Have you ever noticed that there aren’t many blue animals? You won’t find blue tigers, blue bats, or blue dogs. Even blue whales aren’t truly blue. While animals come in all sorts of colors, blue is one of the rarest. But when we do see a blue animal, it’s often breathtaking. Nature seems to go all out when it comes to blue.
To understand why blue is so rare, we need to look at evolution, chemistry, and physics. But first, let’s explore why animals have colors at all. Butterflies are a great example because they have some of the most vibrant and complex patterns.
Butterflies evolved from moths to be active during the day, which allows them to use light to communicate. Their colorful wings send messages like “I’m toxic” or “This is my territory.” But not all colors are created the same way.
If you look closely at a butterfly wing, you’ll see tiny scales. Colors like orange, red, yellow, and brown come from pigments—molecules that absorb all colors except the one we see. Black scales absorb all colors. Animals, including butterflies, birds, and humans, get these pigments from their diet. For example, flamingos turn pink because of the food they eat.
Blue is different. There’s no blue pigment in most animals. Instead, the blue color comes from the structure of the wing or feather. For instance, if you zoom in on a blue butterfly wing, you’ll see tiny ridges shaped like Christmas trees. These structures reflect light in a way that makes the wings appear blue.
When light hits these structures, some of it bounces off the top, while some passes through and reflects off the bottom. For most colors, the light waves cancel each other out. But blue light waves align perfectly, making the blue color visible to our eyes.
These butterflies live in rainforests, so you might think they’d lose their color when wet. However, their wing scales are water-resistant. Similarly, blue jay feathers have microscopic beads that scatter light, canceling out all colors except blue.
Peacock feathers also get their color from structure, not pigment. The light-reflecting structures are more ordered, making them shine brightly from certain angles. Even some primates and human blue eyes get their color from structures, not pigments.
Outside the ocean, almost all blue animals use structures to create their color. No vertebrate—no bird, mammal, or reptile—has been found to produce a blue pigment. There’s only one known butterfly, the olivewing, that has a true blue pigment, and it’s quite rare.
Why does nature use structures instead of pigments for blue? Scientists believe that at some point, animals evolved to see blue light, but they couldn’t produce it. Creating blue pigment would have required new chemistry, which was difficult. Instead, evolution found a way to create blue using physics by changing the microscopic structures of their bodies.
These colors have fascinated people for centuries. Even in the 1600s, scientists like Robert Hooke and Isaac Newton were intrigued by the unusual blues in nature. Today, scientists continue to study these colors, not only because they’re interesting but also because they’re beautiful.
Thanks for exploring the world of blue with us, and keep being curious!
Research and create a presentation on how different colors are produced in animals. Focus on the difference between pigment-based colors and structural colors. Share your findings with the class, highlighting examples from the article, such as butterflies and peacocks.
Using materials like paper, cardboard, and cellophane, construct a simple model that demonstrates how structural colors work. Try to mimic the microscopic structures found in blue butterfly wings. Present your model and explain how it reflects light to create the color blue.
Design and draw your own blue animal using art supplies. Use your imagination to create an animal that could exist in nature. Think about how its blue color might be used for communication or camouflage. Write a short description of your animal and its habitat.
Go on a nature walk or visit a local park to observe and document any blue animals or plants you find. Take notes or photos and research how these organisms achieve their blue color. Share your observations with the class and discuss the rarity of blue in nature.
Participate in a class debate on why blue pigments are rare in animals. Use evidence from the article to support your arguments. Discuss the evolutionary challenges and advantages of structural colors versus pigments. Reflect on how this understanding can influence future scientific research.
Here’s a sanitized version of the YouTube transcript:
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There are no blue tigers, blue bats, blue squirrels, or blue dogs. Even blue whales aren’t that blue. Animals come in pretty much every color, but blue seems to be the rarest. What’s fascinating, though, is that when we do find a blue animal, they’re stunning. Nature doesn’t do things halfway with blue.
To understand why this is, we’re going to explore evolution, chemistry, and some interesting physics. But first, we need to understand why animals have any color at all, and to do that, we need to look at some butterflies because butterflies are amazing.
This is Bob Robbins, curator of Lepidoptera at the National Museum of Natural History in Washington D.C. Butterflies are indeed remarkable. They evolved from moths to be active during the day, which gives them an advantage: they can use light to communicate. Out of all insects, butterflies display the brightest and most intricate patterns, and there’s a good reason for that. The colors in butterfly wings convey messages, such as “I’m toxic” or “I’m a male and this is my territory.” However, not all butterfly colors are created equal.
If we zoom in on a butterfly wing, we see that the colors come from tiny scales. This is actually how moths and butterflies get their scientific name. Oranges, reds, yellows, and browns come from pigments—organic molecules that absorb every color except what we see. Black scales absorb all colors. Animals, from butterflies to birds to humans, don’t create these pigments from scratch; they are derived from ingredients in our diet. For example, flamingos are born gray but turn pink due to carotenoids in the crustaceans they eat. So when it comes to these colors, you are what you eat.
