Monarch Butterflies Losing Food Source, Numbers Declining Sharply

  • The federal government is considering whether to add the monarch butterfly as a threatened species. Tiago J. G. Fernandes Wikimedia Commons

February 6, 2015

The Natural Resources Defense Council (NRDC) has filed suit against the U.S. government, accusing regulators of discounting the dangers of a widely used herbicide to monarch butterflies. The NRDC claims the Environmental Protection Agency has failed to heed warnings about glyphosate, the key ingredient in Monsanto’s widely used herbicide Roundup, and other products.

The NRDC and other environmental organizations have asked the EPA to review what they say is a large body of scientific evidence demonstrating glyphosate's "devastating" effects on monarchs. According to the lawsuit, the EPA has not acted.

In response, the agency issued a statement saying it is taking several steps to protect the butterflies but the science on the issue, "is still evolving" and that many factors may be effecting monarchs including loss of habitat, weather and pesticides."

Monarch, threatened species?

The U.S. Fish and Wildlife Service is considering whether to add the monarch butterfly as a threatened species under the Endangered Species Act. It has launched a one-year review of the butterfly’s status.

Monarch butterflies are famous for their amazing migration. They travel thousands of miles each year from Mexico to the U.S. and Canada and back.

But the butterflies that make that trip have declined by more than 90 percent over the past 20 years.

Monarchs need milkweed

Tierra Curry is a senior scientist with the Center for Biological Diversity. It’s one of the groups that filed a petition to launch a review by the federal government.

Curry says in the mid-1990s, there were about a billion monarchs over-wintering in Mexico.

"Now we’re down to about 35 million monarchs. And the reason for that is largely the decline of milkweed in the Midwestern United States, because milkweed is the only plant that monarch caterpillars can eat.”

One major reason for that is the growth in Roundup Ready crops over the past twenty years. Roughly 90-percent of the corn and soybean crops in the U.S. are now sprayed with Roundup or similar herbicides. But Curry says that kills milkweed.

"That has just caused milkweed to decline; before that, monarch butterflies successfully bred in corn and soybean fields.”

She says the push for more biofuels has also played a role.

“So with the big push for ethanol, farmers started planting corn on conservation reserve lands.”

So as land and food for monarchs has declined, the butterflies’ numbers have dropped.

The difference between 'threatened' and 'endangered'

Curry says her group petitioned the U.S. Fish and Wildlife Service to list the monarch butterfly as threatened rather than endangered.

"And the reason we petitioned for a threatened listing is because kids forever have brought monarch caterpillars inside to watch them metamorphose. We want people to still be able to handle them and interact with them. Everyone loves monarchs and we want that love to continue. We think that love will help save them."

She says if the Fish and Wildlife Service decides to list the monarch as threatened, it's likely the agency would develop conservation measures.  She says they could set aside land for milkweed and monarchs and make sure farmers can still do their jobs.

Backyard butterfly gardens

Because milkweed is the only thing that the monarch larvae eat, conservationists are encouraging people to plant it.

"The only complicated part of it is, there are a lot of different kinds of milkweed. So if people do want to plant milkweed at their school or park or their home, they need to find a variety of milkweed that is native to the region where they live.”

She says when you buy milkweed plants, you should also make sure they haven’t been treated with insecticides that can hurt butterflies.