Monarch Butterfly Population Decline

According to Newsweek magazine, the Monarch Butterfly population numbers have decreased by 90% in the last 20 years.  Many of us have believed that the main reason for this catastrophic decline is the loss of wintering habitat in Mexico.  Recent studies show that that is not the case.

According to research done at the University of Guelph, the main reason is habitat loss on breeding grounds in the United States (Journal of Animal Ecology).  The butterflies depend on the availability of milkweed plants to complete their life cycle.  Because many farmers in the Corn Belt in the US are growing genetically-modified crops (Roundup-ready corn and soybeans) that are resistant to traditional herbicides, they are now using more and more herbicide sprays on their land.  This is eliminating the milkweed plants causing huge population declines in the butterflies.  According to the Guelph research, 70% of the milkweed in the region grows on farms where genetically-modified crops and heavy herbicide spraying are on the increase.

Unless something is done to prevent the loss of milkweed immediately, we may lose our Monarch Butterflies permanently.