Unlike most butterfly species, Monarchs DO NOT overwinter in Pennsylvania.
Instead, as the end of summer approaches, they do something that seems impossible for such a small, delicate creature.
Believe it or not, Monarchs leave Pennsylvania and migrate south to overwinter in Mexico! It still seems hard to believe that these beautiful butterflies flutter all the way from Pennsylvania to mountainous areas in southwestern Mexico.
So when exactly do Monarchs leave Pennsylvania?
As you can imagine, there is not an exact day that all the Monarchs get together and decide to start migrating. Instead, something triggers their instinct to leave. Scientists believe that a combination of lowering temperatures, diminishing daylight, and aging nectar sources all help these butterflies determine when to depart.
But with that being said;
Most Monarchs leave Pennsylvania in mid to late September.
From there, it takes many weeks for them to reach their final Mexican destination. Most individuals arrive in early November. Along the way, Monarchs encounter many dangers, including predators, cars, cold and windy weather, and lack of nectar sources.
Here are a few more CRAZY facts about Monarch migration:
- Almost any Monarch born after August 15th won’t reproduce in Pennsylvania. Instead, these are the “migratory” butterflies. They won’t lay eggs until the following spring when these same individuals migrate BACK to the southeastern United States after spending the winter in Mexico!
- The Monarchs that leave Pennsylvania to migrate south can live up to 9 months long! This is about eight times longer than their parents and grandparents that reproduced earlier in the summer.
- Nobody knows exactly how Monarchs find their way on these incredible migrations. Some hypotheses include using Earth’s magnetic fields, using the sun as a compass, or something in their genetics.
- Monarchs are the ONLY butterfly species in North America that migrates!
The more that I learn about the migration of these butterflies, the more fascinated I become. It’s incredible that the Monarchs that leave Pennsylvania at the end of summer are going to Mexico!
Luckily, we can all help Monarchs on this journey!
Making sure your yard is FULL of native plants is one of the best things you can do. Try to pick flowers with different bloom times, so you always have fresh blossoms full of nectar.
In addition, try reading this article, which is full of tips that will make your yard more friendly to butterflies, including Monarchs:
When do you usually see the last Monarch in Pennsylvania?