About This Species
Each year, the orange, black and white monarch butterflies of North America set off on a massive migration. Millions of the butterflies travel between the winter homes in central Mexico and California and their summer homes further north in the U.S. They travel northward through the warm months until the weather starts to turn cooler, triggering a return to the south. The butterflies travel between 50 and 100 miles a day.
The monarch's large geographical range helps make it resistant to climate change. Its short generation time and high reproductive rate also make it more able to adapt to incremental climatic changes.
But the monarch's migration—one of the things that make it so unique—may also make it particularly vulnerable to climate change. Monarchs, like most butterflies, rely on temperature cues to trigger reproduction, migration and hibernation.
The monarch population has been in steep decline, according to WWF. Researchers measure the abundance of the population by assessing the amount of forest that the butterflies occupy during winter. At the end of 2014, the habitat occupied by the eastern population, which is found east of the Rocky Mountains and winters in central Mexico, was the second-smallest since monitoring began in 1993. This migration has been classified as endangered. The western monarch population, which stays west of the Rockies and winters on the coast of California, is estimated to have declined by 50 percent compared with long-term averages. Over the past 20 years, monarchs have lost more than 165 million acres of habitat, including nearly a third of their summer breeding grounds.
The Monarch Butterfly's Range
The largest populations of monarchs are in North America, though there are smaller groups elsewhere. In addition to the large eastern and western migratory populations in North America, there is a small non-migratory population in southern Florida.
As temperatures continue to rise, the prognosis for monarchs is bleak. Monarchs rely on cues from the environment to trigger its migration in both directions. The butterfly's reproductive development—and development across all life stages—is triggered by temperature. The climate affects the butterfly's body temperature, which helps it find a mate, increase fecundity and lay eggs.
Climate change has already had a significant impact on monarch's primary food source: milkweed. The plant has several impacts on the butterflies' entire life cycle. Monarchs lay their eggs on the plants; during the larval stage, caterpillars feed on it; and adult butterflies feed on the flowers' nectar. With rising temperatures and increased drought, milkweed is declining. The plant faces a second threat from farmers, who use herbicide to fight the weed's spread. If monarchs are able to survive changes in climate, they may have to change their migratory patterns to seek out milkweed in new locations.