The first sighted monarch, migrating from the United States to its overwintering sanctuary deep in the mountains of central Mexico, reached its destination on November 6^th, as reported by Journey North. Soon it will be joined by tens of thousands. Then by hundreds of thousands.

The spring and fall migration of the monarch butterfly is truly an amazing phenomenon. The monarch is the only butterfly known to make a two-way migration, similar to birds. Unlike other butterfly species that can overwinter here as larvae, pupae, or even as adults in some species, monarchs just can’t make it through our cold winters.

Using clues from the environment, monarchs know when time is approaching to move on. Scientists believe shortening days and lowering temperatures, along with aging milkweed and nectar sources trigger a change in monarchs. And it’s this change that makes the monarch migration even more extraordinary: monarchs are the only known species to have a multi-generational migration.

a generation unlike the others

Generally, monarchs produce four generations a year. The first three generations are bred and born in the United States after they arrive during the spring migration north from Mexico. Each of these generations makes its way northward with some reaching as far north as Canada. Individuals of the first three generations live from two to six weeks.

When the fourth generation is born, something happens—and what happens, exactly, is unknown. What is known is that this generation enters reproductive diapause as adults and can live as long as nine months. These are the little guys that make the great trip south, starting in the late summer (in the north) and fall. Somehow, this generation of butterflies knows exactly where they’re headed while never having been there before: the high elevation oyamel fir forests in the Transvolcanic Range of central Mexico. The trip can be an astonishing 3,000 miles long for the northern-most butterflies and can take about two and a half months to complete.

It is hard to contemplate a world without the monarch—it’s woven into the very fabric of our culture. But the monarch migration is now recognized as an “endangered biological phenomenon” by the International Union for the Conservation of Nature and our northern neighbors in Canada have already identified the monarch as a species at risk.

To see the monarchs gather in Mexico over the winter months is something to behold. Watch this short video by National Geographic to get a glimpse of a monarch sanctuary in Mexico:

more interesting bits about the monarch’s incredible journey…

• Although the monarch migration is visible from the ground, glider and airplane pilots have reported monarchs flying at heights from 1200 to as much as 10,000 feet.
• Monarchs have two speeds: powered flight (greater than 12 miles per hour) and gliding.
• When gliding, monarchs catch thermals to gain altitude and then glide south to southwest with the help of the wind. If conditions are favorable, monarchs can maintain altitude by flapping their wings only once every 20 to 30 feet.
• Flight requires sunny days, light winds, and temperatures greater than 55 degrees. Headwinds greater than 10 miles per hour and temperatures greater than 88 degrees impede migration.
• Tracking migrating monarchs from various starting points in the interior United States shows that no matter where they begin their journey, they all fly, more or less, on a direct path toward central Mexico. Scientists don’t know how the butterfly determines its particular geographically appropriate direction.
• Although the total migration advances southward only 25 to 30 miles per day, individuals have been recorded to have covered hundreds of miles in just a few days.
• Monarchs overwinter in dense clusters on oyamel firs in a semi-dormant state. They become active when temperatures rise above 55 degrees to find water. Nectar is not required—they live off stored fats all through the winter months.

One late season monarch averaged 61 miles per day for two weeks while flying from Virginia to Texas.

See Journey North’s  interactive map to see the progress of the fall migration. And if you have citizen scientist interests, consider adding your monarch sightings in their interactive spring 2019 migration map.

What a perfect time to contemplate a new or improved pollinator garden to make ready for the spring migration back north!