Monarch Migration

Jennifer NicholsField Notes

As the days grow shorter and the weather gets colder, both plants and animals need to adjust to these seasonal changes. In our area, most plants go dormant which leaves the animals that depend on them several choices for survival.

Some animals, such as chickadees, nuthatches, and field mice change their food source to what is available, such as seeds. Other animals, such as groundhogs and bears hibernate. And still others including Canada geese and songbirds such as warblers migrate.

Monarchs migratingSurprisingly, another animal that migrates is the Monarch Butterfly, sometimes up to 3000 miles! According to Monarch Watch, Monarch butterflies are the only butterfly that travel these amazing distances. But that is just the beginning of their amazing story.

While Monarch Butterflies west of the Rocky Mountains migrate to Southern California, Monarchs from the east travel to specific mountain sites in central Mexico. There are several generations of Monarchs every year, but only the fall generation makes this incredible trip While spring and summer generations of Monarchs mate and lay eggs, the fall Monarchs emerge from their chrysalises ready to fly extended distances. They can even gain body fat on their trip south, which will help them survive the winter in Mexico.

No one knows how these Monarch butterflies know to migrate to the same location as their great-great grandparents, astonishingly sometimes even finding the same tree.

So why do these insects travel these amazing distances? Like all insects, Monarchs are cold-blooded, and cannot survive the freezing temperatures, so they travel to a location that has everything they need to survive the winter. The oyamel fir forests of Mexico’s Transvolcanic mountains provide the exact conditions that the Monarchs require. The high elevations (over 10,000 ft) provide cool air which slows the Monarchs’ metabolism, preserving stores of fat they will need to travel back north. Fog and streams provide water and the trees provide protection from rain wind, and snow.

When temperatures start to warm and spring arrives, these amazing animals start their trek back north, mating and laying eggs on milkweed plants along the way. Several generations breed in their summer locals before the journey starts over again.

Sadly, Monarch populations are in severe decline. According to the Xerces Society for Invertebrate Conservation, North American populations have declined by 90% since the 1990’s. This is largely due to habitat destruction, both in Mexico and the US.

Monarch butterfly caterpillar on Butterfly Weed

Monarch butterfly caterpillar on Butterfly Weed

The good news is that you can help. Because milkweed is the food source for Monarch caterpillars, Monarch butterflies only lay eggs on milkweed plants (Asclepias sp.). So in addition to supporting conservation organizations, here are a few things you can do at home:

  • Plant milkweed. Butterfly Milkweed (A. tuberosa) and Swamp Milkweed (A. incarnata) are both beautiful, garden-worthy perennials which will add color and life to your garden. For the true Monarch enthusiast, Bloodflower (A. curassavica) can be found in the annual section of well stocked garden centers, while Common Milkweed (A. syriaca) can be used in natural areas.
  • Avoid pesticides on your property
  • Support organic agriculture
  • Assist in monitoring Monarch populations.

For more information about these fascinating creatures, see:, or