Eastern and western monarch butterflies of North America are genetically similar, a new genomic analysis has found.

In eastern North America, monarch butterflies make long treks from their summer homes as far north as the US-Canadian border to their winter homes in Central Mexico, a flight that can be 3,000 miles long. West of the Rocky Mountains, monarch butterflies take a shorter trip of about 300 miles to California, suggesting that the two populations may be genetically distinct.