In 1835, Charles Darwin, on his historic voyage, visited Chile, where he met a German naturalist called Renous. Renous had recently been jailed for heresy (of all things). He was raising caterpillars to study butterflies, but the good people of San Fernando did not know that caterpillars turn into butterflies. Surely, turning one animal into another was witchcraft!
We now know what a caterpillar is, but even so, more than 180 years later, we still know little about butterflies. Each year, Monarch butterflies make a voyage far more impressive than Darwin’s, flying over 7500 km (4700 miles) from the eastern U.S. to Mexico and back – that’s like a human being circling the globe 2325 times!  Their migration routes were a total mystery till 1975! And it took another 40 years to discover how they find directions.
Amazingly, Monarchs time-compensate the sun’s location to navigate correctly (meaning that they know that the sun is in the east in the morning, and in the west in the evening). But how do they navigate when the sky is overcast? The answer: They can see guiding lines in the sky!
The eye of the beholder
Like many organisms, butterflies carry proteins called cryptocromes, which are sensitive to blue light. It’s suggestd that under blue light, cryptocromes lose electrons to form a pair of radicals. Radicals are sensitive to magnetic fields, so the correlation of their spins changes with their location. And since cryptocromes affect neurons in the retina, butterflies can actually see the Earth’s magnetic field.
With this special power (called ‘magnetoception’), butterflies can see dark parabolic arcs gently arcing toward the North across the sky. To a butterfly, the sky is not plain blue – it’s striped!
What makes a butterfly’s vision even cooler is that they can see all around and above them at once – a 360° panorama. Butterflies have compound eyes – eyes comprised of thousands of ‘mini-eyes’ called ommatidia (singular: ommatidium. Let’s just call them ‘eyelets’). Each eyelet captures a small portion of the overall picture, like pixels in a photograph. Also, butterflies have different kinds of eyelets. For instance, the eyes of a swallowtail butterfly look black, but hold a microscope over them and here’s what you’ll see. Trippy.
Image credit: Invertebrate Brain Platform
A typical swallowtail species has around 12,000 eyelets in each eye. The eyelets have distinct colors because they’re coated with different pigments – red, fluorescent pink and yellow in this case – sort of like wearing shades. The red eyelet looks red because it absorbs all wavelengths except for red, and the yellow absorbs all wavelengths except for yellow, and so on. So these eyelets let in different mixes of colors.
The cells in each eyelet can absorb two colors from this filtered light. Theoretically, butterflies with 3 eyelet colors can detect 3×2 = 6 colors. Most butterflies actually detect four – they’re tetrachromatic, because can do just fine by seeing 4 colors, and natural selection doesn’t waste resources on useless abilities. Some, like the Chinese Yellow Swallowtail, see colors made of five wavelengths – red, green, blue, violet and ultraviolet. By contrast, we humans have trichromatic vision – all colors we see are a mix of 3 wavelengths – red, green and blue. And since butterflies can see light of 4 or 5 wavelengths, they can see colors we cannot imagine. They don’t simply see things as gaudier or flashier – they actually see a lot of things that we can’t.
A huge part of this is seeing ultraviolet (UV) light. Like a lot of fluids, nectar lights up under UV light. Plants advertise their nectar by using UV-sensitive pigments on their flowers to butterflies, bees, hummingbirds and anyone else who can see UV light.
We might grow lilies for their beautiful, glossy petals, but under UV light, it’s plainly obvious where they store nectar. And as a butterfly is drawn to the dark center, it rubs against the lily’s anthers and gets pollen on its body, which it then (unintentionally) rubs into the next lily it visits and thus fertilizes it. Is that awesome, or what.
Even homely-looking flowers are downright gaudy to anyone who can see UV in addition to the usual colors.
Some plants have evolved to bear flowers that have helpful lines to help visitors land on them, like those rows of lights alongside runways. These are called nectar guides. You might think that a buttercup is plain, all-yellow and small, but to animals that see UV, this flower has a big, distinctive center that screams “NECTAR HERE!!!” And to compensate for their small size, they have very distinctive nectar guides.
