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A Primer on the Beautiful Monarch Migration Season

Monarchs are in danger because climate change and humans are destroying their travel food.

It's that time of the year when one of the world's most iconic butterflies, the Danaus plexippus, also known as the monarch butterfly, takes to the skies and migrates for the winter. Along the way, they create breathtaking scenes—but the monarchs are actually in grave danger during these trips.

The monarch butterfly is an important pollinator across the US, and they migrate to Mexico every winter, where they spend the colder months eating and getting ready to lay eggs. The U.S.'s agriculture industry relies on wild insects to supplement its crop pollination, especially for farms who can't afford their own hives of bees.

Colonies in the West Coast typically migrate through California to get to Mexico, while colonies along the East Coast will make a pit stop in Florida's panhandle before flying over the Gulf of Mexico.

The migration itself is breathtaking.

Thousands and thousands of monarchs travel in swarms across continents, knowing where to go through an evolutionary navigational tool—like a GPS in their brain. The technical term for a group of butterflies is a kaleidoscope, which is pretty much what a group of flying monarchs looks like.

But the species is facing a big problem. Monarchs' primary food source, especially during these migrations, is milkweed, a plant with small purple flowers named for its milky sap.

Milkweed used to be a common plant that grew in abandoned lots, undeveloped forest areas, and along the sides of commercial crops. But so much of this land has been developed and has been sprayed with commercial herbicides that it's harder for these butterflies to find milkweed along the way, according to butterfly advocacy non-profit Monarch Watch.

Climate change is also making things worse because milkweed can't grow well in hot, dry conditions.

A lack of food means a larger portion of migrating butterflies won't make it to their destination. Researchers estimate the monarch butterfly population has declined 80 percent since 1990 due to various factors including a lack of food, according to the Xerces Society, a wildlife advocacy nonprofit.

Some monarch advocacy organizations encourage residents to plant milkweeds in their gardens to give monarchs a stop-over snack during these long journeys.

In the meantime, wildlife advocates say, just knowing there's a problem is the first step toward addressing it. California and Florida have various monarch butterfly festivals this month, so that's an opportunity to learn more and to gawk at these fluttering beauties.