Taylor says the populations have dropped by an average of 40 percent since the beginning of the decade, and he says he thinks he knows why.

A leading culprit, he says, is the widespread adoption of genetically modified crops — strains of corn and soybeans with genes added so they are herbicide-tolerant.

http://abcnews.go.com/Technology/monarch-butterflies-genetically-modified-gm-crops/story?id=14057436#.Th2GWo7G2Wk.facebook

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