Centaurea cyanus (Photo by: Nik Taylor / Education Images / Universal Images Group via .)
If we stop to think about it, there are not many blue animals. And even fewer plants, some flowers but blue fruits we may not even think of any. And it’s for a good reason.
But to understand the part of biology where the color blue is very rare, you have to go above in the physical part. And the first thing is to understand that the colors of the light depend on the wave that produces it. If the wave has more or less energy, it is perceived as one color or another.
When white light illuminates an object, it absorbs some of the waves and reflects others. And it is these that our eyes perceive are reflected. Therefore, the color that we see in objects is the one that the object does not absorb.
And why is this important? Because organisms have pigments that absorb part of the light, and that gives them that color. And since each wave has an amount of energy, there are colors that are easier, from a biochemical point of view, to absorb than others.
A blue flower is actually a flower that mainly absorbs the color red. That it is a color with low energy, and therefore the molecules that absorb it are cheaper, from a biological point of view, to generate.
And like everything else in biology, this energy expenditure is important when it comes to understanding why things happen. Generating blue flowers involves a high cost, therefore the benefit needs to be very high for the plant to be worth doing.. And there is the reason that there are hardly any blue flowers.
The blue color is very striking to certain pollinators, and that is why there are some blue flowers. But For the vast majority of plant species, the cost of generating blue pigments does not outweigh the benefit.
With animals the case is different. Because animals either obtain their pigments from plants, or they use other types of strategies to generate color. Because in animals the blue color is rare, but more common than in plants.
There are blue insects. Dragonflies, for example. But they are not very common. And among vertebrates it is even rarer. It can be seen in the plumage of certain birds, which get that blue color thanks to microstructures in the feathers that scatter light in a certain way, but not many. And in mammals, the examples are few and difficult to find: some cetaceans – dolphins and whales – have bluish tones, certain primates too …
And here is an also important detail: not all animals see the same colors. Humans have three types of color receptors, while birds have four. So the blue that the birds see does not have to be the blue that we see.
So we return to the idea of how much it costs to be blue, and what benefit does it bring. For an animal, being blue is still expensive, and it doesn’t seem like it has many benefits. Maybe even less, but we cannot know it since not all animals see colors the same.
That is the color blue is “expensive” to produce, and its benefits meager. That is why there are hardly any blue organisms.
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