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Monarch butterflies are in trouble, but it’s not Roundup’s fault

“The everyday kindness of the back roads more than makes up for the acts of greed in the headlines.”

Headlines are written to get attention. But sometimes they get the wrong attention for the wrong reasons, triggering the wrong reactions. Such is the case for this headline on a recent study on Monarch butterfly population declines, written by Cornell University’s Alliance for Science:

“Herbicide blamed for monarch butterfly population decline”

The article’s author, Denmark-based journalist Justin Cremer, leads with an inflammatory paragraph:

“A new study suggests that extensive agricultural use of glyphosate herbicide is to blame for the decades-long decline in North America’s monarch butterfly population.”

Later, Cremer writes that…the results instead bolster the “milkweed limitation hypothesis.” This theory points to the widespread use of glyphosate as the main cause of the population decline.”

But Cremer’s own article, as well as other scientist reviewers, point out that the paper claims nothing of the sort. The actual study, published in Frontiers in Ecology and Evolution, and headed by University of Kansas emeritus professor (and Monarch expert) Orley Taylor and Iowa State University butterfly authority John Pleasants, instead refuted a stubborn hypothesis that the severe (more than 90 percent) Monarch population decline over the past few decades was due to losses during its southern migration. The paper supports another hypothesis that milkweed supply declines were the real culprit, among many other problems. Milkweed is used exclusively by the Monarchs for egg-laying on their multi-generational migration from Mexico to Canada and back.

And what’s behind the milkweed decline? According to anti-GMO groups, it’s glyphosate. The world’s most-used herbicide is a popular target of opponents to genetic engineering because of the use of modified “Roundup Ready” corn and soybean, which now comprise more than 90 percent of all such crops grown in the United States. Previously, these groups blamed the GM plants for milkweed and Monarch decline.

This call for a glyphosate ban from Environmental Action is typical:


If we want to save the monarch migration, one of nature’s greatest phenomena, we need to stop the habitat destruction that’s been causing their numbers to plummet.

A great step that your state can take? Ban Roundup, the weed killer whose active ingredient, glyphosate, decimates the milkweed plant monarchs rely on to survive.2

More recently, groups have called for Home Depot and Lowes, home improvement retail giants, to stop selling Roundup (and its generic equivalents) because of what they see is harm to butterflies. Not long after the paper and Alliance for Science story were published, groups like Friends of the Earth and CommonDreams called for the sales ban:

In their pleas, the groups also include references to the WHO’s International Agency for Research on Cancer (IARC) 2015 monograph which linked glyphosate to certain cancers (a conclusion refuted by every other regulatory agency in the world, including WHO proper), and ask for switches to organic methods (which can also include pesticides).

Perhaps ironically, the few media groups that covered the paper got the story right, making the Alliance for Science story stand out even more:

What’s really behind the milkweed decline? This is where things get complicated.

Taylor, who now heads up Monarch Watch, a website dedicated to Monarch butterfly research said in an interview with the Genetic Literacy Project that once glyphosate became popular years before the introduction of GM corn and soy in the mid-1990s, it did almost eliminate the presence of milkweed in farmland. But, Taylor added, that effect ended around 2006. Taylor, Pleasants and others were more concerned in 2000 about the use of crops bred to express Bt (Bacillus thuringiensis) Cry toxin, which kills caterpillars.

Since 2006, corn and soy production have surged, partly due to overall demand and largely due to the 2007 Renewable Fuel Standard (RFS), signed by President George W. Bush, that encouraged corn-based ethanol to be used in gasoline.

In fact, research has shown recent resurgences of Monarch butterflies, though their populations still remain significantly lower than their peak. The Genetic Literacy Project’s GMO FAQs page shows that:

According to the independent Illinois Butterfly Monitoring Network, the population in 2018 reached the highest levels of the past 25 years, and the fourth highest level since 1993. The number of butterflies heading south to Mexico may reach as many as 250 million over the 2018–19 winter. At its peak in the 1990s, the population reached an estimated 900 million.

As for the Alliance for Science article, Taylor said “The text shows there is a failure to understand that long-term trends in populations are based on long-term trends. The trend here is loss of habitat and not mortality during migration or at other times in the annual cycle.” The RFS passage spurred production, and, according to Taylor, led to 24 million acres of marginal land to corn crop — more than three quarters of this land was grassland that probably once had milkweed.

Andrew Kniss, weed scientist at the University of Wyoming, tweeted shortly after the Alliance for Science article ran. Like Taylor, he weighed in that this was an issue of milkweed habitat losses because of land use, not herbicides. And if not glyphosate, farmers would use something else:

And, in 2016, a Cornell University study reported that

“In the face of scientific dogma that faults the population decline of monarch butterflies on a lack of milkweed, herbicides and genetically modified crops, a new Cornell University study casts wider blame: sparse autumnal nectar sources, weather and habitat fragmentation.”

So, what kind of “everyday kindness” has been going on for the Monarch butterfly?

Monarch Watch and other groups have spent years advocating for accelerated planting of milkweed, especially along the migratory corridors through the US and Canadian Midwest. If farms can’t do it (or won’t, because milkweed is a weed and farming is a precarious business), other areas would work: public areas, highway medians, federal lands, parks, homes and schools. Taylor’s paper called specifically for replanting 1.4 million stems of milkweed to return to levels seen 40–50 years ago.

At Monarch Watch, “we now have over 30,000 registered sites with at least twice that number that have been created but not registered,” Taylor said. “There are plenty of opportunities to provide habitats for monarchs and pollinators in lots of marginal areas around farms and even in suburban and urban environments.”

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