Monarch Butterfly

Milkweed is the only plant on which monarchs will lay their eggs and the only source of food for baby caterpillars. But urban planning and agricultural expansion in the United States and Canada have paved and plowed over millions of acres of milkweed. The development of genetically modified (GMO) Roundup Ready crops has played a major role in the loss of milkweed in agricultural areas. These GMO crops don’t directly harm the butterfly. Rather, it is their ability to resist Glyphosate, a weed killer and the primary active ingredient in Roundup, that has eliminated 99% of the milkweed that once grew in corn and soybean fields. A second factor that has harmed monarch butterflies is neonicotinoids (neonics), a class of neurotoxic insecticide. Although marketed as a safer option for selectively killing pests, neonics have instead made US agriculture 48 times more toxic to most insects, including pollinators. These pesticides are affecting entire food chains as they are persistent in the environment, infiltrate groundwater (highly water soluble), and have cumulative and largely irreversible effects on invertebrate populations.

Migratory monarch populations need large, healthy forests to protect them from winds, rain, and low temperatures common at night in the forests where they overwinter in Mexico and California. While logging of the monarch butterfly’s overwintering habitat in central Mexico has harmed the species, the impacts of habitat destruction, insecticides, and herbicides within the species breeding grounds in the US and Canada, along with the effects of climate change, are the major drivers of its decline today.