecules capable of absorbing all colors except the ones we perceive. On the other hand, black scales have the ability to absorb all colors. It is interesting to note that animals, including butterflies, birds, and humans, do not produce these pigments from scratch. Rather, they are derived from the ingredients present in our diet.

You may be familiar with the fact that flamingos undergo a color transformation from gray to pink due to the carotenoid pigments present in the crustaceans they consume. This phenomenon highlights the influence of diet on an organism's appearance. However, the case of the color blue is quite distinct. Unlike other colors, blue exhibits a unique characteristic. When you adjust the camera angle, you will notice that the color of blue changes accordingly. It's almost like observing a hologram. This peculiarity arises because blue butterflies lack blue pigments. Surprising, isn't it? So, even though they appear blue, they are not truly blue. That's right! You see, these butterflies, known as Blue Morpho butterflies, are renowned for their exquisite beauty. They have even been immortalized as the butterfly emoji. However, their blue coloration does not stem from pigments. Instead, it originates from the structure of their wing scales. When I discovered this fascinating fact, it truly amazed me. If we magnify a blue wing scale, we can observe the presence of tiny ridges. Upon closer inspection, these ridges resemble miniature Christmas trees.

The configuration of the branches is responsible for the distinctive blue hue of Morpho wings. When light enters, a portion is reflected off the upper surface, while some penetrates the layer and reflects off the lower surface. In the case of most light colors, the waves reflecting from both surfaces will be out of sync, resulting in cancellation and removal of that light. However, blue light possesses the ideal wavelength: the reflected light waves are in harmony, allowing that particular color to reach our eyes. This intricate system only permits blue light to be emitted. Additionally, there is a pigment at the base that absorbs any stray red and green light, enhancing the purity of the blue color. This is how the stunning iridescent blue is achieved. The unique microscopic structure of the wing plays a crucial role in this process. All of these phenomena occur due to the way light refracts when transitioning from air to another substance. If we replace the air in those minuscule gaps with a different substance, such as alcohol, the blue color vanishes.

From a technical standpoint, the phenomenon referred to as "changes the index of refraction" can be explained in simpler terms. Essentially, it means that blue light no longer bends in the correct manner. This can be observed when the microscopic light filter is damaged, but only until the alcohol evaporates and the color returns. Interestingly, despite living in the rainforest, these butterflies do not lose their color when they get wet. This is because their wing scales are made of a naturally water-resistant material. Now, let's consider a blue jay feather. When we look through it, the color completely disappears, as there is no blue pigment present. Instead, each feather bristle contains microscopic beads that scatter light, effectively canceling out everything except for blue light. Unlike the organized structures found in butterfly wings, the feather structures are more chaotic, resembling foam. As a result, the color appears more even from every direction as we move. What about peacock tail feathers? Once again, it is not the presence of pigment that determines the color, but rather the shape of the feather. The light reflecting structures in peacock feathers are more ordered, resembling crystals, which makes the color appear brighter from certain angles. Even the color seen in certain monkeys is not due to pigments, but rather the manipulation of light waves through structures in their skin. This holds true for blue eyes as well, where the color is determined by structures rather than pigments. Interestingly, outside of the ocean, the majority of living things that exhibit blue coloration do so through microscopic structures, each with its own unique characteristics. Among vertebrates, including birds, mammals, and reptiles, there is no known instance of blue pigment being produced on their bodies. In fact, the olivewings butterfly is the only known exception that has managed to produce a true blue pigment. Blue pigmentation in nature is incredibly rare, with olivewings being the only known example so far.

They have developed a blue pigment. They are quite rare and remain largely mysterious, with no other blue pigment known to us. This particular butterfly is truly unique. Why is the majority of nature's blue color created through structures rather than pigments like other colors? I have posed this question to multiple color study scientists, and their leading theory is this: at some distant point in history, birds and butterflies acquired the ability to perceive blue light. However, they had not yet developed a method to display that color on their bodies. If they could, it would be akin to transitioning from the early Beatles to Sgt. Pepper's Beatles. This newfound ability opened up new avenues for communication and survival. Producing a blue pigment from scratch would have necessitated the invention of new chemistry, which could not simply be added to their genetic makeup. It was much simpler for evolution to alter the shape of their bodies ever so slightly at the microscopic level and create blue using the principles of physics. They essentially solved a biological problem through engineering. What I find fascinating is that these colors have captivated inquisitive minds for centuries. After observing peacock feathers under one of the earliest microscopes in the 1600s, Robert Hooke remarked: "these colours are only fantastical ones." Even Isaac Newton recognized the uniqueness of these blues, and scientists have been studying them ever since. Not only for the scientific intrigue, but also for their sheer beauty.