With its iconic orange and black markings, the monarch butterfly is one of the most recognizable species in North America. Monarchs are particularly remarkable because they migrate each year, flying from as far as Canada and across the United States to congregate at a few forested overwintering sites in the mountains of central Mexico and coastal California. These sites are an amazing phenomenon: thousands of monarchs cluster in the trees in California, and millions of monarchs drape large swathes of forest in Mexico.
Monarch butterflies east of the Rocky Mountains used to number in the hundreds of millions but the population has declined by approximately 80%. Loss of habitat due to genetically modified crops, overuse of herbicides and insecticides, urban, suburban and agricultural development, disease, climate change, and overwintering site degradation are the leading causes of monarch decline.
Monarchs begin their southern migration from September to October. Eastern and northeastern populations, up to 500,000 monarch butterflies, migrate at this time. Originating in southern Canada and the United States, they travel to overwintering sites in central Mexico. The butterflies arrive at their roosting sites in November. They remain in their roosts during the winter months and then begin their northern migration in March. No individual butterfly completes the entire round trip. Female monarchs lay eggs for a subsequent generation during the northward migration. Four generations are involved in the annual cycle and the generation undertaking the southbound migration live eight times longer than their parents and grandparents.
Milkweeds are the required host plants for monarch butterfly caterpillars (female monarchs lay their eggs on milkweeds) and their flowers provide nectar for bees, butterflies, and other beneficial insects. By planting milkweed, you can provide habitat for monarchs and also attract and support pollinators.
While restoring the millions of milkweed plants that have been lost is certainly an important strategy, monarchs need more than milkweed to support them throughout the year. Adult monarchs need nectar to fuel them during spring migration and breeding and to build up stores of fat which sustain them during fall migration and winter. Too few nectar plants in the landscape may reduce the number of monarchs that successfully arrive at overwintering sites in the fall.