As many as 1.8 billion additional stems of milkweed plants may be needed in North America to return imperiled monarch butterflies to a sustainable population size, according to a recently published U.S. Geological Survey study.
As many as 1.8 billion additional stems of milkweed plants may be needed in North America to return imperiled monarch butterflies to a sustainable population size, according to a recently published U.S. Geological Survey study.
Monarchs rely on milkweeds for food and for breeding habitat, but over 860 million stems were lost in the northern United States over the last decade. Scientists with the USGS and partners examined the density of Eastern migratory monarch butterflies overwintering in Mexico from 1979-2002 and the amount of milkweed plants available to them in North America. The study found that 3.62 billion milkweed stems are needed to reestablish this monarch population, but only 1.34 billion stems remain in the U.S.
“Monarchs in eastern North America are a beloved insect, but they’re in jeopardy, partly due to the loss of milkweeds in cropland,” said Wayne Thogmartin, a USGS scientist and the lead author of the report. “Our study is important because it helps specify the conservation needs of this charismatic species.”
The Eastern migratory population of monarch butterflies, which spends the winter in Mexico but migrates to the eastern U.S. and Canada to reproduce during warmer months, declined by about 80 percent over the last decade. The U.S. Fish and Wildlife Service is considering a petition to list monarchs under the Endangered Species Act. The population is at risk of extinction unless its numbers increase significantly.
Continue reading at USGS.
Photo via USGS.
