The long migration

Monarch flying: Some monarch butterflies will travel thousands of miles in their short lives.
Some monarch butterflies will travel thousands of miles in their short lives.
Courtesy Grant and Caroline @ www.flickr.com

A chubby little monarch caterpillar can be happy to spending its days trundling around a single patch of milkweed. (If your house were made of your favorite food, you might spend all your time there too.) But once a monarch pupates and gets its wings, life is a whole different story. With wings more delicate than paper, measuring just a few inches across, some adult monarch butterflies take to the air and journey further in one year than many people may travel in their lifetimes.

While some butterflies hatch, mature, and die in the species’ summer homes, the monarchs that survive until the fall must begin a journey that can take them thousands of miles across North America.

When the weather in Canada and the northern states begins to turn cold, monarch butterflies will migrate south, like birds and retired people. The butterflies ride the wind for hundreds and hundreds of miles, navigating by the sun, until they reach their winter home in the mountains of central Mexico. Scientists think that monarchs compare the position of the sun in the sky with an internal clock, so they always know which direction they should be going.

Because of the milkweed they eat as caterpillars, most monarchs are bitter and poisonous to predators. That doesn’t mean that all predators will ignore the bright warning of the monarchs’ wings, and the trip south can be a dangerous one. Still, enough of the butterflies reach Mexico that in some areas over wintering monarchs can be so densely populated that entire trees will be blanketed in fluttering orange and black wings.

Monarchs: Monarchs cover the trees in a nature reserve in Michioacan, Mexico.
Monarchs cover the trees in a nature reserve in Michioacan, Mexico.
Courtesy Aviruthia @ www.flickr.com

After a winter in the sun, the surviving monarchs begin the trip back to their northern homes. The oldest of them, having already flown across the continent in the fall, will only may it to Texas before they mate, lay eggs, and die. Because most monarchs live less than two months, the butterflies that return to states like Minnesota in the spring will probably be the grandchildren of those that left in the fall. And in a few short months, their children or grandchildren will make the journey once again…