Climate Change Cripples the Great Monarch Migration

Image: Ron Magill

The North American migration of monarch butterflies is truly extraordinary. The 3,000-mile journey from Canada to Mexico draws spectators from around the world to behold its magic. In fact, in Mexican folklore, the butterflies are believed to carry the souls of loved ones.

But although their migration and entire lives depend on adapting to climate, climate change is making the consistent weather patterns they rely on inconsistent. As the Washington Post reported: “Now summer temperatures in the Midwest are soaring. The milkweed in Texas is drying up. Winter storms, once rare, are snaking through central Mexico regularly as air warms over the Pacific Ocean and blows across the region.”

What’s Happening? As the World Wildlife Fund explained, a number of traits make monarchs vulnerable to a changing climate.

  • Like most butterflies, monarchs are highly sensitive to weather and climate: They depend on environmental cues (temperature in particular) to trigger reproduction, migration, and hibernation.
  • Their dependence on milkweed alone as a host plant is a further vulnerability, particularly as milkweed abundance is declining throughout the monarch range.
  • They also face a decline in their over winter habitat, and the effects of an increasing frequency of extreme weather events such as drought and severe storms, and extremes in hot and cold temperatures.

By the Numbers: According to the Washington Post, between 1990 and 2015, the U.S. Fish and Wildlife Service says, a billion butterflies vanished.

  • Because over 95 percent of the population migrates en masse to a few patches of Mexican forest, each smaller than half a football field, a single storm or heat stroke could effectively kill off the population. (A smaller percentage of the butterflies winter in Southern California or Florida, where they face their own challenges.)
  • That nearly happened in 2002, when a winter storm killed about 75 percent of monarchs. And again in 2012, when a heatwave in the Midwest killed tens of thousands.

Bottom Line: As temperatures keep rising and heatwaves keep occurring, scientists don’t know how much longer the monarch migration will be sustained.

Why This Matters: We wrote the other day about the lengths that scientists are going to protect insects. One of the biggest drivers of the “insect apocalypse” is a rapidly warming planet and unless we get a grip on our emissions then efforts to restore monarch habitat by good samaritans will all be in vain. We need these important pollinators!

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