At this point, you might be cursing your luck for being born human. It’s impossible to imagine life without colors – we wear patterned clothing, obey traffic lights, and the last I checked, L’Oreal carries 51 shades of nail color, 54 shades of lip gloss and 163 shades of lipstick, because 10, 20 or even 40 clearly aren’t enough. And here’s a little insect that can see stripes on a buttercup. You see, (no pun intended) human eyes are optimized for detail. With your two eyes, you can spot an ant in your soup or scratches on your newly waxed car. But for a little creature with 12,000 eyelets and a tiny brain, the hardware and software specs aren’t right for processing all that detail. It needs to see where the nectar is, where its predators are, and it needs to see all around at once. And butterflies are very good at that. Every evolutionary solution has limitations, but if it’s good enough to keep the creature alive, then that’s that. Where we see the world in high definition, a butterfly sees an Impressionistic painting.
And that’s just fine, you know. Take an aster (Michaelmas daisy), for example. You and I might see its beautiful flowers, but its center is a mishmash of yellow and orange to us. On the other hand, a butterfly, despite the blur, can see exactly where the nectar is within all fuzz at the center. Once it spots the flower from a distance (thanks to its petals), the petals would only distract it from getting to the good stuff. While our eyesight lets us admire the flower, the butterfly’s helps it get the job done.
Under visible light (visible to us), a hawkweed is a glorious splash of orange, but to a swallowtail, which can see visible and UV light (with extra sensitivity for violet), the flower shows details that we can’t see. The blue and UV sensitivity actually help the butterfly focus exactly where it needs to focus.
A chrysanthemum, also very attractive, has a more complicated structure. Later in this post, I’ll explain why.
A daisy’s center looks plain yellow to us, but a butterfly can clearly see that the nectar is at the center and not at the outer rim. These abilities work so well that even the few species that are red-green colorblind (meaning that green and red look like the same color to them) have no difficulty finding nectar in a flower.
Two to tango
As far as color vision goes, we are an aberration among mammals. Most mammals either see the world in black and white, or only one color faintly. On the other hand, we humans (and the other 6 species of ape, and Old World Monkeys) see the world in vivid color. Genetic studies indicate that a mutation that allowed a gene replication gave one of our evolutionary ancestors trichromatic vision, and this trait was retained through natural selection because of the advantages it offered, like finding better fruit, seeing threats from a longer distance and better judging the health of other individuals. We certainly no longer use color vision for just finding ripe fruit or spotting orange tigers in green foliage. We use colors for everything from managing traffic to choosing wallpaint that is “more teal than sky-blue” My point is that, whatever be the original evolutionary reasons for this ability, we use it for a lot more than mere survival.
So you might imagine that butterflies use their incredible eyesight for more than merely finding nectar. For one, just as our eyesight lets us guess the gender, age and health of another human being, butterflies can also identify someone’s gender and health by sight.
And that’s actually pretty incredible, because for many species of butterfly, males and females look almost alike. Here, for instance, is a species called the Clouded Yellow. Unlike birds and many mammals, whose males and females look quite different, it would be hard to guess the gender from a cursory glance.
Here’s another example:
Sure, the male and female look somewhat different here, but if an Eastern Tiger Swallowtail were 10 feet away, would you be able to guess the gender correctly? Then how do butterflies do it with their blurry vision?
The answer, again, is hidden in the world of ultraviolet. We all think of butterflies as gorgeous – even the plainer ones. But to eyes that can see in ultraviolet, they are truly dazzling!
I’ve used my graphics design software to simulate how different a butterfly looks, but it’s hard to do justice to the shimmering, glittering, glorious display of a butterfly as it moves its iridescent wings. Imagine if the white part you see here were actually liquid silver, shining with the splendor of a million tiny diamonds. Imagine, then, if the butterfly closed and opened its wings, like a lighthouse beaming out a signal far out to sea. And what if, instead of sitting contently on a flower, this miniature peacock took to the sky, hovering above you, his wings flickering like a twinkling constellation, a sun-lit chandelier just out of reach, a gentle rain of sparkling fireworks? Could you not be dazzled then, by this seemingly plain, humble specimen of insectile magnificence? Then how could a female of his own kind?
