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Yellow, light, orange, green, red … or simply black and white. The wings of these lepidoptera (Greek for ‘scaled wings’) have an exquisite color palette, which provides them with eye-catching designs and exceptional coloring.
Some butterflies can boast of having the most striking iridescence of all nature, traced from specific genetic patterns, where a single gene, WntA, acts as a designer. It is really fascinating to think that this gene is the same for all species but that, at the same time, it works in such a different way in each one of them.
Pigments and iridescences
If we go into the studio of the painter, the range of tones with which he plays are two, on the one hand, he has pigments that stain the cells and, on the other, he plays with light, with its behavior after colliding with the wings.
Technically the first case is known as pigment colors and the second as structural colors.
Before going into details, it should be noted that the wings of these insects are made up of a large number of scales (thyroid), which vary, depending on the species, both in shape and size. Each scale corresponds to a single flattened cell measuring about 100 microns long and 50 microns wide.
The scales can overlap, as if it were tiles, or cover the entire surface of the wing. In both cases, the diversity of colors is basically due to the presence of four pigments: melanins, pterins, flavonoids and ommochromes.
Melanins are responsible for the blackish or brownish coloration; the pterinas of the spectrum that goes from pale yellow to red; the flavonoids of the white and yellow tones and, finally, the ommochromes, those responsible for the brown, red or yellow colors.
In addition, scientists have described bile pigments, including several blue dyes (pterobilins) that would be responsible for the beauty of bile ducts. Nymphalidae and of the Papilionidae.
To all this, we must add that when white light hits the wings of butterflies it glows in various directions and breaks down into many colors. If we carefully observe a butterfly moving discreetly around it, we will see how the tone of its wings varies ostensibly with our movement, it is what is known as iridescence. This chromatic peculiarity depends to a great extent on the angle with which we observe the lepidopteran.
The power of colors
Colors play a very important role in their lives, since it can serve as camouflage, help them find a mate or as a warning against possible predators.
Cryptic mimicry is the ability to camouflage itself by adopting other colors, so that the insect can go unnoticed in the face of potential danger. This is observed in butterflies that have the upper part of the wing of bright color, while the rest adopt a more discreet coloration. If these Lepidoptera do not want to be seen, they close their wings and hide their colors. When this happens in Kallima butterflies, the appearance they adopt is practically the same as a dry leaf.
In other cases, the colors are very striking to warn predators that they are poisonous. This is found, for example, in butterflies of the genus Monarch, which exhibit beautiful black-orange colors.
In addition, these insects have put colors at the service of seduction. Males use their striking patterns to signal to females that they are choosing the correct species to mate with. This is not trivial, since when two similar species of butterflies coincide in the same place, it is possible that they hybridize, but the resulting offspring, generally, will not be fertile. Therefore, the individuals who end up perpetuating their genes are those who are able to unequivocally identify their peers. It could be said that thanks to color they have transformed necessity into a virtue.
In some species, females announce their lack of predisposition to maintain sex by closing their wings, hiding their colors and becoming less visible to males. Thanks to this uniqueness, the females of the Lycaenidae are able to scare away the most stubborn and inopportune males.
Pedro Gargantilla is an internist at the Hospital de El Escorial (Madrid) and the author of several popular books.
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