The monarch butterfly population has plummeted in less than 20 years, leading one environmental group to sue the U.S. Environmental Protection Agency to take action.

The Natural Resources Defense Council filed suit in a New York City federal court seeking an order to force the EPA to review an emergency petition that it filed last year. The NRDC claims the EPA never responded to the request.

The group also wants the agency to review within six months its rules governing glyphosate, the main ingredient in Monsanto’s Roundup, a commonly used herbicide that has wiped out the milkweed plant in many parts of the country. Monarch butterflies rely on the milkweed for their survival.

The monarch population has dwindled from 1 billion in 1997 to 56.5 million this winter—a drop of 90%, according to the complaint (pdf).

The NRDC says the “distinctive butterfly” is “in peril,” and faces the risk of completely dying off. “The remaining population is so small that a single severe weather event could eradicate it,” the group wrote. “Scientists have warned that the monarch migration is at risk of vanishing.

“In 2002, a single snowstorm on the Mexican wintering grounds killed more monarchs than currently comprise the entire population,” the complaint states. “The continued loss of butterflies will make this already imperiled population increasingly vulnerable.”

Use of Roundup has increased as Monsanto has developed and promoted “Roundup-Ready” crops that are resistant to the herbicide. However, farmers using the chemical are killing neighboring milkweed plants on which monarchs thrive.

-Noel Brinkerhoff

To Learn More:

Environmentalists Link Plunge of Monarch Butterfly to Herbicide (by Lorraine Bailey, Courthouse News Service)

Natural Resources Defense Council v. U.S. Environmental Protection Agency (U.S. District Court, Southern New York) (pdf)

Public-Private Partnership Tries to Save Monarch Butterflies as Population Collapses by 970 Million in 25 Years (by Noel Brinkerhoff and Steve Straehley, AllGov)