Some farm groups are criticizing a new report about the hazards of atrazine, a herbicide that was banned by the European Union more than 10 years ago.

The population of the monarch butterfly -- seen here in Chicago's Grant Park -- has declined by more than 80 percent over the past two decades. A 2016 study claims the decline of milkweed plants in the Midwest is a contributing factor. (Oriol Gascón i Cabestany / Flickr)

Their annual migration from North America to Mexico has been called “one of the most spectacular natural phenomena in the world,” but the monarch butterfly is not only in decline – it’s closer to extinction than previously thought, research shows.