Butterflies the world over employ these invisible patterns on their bodies to dazzle, communicate, seduce, show off, terrify a predator, impress, confound or speak plainly. The language of butterflies is a complex orchestra of color, shimmer, codes of etiquette, and the quiet confidence of using beauty as their weapon and armor. Here’s another example: the male Japanese Emperor is known for the iridescent, dark blue gleam at the center of his wings, but to a female’s eyes, the understated blue is replaced by a splash of color, uninhibitedly brilliant, like a chest of amethysts and topazes exploding in slow motion. Females themselves are relatively plain under UV light, so it’s easy to see how a Japanese Emperor can identify the gender of another even from a distance.
How the Common Leopard got its spots
Like miniature, fluttering Birds of Paradise, butterflies use their aerial waltzes to seduce partners or warn off rivals. But why do butterflies have such a diverse range of patterns on their wings? Susan Paulsen studied the genes of two closely related species – the Common Buckeye (precis coenia) and the Mangrove Buckeye (precis evarete), which look quite distinct even though have similar colors and eye patterns.
Her study revealed two facts: First, that slight variations in genes can lead to distinctive patterns on wings – that’s why closely related species of butterflies can look so different. Second, that entirely different genetic variations can make very different species have patterns that look similar – for example, the Monarch of the Americas and the Common Tiger of South and Southeast Asia.
Some patterns evolved for reasons entirely different from what they are used for today. Researchers have studied the East African Squinting Bush-brown to see if its eye patterns, which it uses to frighten potential predators, are affected by sexual selection. The Squinting Bush-brown is a small and brown butterfly, but has eye patterns at the edges of its wings, which have UV-sensitive centers. They masked the eye patterns in various combinations, on either side of the wing. Their study showed that females prefer males who have bright UV-sensitive centers to their eye patterns. They don’t like those patterns to be too small or large – this is an evolutionary strategy called stabilizing selection. In evolutionary terms, although the eye patterns grew more prominent over generations due to sexual selection, they also (incidentally) acted as a handy defense against predators such as birds (birds are also sensitive to ultraviolet). And those who happened to have ‘eyes’ on their wings had a better chance of surviving predation and passing on those genes. And over generations, the patterns have come to closely resemble the eyes of larger animals, without the butterfly ever choosing this strategy. This also explains how poisonous butterflies gain their warning coloration, and how non-poisonous species can also end up imitating them.
So interestingly, butterflies do not even know what they really look like (and that’s all right. We humans have stripes that are invisible to us, so how someone looks is merely a point of view). Their gaudy patterns evolved through natural and sexual selection, over hundreds of generations. What makes nectar-rich flowers attractive to butterflies – UV vision and a sense of aesthetics – also makes it prefer partners with gaudier colors and dazzling courtship dances. And that, in turn, makes it more likely to mate and pass on these genes to offspring who have better chances of surviving and passing on these genes.
What a caterpillar calls the end of the world …
The Act of Metamorphosis – its drama, pause and climax – is nothing short of one of the all-time greatest hits on Nature’s Broadway. This is a strategy that has let butterflies thrive in almost every part of the world. Consider this – there are 5416 species of mammals – these include everything from tiny shrews, to giant whales in the oceans, to bats flitting in the sky and humans like us. The total number of known butterfly species is over 20,000 – add moths into the mix and we have 150,000 known species of butterflies and moths (Lepidoptera). Factor in the species we haven’t documented yet, and there may be 400,000 kinds of butterfly and moth in the world! They live everywhere, except for the Poles. And the reason for their runaway success is metamorphosis.
