Climate Change Threatens Monarch Butterfly Migration
Scientists have issued new warnings that climate change is threatening the migration patterns of monarch butterflies. Rising temperatures are causing suitable milkweed habitats in Mexico, the butterflies' critical wintering grounds, to shift southward. This displacement threatens to fracture migration routes and could place some monarch populations at risk of collapse.
The eastern monarch population, migrating from the U.S. and Canada to Mexico, has plummeted by over 80% since the 1990s. The western population, which overwinters in California, has fared even worse, declining by more than 95% since the 1980s. In the 2023-2024 winter season, the eastern monarch population occupied only 2.2 acres in Mexico, a 59% decrease from the previous year and the second-smallest area ever recorded. A monarch's migration is a multi-generational relay covering up to 3,000 miles. The generation that flies south lives up to eight times longer than their parents and grandparents. Scientists believe they navigate using the sun's position and the Earth's magnetic field to find the same overwintering sites as their ancestors. Beyond climate change, the most significant threat to monarchs is the loss of milkweed, the only plant their larvae consume. The proliferation of herbicide-resistant crops has allowed for widespread spraying that eradicates milkweed from agricultural fields, a primary monarch breeding ground. Pesticides, particularly neonicotinoids, also pose a major threat. These insecticides are absorbed into the plant, making the entire plant toxic to insects that feed on it, including monarch caterpillars on milkweed and adult butterflies drinking nectar. Conservation efforts are underway to address these threats. In December 2024, the U.S. Fish and Wildlife Service proposed listing the monarch butterfly as a threatened species under the Endangered Species Act. Canada listed the monarch as endangered in 2023, and Mexico protects their overwintering sites within the Monarch Butterfly Biosphere Reserve. Organizations and individuals are working to restore monarch habitats by planting milkweed and other nectar-producing flowers in gardens, schools, and along roadsides. The "Monarch Waystations" program, for example, encourages the creation of these habitats to support the butterflies during their long migration.
