The intricate patterns on butterfly wings come in all sorts of colors - dull grays and browns, iridescent blues and greens, red and yellow checkers. The colors help attract mates and fend off predators. But how those hues evolved has been a bit of a mystery. As NPR's Rae Ellen Bichell reports, scientists now say they've gotten a glimpse of how butterflies make their colors and how quickly they can change.

RAE ELLEN BICHELL, BYLINE: Zoom down to the surface of a soft, smooth looking butterfly wing and a biologist Antonia Monterio says it's actually covered in rugged, textured scales.

ANTONIA MONTERIO: That overlap like shingles on the roof.

BICHELL: Zoom in even more to the nanoscale and you'd find a labyrinth of hard, transparent architecture - pillars, ridges, archways, sometimes even spiral tulips.

MONTERIO: And all kinds of other intricate things all made out of chitin.

BICHELL: That's the same material that makes crab shells so tough. In butterflies, the way those chitin structures bend and reflect light is what creates such an extraordinary range of bright colors. Beams of light come in and ricochet off the scaly maze in all directions.

MONTERIO: As they bounce these structures, they go through the process of constructive interference or destructive interference.

BICHELL: It all has to do with geometry and spacing. Tweak those, and you change the wavelengths reflecting back out, which gives different colors. The question was - what exactly would have to change in those tiny, transparent structures to make a dull looking butterfly brilliant? And how long would it take? Monterio decided there was only one way to find out - to try to do it in the lab.

MONTERIO: To try and evolve color.

BICHELL: Monterio, who's now at the National University of Singapore, teamed up with some Yale physicists and picked a butterfly species called the squinting bush brown. It lives up to its dull name - goes well with tree bark. But it has some flashy close cousins with streaks of blue and violet on their wings.

MONTERIO: So we wondered whether this specific species that was not showing any of those colors, could also evolve those colors if we forced it to through artificial selection.

BICHELL: So here's what they did - some of the dull brown butterfly wings did reflect slightly shorter wavelengths of light.

MONTERIO: Meaning towards the bluer wavelengths of the light spectrum, and we mated those individuals with each other.

BICHELL: One year and six generations later, they had bred squinting bush browns that were sporting purpley streaks across their wings. Monterio was surprised to find that the new decor was the result of only very slight changes to the scales. The chitin had become a smidge thicker.

MONTERIO: It seems to be incredibly easy to evolve these new colors in butterflies.

BICHELL: So should this modest brown butterfly species need to adapt, it has a powerful color technology in his back pocket - tweak a little chitin and boom - from brown to brilliant. Monterio's work was published this week in the journal proceedings of the National Academy of Sciences. Rae Ellen Bichell, NPR News.

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