To us, metamorphosis seems like a 3-step process – a caterpillar turns into a pupa, and out comes a butterfly. It’s actually incredibly complex. A caterpillar’s story actually starts before it is even born. When butterflies mate, the eggs are not immediately fertilized. Instead, the female actually stores the spermatophore (sperm + nutritional packet) in little pouches called bursa (short for burlap sack? Heh). And when she wants to lay eggs, each egg gets a sperm and some nutrition just before it’s laid. This way, a female butterfly can actually control where she lays her eggs, and lay them a few at a time, spread over an area. As the eggs are undefended, this greatly improves their chances of surviving. She also lays them on the underside of a leaf, so that they aren’t seen by predators.
When the caterpillar is born, it commences eating at a frenzied pace, starting with the remains of its egg. There isn’t a lot of nutrition in a plant leaf, so it eats, and eats, and eats. Like all insects, its body is protected by a tough exoskeleton called a cuticle. Now as anyone who’s ever seen a caterpillar knows, it’s body is long and grooved, made of segments like a train. The cuticle on each segment is pretty tough, but on the grooves, it’s thinner to allow it to move. As the caterpillar feeds, it grows rapidly, but its cuticle can only stretch so much. So it sheds its cuticle, and sucks in air like a tiny balloon to stretch its new, soft cuticle before it hardens. Then it eats merrily till it fills out the bigger cuticle, and then sheds again.
So rather than having a three-stage life cycle, a butterfly has a multi-stage life – a caterpillar transforms into a bigger caterpillar, which turns into an even bigger caterpillar, and on and on, till its big enough, and stops producing something called the Juvenile Hormone, and that lets it turn into a pupa. And as we don’t choose puberty, the caterpillar doesn’t thoughtfully decide to metamorphose either. It just happens when it happens, and if the caterpillar is not big enough or healthy enough, well, tough luck for that little guy.
That’s why it’s super-important for a butterfly to lay her eggs on a plant that her babies can feed on. For an experiment, scientists divided some Monarch caterpillars into 3 groups – one was allowed to feed normally, the second was starved for 24 hours, and the third for 48 hours. They found that if the caterpillars starved even for a few hours, their wings had paler colors. For the control group that was starved for 48 hours, the wings were smaller by 2% and also paler. This means that if a caterpillar missed out on some of its meals, it can never make up for the loss. It cannot simply eat more, delay metamorphosis and bulk up. It’s amazing that the size and brilliance of a butterfly is decided by something as mundane as how many leaves it chewed on. A butterfly with smaller wings will not fly as far or as powerfully as a larger one – and the food that powers the size of its wings also gives them their shimmer. So when a female butterfly chooses a male with the brightest, shiniest wings, she isn’t being shallow – she knows, instinctively, exactly what she is doing.
… The Master calls ‘a butterfly’
A female butterfly typically measures up a male at ‘first glance’. Some are monogamous. Some have multiple partners. Some simply do not want a partner. Some are homosexual.
We are often dismissive of insects, seeing them as little more than carbon-bodied robots. But although there may be a genetic drive for the diversity of sexual preferences, is it not possible that butterflies, with their simple insectile minds, simply know what they like? Is it too much of a stretch to imagine that when a female butterfly lets a male court her, it’s because she enjoys the way he dances, and not because she is hypnotized by him? And that he is dancing mid-air, showing off, because he enjoys to be doing that, and not driven by mere ‘programming’?
I’m not saying that a male butterfly studies various dance forms, analyzes his moves and decides what works for him best. Or that a female edits a mental spreadsheet, scoring him on a range of parameters. Just because we enjoy a song doesn’t imply that we understand it, or even know what kind of song it is. The music simply ‘moves’ us. The beauty of a butterfly moves us. The beauty of a flower inspires us. If we, as apes with trichromatic eyesight are affected by their beauty, is it really so outrageous that a butterfly, who depends on flowers and other butterflies for its very life, is also moved by their splendor?
Instinct is not driven by logic or foresight. We do not smile when we’re happy, or blink when we hear a bang because we think and decide that we should. But just because something is instinctive and helps us stay alive, doesn’t mean that we don’t enjoy it. In fact, enjoying something important makes us more likely to thrive in our circumstances. So even if finding flowers, dancing mid-air, and mating (or not) is driven by instinct, doesn’t mean that the butterfly doesn’t gain satisfaction out of it. In fact, it’s more likely that it does.
