Sunday, March 9, 2014
By Mary Beth Breckenridge
The people who are working to turn around the decline of the monarch butterfly wish you did.
The monarch population has declined dramatically in recent years. This winter, the number of monarch butterflies reaching Mexico in their annual migration hit its lowest level since scientists started monitoring their colonies in 1993, according to the results of a scientific survey released earlier this week.
The amount of Mexican forestland occupied by the monarchs declined 43.7 percent from the previous winter, the research showed. That followed a 59 percent drop the year before.
The reasons for the decline are many, but one of the biggest is the loss of much of the milkweed that’s so important to the showy orange-and-black butterflies, said Orley R. “Chip” Taylor, an insect ecologist at the University of Kansas and the founder and director of the educational outreach program Monarch Watch.
That’s why Taylor’s organization and other monarch advocates are turning to gardeners for help. By planting milkweed, they say, gardeners can help restore the monarchs’ habitat and bolster their numbers.
It doesn’t have to be a big effort. Just a few plants make a difference.
“You don’t have to have acres of milkweed,” Taylor said. In fact, he said it’s better to have small, scattered sites than large plots, because big stands of milkweed attract predators and parasites.
Milkweed is critical for monarch butterflies because it provides food and, even more importantly, a place to reproduce.
Milkweed plants are the only host plants for monarchs, meaning they’re the only plants on which monarchs will lay their eggs. When caterpillars hatch from those eggs, they feed on the milkweed leaves.
Besides providing nourishment, the leaves help protect monarchs from predators. Chemical compounds in the milkweed plant make the caterpillar poisonous to many of its enemies, which are usually repelled by the insect’s foul taste. That poison stays in the insect’s body when it turns into a butterfly.
Milkweed also provides nectar that helps fuel the adult monarch’s long flights to and from Mexico. It’s not the only plant monarchs will feed on, but it’s the only one that does double duty for the butterflies as both a host plant and food plant.
Unfortunately, there are far fewer milkweed plants to support monarchs today than in the past. Since 2000, about 180 million acres of monarch habitat has been lost, Taylor said. That’s about 30 percent of the butterfly’s summer breeding habitat.
The biggest contributor to that loss is the spraying of broad-spectrum weed killers on farm fields, he said. Many farmers, particularly in the Midwest, are planting Roundup Ready corn and soybeans that aren’t killed by glyphosate, the herbicide used in Roundup. When those farmers spray their fields to kill weeds, they kill the milkweed.
Taylor said ethanol production has also had a big effect, because monarch habitat has been turned into cropland to grow the corn used for the biofuel.
Development has hurt, too, as has forest degradation in the area of Mexico where the monarchs spend the winter. It hasn’t helped that milkweed is considered a noxious weed and eradicated in some areas, said Bob Kehres of Ohio Prairie Nursery in Hiram Township, which sells the plant. And Taylor said the unusual weather of the last two summers is another factor, because conditions have been poorly suited to monarch reproduction.
Taylor pointed out that it’s the migration of the monarch butterflies that’s threatened, not the butterflies themselves. Their population has dropped so low that recovery will take several years, but “it will come back,” he said.
Nevertheless, Taylor said that if we want to continue to enjoy the sight of monarchs here in the North, we need to support their long annual migrations to and from Mexico by making sure there are habitats they can visit all along the route.
The beauty of native plants like milkweed is that they grow easily. Taylor said. He recommends planting it along with a variety of other native flowers that bloom at different times, so nectar is always available to the butterflies.
“Anybody can do this,” he said. “It’s a very low-effort thing to do.”