VIDEO: Monarch Butterflies Tagged for Trip South
The review was launched in response to a petition by the Center for Biological Diversity, the Center for Food Safety, the Xerces Society for Invertebrate Conservation and renowned monarch scientist and University of Florida professor emeritus Lincoln Brower, who has been studying the species for 60 years and has published more than 200 scientific papers on the subject.
In a press release, the Xerces Society said the North American population of monarchs has declined from 1 billion in 1996 to just 35 million this past winter, the lowest number ever recorded.
VIDEO: Monarch Butterfly Fast Facts
Xerces tied the decline of monarchs to the widespread planting of genetically modified corn and soybean crops in the U.S. Midwest, where most of the butterflies are born. The GMO plants are designed to be immune to an herbicide that kills off milkweed.
Over the last two decades, monarchs have lost more than 165 million acres of habitat - an area roughly the size of Texas. In addition, butterflies are threatened by climate change, drought, urban sprawl and logging on their Mexican winter range.