There are over 18,000 species of butterflies in the world, displaying a stunning array of colors and patterns on their wings. While most butterflies have wings featuring one or two main colors, some rare species exhibit an unusual color combination – purple and blue. So do purple and blue butterflies really exist in nature?
The Origins of Butterfly Wing Color
Butterfly wings get their color from tiny scales that cover the wings like shingles on a roof. These scales contain pigments that reflect specific wavelengths of light, creating the color we see. Some of the most common pigments are:
- Yellow and red pteridines
- Orange and black melanins
- Blue and green structural colors from light scattering
Combining multiple types of scales on one wing produces additional colors. For instance, a mix of yellow and blue scales results in a green color.
This explains how butterflies can display such a wide spectrum of hues in different patterns. But it also illustrates why certain color combinations, like purple and blue, are rare. They require a precise mix of multiple specialized scale types that few butterflies possess.
Where to Find Purple and Blue Butterflies
Very few butterfly species worldwide exhibit an overt purple and blue coloration. Here are some of the few that do:
Purplewing (Eunica)
This brush-footed butterfly genus includes over 20 mostly tropical species. As their name suggests, they are characterized by primarily purple upperwing surfaces, along with blue, black, and sometimes green markings. The undersides of the wings tend to be brown, providing camouflage when the wings are closed. Some examples include:
- Eunica monima – Purplewing found in Central and South America
- Eunica tatila – Florida purplewing found in southern Florida and the Caribbean
- Eunica caelina – Dingy purplewing ranging from Mexico to Brazil
Blue Morpho (Morpho)
The blue morpho butterfly is among the most brilliantly colored in the world. Its upperwings are an iridescent electric blue edged with black, while its underwings are a dull brown. However, the blue color is not from pigmentation. Instead, it results from the microscopic structure of the scales, which refracts light to produce the blue hue. There are over 30 Morpho species, mostly found in Central and South America.
Green-underside Blue (Udara)
This genus features over 50 species found across Asia and parts of Africa and Australia. As their name denotes, they have vivid blue upperwing surfaces contrasted with a green underside. One widespread example is Udara dilecta, ranging from India to Japan.
Why Aren’t More Butterflies Purple and Blue?
If purple and blue butterflies exist, why aren’t more species colored this way? There are a few reasons:
Limited Pigment Options
As mentioned earlier, butterflies can only manufacture specific types of pigments. While melanins provide black and orange, and pteridines create reds and yellows, there is no single pigment that generates purple or blue hues well. Only a precise combination of multiple pigment types results in these colors. This combination is biologically difficult to produce.
Structural Color Rarity
Butterflies like the blue morpho use physical structures to scatter light into blue wavelengths. But this phenomenon is uncommon and requires specialized scale architecture. Most butterflies lack the intricate nanostructures needed to structurally produce blue.
Camouflage Pressures
Vivid colors increase visibility to predators. As a result, natural selection often favors drab, camouflaging colors in butterfly wings. The exceptions are species that have evolved to use their bright colors as warning signals of toxicity or foul taste. However, these survival strategies are also uncommon.
Temperature Regulation
Darker colors absorb heat better than light colors. Some research suggests butterflies rely on this property to help regulate body temperatures for optimal flight. Consequently, lighter blues and purples may be less thermally suited for certain environments than darker melanic oranges and blacks.
Existence of Other Rare Butterfly Colors
While purple and blue butterflies are uncommon, they aren’t the only butterflies with rare wing colors:
Glasswing (Greta and Cithaerias)
These see-through butterflies have mostly transparent wings, dotted with small black or purple spots along the edges. This helps them camouflage against vegetation and avoid predator notice.
Yellow and Black (Eurema)
Typically, no single pigment creates a true, bright yellow. But some grass yellow butterflies, like the little yellow Eurema lisa, have evolved specialized pteridine pigments to achieve vivid yellow wings with black borders.
Red (Atrophaneura)
Red is also a rare butterfly color, limited to select tropicalspecies that have enough pteridine pigments to strongly express red hues. A few red lacewing butterflies, like Atrophaneura varuna, exhibit brilliant scarlet wings.
Could Purple and Blue Butterflies Be Created?
Even if naturally rare, could we artificially create purple and blue butterflies in a lab? Possibly in the future, though significant challenges exist:
Genetic Difficulty
We would first need to decode the specific genetics around pigment and structural color production in butterfly wings. The intricate gene interactions are not yet fully understood.
Precision Engineering
If genetic mechanisms were uncovered, we would need genetic tools capable of precisely altering butterfly wing development. Our current biotechnology is not refined enough for such targeted changes.
Unintended Effects
Modifying wing color could unintentionally impact other aspects of butterfly development, fitness, or behavior. Extensive testing would be critical to avoid ecological issues.
Ethical Concerns
Some argue artificially modifying organisms purely for aesthetic reasons is unethical, especially when not solving an important problem. These moral objections could restrict applications.
Conclusion
While uncommon, a select few butterfly species in tropical locales exhibit an unusual combination of purple and blue wing coloration. This results from either specialized pigment combinations or structural scale properties. Vivid blues and purples remain rare in butterflies due to limitations of pigment production, the prevalence of camouflage, and thermoregulatory demands. But advances in genetic knowledge and biotechnology could one day make it possible to engineer these colors, though significant hurdles around feasibility, unintended consequences, and ethics would still need to be overcome. Ultimately, the rarity of purple and blue butterflies makes them fascinating examples of nature’s diverse palette.
References
Butterfly facts and information. National Geographic. https://www.nationalgeographic.com/animals/invertebrates/facts/butterflies
Chittka, Lars, and Remy Waser. (1997). Why Red Flowers Are Not Invisible to Bees. Israel Journal of Plant Sciences. 45. 169-183. 10.1080/07929978.1997.10676678.
Liu, Feng et al. (2016). Pteridine, not carotenoid, pigments underlie the female-specific orange ornament of striped plateau lizards (Takydromus septentrionalis). PeerJ 4:e2590 https://doi.org/10.7717/peerj.2590
Sweeney, Alison et al. (2003) How to Make a Butterfly’s Wing. Proceedings of SPIE. https://doi.org/10.1117/12.506646
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