No one knows for sure just how or why monarchs undertake their massive migration, the only one like it in the butterfly world. Their fall journey is currently underway, so it’s the perfect time to learn a little more about these fascinating flyers.
Not all monarchs migrate. While most North American monarchs undertake amazing migrations each year, there are many monarchs in other parts of the world that do not migrate at all. Monarchs resident in Florida from around Orlando south do not need to migrate, as the climate allows their nectar and host plants to grow year-round. The same goes for Monarchs in Central and South America, the Caribbean, and other places around the world where monarchs live. That actually makes the North American monarch populations unique in their migratory behavior.
There are two groups of monarchs in North America that migrate to separate winter locations. Those living east of the Rocky Mountains generally migrate south to Mexico, while those living west of the Rockies move west to California. The most famous wintering grounds in the Oyamel Fir Forests of Central Mexico. The climate of these forests is not as tropical as many might expect, as they are high in the mountains, with daytime temps around 65 degrees or so and nights in the 30s. Monarchs that migrate west winter along the central and southern coast of California, in groves of eucalyptus trees. (Get a list of California over-wintering sites here.)
Monarchs don’t migrate south for food. When they arrive in their wintering grounds, these butterflies enter a state called “diapause”, which means that they do not eat or reproduce. Instead, they join together in huge roosting groups, so numerous that tree branches have been known to break under their weight, and stir themselves only to seek water on sunny days. They exist otherwise on stores of fat they accumulate along their journey south.
Migration peaks in September and October. The further north the monarchs are, the sooner they must begin their southward journey. Monarchs in Canada will begin moving south as early as August, but the largest numbers are usually seen in the middle of the country through September and October. You can track their journey and report your own sightings at the Journey North website. The butterflies take several months to make their journey south, which can be well over 2,000 miles depending on how far north they started, and it’s extremely important for them to eat as much as they can along the way. Be sure to have plenty of nectar plants available for butterflies well into the fall. You’ll recognize migrating groups when you see large numbers gathered together on nectar plants, or flying purposefully in a southern direction.
Migrating monarchs are larger and longer-lived than those that don’t migrate. Often called the “super-generation”, the monarchs that undertake fall migration have a lifespan much longer than other monarchs. Most monarch butterflies live about two to four weeks, eating and reproducing the whole time. The generation that migrates in the fall will live up to nine months, and only reproduce at the very end of their life when they begin their journey north again in the spring. This super-generation is also built somewhat differently, with much larger bodies for storing fat and longer, larger wings for improved flight.
There is so much more to know about monarchs and their astounding migration. Monarch Watch has detailed information on the topic – click here to learn more. Are you seeing groups of migrating monarchs in your area? Tell us where and when in the comments below!