One of my favorite activities to do with school groups is a color scavenger hike. I will take students to a patch of prairie, hand them a paint sample card, and ask them to find something in nature that matches their color. After a few seconds, students with green and brown cards start exclaiming “I found it! I found it!” Students with blue cards, however, often struggle to find something blue beside the sky. There is a reason for that.
Blue is rare in nature. While we are blessed with bluebells, blue asters, and blue flag irises, yellow and white wildflowers are still far more common than their blue counterparts. Blue animals are even rarer. We have some local animals who bear that striking shade- bluebirds, blue jays, and blue-spotted salamanders- but they are few and far between. Why is blue so rare in nature, though?
Let’s start with plants. Since elementary school, we have been taught that plants need sunlight to survive. Sunlight, for our purposes, is a stream of energy-packed particles called photons. When these photons hit a chloroplast, they kick-start a chain reaction of chemical processes that help plants make sugar, its food. Our sun emits photons that vibrate at different frequencies which we see as different colors. Photons that vibrate at a low frequency occur to us as red light and are the most abundant in our atmosphere. Blue photons are less common but vibrate at a higher frequency, which translates to more energy for the plant (“Energy of Photons in Photosynthesis”). Plant pigments have evolved to absorb red photons because of their quantity and blue photons because of their quantity (“Sunlight and Photosynthesis”). “Low quality” green photons bounce off of plants and back to us, which is why we see most plants as green.
Some plants have vibrant blue flowers to attract pollinators, but we can’t attribute that shade to blue pigment. Many plants contain a pigment called anthocyanin, which can appear red, purple, black, or blue depending on pH. A careful mix of natural light, pH, and the chemical composition of anthocyanin can make flowers appear blue to us. Even still, there is no plant pigment that strictly makes the color blue (David Lee, “Nature’s Palette..”).
As far as we know, only one animal has cracked the code on making blue pigment. Obrina olivewings boast a brilliant blue spot on their wing that is the result of true blue pigments (Priscilla Simmons, “How Nature…”). All other blue animals, including bluebirds and blue jays, lack blue pigments. The chemistry of their pigments should make these animals appear anything but blue to us, but that isn’t the case. This is due to a phenomenon of physics that varies slightly from species to species (“Why is Blue…”).
Blue Morpho butterflies, for example, have microscopic structures in their scales that bend light in a way that bounces blue light back to our eyes. These structures are so ordered that they require certain angles of light to appear blue, which makes them appear to shimmer in different lights (“Wing Scales…”). Blue jays, on the other hand, have microscopic beads in the barbs of their feathers that serve a special purpose. They contain pockets of air that reflect blue light back to us thanks to something called the Tyndall Effect, which also makes the air in our atmosphere appear blue. These beads have a messy composition, which causes the blue of blue jay feathers to appear more uniform than the blue of the Blue Morpho butterfly (“What color is a bluejay?”). There are other examples of blue in the animal world, but the blue in each case can be attributed to the shape and physics of their bodies, not their chemical composition.
While blue can be found among non-living things, it is often hard to come by. For example, Cobalt is a rare element with a silvery-blue hue. Sapphires get their brilliant blue from a chemical compound called Sapphyrin, but they are relatively rare as well (“Chemistry Chat- Focusing on…”). Copper-derived compounds like such as azurite or malachite can be heated to 1,500 °F for several hours to achieve a blue color, but this process requires careful temperature maintenance. Ultramarine blue pigments are derived from a gemstone called lapis lazuli, which is found only in a mountain range in Afghanistan. Potash mixed with animal blood can make a pigment known as Prussian Blue (“A brief history of Blue”). In 2009, a team of researchers at Oregon State University accidentally mixed yttrium, indium and manganese oxide- an expensive combination of elements- to produce a blue pigment now called YInMn blue (“YInMn Blue”). With this said, it is rather difficult to find things that are truly, chemically blue in nature.
Scientists think that may be part of the reason that blue is so rare in animals. Many animals get their pigmentation from their diet, like the way Flamingos achieve their pink coloration from carotenoid pigments in the shrimp that they eat (“Why are Flamingos…”). The chemicals that make up red, orange, yellow, and brown pigments are common in nature and easily accessible in food sources, so they are also common among animals. Blue chemicals are hard to find, so animals have evolved not to depend on blue pigments to make them blue. Instead of achieving blue through chemical means, our animal friends have evolved to achieve it through physics by manipulating light itself before our very eyes (“Why is Blue…”) .
I hope that you are able to look upon the bluebells, bluebirds, and blue jays of springs with newfound appreciation. If you learned something from this article, please share it with a friend so we can spread the word about the amazing nature around us!