Earth Matters: It’s not easy being blue in nature

  • A bluejay in Brooklyn’s Prospect Park. Microscopic air pockets that scatter and reflect blue light, and melanin granules that absorb all other colors, result in a strong true blue reflected back to our eyes. Rhododendrites/via Wikimedia

  • Layers of nanostructures on the surface of the blue morpho butterfly’s wings work to spread light waves, which then interfere with each other, absorbing some wavelengths while reflecting blue. air pockets that scatter and reflect blue light, and melanin granules that absorb all other colors, result in a strong true blue reflected back to our eyes. Didier Descouens/via Wikimedia

For the Recorder
Published: 11/29/2021 2:44:17 PM

I’m a really big fan of color. When people ask me what my favorite color is, I explain, “Well, I have different categories of favorite colors.”

The kids in my nature programs nod in understanding. You see, favorite things are important to kids, and you have to be specific when you’re talking about them. For example, my favorite color in the nature category? Blue.

In my programs I like to do an activity called Colors of Nature, in which I hand participants an empty egg carton and challenge them to fill it with samples from nature that represent a dozen unique colors. We always notice that blue is the hardest color to find. By the end of the activity, almost no one has something blue in their carton.

There might be a bluish gray piece of stone or a purplish-blue flower petal, but almost nothing is really, truly, just blue. Why?

Well, it turns out that even the few things that do appear as really, truly just blue in nature — morning glories, blue jay feathers, cornflowers, to name a few — aren’t blue for the same reasons as other nature colors. That is, unlike the other colors in the visible light spectrum, the color blue in nature is usually not due to a specific blue pigment.

Leaves are green because the chlorophyll within in them has green pigment, absorbing all visible light wavelengths except green, reflecting the green wavelengths back to our eyes. In autumn, leaves turn red because of the presence of anthocyanins (reddish pigments), which absorb all wavelengths but red, reflecting the red back to our eyes.

Most of the color we see all day long is due to this mechanism of objects absorbing some wavelengths and reflecting others back. But blue pigments in nature are extremely rare. So if nature wants to be blue, it has to get creative.

One way nature gets creative with making blue is by modifying anthocyanins, the pigments responsible for red. This is the case with most blue flowers. The blue petals of chicory, bluebells and bachelor’s button owe their blueness to a special mix of altered pH, other pigments and adding on molecules and ions to the anthocyanin compound, which shifts its reddish color to blue. Horticulturalists continue to manipulate these compounds in the lab, trying to achieve that coveted blue that so few flowers naturally have.

Another way to make blue without pigment is structurally. In the case of the blue morpho butterfly, layers of nanostructures on the surface of the butterflies’ wings work to spread light waves. According to the Biomimicry Institute, the “light waves then interfere with each other so that certain color wavelengths cancel out (destructive interference) while others are intensified and reflected (constructive interference).” So blue is what we see.

Blue jay and bluebird feathers achieve the same effect of electric blue slightly differently. With a combination of microscopic air pockets that scatter and reflect blue light, and melanin granules that absorb all other colors, a strong true blue is reflected back to our eyes.

Fascinatingly, structural colors will not appear the same from different angles the way pigmented colors will. Once I was certain I saw a small gray owl hopping in a tree on a cloudy day, until it revealed itself to be a blue jay that appeared gray! I watched long enough and did see a flash of blue feathers. Later I learned this is normal, since the blue in their feathers is due, essentially, to an illusion.

Even this physical manipulation of structural colors is rare, though. The creation of complicated nanostructures and altered molecules requires a huge amount of energy. Why would a plant or animal go through all that effort?

Well, blue is dazzling. It is the most popular favorite color of people throughout the world, and perhaps it is its very rareness that makes it so appealing. In the world of flowers, blue is highly visible to bees and other pollinators. The unusualness of a blue flower may catch the eye of pollinators in a way that other colors do not, perhaps making it more attractive and increasing the plant’s likelihood of pollination.

At the end of my Colors of Nature activity, I ask the children why they think they can’t find blue. Usually no one knows. But I don’t leave them hanging. I always end the activity by taking them to a patch of jewelweed, also known as touch-me-not flowers.

Many people know jewelweed as the cool plant with the exploding seed pods. Well, it’s also my favorite example of the color blue in a native plant. To find that blue, I ask every kid to gently explode a seed pod in their fingers, catch a seed in their hand, and gently scrape away the thin green or black casing with their fingernail. The ripened seeds underneath are a beautiful robin’s egg blue — the perfect finishing touch to their rainbow collection.

So while we may need to look a little harder to find blue in nature, there’s a lot to appreciate in the fact that it exists at all.

Katie Koerten is an environmental educator at the Hitchcock Center for the Environment.




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