Monarch Butterfly Survey Indicates Lowest Numbers in 20 Years

Extreme weather and a decrease in a primary food source threatens monarchs.

Monarch on yellow flower

The percentage of forest occupied by monarch butterflies in Mexico, used as an indicator of the number of butterflies that arrive to that country each winter, reached its lowest level in two decades. According to a survey carried out during the 2012-2013 winter season by the WWF-Telcel Alliance, and Mexico’s National Commission of Protected Areas (CONAP), the nine hibernating colonies occupy a total area of 2.94 acres of forest—representing a 59% decrease from the 2011-2012 survey of 7.14 acres

The latest decrease in monarch butterflies is likely due to a decrease in the milkweed plant (Asclepias)—a primary food for monarchs—from herbicide use in the butterfly’s reproductive and feeding grounds in the US, as well as extreme climate variations during the fall and summer affecting butterfly reproduction.

“Extreme climate fluctuations in the U.S. and Canada affect the survival and reproduction of butterflies,” Omar Vidal, director general of WWF-Mexico, said. “The monarch’s lifecycle depends on the climatic conditions in the places where they develop. Eggs, larvae and pupae develop more quickly in milder conditions. Temperatures above 95°F can be lethal for larvae, and eggs dry out in hot, arid conditions, causing a drastic decrease in hatch rate.”

“The conservation of monarch butterflies is a responsibility shared by Mexico, the US and Canada. By protecting its sanctuaries and practically eliminating large-scale deforestation, Mexico is doing its part. It is necessary that the US and Canada also do their part and protect the habitat of the monarch in their countries,” Vidal addedWWF-Telcel Alliance, for the last 10 years has supported conservation and sustainable management of natural resources in Mexico, along with the well-being of the people who depend on those resources. WWF projects include the development of sustainable business—such as tree nurseries, mushroom production modules and art craft production—and support for sustainable tourism.