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It’s been a dismal year for North America’s favorite migratory species, the monarch butterfly, beginning with the report that populations at overwintering sites in Mexico were down 59 percent from the previous winter. When researchers there measured the total area of trees occupied by monarchs—the stock for most of the continent—it added up to less three acres, an all-time low.
Nothing about the spring migration, which recently ended, gave new cause for hope. Monarch numbers are now so low that any catastrophic event could “send the population spinning downward even more,” says University of Kansas insect ecologist Chip Taylor, whose advocacy group Monarch Watch works to protect and rebuild monarch butterfly populations. The thin population could weaken conservation efforts, he says, “because if you don’t see them, you don’t have the motivation to do something about it.” He expects that the numbers will probably go even lower this coming winter.
The tendency is to blame the problem on Mexico, where logging of critical forests has been a perennial issue. Taylor says Mexico has made “a terrific effort to control illegal logging” and has largely put a stop to “the organized mafia-like groups that go in there with guns and cut down a hectare of forest in one night.” But serious incidents still sometimes occur.
A far larger problem, though, is the increasing intensity and efficiency of agriculture in the United States. Taylor dates the dramatic decline in monarch butterflies to the introduction of Roundup Ready corn and soybeans by the Monsanto Co. in the late 1990s. Until then, farmers typically ran a tiller through their fields to chop up weeds and turn over the soil. It was an inefficient method that generally left as many as 40 milkweed plants per acre across the Corn Belt. That was a good thing for monarch butterflies, which depend on milkweed as the host plant for their larvae.
Then the new genetically-engineered crops made it possible for a farmer to spray the herbicide Roundup on a field, eliminating all the weeds without harming the crop. As a result, use of Roundup, also manufactured by Monsanto, has tripled since the late 1990s. For Monsanto, says Taylor, “that was a pretty good system. You could make money on both, right?”
Milkweed has also become far scarcer, he says, because the government mandate for biofuel has pushed U.S. farmers to plant an additional 25.5 million acres of corn and soybeans since 2006. Farmers used to put about 10 million of those acres in the federal Conservation Reserve Program, which pays them to set land aside for wildlife. The other 15.5 million acres was largely marginal land that would have been ideal habitat for milkweed.
Taylor doesn’t blame the farmers for their choices: “If I was a farmer and I was holding two jobs to keep my farm, and I didn’t want to have my rear end sitting on the tractor too long, I would use that product as well, because the ordinary mechanical tillage took a lot more time and cost a lot more money.”
But it has in effect left monarch butterflies homeless. And Taylor worries that other genetically engineered crop lines are now being developed to tolerate three or four different herbicides. “And that could have a tremendous impact on the vegetation, on the pollinators, and of course, on the monarch butterflies.”
To save the monarchs, Taylor believes people should begin cultivating milkweed on any available patch of land, on the model of the Victory Garden movement during the First and Second World Wars. You can buy milkweed seed from Monarch Watch, which is a nonprofit organization. But Taylor says a better option is to buy milkweed plugs, with well-established roots, so they will begin flowering as quickly as possible. His group focuses on 30 different North American milkweed species commonly used by monarchs, with different species suited to different geographic regions and habitats. It still has 4,000 plugs left to sell for planting this fall and expects to produce 30-40,000 for the spring. The Monarch Watch website also lists commercial plant suppliers offering milkweed for different regions.
In addition to milkweed, says Taylor, monarchs and other butterflies depend on nectar plants to fatten up. Zinnias, cosmos, Joe Pye weed, boneset, and verbena are all good choices. So is butterfly bush, he says, but because it can become invasive, use only sterile male plants.
Image: Butterfly migration map via Monarchwatch.org
A larger challenge for anyone who loves the monarch butterfly migration is to lobby states and the Federal Highway Administration to plant its vast acreage of roadside land with milkweed and other flowering plants instead of grass. Alabama, Idaho, Illinois, Minnesota, Texas, and West Virginia States have all named the monarch their state butterfly and could logically lead a national campaign. But every state in the monarch’s migratory range has a highway department, and studies have demonstrated that roadsides can make ideal butterfly habitat. In England in the 1990s, for instance, 25 butterfly species quickly moved in after the government designed a section of the M40 highway near Oxford as a butterfly travel corridor between protected woodlands.
Failing that kind of campaign, Taylor acknowledges, the annual monarch butterfly migration, like that of the passenger pigeons, could vanish into the American past.