If you've spotted a striking monarch butterfly gracefully flitting through the air this fall, it's in the midst of a spectacular journey thousands of miles long to overwinter down south. Millions of these iconic insects make an impressive seasonal migration twice a year that spans North America, starting as far north as Canada in late summer and early fall and, about 3,000 miles later, arriving in Mexico or California for the winter months. When temperatures start to warm in the spring, these monarchs breed and lay the eggs of the next generation, which will start the journey back up to the northern United States and Canada.
Unlike their predecessors, the monarchs making the northern trip won't tackle the journey in one fell swoop; it will take four consecutive generations of monarchs to complete the migration. Each successive generation travels farther and farther north until they reach the northern United States or Canada, where the process starts all over again.
Incredibly, monarchs traveling in both directions follow the same routes as generations before them and know exactly where to go—even though they've never made the trip before. Researchers are still unsure of how monarchs navigate so precisely, but a combination of directional cues, such as the position of the sun and magnetic fields, likely play a role.
Monarchs are the only known species of butterfly that make a two-way migration, like birds do.
On their multigenerational migrations, monarchs rely on one plant in particular for their survival: milkweed. It's the only plant that monarch caterpillars will eat, and the only plant that reproducing monarchs will lay their eggs on. As a result of this dependence, a decline of milkweed habitat in recent years has been directly correlated to a serious drop in monarch butterfly populations, which have plummeted by approximately 90% in recent decades, according to the National Wildlife Federation.
This population decrease is all the more concerning because monarch butterflies are considered an important indicator of ecological health, as well as a key representative of pollinator populations. Waning milkweed habitat isn't the only culprit—severe weather and illegal deforestation of winter habitat have both played a role in the monarch's decline as well. Research from the World Wildlife Fund Mexico and the Monarch Butterfly Biosphere Reserve points to large-scale use of herbicides that destroy milkweed as the main cause of the monarch's decline.
If you want to help monarch populations recover, you can take action right in your own backyard or neighborhood green space. Planting milkweed helps to restore critical habitat for migrating monarchs and is the most effective step you can take to support the recovery of monarch populations.
As an added bonus, planting milkweed will put you one step closer to creating a certified wildlife habitat through the National Wildlife Federation's Garden for Wildlife program. Creating a certified wildlife habitat is as simple as providing food, water, cover and places to raise young for local wildlife, and practicing sustainable gardening techniques.