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A monarch butterfly's spots may be key to its epic yearly migration

Jorge Valencia/KJZZ
The eastern monarch butterflies spend their winters in forests in Mexico State and the state of Michoacan.
You probably know that monarch butterflies make an epic journey each year, from the northern United States and Canada to Mexico, where they winter in the mountain forests outside of Mexico City.
But, we don’t know a lot about how they actually do it.
How does a tiny, paper-thin butterfly make it so far each year? Well, scientists have a new theory — and it has to do with the spots on their wings.
The Show spoke more about it with Jason Bittel, who wrote about it recently for National Geographic.