North America's Monarch butterflies use a "clock" sensor in their antennae to guide them on winter migration to Mexico.

Every autumn about 100 million Monarch butterflies migrate to the south.
The insects navigate according to the position of the Sun, adjusting their calculations as it appears to move across the sky.
A paper in the journal Science shows the location of the clock is the antennae rather than the brain.
Scientists say the finding is a surprise as it has always been thought that the butterflies used a 24-hour clock in their brains in conjunction with their "Sun compass" when they migrated.
But some observations from 50 years ago indicated that when the butterflies' antennae were removed the insects no longer flew in the right direction.
A research team from University of Massachusetts Medical School, US, was also interested in studying the role of the antennae in butterfly social reactions as Monarchs are extremely gregarious when they migrate.



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