Monarch Population Hits Lowest Point in More Than 20 Years

Decrease due to less food, illegal logging and extreme weather conditions

monarchs in sky

Every November, monarch butterflies arrive in the mountain forests of central Mexico to hibernate for the winter, having travelled up to 2,800 miles from Canada and the United States. Their two-month journey is the second longest migration of all known insects.

In the most recent migration, fewer of the orange- and red-winged monarchs made it to the end of the journey than ever before. The monarch butterfly population in Mexico was the lowest ever since 1993 (the year scientists started to monitor monarch butterfly colonies), according to research just released by the WWF-Telcel Alliance and the Monarch Butterfly Biosphere Reserve Office of the Mexican government.

The research shows a 43.7% decrease (nearly three acres) in the total amount of forestland occupied by monarchs in and near Mexico’s Monarch Butterfly Biosphere Reserve. The research was conducted over several weeks in December 2013 and the decrease is in relation to December 2012 research.

Why has the population dropped?

The decrease is due to threats monarchs experienced during their journey. At the beginning, their primary food source (milkweed plants) was in short supply because herbicides used more regularly for agriculture in the US had killed many of the plants.

While en route, they faced extreme weather conditions, including higher than normal temperatures and storms. Temperatures above 95°F can be lethal for monarch larvae. Eggs dry out in hot, arid conditions, causing a drastic decrease in hatch rate. Monarchs prefer milder temperatures.

Once they reached their hibernation sites in Mexico, they encountered scarce and deteriorating forests, the direct result of illegal logging.

Area of forest occupied by colonies of hibernating monarch butterflies

Year (data collected during December) Total area (acres)
1993 15.39
1994 19.3
1995 31.16
1996 44.95
1997 14.26
1998 13.74
1999 22.16
Year (data collected during December) Total area (acres)
2000 9.46
2001 23.13
2002 18.63
2003 27.48
2004 5.41
2005 14.6
2006 16.98
Year (data collected during December) Total area (acres)
2007 11.39
2008 12.5
2009 4.74
2010 9.93
2011 7.14
2012 2.94
2013 1.65
  • monarch up close
  • monarch in trees
  • monarch research
  • monarch on branch

What is WWF doing to help?

WWF works with the local communities, government and private sector to preserve butterfly habitat—mainly oyamel fir and pine trees—in Mexico by promoting good forest management and sustainable tourism. More than 80,000 tourists visit the monarch hibernation colonies annually.

WWF and its partners also support sustainable businesses, such as mushroom production and tree nurseries that help restore forests. The businesses create new sources of income and food for the local communities that live among the butterflies. And WWF helped create the Monarch Butterfly Conservation Fund to offer long-term economic incentives to communities committed to preserving forest in the reserve’s core zone. The fund’s benefits accrue to those communities which succeed in reducing illegal logging in the area.