Have you ever spotted flashes of orange in eucalyptus trees along the coast of California? Chances are, you were looking at a cluster of monarch butterflies overwintering! Every year, the western population of monarch butterflies (those west of the Rocky Mountains) make the long journey from as far north as southern Canada to coastal California to escape freezing winter temperatures. The complete migration takes place over multiple generations, but it is the fall generation, also known as the “super-generation,” that travels upwards of 1,000 miles south. Wow! Monarch butterflies typically arrive at their overwintering sites around October and remain until around February, which is when they start to make their journey back north.

So, what makes coastal California a good winter home for monarch butterflies? They need specific conditions in order to overwinter. It can’t be too hot or too cold. It needs to be just right. There need to be creeks nearby or fog to help the monarchs rehydrate. Most importantly, these sites need to have trees in which the monarchs can cluster to save energy and keep warm. The tree canopies also shield them from harsh winds and weather. Together, these features combine to form pockets of habitat along the California coast that are ideal refuges for monarchs to return year after year.

Although clusters of overwintering monarchs can be hard to spot within Contra Costa County, you may be able to find them at the UC Berkeley Richmond Field Station, Point Pinole, Booker T. Anderson Jr. Park, and the SF Bay Trail near Pacific Avenue in Rodeo. You can explore overwintering sites on the Xerces Society Map of Overwintering Sites webpage.

While monarchs do not need milkweed during the overwintering period, milkweed plays a vital role in their survival throughout their life cycle. Milkweed is the monarch’s host plant, meaning that monarch caterpillars are completely dependent on milkweed as food for their growth. Unfortunately, milkweed populations have been slowly disappearing due to habitat loss, climate change, and pesticide use, leading to a 99% reduction in the western monarch population since the 1980s. This is why it is so important for us to plant native milkweed and help re-establish their populations.

Learning about the monarch butterfly’s perseverance and strength has inspired my own passion for monarch conservation. This inspiration motivated me to host a Milkweed Planting Party in early November, where we planted 120 narrowleaf milkweed to help support the monarch butterfly population. It was wonderful to see the community come together on a Saturday morning to plant milkweed and create habitat for pollinators and wildlife. Although we may not see monarchs right away, our efforts will continue to make a difference for years to come. 

Want to help monarchs, too? Consider joining volunteer planting events near you and/or growing your own native milkweed at home. Be sure to check that the milkweed is native to your region, and avoid planting milkweed within 1 mile of monarch overwintering sites. Also consider planting other flowering natives to support monarch adults and other pollinators. Check out the Xerces Society’s Planting and Establishment Guide for more information.

Together, we can make a difference and conserve monarch butterflies for generations to come!