Restoring milkweed could save the eastern monarch butterfly

The eastern monarch butterfly is disappearing alongside its primary food source, the milkweed plant. Researchers at Simon Fraser University have analyzed current conservation strategies and recommended where declining milkweed can be restored.

Study lead author Rodrigo Solis-Sosa said researchers hope to prevent the eastern monarch butterfly from the same fate as the western population, which typically migrated from the Okanagan to California each winter. 

Solis-Sosa noted that this year’s measurements of western monarch butterfly colonies found zero overwintering populations, putting them at an all-time low and closer to extinction.

Eastern monarch butterflies spend the winter months in Mexico, migrate and reproduce in the United States in the spring, and reach eastern Canada in late August.

Factors including climate change and the clearing of land for agricultural use has led to a decline in milkweed throughout the U.S. 

The team identified the Midwest as the best place to focus on restoration efforts, given optimal weather and milkweed availability when the monarch butterfly arrives. The researchers also found some overlooked potential for restoring milkweed in the South.

“While increasing the number of milkweed stems in the South wasn’t as effective as in the Midwest, decreasing their number in the South was catastrophic,” said Solis-Sosa. “While the South may not play a huge role in increasing the eastern monarch butterfly population, it acts as a safety net.”

The experts discovered that current conservation models fail to account for the effects of drought, changes in temperature, and the stem’s effective usability by the monarch butterflies. 

The study also revealed that estimates of between 1.2 and 1.6 billion milkweed stems fall short of supporting butterfly populations by 50 to 90 percent.

“Monarchs may need at least three billion stems to reach a safe minimum threshold population of six overwintering hectares,” said Solis-Sosa.

Eastern monarchs once covered the equivalent of 18 hectares during the winter, but the latest measure has dwindled to just 2.3 overwintering hectares.

Communities in Mexico depend on the monarch butterfly as an essential part of their culture. 

“Monarch butterflies also hold a special significance in traditional Mexican culture,” said Solis-Sosa. “They arrive in Mexico by November 2 – the Day of the Dead – and symbolize the dead souls of loved ones arriving to comfort them through the dark and cold winter season. Losing the monarch butterfly would represent a cultural loss to the Mexican people.”

The study is published in the journal Frontiers in Environmental Science.

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By Chrissy Sexton, Earth.com Staff Writer