Butterflies use the polarized light reflected from their wings to transmit messages
Carol Keisuk Yun New York Times
The Cydno butterfly (on the left) which polarizes light, and the Malpomena butterfly which does not polarize. Photo: New York Times
Anyone who has explored the tropical jungles of America must have marveled at the colorful butterflies that are everywhere, fluttering under the canopy of trees through which very little light penetrates. But although equally fascinated scientists have studied the lives of these insects for decades, they had no idea that some of those beautiful wings were transmitting messages from one butterfly to another in a way that was hidden from the human eye.
In a study published in the latest issue of the journal Nature, researchers reported that at least one species of butterfly had patterns on its wings that reflect polarized light - light invisible to the human eye but visible to other butterflies, which attracts potential mates.
According to the researchers, this is the first study showing the use of patterns that polarize light by a land creature to identify another animal, or some object. The research raises the possibility of an entirely new world, of potential signals and patterns - of butterflies and possibly other insects - all occurring before the limited eyes of scientists.
"There's a huge amount of information out there that we don't know anything about," said Alison Sweeney, an optical biologist and research student at Duke University. Sweeney is the lead author of the new study on two tropical butterflies, Heliconiuscydno and Heliconius melpomene. "The only way to find it is to look," she said.
The light waves can be considered as waves oscillating in different axes when they leave the sun. When they are reflected from a certain object, the light can be polarized, that is, the reflected light oscillates only in a certain axis.
The researchers found that the light reflected from the wings of the Sidno is indeed polarized, while the light reflected from the wings of the Melpomena is not. In addition, when male Cydno were shown wings of female Cydno with the polarized light patterns on them, the males responded very positively: they flapped nearby to get a closer look and get a chance to rub the wings.
When the polarized light models were removed, the males' response was less. According to scientists, the Cydno butterflies may have acquired in the process of their development the skill of creating a clear visual signal that stands out in their forest habitat, which is covered by a canopy of trees and illuminated only by patches of light that is mostly unpolarized.
In comparison, to see the normal pigments on the wings of the butterfly requires full light, which cannot be found in the forest. The researchers claim that this may also be the reason why the Malpomena butterflies, living in an open area, in full sunlight, did not develop light-polarizing patterns on their wings.
Previous studies have shown other uses that animals make of polarized light. For example - bees and ants use patterns of polarized light in the sky, which changes during the day, to better navigate.
Other researchers have also demonstrated that at least one underwater creature, the squid, can produce polarized light patterns on its arms, eliciting responses from other squid. But what exactly the squids say to each other, while the scientists are watching them, is still unknown.
Naturalists
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