The Spectrum of Wings: Exploring Butterfly Coloration

By Umang Rajpurohit

Butterflies are among the most eye-catching organisms, known for their wide spectrum of colors. But what makes them so eye-catching ? Their colors. To understand how these colors come to be, let's start our journey for understanding the anatomy of butterfly wings and the science behind their vibrant hues.


Now a question may arise: What led to so many colors in this species alone and not others. This question struck me when on one pleasant morning i was looking at Common Jay butterfly near my apartment, this butterfly had all the striking colors which will grab the attention any normal person. That very morning i started reading about what could be the possible reason behind this. Also, not every creature is blessed as butterflies.



In this exploration of butterflies we will delve deep into their wing anatomy, the variety of colors, pigment science as well as the gene's role in butterfly wings and their colors. Let's first understand the most basic component of this scaly insect, their wings, which got them their name Lepidotera, which means scaly wings.


Not to be mistaken, this term is also referred to moths which comes under the same order. To be precise, Butterflies comes under the suborder Rhopalocera and the moths belongs to Heterocera. Lepidotera is a broader term, just like how we use the word dogs for a dog and not Canidae, because Canidae involves all the members of dog family.

Wing anatomy

First and foremost, it's all biology and physics. Butterfly wings are made up of Chitin, emerging from their exoskeleton. Chitin is a fibrous substance made up of polysaccharides(esentially it is a form of Carbohydrates composed of the molecules of sugar which are bonded together). They have four wings in total, two forewings(front wings) and two hindwings(back wings).


An important thing to keep in mind is that if they lose their hindwings they can still fly(though they may struggle with speed and control), but without forewings they can't function at all.

Science of colors

Collage: Showing butterflies of different families having variety of colors

According to the laws of physics, color is perceived based on light interaction, which is also true for butterflies. The three major factors for such a wide variety of colors are:


(i) Light
(ii) Pigment present in their wings
(iii) Genetics

Light

The wings of butterflies are covered with thousands of microscopic scales, which is further split into more layers. Let's understand the concept of light that makes so many colors visible to us in the butterfly wings: constructive interference. It is when the two waves or more waves overlap each other and form a wave which have much more amplitude then two collided waves, it is said to be a constructive interference.


So, when the light passes through a wing, which have thousands of microscopic scales and hence each scale(each minute scale) having the chances of creating a new color or new shade of color and hence so many colors are visible to us.


If it's still unclear, imagine a palette of colours with more than a thousand colors. If you mix all of them, a new color or a wide spectrum of color will emerge and that's how butterflies get their wide range of colors.

Pigment

There are four major pigments which works in the factory of a butterfly wing, which are melanin, ommachrome, pterin and papilliochrome.

Figure: Showing the different pigments with their respective butterflies species

a). Melanin

Also present in human body, melanin is a pigment which makes the wings look grey, black or brown.
So we can simply say that butterflies species like the Common Mormon(which is around 80-90% black in color) have more melanin present in their body than species like Crimson tip or any non-black colored butterfly.


Not only black but also grey and brown have melanin content. Example would be Plains cupid, Grey hairstreak and common evening brown butterfly.


In a paper on Himalayan butterflies, Krushnamegh kunte and Shubham Gautam has mentioned that elevation has been a factor in wing melanisation in the Cabbage white butterfly(Pieris Canidia) with higher melanisation observed at increasing elevation in Pieris canidia.


b). Ommachrome

Ommachrome is a pigment which creates red, orange and tan color in butterflies wings.
Butterflies species like Red flash, Painted lady, Yellow pansy, Tawny coster, Red pierrot, Indian Jezebel. All of these species have a range of ommachrome present in their wings.


c). Papilliochrome

As the name suggests, Papilliochrome as the papillio family butterfly(swallowtails) have this pigment in their wings.

Papilliochrome consists of two main colours of yellow and creme.


d). Pterin and cartenoid

Common crow, chocolate pansy, tawny coster, yellow pansy, leopard butterfly.


Note: As mentioned for all the pigment their are various ranges of colours but the mentioned colors are the dominant one for each pigment.

Infographics: Showing the different pigment(all the pigments are colored on the color of pigment) and butterflies associated with it.



(iii). Genetics


There are many genes in an insect's body but we will focus on the most dominant ones:


(a). Optix

So where Optix is active and playing it's role ommachrome and melanin will be produced including the blue color(which is a structural color).


Structural colors are pigment-independent; they result from light interacting with the butterfly's wing and how the color is perceived.


(b). Cortex

Cortex on the other hand is a bit trickier one(biology have it's job to perform and hence there are various factors which result in a certain color in a species), in some species it acts a black dominant color or yellow and white.


(c) Aristaless

Basically the white and yellow colored dominant gene. We can observe butterflies species like bushrown and Painted lady have Aristaless working on it's wings.


(d). wntA

wntA acts like a designer, placing the colors in their correct positions. such as the spots and stripes which are produced by Optix and Cortex. So all the patterns you observe in this mighty creature is done by wntA. You can think of any pattern, shape of spots in butterfly like Common Mormon have white patches in the end of the hind wings, while the Lemon Pansy have eyespots in between their wings these are all wntA's role.

Figure: Genetic dominance of colors in butterflies


End note-
I hope this whole text on butterflies has been helpful for you and that from now on,whenever you look at other species of butterflies or any other insect you will be curious about their colors and anatomy.


All the information shared in this blog is inspired by some world class papers and also some parts of this was my own experiences as a butterfly enthusiast. So the references to some papers are given below for your convenience


Happy reading!!

References-


1. Link to Krushnamegh kunte and Shubham Gautam's Himalaya paper


2. Butterfly wing scales: Pigmentation and structural properties


3. Ommochrome Wing Pigments in the Monarch Butterfly Danaus plexippus (Lepidoptera: Nymphalidae)


4. The evolution of structural colour in butterflies

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