Sadly, studying the minds of animals is a relatively new scientific field, and we haven’t yet either proved or disproved this. But maybe we should be cautious of simply dismissing of anything an insect does as ‘mindless’.
The minds of butterflies
While scientists were studying the eyesight of butterflies and proving that they see in true color (meaning that they can identify a color under all conditions), they also discovered something amazing. They had mosaics of colored squares and were placing food on specific colors to see if butterflies could choose the right color, and found that they actually memorized what shape, color and size that patch had. A Monarch fed on a yellow square would repeatedly land on yellow squares to find food, even if there was none. It was actually learning and molding its behavior as its circumstances changed. Cool! What else have we learned about their minds?
For one, we know that like us, while butterflies can learn, they forget some skills over time without practice. Have you ever driven a stick-shift car for a while, then an automatic, and then switched back to stick-shift? It gets confusing, doesn’t it? A butterfly’s brain is a lot smaller and simpler than ours, so its processing power is much lower, and memory shorter.
Plants have evolved to have complex flowers to exploit this. If a butterfly visits a rose (which deposits pollen on it), and then visits a sunflower, that’s a loss for the rose – losing pollen with no reproductive success (since roses cannot reproduce with sunflowers). So some plants store their nectar within complex floral structures, which a butterfly must solve like a puzzle. This takes some practice. Once a butterfly gets the hang of it, it can use the same strategy to ‘unlock’ other flowers of the same species, thus ferrying pollen to the right species of plants and fertilizing them. But if it visits a different species, it will have to learn and solve a different kind of puzzle (floral structure), requiring a different strategy, and that can often make it forget how to unlock the earlier floral structure. So to the butterfly, it makes more sense to visit the same kind of flower, rather than waste its limited time and energy learning a new puzzle each time.
The more complex the floral structure is, the harder it is for a butterfly to learn it. As in the world of business, specialization in Nature is born of intense competitive pressures, so this strategy is more common in ecosystems with lots of biodiversity. This is one reason why tropical flowers are so much elaborate than temperate varieties. In a highly competitive ecosystem, a plant would prefer to have a species of butterfly (or moth, or bat, or bird) all for itself to maximize chances of reproductive success.
In less biodiverse places such as grasslands, deserts or colder regions, there are fewer species of plants that can thrive in the inhospitable conditions. Their flowers bloom only for a short span of time and in profusion, and are visited at a frenzied pace by a wide range of pollinators trying to make the most of a brief bounty. On account of lower biodiversity, there’s a high probability of pollinators visiting many plants of their species. So the tables are now turned: a butterfly can generalize its experiences and apply its mental template to unlock nectar from a variety of flowers. For these plants, this hit-or-miss strategy works just fine, and there’s no evolutionary pressure to evolve complex flowers.
But how far back does a butterfly’s memory really go? Until recently, scientists thought that when a pupa is formed, the caterpillar turns entirely to mush, and the cells are recycled into a fully new structure that emerges as a butterfly – effectively, the butterfly is an entirely different individual from the caterpillar. I mean, that’s what you’d expect if all the cells turned into a soup and were reused.
But then a team of scientists decided to check, just to be sure. They exposed tobacco hookworm caterpillars to ethyl acetate, which gives nail polish removers their characteristic scent. And they then gave a mild electric shock to the little fellow, which was harmless, but still a pretty awful thing to do. The caterpillars, which typically don’t care about that gas, quickly learned to associate its smell with electric shocks, just as Pavlov’s dogs linked the ringing of bells to dinner time. When a trained caterpillar was then placed in a Y-shaped tube, in which one end led to air and the other to ethyl acetate, it always avoided the tube with the gas in it. The caterpillar then formed a pupa after some days and, as expected, turned to mush. But when it reformed as a butterfly and emerged out of its chrysalis, it remembered, with much disgust, the smell of ethyl acetate. 77% of adult butterflies steadfastly avoided ethyl acetate – the researchers found that the ones who didn’t seem to remember it had been too young when they were shocked – time had healed their early childhood memories and given them a clean slate. But for all the caterpillars who had been a little older, the butterflies clearly remembered what that experience was like, presumably with as much bitterness and malice that they could muster toward those darned homo sapiens.
