From dragonflies to kingfishers: The science behind nature’s brilliant blues

Sitting by a river on a lazy summer day, the sky is a beautiful blue overhead. Lush greenery spread in the bank. The river is alive: miners, coots and water gulls make a fuss at the water’s edge.

Amongst this truly idyllic sight, the most striking are the bright blue hues: on the bodies of dragonflies, the feathers of mallard drakes, and the alluring feathers of any fast-moving kingfisher patrolling the river.

These creatures glow with the same distinctive blue color we see in peacock feathers and Amazon butterflies. It’s a jewel-like, metallic color that serves a special purpose: to help these creatures stand out against their comparatively dull environment.

But how do these plants and animals get their magical blue shimmer? A true blue pigment is actually relatively rare in nature, so plants and animals do tricks with light to produce this glowing effect.

complex molecules

In the natural world, we come across blue pigments less often than red, green or black pigments, because the molecules that reflect blue light are inherently more complex.

To produce a particular colour, molecules must absorb all the light they do not reflect. For blue pigments this means absorbing red light, which has less energy than blue light. But low-energy light is harder to absorb, so any molecule that reflects blue has to work harder to absorb red light.

The molecules that accommodate this process are large and complex, making them more resource-heavy for organisms to produce. So they are less likely to rise and persist through the long slog of evolution – they are often too expensive for organisms to sustain the survival of the fittest.

Many plants and animals that are blue have evolved this way for an important reason—perhaps to entice a particular pollinator, to attract a mate, or to warn a predator. For example, cornflowers are blue to attract insect pollinators, and use a complex arrangement of molecules to customize the molecule that makes a rose red so that it reflects blue light.

Read more: The secret of the blue flower: the existence of nature’s rare color from the eyes of the bee

a trick of mother nature

Rather than develop complex molecules that absorb red light, nature has devised another trick that produces blue – the process we have to thank for the iridescent blues that produce much of the blueness of the living world. constitute.

The shimmering blue organic material is composed of the same components as the back of any beetle, bird feathers or plant fruit (mostly the biomolecules chitin, keratin and cellulose, respectively). But these materials are essentially transparent. It is the structure of their surfaces that makes them appear blue.

Instead of smooth and continuous materials, such surfaces are structured with layers and ridges – or small spheres. These patterns create new surfaces that interact differently with the light falling on them.

These repeating patterns are so small that a wavelength of blue light, which is just 450 nanometers wide, spans the two pattern elements. It is this match between the subtle material patterning and the width of the wavelength of light that is important in deciding which colors of the spectrum are reflected back to the naked eye.

Nature’s subtle patterning has been honed by evolution to be perfectly in sync with blue light. Even though only a small portion of the blue light is reflected, with the rest passing through the transparent material, the additive effect is so strong that only a few repetitions of the pattern reflect the maximum amount of blue light – compared to two or three pigments. Times stronger reflection The remaining colors in white light are erased by the black pigment that lies beneath the surface.

This amazing effect is found in every shimmering material. It is also present in beetles, seaweed, fruit, magpie, begonia and even in the luster of bullseye flowers.

Read more: Bright Skies Named Color of the Year – Here’s Why There’s So Much More in the Sky Than Blue

While this spectacular effect can be produced in any color – by altering the spacing of the pattern elements – it is remarkably prevalent in blue.

The production of these apparently complex surfaces is actually easier than producing natural pigment molecules that can absorb red light. It’s so effective, in fact, that the resulting brilliant, shimmering blue reflects off hundreds of different surfaces across the natural world.