Butterflies are renowned for their dazzling color displays, which can seem to shimmer and shift as they flutter from flower to flower in search of nectar.

The vivid hues of their wings are so striking that pilots flying above the rainforest can spot the bright blues of the morpho butterfly from as far as half a mile away.

These brilliant colors serve multiple purposes: camouflage, mate attraction, and warning signals.

But what gives butterfly wings such vivid, ever-changing colors? Butterfly colors arise from two primary sources: pigmented color and structural color. Pigmented color comes from chemical compounds that absorb certain wavelengths of light while reflecting others. For example, the green of plants comes from chlorophyll, which absorbs blue and red light, reflecting the green that our eyes see. Many butterflies get their shades of brown and yellow from melanin, the same pigment that gives human skin its tan or freckles.

The more fascinating source of color is structural color, which explains the intense and shifting hues on a butterfly’s wings. This iridescence happens when light interacts with the transparent, multilayered surface of the wings. As light reflects and refracts multiple times through these layers, the colors intensify and appear to change depending on the angle of the viewer.

This effect is not unique to butterflies—think of the shimmer of a peacock’s feathers or the iridescent glow of mother-of-pearl—but it is most pronounced in butterflies, making their wings one of nature's most captivating spectacles.

Iridescence in Nature: How Butterfly Wings Shine

Iridescence is a fascinating optical effect that amplifies the colors of a butterfly's wings, creating intense, shimmering hues. To understand how this works, it’s helpful to remember that light behaves like a wave, with specific wavelengths (the distance between two identical points) and phases (the position of light's crests and troughs). When two light waves are in the same phase, their crests and troughs align when overlaid.

You’ve probably encountered iridescence before, even if you didn’t realize it. Think back to childhood moments with soap bubbles—whether you blew them with a wand or played in a bubble-filled bathtub. When light hits a soap bubble, it passes through the top layer, reflecting some light while the rest travels through to the bottom layer. There, more light is reflected. If the time it takes for the second reflection to reach the first causes the waves to line up in phase.

In butterflies, this constructive interference is what makes their iridescent colors so striking. The intricate structure of their wings causes light to reflect in such a way that the colors intensify. This creates a vivid, shifting display that is far more powerful than the static hues created by ordinary pigments.

Iridescence in Butterfly Wings

When light strikes a butterfly's wings, it passes through multiple layers of microscopic scales, reflecting several times before reaching the observer. This series of reflections is what creates the intense, shimmering colors seen in many butterfly species.

The principle behind the iridescence in butterfly wings is similar to that of soap bubbles. However, butterfly wings amplify this effect because they have numerous layers for light to pass through. These layers create more opportunities for light waves to interact, reflecting and magnifying each other.

Butterfly wings are covered with thousands of tiny scales, typically arranged in two or three layers—hence the name Lepidoptera, which means >scaled wings in Greek. Each scale contains multiple layers separated by air, and this layering is key to creating the striking colors. Instead of just a simple reflection like a soap bubble, butterfly wings feature multiple instances of constructive interference, where light waves align and intensify, producing vibrant colors.

The combination of structural and pigmented colors on butterfly wings can create unique effects. For instance, if a butterfly has yellow pigment beneath a layer that creates blue iridescence, you may see a greenish hue, formed by the merging of both colors. Depending on the angle of light and the butterfly's movement, you might see varying shades of blue, yellow, or green as the light shifts.

From camouflage to communication, the stunning, complex wings of butterflies like painted ladies and red-spotted purples owe much of their beauty to the phenomenon of iridescence and structural color!