Following this experiment, we learned that although most of the caterpillar is disintegrated and reused during metamorphosis, its nervous system remains intact. Even as a gorgeous, winged creature that soars in the sky, a butterfly clearly remembers what its life was like as an earthbound, squirmy bug, manically eating cabbages and hiding in the scrub.
In 1974, philosopher Thomas Nagel wrote a paper titled ‘What Is it Like to Be a Bat?’ In this paper, he concluded that it might be impossible for a human being to understand what it means to be a bat. We conduct experiments and watch a creature in motion, and yet some petty and egotistical part of us convinces us that they are merely going through the motions of their existence, driven by instincts and genes. To an extent, this is true, and it is equally true for us as well. And yet, we offer ourselves the concession of being emotional beings, creatures who feel, learn and delight in existing. We don’t extend the same courtesy to another species of animal. And the smaller the animal, the more disdainful we are. We barely acknowledge the emotional richness of the mammals that we eat, what to speak of an insect like a butterfly.
I’m not saying that a butterfly is capable of worrying about the purpose of life, or solving calculus or sending text messages or whatever else it is that humans do; I’m advocating that a butterfly is capable of enjoying its own existence. That its own life is rich and full of meaning to it, even if it means nothing to us when we pin them for a framed collection or spray plants with pesticides. The purpose of this post was not to present a dead-accurate portrayal of how a butterfly sees the world around it – indeed I don’t think that is entirely possible, no matter how sophisticated our software. It was to introduce you and me to the little marvels all around us, which once filled us with wonder but are casually dismissed as adults. Writing this post has made me wonder what life is like for ants, bees, reptiles and amphibians and other creatures we often dismiss as ‘mindless’. I hope it did the same for you and made you smile.
 Assuming the average weight of a Monarch to be 0.5g and that of a human being as 62kg
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All images used in this post, especially those of floral color variations, were created by me, often after considerable research and editing. However, this wouldn’t have been possible without people who originally photographed the flowers and generously uploaded the images with a free-to-use license. These are the sources of original images.
- Yellow Day Lily: From Wikimedia Commons. Original by David Kennard / http://www.davidkennardphotography.com
- Winter Jasmine: From Wikimedia Commons. Original by David Kennard / http://www.davidkennardphotography.com
- Bulbous Buttercup: From Wikimedia Commons. Original by David Kennard / http://www.davidkennardphotography.com
- Michaelmas Daisy: From Wikimedia Commons. Original by David Kennard / http://www.davidkennardphotography.com
- Orange Hawkweed: From Wikimedia Commons. Original by David Kennard / http://www.davidkennardphotography.com
- Chrysanthemum: From Wikimedia Commons. Original by David Kennard / http://www.davidkennardphotography.com
- Daisy: From Wikimedia Commons. Original by David Kennard / http://www.davidkennardphotography.com
- Featured Image: Indian Skipper. Photographed by me.
- Clouded Yellow: Colias Croceus plate. https://commons.wikimedia.org/wiki/File:Colias_croceus_plate.jpg
- Eastern Tiger Swallowtail: Adapted from ‘Dorsal and ventral sides of Papilio glaucus adults’ by Megan McCarthy. https://en.wikipedia.org/wiki/File:Papilio_glaucus_adults,_MM.jpg
- Cleopatra: From Causes of Color: http://www.webexhibits.org/causesofcolor/17C.html
- Jujonia Coenia: Adapted from ‘Common Buckeye variation (upper side of the wings), Junonia coenia’ by Megan McCarthy. https://en.wikipedia.org/wiki/File:Common_Buckeye_variation,_Megan_McCarty41.JPG
- Junonia Evarete: West Indian buckeye, dorsal side. By Didier Descouens. https://fr.wikipedia.org/wiki/Fichier:Junonia_evarete_evarete_MHNT_dos.jpg