Monarch butterflies are known for migrating from the U.S. and Canada to Mexico for the winter. Now a new study suggests the species itself also started out in North America approximately 2 million years ago.

Researcher Marcus Kronforst of the University of Chicago said monarchs were widely believed to have evolved in South or Central America. DNA from 80 monarchs sampled from the Americas and as far away as Europe and Australia points to a North American origin, according to the Associated Press.

Their study, published this week in the journal Nature, also identified the gene behind the butterfly's striking orange-and-black coloration.

"I find it amazing that these little butterflies live for months and fly thousands of miles to perform this annual migration," said one the researchers, University of Chicago professor of ecology and evolution Marcus Kronforst.

"Our study shows that monarchs have been doing this every year for millions of years. There is nothing else like this on the planet," 

The number of migrating monarchs has dropped in recent years. Kronforst said during an estimated one billion monarch butterflies migrated to Mexico in 1996, a number that stood at 35 million this winter.

Threats to monarch butterflies include habitat loss due to human activities, climate change, and pesticides that kill milkweed.

Though mainly a North American species, monarch populations also can be found in Central America, South America and elsewhere. Those outside North America do not migrate.

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