Monarch Butterfly Numbers Remain Dangerously Low

The World Wildlife Fund and their partners announced the results of their yearly monarch butterfly survey today at 2.48 hectares, down 14% from last year’s count of 2.91.  While this year’s count is not as dire as the numbers have ever been, the population remains dangerously low.

2.48 hectares translates to approximately 93 million monarch butterflies and although that may sound like a lot, it is well below the population’s high which was nearly 10 times greater two decades ago. It is also less than half of what some scientists have called for to ensure a stable population. The monarchs have been in steep decline—and now hovering around their lowest numbers—since the introduction of genetically modified corn and soy crops that were engineered to resist the application of the herbicide glyphosate, commonly known as Round Up. This invention allowed for the massive removal of weeds from agricultural fields including milkweed—the only food source for monarch caterpillars. This loss of breeding habitat has been widely attributed to the decline of the North American monarch butterfly population which migrates from Mexico across the eastern United States as far north as Canada and then back again every year.

While there have been increased efforts over the last couple of years to re-establish milkweed along roadsides, rights-of-ways and in people’s own backyards, the agricultural industry has continued with business as usual. In fact, because many types of weeds (though not milkweed) have now grown resistant to glyphosate, the agricultural industry has engineered crops that are resistant to combination pesticides such as Dow’s Enlist Duo which brings together glyphosate with another pesticide called 2,4 D. These combination pesticides will continue to keep milkweed out of agriculture while also increasing the public’s exposure to more pesticides—and yet these pesticides will only perpetuate the cycle of weed resistance requiring even greater pesticide use.

NRDC is challenging EPA’s approval of Enlist Duo for failing to adequately consider the impacts of the pesticide on monarch butterflies and public health. That court case is finally moving forward and briefing will be completed this spring. If we are going to protect monarch butterflies, it is critical that the agricultural industry be part of the solution.

A study last year showed that for the US to plant enough milkweed to maintain a stable and resilient population of monarchs, the conversion of some agricultural land would be essential, assuming current agricultural practices remain the same. That’s because agricultural land currently occupies 77% of the potential monarch habitat in the US. The study estimated that between 6-12% of current agricultural land would need to be converted to diverse herbaceous grassland cover.

Fortunately, this exact solution has been shown to benefit both pollinators and agriculture. A program out of Iowa State University called STRIPS has demonstrated that converting 10% of a given agricultural field into strategically placed native prairie strips can bring overall benefits not only ecologically (including increasing pollinator abundance 3.5 fold), but to the farmer as well in the form of reduced nutrient and water runoff and enhanced soil quality with minimal impact to production.

We know how to save the monarch butterfly—and doing so can even bring additional benefits to ecosystems and people. We need to reduce pesticide use and increase pollinator habitat. But it is going to take a combined effort that includes action by the EPA and the agricultural sector if we want to ensure a future in which monarch butterflies continue to fly.

Monarch butterfly

USFWS

About the Authors

Sylvia Fallon

Senior Director, Wildlife Division, Nature program

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