National Geographic News
Monarch butterflies drinking from a stream.

Butterflies in Mexico's Monarch Butterfly Biosphere Reserve drink from a stream.

Photograph by Medford Taylor, National Geographic

Christine Dell'Amore

National Geographic News

Published March 18, 2013

The king of the butterflies may reign no more: Monarch butterflies are experiencing a steady decline, a new report says, with the insects occupying the smallest area of land in one Mexican butterfly reserve than they have in two decades.

In December 2012, scientists surveying monarch habitat in Mexico's Monarch Butterfly Biosphere Reserve found the insects occupied 59 percent less land than the previous year—the smallest area recorded in 20 years. (Watch a video of monarch butterflies.)

Nine butterfly colonies were found in just 2.94 acres (1.19 hectares) of land, compared with 7.14 acres (2.89 hectares) in 2011 and a high of 44.9 acres (18.19 hectares) in 1997, according to the report, released March 13.

vThe insects are plummeting due to two main causes: widespread loss of a plant called milkweed, which their young rely on for food; and extreme climate fluctuations, including freezing temperatures and heavy rain.

Like many insect species, monarchs undergo natural booms and busts—but lately there have been more busts, said Omar Vidal, director of WWF-Mexico, which participates in the survey. "That's why it's worrisome."

Chip Taylor, founder and director of Monarch Watch, wasn't surprised by the report. He'd been expecting the low numbers, saying that his butterfly-tagging program has revealed a "real decline" in monarchs in parts of the U.S. Midwest. (Watch video: "Growing Up Butterfly.")

Amazing Migration

Monarchs have "the most amazing migratory phenomenon in nature," Vidal said. (Read more about great migrations.)

Every autumn, millions of monarchs fly south and west from southern Canada and the United States, stopping at sites along the way to feed—a process that takes thousands of miles and spans three to four generations.

Most adult butterflies live only about a month, but the final generation lives about seven to eight months—the time required to make the "incredible feat" of flying from Canada and the U.S. to central Mexico, according to WWF. (See video: "Great Migrations : Monarchs and Milkweed.")

The last leg end up in the forests of the Mexican states of Michoacan and Mexico, where they spend the winter before the cycle begins anew. (Read about the discovery of the monarchs' winter home in a 1976 issue of National Geographic magazine.)

To complete the migration to Mexico, butterflies need to lay their eggs on a specific plant: milkweed. Once hatched, monarch larvae eat milkweed leaves as their first meal.

Habitats vs. Herbicides

Milkweed is not a favorite of farmers, though. Once widespread throughout the U.S., the plant's range has fallen considerably due to herbicide use on corn and soybean fields in several parts of the U.S., according to WWF.

Farmers increasingly grow herbicide-resistant crops that can withstand the chemical spraying that is killing off large swaths of milkweed. Research has shown that butterflies often frequent corn and soybean fields, where milkweed plants used to be plentiful.

Another threat to butterflies is climate extremes, including the droughts, heat waves, and storms that have hit North America in recent years, Vidal said. For instance, monarch numbers were very low in 2005 and 2006 most likely because of a severe drought in the U.S. (Read more about extreme weather.)

What's more, eggs, larvae, and pupae develop more quickly in milder conditions, according to WWF: Temperatures above 95˚F (35˚C) can be lethal for larvae.

Such extreme events could wipe out all Mexican butterfly colonies, Taylor said.

"That's the big concern—the smaller the population gets, the more vulnerable it gets."

Helping Monarchs

It may be tough to change the weather, but there are other ways to help the butterflies, advocates say. (Learn more about monarchs at the movie Flight of the Butterflies 3D.)

For instance, the U.S. government could impose rules regulating herbicides that are killing off milkweed, Vidal said.

Taylor encouraged people to support monarch-restoration programs, in which landowners and others create butterfly habitat by planting milkweed plants.

"We've got to make this a national priority," Taylor said.

"We're losing a lot if we lose monarch butterflies."

