Sun helps orient migrating monarch butterflies: study

A flight simulator has helped scientists crack the secret of how monarch butterflies can fly thousands of kilometres every fall without getting lost.

To figure it out, the researchers built a simulator that allowed butterflies to fly in any direction they chose while tethered to a device. The device recorded an insect's direction about five times a second as it flew in loops and twists.

When Queen's University neurobiologist Barrie Frost and his colleagues reconstructed the butterflies' migration path, they found the insects used a sun compass to get their bearings.

The butterflies would orient themselves to the sun. For example, at 9:00 a.m., the butterflies would face south so the sun is 45 degrees to their left.

"We were just amazed with the precision," Frost told CBC Radio's As It Happens.

Cloud-proof compass

The researchers shifted the internal clock in some of the butterflies by turning the lights on at midnight. The butterflies responded by going off course by 90 degrees.

"Control monarchs on local time fly approximately southwest, those 6-h time-advanced fly southeast, and 6-h time-delayed butterflies fly in northwesterly directions," the researchers wrote.

Frost also simulated what happens on cloudy days. Humans can't see the patches of polarized light in the sky, but insects can.

By using sheets of polarized material like that found in sunglasses, the researchers found the butterflies oriented in the direction of the filter. They think even on cloudy days, enough polarized light comes through the clouds for the butterflies to orient themselves.

But the experiment didn't offer any evidence that butterflies use a magnetic compass. When a magnetic field was rotated in the apparatus, the butterflies did not change direction.

The study appears online in the Proceedings of the National Academy of Sciences.