The monarch butterfly occurs globally, however the subspecies that inhabits North America, Danaus plexippus plexippus, is imperiled. This includes both of the two main populations in North America, the larger eastern population and the smaller western population.
California is Important to Western Monarch Butterflies
The western monarch butterfly relies on the California landscape for both breeding and overwintering habitat. Unlike the main eastern population of monarch butterflies that migrates to central Mexico to overwinter in huge concentrated clusters, the western population migrates to the coast of California. Here they find moderated temperatures and protection from winter storms by clustering in groves of trees scattered along the coast from Mendocino County to Baja California.
In the spring, adult butterflies begin to move inland feeding on flower nectar, and mating and laying eggs on a variety of milkweed plants, the sole source of food for monarch caterpillars. These individuals then die, leaving their offspring to repeat the cycle. Several generations later, the last adults produced in late summer/fall migrate to the coast of California to survive the winter in groves of trees that provide the appropriate conditions. Even though the individuals have never been there before, they somehow find their way to the same groves used by previous generations.
Monarch Butterfly Populations are Declining
This unique multiple-generation migration phenomenon has continued for thousands of years, but a notable decline in monarch populations has been documented relative to what was observed 20 years ago. This decline is likely due to a combination of factors, from habitat loss due to development, changing agricultural practices, and invasive species, to pesticide exposure and climate change.
Monarch Butterfly Represents All Pollinators
These environmental pressures affect not only the monarch butterflies, but the myriad of other native pollinators (e.g., bees, beetles, flies, moths, other butterflies) that rely on a diversity of flowering plants. Pollinators provide essential ecosystem services for humans and wildlife, from assisting plant reproduction and production of human food, to serving as high-energy food themselves for other wildlife. The monarch butterfly, well-known and appreciated by many, has become a “flagship” species, representing the need to do more for the conservation of all pollinators nationwide.
You Can Help!
The good news is there is a lot people can do now to help the plight of monarch butterflies and pollinators in general.