By: Carol Polsgrove

As monarch butterflies make their long journey from the U.S. to Mexico this fall, let's pause to consider the 90 percent drop in their numbers over the past twenty years. So steep has been their decline that a petition has been filed with the U.S. Fish and Wildlife Service requesting protection for the monarch under the Endangered Species Act.

This eloquent and detailed document lays out the research showing not only the decline but the causes of it. At the top of the list is the use of the herbicide glyphosate – best known as the active ingredient in Roundup – on vast Midwestern fields of crops genetically engineered to be unaffected by it.

Among the unwanted plants zapped, alas, is milkweed, the only plant where monarchs lay their eggs and monarch caterpillars feed. With the coming of glyphosate-resistant corn and soybeans, milkweed has virtually vanished across the industrially farmed fields of the Midwest.

To make matters worse, farm fields have been covering ever more of the landscape in response to government incentives for growing corn and soybeans for biofuels.

The petition notes other causes of the monarch's decline – including expansion of the built environment, climate change, and logging on Mexican land where most of them cluster in trees for the winter. And new herbicide-resistant crops, awaiting regulatory approval for commercialization now, threaten the nectar plants monarchs depend on during migration.

But the loss of milkweed in their breeding areas is crucial. Monarchs have evolved to be dependent on the protection milkweed provides to make them unattractive as food to other animals. The document describes their plight in strong terms:

"The majority of the world's monarchs originate in the Corn Belt region of the United States where milkweed loss has been severe, and the threat that this habitat loss poses to the resiliency, redundancy, and representation of the monarch cannot be overstated."

The petitioners argue that because of monarchs' high vulnerability to predators and severe weather conditions, their survival as a species depends on ensuring a vast population, now woefully diminished.

The petition was filed by the Center for Biological Diversity, the Center for Food Safety, the Xerces Society, and long-time monarch scientist Lincoln Brower, distinguished service professor of zoology emeritus at the University of Florida and professor of biology at Sweet Briar College.

The Fish and Wildlife Service has 90 days from the filing date (Aug. 26) to decide whether the evidence presented merits further review under a process outlined by the Endangered Species Act.

Originally Published: The Huffington Post