Monarch butterflies have started their annual migration. These colourful butterflies spend the spring and summer in southern Canada and the northern U.S. Each fall, a new generation flies to Mexico for the winter. 

They begin to arrive in November. But what happens along the way? 

Which way did you go?

It’s a long way to Mexico – about 4000 to 5000 kilometres. Scientists know where their journey starts. They know where it ends. But they know very little about how they get there.