North American monarch butterflies migrate for thousands of miles every year.
There are other populations of monarch butterflies who don't migrate, but permanently live in warm tropical climates.
So what makes some butterflies want to take to the skies and others happy to stay put?
Marcus Kronforst, University of Chicago, US, and colleagues have sequenced the genome of 101 butterflies and discovered genes that might answer that very question.
Scientists still have many questions about these butterflies, such as how they know the way on their great migration, and how they known when to leave.