What do Iran and our plummeting population of monarch butterflies have in common? Nothing, really—except maybe to get you to rethink the value of letters postmarked from Capitol Hill.

Senate Republicans may have dominated headlines recently with their foreign-policy stunt turned PR disaster, but another letter—this one signed by 52 House Democrats—would appear to put the letter-writing skills of Congress to better use.

Related One Beautiful Thing You Can Do to Help Monarch Butterflies

At issue is the alarming drop in the number of monarch butterflies making their annual migration to Mexico over the past two decades. Back in the mid-1990s, almost a billion butterflies were estimated to have made the trek, blanketing some 44 acres of evergreen forest in the mountains west of Mexico City each winter. This year, just 56.5 million made it, covering a scant 2.8 acres of forest—the second-lowest count on record.

The situation is so dire, scientists and environmental groups warn that we could see the great monarch migration virtually disappear in a generation, if not sooner.

Now, it seems, the monarchs’ plight has led to the formation of something like a butterfly caucus in the House. In a letter to the president this week, congressional Democrats called the Obama administration to protect the monarch butterfly under the Endangered Species Act.

“As we have learned from examples like the passenger pigeon, formerly vast populations of species can disappear without the proper protections,” the members of Congress wrote, calling the ESA “the last best chance to save this amazing species and its incredible migration.”

It’s no coincidence, however, that only a scant handful of representatives who signed the letter hail from Farm Belt states—a mere three by my count—just as it’s no coincidence that the monarch’s precipitous plunge can be traced to the mid-1990s. That’s when agri-tech giant Monsanto released the first in its patented line of “Roundup Ready” crops: soybeans and, later, corn, cotton, canola, alfalfa, and sugarbeets that were genetically modified to withstand a virtual deluge of Monsanto’s own Roundup herbicide, generically known as glyphosate.

Between 1992 and 2011, glyphosate use skyrocketed more than a hundred fold, from 20 million pounds per year to more than 250 million pounds. It was a boon to Big Ag, but not so much for monarchs—all that glyphosate was killing off the native milkweed the butterflies depend on to survive.

It can’t be overstated how cruicial milkweed is for the species. It is the only plant on which monarchs lay their eggs and that their larva can feed on. Yet Big Ag’s herbicide free-for-all is causing upwards of a million acres of monarch habitat to disappear each year in the central U.S., according to the nonprofit Monarch Watch. The irony is that milkweed presents little threat to harvests, unlike, say, palmer amaranth or pigweed; it is an innocent bystander.

To be sure, the House Democrats applaud “the early efforts by farmers, local, state and federal agencies to plant milkweed and to educate the public on the plight of the monarch.” But it’s not enough: “Without a sea change in how the federal government addresses the use of herbicides, especially as applied to herbicide-resistant crops, vital monarch habitats will simply continue to disappear.”

How amenable the Obama administration might be to stemming the tide of herbicide is debatable. While the Fish and Wildlife Service has said monarchs “may” merit federal protection, the Environmental Protection Agency is currently facing not one but two lawsuits from environmentalists over its handling of the monarch crisis. The first suit charges that the agency has failed to respond to an urgent petition to limit the use of glyphosate. The second seeks to block the EPA’s recent approval of Enlist Duo, a next-generation chemical herbicide made by Monsanto rival Dow that contains significant quantities of—you guessed it—glyphosate.