But blue is different. If you move the camera, you can see that the color changes. This is because there’s no blue pigment in these butterflies. The blue color comes from the structure of the wing scale itself. When we zoom in on a blue wing scale, we see tiny ridges. If we slice across the scale and look closer, we see those ridges are shaped like tiny Christmas trees. The arrangement of the branches gives Morpho wings their blue color. When light enters, some bounces off the top surface, while some light passes into the layer and reflects off the bottom surface. For most colors of light, waves reflecting from the top and bottom will be out of phase, canceling each other out. However, blue light has just the right wavelength: the reflected light waves are in sync, allowing that color to reach our eyes.
There’s even a pigment at the base that absorbs stray red and green light to enhance the purity of the blue. This is how we get that beautiful iridescent blue. The microscopic structure of the wing itself plays a crucial role. If we fill those tiny gaps with something other than air, like alcohol, the blue disappears. This changes the way light is bent, breaking the microscopic light filter. But when the alcohol evaporates, the color returns.
These butterflies live in the rainforest, so you might think they’d lose their color when wet. However, their wing scales are made of a material that’s naturally water-resistant. What about a blue jay feather? If we look through it, the color completely disappears. Each feather bristle contains light-scattering microscopic beads, arranged so that everything but blue light is canceled out. Unlike the highly ordered structures in butterfly wings, feather structures are messier, resulting in a more even color from every direction.
Peacock tail feathers also derive their color from structure, not pigment. The light-reflecting structures here are more ordered, like a crystal, making them brighter from certain angles. Even in some primates, the color is created by the addition and subtraction of light waves due to structures in the skin, not pigments. Yes, even human blue eyes are colored by structures, not pigments.
Outside of the ocean, almost all blue living things create their colors with microscopic structures, and each one is a little different. No vertebrate—no bird, mammal, or reptile—has been found to produce a blue pigment. In fact, there’s only one known butterfly that has developed a true blue pigment: the olivewings. They’re quite rare, and we don’t know much about them, but they are a special case.
Why is almost all of nature’s blue made from structures instead of pigments? I’ve asked several scientists who study color, and here’s their best theory: At some point in the past, birds and butterflies evolved the ability to see blue light, but they hadn’t yet developed a way to produce that color on their bodies. If they could, it would open up new opportunities for communication and survival. Creating blue pigment would have required new chemistry, which couldn’t simply be added to their genes. It was much easier for evolution to change the shape of their bodies at a microscopic level to create blue using physics instead. They solved a biological problem with engineering.
What I love about this is that these colors have fascinated curious minds for centuries. After examining peacock feathers through one of the first microscopes in the 1600s, Robert Hooke noted, “these colors are only fantastical ones.” Even Isaac Newton recognized something unusual about these blues, and scientists have been studying it ever since—not only because the science is intriguing, but also because it’s beautiful.
Thanks for watching, and stay curious!
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This version maintains the essence of the original transcript while removing any inappropriate or informal language.
Blue – A color that is often seen in nature, such as in the sky and ocean, and can be found in some biological organisms due to specific pigments or structures. – The blue color of a butterfly’s wings is often due to microscopic structures that reflect light.
Animals – Living organisms that can move and consume organic material for energy, and are classified into various groups based on their characteristics. – Animals like birds and mammals have evolved different adaptations to survive in their environments.
Colors – Different wavelengths of light that are perceived by our eyes, often used by organisms for camouflage, mating, or warning signals. – The bright colors of a poison dart frog warn predators that it is toxic.
Light – A form of energy that travels in waves and can be seen by the human eye, essential for processes like photosynthesis in plants. – Plants use light from the sun to convert carbon dioxide and water into glucose and oxygen.
Structures – Arrangements or organizations of parts in an organism or object, which can serve specific functions. – The structures of a bird’s wings are adapted for flight.
Pigments – Substances that give color to living organisms, often used for protection, attraction, or photosynthesis. – Chlorophyll is the green pigment in plants that helps them absorb light for photosynthesis.
Evolution – The process by which different kinds of living organisms develop and diversify from earlier forms over generations. – The evolution of giraffes’ long necks is thought to be an adaptation for reaching high leaves.
Chemistry – The study of substances and how they interact, combine, and change, which is fundamental to understanding biological processes. – The chemistry of enzymes allows them to speed up reactions in the body.
Butterflies – Insects with large, often brightly colored wings, known for their metamorphosis from caterpillars. – Butterflies undergo a complete transformation during their life cycle, starting as caterpillars and becoming winged adults.
Physics – The science of matter and energy and their interactions, which helps explain natural phenomena like gravity and motion. – Physics helps us understand how birds can fly by studying the forces of lift and gravity.
