Fossil moth reveals colorful hue

Paleontologists deduce how ridges on the creature’s wings reflected light

MINNEAPOLIS — Ancient moths have for the first time shown their true colors to modern humans.

Ancient ancestors of Pollanisus moths, one of which is shown here, sported a yellow-green color that helped the insect protect itself, new researchers report. KeresH/Wikimedia Commons

By piecing together clues from a fossil unearthed in a former German quarry, a team of scientists has figured out how light bounced off a moth that lived 47 million years ago. Today, the insect’s remains are bluish. But before time alchemized its wings, the creature was mostly yellow-green, with only a fringe of blue.

“The original colors aren’t preserved, but they can be reconstructed,” said Yale paleontologist Maria McNamara, who presented the new findings October 9 at the Geological Society of America annual meeting.

Like beetles and dragonflies, modern moths and butterflies owe their brilliant hues not only to chemical pigments but also to the shape of tiny structures on their wing scales. Parallel ridges redirect incoming waves of light, which bounce around and interfere with each other like ocean waves crashing together. Depending on how the peaks and troughs of the light line up, this interaction boosts some colors at the expense of others. Ridges with different shapes, sizes and spacings can give rise to a variety of colors, including iridescent colors that seem to shift and shimmer.

McNamara’s fossilized moth relied on structure to produce color, which became obvious when she cleaned off its glycerin preservative and it changed color. Using a microscope, the scientists found that the shape of the moth’s ridges had survived the transformation from chitin to fossil without shrinking or swelling. Further analysis showed that, when the moth was alive, these chitin structures would have favored a wavelength of about 565 nanometers, turning the moth’s wings yellow-green. Small holes in the layers of these ridges suppressed iridescence, giving the creature a hue that looked the same from all directions.

This consistent color probably protected the moth. Seen at rest against a leaf, the creature would have been well concealed from any point of view. But when feeding on a flower, it stuck out — just like the insect’s most likely descendants, Pollanisus moths, which use color to warn predators that the toxic chemicals in their bodies are a dangerous snack.

“This is bloody brilliant work,” says Phil Manning, a paleontologist at the University of Manchester in England who studies pigments. “This group is the first to work out structural color in insect fossils.”

McNamara’s team had already revealed the color of beetles dug up from the same German quarry, as described online September 28 in Proceedings of the Royal Society B. Flies and dragonflies are next, as the scientists continue to explore the evolutionary history that gave today’s insects such a brilliant palette to play with.

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