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Study: World's Largest Monarch Population Could Disappear in 20 Years

March 21st, 2016
Center for Food Safety

84 Percent Decline Driven by Loss of Milkweed Due to Genetically Engineered Crops

The eastern population of the monarch butterfly — which includes 99 percent of the world’s monarchs — is at high risk of extinction within two decades unless the population rebounds dramatically, according to a new study published today Nature Scientific Reports.

The study from the U.S. Geological Survey and other scientists predicts an 11 percent to 57 percent chance of extinction for the monarch migration in the next 20 years. The study reports that well-documented declines in milkweed, the monarch caterpillar’s only food source, are highly correlated with increased use of herbicide-resistant, genetically engineered corn and soybeans, which now make up about 90 percent of all corn and soy grown in the United States.

“This new study confirms that GE crops are the driving cause of monarchs’ precipitous decline, as we have warned for years. Monarchs need protection under the Endangered Species Act or face extinction,” said George Kimbrell, senior attorney at the Center for Food Safety.

“We need to protect monarchs under the Endangered Species Act and increase protections for their summer breeding habitat, or the next generation of children may never see a monarch butterfly,” said Tierra Curry, a senior scientist at the Center for Biological Diversity.

The vast majority of the world’s monarchs are found in the Midwestern and eastern United States. They undertake an annual multigenerational migration from Mexico to Canada. A smaller population of around 260,000 butterflies is found west of the Rocky Mountains and overwinters on the California coast. Today’s study estimates that the eastern population must increase to at least 225 million butterflies to cut the extinction risk by half. This year’s population was estimated at 150 million butterflies, though up to half of those may have been killed by a severe winter storm.

Earlier this month the Center for Food Safety and the Center for Biological Diversity filed a lawsuit against the U.S. Fish and Wildlife Service over the agency’s failure to protect monarch butterflies under the Endangered Species Act. The two groups and allies formally petitioned the Service in August 2014 to protect the monarch as a “threatened” species following a 90 percent population decline over the preceding two decades. In December 2014 the Service determined that protection may be warranted, triggering an official review of the butterfly’s status. The lawsuit was filed because the Service failed to meet a statutory deadline for making a final determination on the monarchs’ status, and requests that the court set a deadline for that decision.

The same day the most recent lawsuit was filed, the overwintering colonies in Mexico were struck by a severe winter storm. Scientists are still tallying the damage, but early estimates predict that 30 percent to 50 percent of the overwintering monarchs may have been killed. This could set the population back to the record lows of the previous two years before this year’s small rebound.

Though monarch numbers increased slightly this past year due to favorable weather conditions, the long-term outlook remains bleak, especially in light of the recent storm. Monarchs require a very large population size to be resilient to severe weather events and other threats. A single winter storm in 2002 killed an estimated 500 million monarchs — more than three times the size of the entire current population.

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