Scientists have finally solved the mystery behind one of nature’s longest and most famous journeys. The monarch butterflies’ ability to migrate from Canada to Mexico every year had always baffled researchers. Monarchs are the only insects to travel such a vast distance while conserving their energy and depending on only a few cues along the way.

Monarch Butterflies Rely On 'Sun Compass' For Migration

The insects always end up in a specific spot in Mexico

Findings of the study were published Thursday in the journal Cell Reports. Lead researcher Prof Eli Shlizerman, a mathematician at the University of Washington, teamed up with biologists to study the monarch butterfly’s internal compass that they use to navigate through vast distances. Researchers also developed a model circuit that mimics the internal compass of monarch butterflies.

Prof Eli Shlizerman said in a statement that he wanted to find out how various neurobiological systems are wired and what rules we can learn from them. The butterflies complete their journey in such a predetermined, optimal way that, even after two months of flying, they always end up in a specific spot in Mexico. Eli Shlizerman collaborated with biologists at the University of Massachusetts to study neurons in the butterflies’ eyes and antennae.

How the monarch butterflies’ internal compass works

They found that the monarch’s input cues rely entirely on the Sun. “One is the horizontal position of the Sun and the other is keeping the time of the day,” said Shlizerman. It gives them an “internal Sun compass” to travel southward throughout the day. The insects fly with the Sun on their left when they have to fly southwest in the morning. But they leave the Sun to their right while flying toward the same direction in the afternoon.

Scientists said the internal Sun compass consists of two control mechanisms. One is the timekeeping “clock” neurons in the butterfly’s antennae, and the second is azimuth neurons in their eyes that monitor the position of the Sun. Researchers were able to develop a model system that simulates the butterfly’s mechanisms. Shlizerman said their goal was to make a robotic monarch butterfly that could follow the insects to track their complete migration.