10 comments
Cathy Brouse
Cathy Brouse

I have been butterfly gardening since 2005 and bring various types of butterfly caterpillars into containers to raise them so they're protected from predators.  I raised Monarchs every summer up until this year, 2013, when no Monarchs showed up here.  I have lots of milkweed plants for them.  I absolutely believe the scientists who say that the Monarch's population is in peril.  I hope that we can save them before it's too late.  I will continue to plant milkweed and hope that I have some show up here and lay eggs in the coming years. 

Vivian Martin
Vivian Martin

This is my first year helping the Monarchs.  I don't even know how many butterflies emerged in my backyard, I'm guessing 60 or so.  Right now I have about 12 chrysalis'.  I live in Southern California where they overwinter.  Through facebook, and word of mouth, I convinced others to plant a few milkweed plants.  I went from zero last year to about 40 plants this year.  I took out part of my grass, and put in a butterfly garden with host and nectar plants.   I have so many caterpillars right now.  I'm just hoping the milkweed will hold out. 

Wendy Wolfe
Wendy Wolfe

We raised 35 caterpillars to adulthood this year.  This year they were late getting to Michigan and I've only seen 2 adults.  Out of the 16 eggs hatched, all but 4 have died.  They are dying in their first and second instars.  

Nicholas DelGrosso
Nicholas DelGrosso

I do volunteer work at the Tallgrass Prairie in Pahuska, Oklahoma. There are a number of different varities of milkweed plants growing on the 40,000 acres of restored tallgrass prairie. There are also numerous Monarchs on the range. Leading a nature hike of 5th graders,  I once came upon thousands of monarchs resting in a small depressions along a creek the children were amazed by the number and beauty of the butterflies. It would be a terrible tragedy to lose this remarkable butterfly. We have been experiencing drought in Oklahoma over the past two years and I have noticed a decline in the number of Monarchs I have seen recently.

Mona Miller
Mona Miller

I visited Mexico with a group from the Loudoun Wildlife Conservancy, which is from Loudoun, Virginia (LWC) from 2/23/13 to 3/1/13.  The number of Monarchs wintering over had declined significantly according to another couple in my group that had visited in 2009.  In 2008/2009 there were 5.06 hectares.  Now in 2012/2013 only 1.19 hectares were counted.  The Loudoun Wildlife Conservancy is working on a county wide Monarch Campaign.  We are encouraging people to create Monarch Watch Waystations by planting more native milkweeds and nectar sources.  We are working with local nurseries to make these native plants available.  We will be working with individuals, schools, businesses, and conservancies.  For more information, please go to this website:  http://www.loudounwildlife.org/Event_Monarch_Butterflies_1.html

Paul Cherubini
Paul Cherubini

Reality check:  last August Monarch butterflies and other pollinators were actually abundant and doing well in the herbicide tolerant GMO corn and soybean belt of the upper Midwest USA. Here's a 16 minute video I shot last August showing the abundant bees and butterflies (including monarch butterflies) that could be found along the margins of these GMO corn and soybean fields: http://www.youtube.com/watch?v=jZCOJnJU1UE

The sky was filled with hundreds of monarchs last September along the Atlantic coast: http://www.youtube.com/watch?v=7Zzkcw6phrI

Lisa Hart
Lisa Hart

We planted a bunch of milkweed seed around our property here in Texas in hopes that the Monarchs will find a spot to stop and visit. Hopefully we will see caterpillars  this year and keep the cycle going before it's too late ~

Pamela Volentine
Pamela Volentine

@Paul Cherubinithis is a quote from the article:  "Research has shown that butterflies often frequent corn and soybean fields, where milkweed plants used to be plentiful."

so they are probably there looking for the ONLY host plants for their larvae, milkweed, but i'm pretty sure there are not any growing between the crop rows since they are herbicide resistant crops.

a video that shows "abundant" bees and butterflies or "hundreds' of monarchs is awesome, and no one is denying that.  but that is not proof that the scientists down in mexico who have been studying the monarchs are wrong when they say the overwintering population is down.   and it doesn't mean that chemicals we use in agriculture are harmless to all life.

do you think the scientists are making up a bunch of baloney just to make gmo crops and chemical spraying look bad?  if so, what do they have to gain by doing that?


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