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Monarchs Use Antennas To Point The Way South

Posted on: Friday, 25 September 2009, 06:25 CDT

After years of theorizing about how Monarch butterflies find their way to Mexico for the winter, scientists have finally discovered that their antennas help them navigate the journey.

Researchers confirmed the finding when they painted their antennas black and observed them losing their way.

Butterflies have only the sun in the sky as a point of reference for direction, and since the sun is always moving, they have to constantly adjust in order to stay on the right path throughout the day.

Monarchs have what most animals use to know the time of day: a ‘circadian clock’ in their tiny brain. Being able to determine the time and position of the sun is what lets them make it to the south.

However, the Monarch butterflies have a special second clock based in their antennas that can also sense the light, according to the new study led by Dr. Steven M. Reppert, chairman of neurobiology at the University of Massachusetts Medical School.

Whatever we learn about the insect ... is going to tell us a little bit more about how our brain works," said Reppert, who studies the internal clocks in the brains of animals, including people.

"It's fascinating biology that's begging to be understood," he added in a telephone interview with the Associated Press.

Previously, researchers believed that the key to their navigation skills were in the butterfly’s brain, but this experiment revealed that the circadian clocks in the brain and antennas actually work together, Reppert said.

The study, published in Friday's edition of the journal Science, involved the researchers gently holding the butterfly's wings and dipping their antennas in enamel paint.

They found that the butterflies that had their antennas painted black lost the ability to find their way south, while those coated with clear paint were able to navigate normally.

This helped the scientists to discover more than just the fact that they used the antennas to sense light. They also realized that the sense of smell played no role in finding their way, with both types of paint blocking that ability.

Even though the butterflies can see light with their eyes, researchers concluded that the antennas were the most important part involved in their navigation.

Butterflies whose antennas were surgically removed also lost their way.

Charalambos P. Kyriacou of the University of Leicester, England, remarked that the experiment suggests that the antennas serve as a sort of natural global positioning system for the insects.

"The antenna clock appears to override any input from the brain clock for navigation," Kyriacou, who was not part of Reppert's research team, said in a commentary on the report