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Monarch Butterfly Die-Off: Is Monsanto's Roundup Really the Issue?

Monarch lays eggs on milkweed | Photo: Quinten Questel/Flickr/Creative Commons License

A large environmental group is charging that a dramatic increase in the use of a popular weed-killer is the culprit in the last decade's plunge in monarch butterfly numbers, and the group is asking the EPA to clamp down on the chemical spray to save the butterfly. But are they blaming a symptom rather than the real cause?

On Monday, the Natural Resources Defense Council announced it had petitioned the U.S. Environmental Protection Agency to start an urgent review of its rules for use of the weed-killer glyphosate, trade-named Roundup, which it says is behind the die-off in monarch butterfly numbers.

The EPA's last Roundup rules were released in 1993, and since then use of the pesticide has multiplied by a factor of 10. And that's the same factor by which numbers of monarch butterflies have fallen in the last decade or so. Many scientists agree that there's a direct link between Roundup use and the die-off of the popular butterfly. But focusing exclusively on Roundup runs the risk of missing the big picture.

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Roundup is a popular villain these days, and that's for one reason: it's closely tied to the issue of genetic engineering. The chemical itself has been in widespread use in both agricultural and household settings since the 1970s as a broad-spectrum herbicide. "Broad spectrum," in this context, means that unlike some herbicides that kill only broad-leaved plants and leave grasses alone, Roundup can potentially kill any green plant that comes into contact with it. When it was introduced, it became extremely popular with homeowners and gardener for its relatively non-toxic constituents.

That's not to say it was safe: concerns have been expressed since the 1980s that commercial formulations of the weedkiller affect frogs and other amphibians, and it is possible to be exposed to enough Roundup to make you sick. But despite recent descriptions of Roundup as "highly toxic," it isn't really, at least not when you compare it to other highly toxic weedkillers that are still used very widely. Back in the 1970s and 1980s Roundup seemed like a magic bullet, and it became the spray of choice for weed control uses ranging from cleaning out dandelions in sidewalk cracks to removing invasive plants in wildlands.

As popular as it was in the 1980s, Roundup's prominence has skyrocketed in the last two decades. That's because Roundup's developer, the Monsanto Corporation, has spent those last two decades developing genetically modified crop plants such as corn and soya that can resist Roundup. That means, in theory, that a farmer could spray her crops with this broad-spectrum plant killer and kill only the weeds between them. That's appealing to many farmers, who would otherwise be spraying weedkillers like atrazine and 2,4-D, which are far more damaging to human and wildlife health.

Since Monsanto released its so-called "Roundup-Ready" soy and corn onto the market in 1995 and 1996, respectively, sales of Roundup have skyrocketed.

And that's what NRDC points to as a main cause of the monarch's die-off. In 2013, farmers planted 259,511 square miles of corn and soy fields, an area just a sliver smaller than the state of Texas. The vast majority of that acreage is planted in Roundup Ready crops: 97 percent of the soy grown in the U.S in 2012 was Roundup-Ready, and about 70 percent of the corn is likewise.

Which means that at least that much acreage in the Great Plains and Midwest has been sprayed repeatedly with Roundup, killing off many of the plants that aren't corn or soy across hundreds of thousands of square miles.

Among the plants being killed is milkweed, which monarch butterflies rely on as a larval food plant. Migrating adults lay eggs on milkweed plants. Those eggs hatch out into jade-green caterpillars that feed on the milkweed stems and leaves until they're ready to metamorphose into the monarch's jewel-like chrysalis, and thence into adults.

No milkweed, no monarchs. But is Roundup really the issue?

There's no doubt that tying Roundup to a certain set of crop plants is a huge problem, and it's a problem from which Monsanto benefits hugely for the time being. Easily one of the five least popular corporations in the world at the moment, Monsanto's Roundup Ready crops are the company's main profit center, allowing the range of Roundup products to bring in half the company's revenue 14 years after the company's patent on the herbicide itself expired in 2000.

NRDC is correct in urging the EPA to assess the environmental effect of the massive increase in Roundup use. But Roundup is a tool being used for a purpose: to convert more and more of the North American plains to agricultural use. It may be a favored tool at the moment, but take that tool away and you don't necessarily end the eradication of milkweed.

What's pushing that eradication? Lots of factors. The U.S. agricultural sector is huge, and it's complex. But part of the answer is in your gas tank.

Since 2007, when the federal government started requiring that oil companies mix billions of gallons of corn ethanol into gasoline nationwide, there's been a boom in corn country. Monsanto stands fully behind this boom: along with other genetech and pesticide companies like DuPont, Monsanto's been one of the ethanol mandate's biggest backers. No wonder: the company stands to make billions. Since 2007, Monsanto has been pushing its Roundup Ready corn as a way to make the notoriously inefficient process of making fuel out of corn a little bit more efficient.

Since 2007, while the amount of corn grown for food for humans and livestock in the U.S. has stayed flat, the acreage devoted to growing corn has increased sharply, by about 29,680 square miles. That's a land area the size of West Virginia and Connecticut combined. Much of that land had previously been taken up with more mixed vegetation: hayfields, soil conservation lands, verges and ditches, and the edges of woodlots.

In other words, milkweed fields. Monarch butterfly habitat.

To its credit, NRDC readily agrees that there are things other than Roundup use involved in the monarch butterfly die-off. "Although other factors like temperature and drought also affect the monarchs," said the NRDC's Sylvia Fallon in a blog post Monday, "...the widespread use of glyphosate in association with genetically modified Roundup Ready crops has been a major contributor to the decline of the monarch population. With glyphosate, says leading monarch expert Karen Oberhauser of the University of Minnesota, 'We have this smoking gun.'"

NRDC is also encouraging the EPA to assess the effect of other herbicides on milkweed and monarchs. That's a very good thing, though those other, more environmentally toxic herbicides aren't getting nearly as much press. It may well be that taking a hard look at Roundup use will be a short-term solution to the monarchs' disappearance. But it may not matter to the monarchs whether we kill off their offspring's food plants with Roundup, atrazine, 2,4-D, or a million underpaid laborers with sharp hoes.

If we clamp down on Roundup use without addressing the counterproductive ethanol mandate that's driven much of the decrease in monarch habitat, we may be taking away that "smoking gun" and ignoring the chemical weaponry remaining in the arsenal.

Let's not let Monsanto's late unpopularity distract us from the bigger picture.

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About the Author

Chris Clarke is a natural history writer and environmental journalist currently at work on a book about the Joshua tree. He lives in Joshua Tree.
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