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Geography in the News: Monarch Butterflies Struggle

By Neal Lineback and Mandy Lineback Gritzner, Geography in the NewsTM and Maps.com


Near the end of February each year, scientists studying monarch butterflies at their overwintering sites in Central Mexico witness signs that the butterfly colonies were “breaking up.” This separation of tens of thousands of butterflies clustered together on single trees indicate that the populations are preparing for their lengthy spring migration from Mexico to the United States and Southern Canada. This year’s colony numbers were depressed by 59 percent and scientists are worried.

Probably the best known of all North American butterflies, the monarch (Danaus plexippus) is a milkweed butterfly, laying its eggs on milkweed plants on which their larvae (caterpillars) exclusively feed.

The monarch butterfly has a wingspan of about 3.5 to 4.5 inches (8.9-11.4 cm) with a highly distinguishable color pattern. The wings are bright orange with black veins. American entomologist Samuel H. Scudder first published the common name for the butterfly in 1874. He chose monarch because “it is one of the largest of our butterflies and rules a vast domain.” Some scholars believe, however, that the name may be in honor of King William III of England.

Monarchs are also found in southern South America, Europe, Russia, Indonesia, Australia and New Zealand. They are migratory in Russia, the Azores, Sweden, Spain and Portugal, but have by far the longest routes in North America.

North America's Monarch Range


The female monarch lays its eggs on a milkweed plant during the spring and summer breeding times.  Four days later caterpillars emerge, first eating their own egg covers. They then eat the poisonous milkweed leaves, acquiring a toxin that can later repel predators. The caterpillar stage lasts about two weeks. Since they eat milkweed plants that inhabit some farmland, they are considered beneficial.

In the pupa or chrysalis stage, the caterpillar spins a silk pad on a twig or leaf and hangs upside down from this pad by its last pair of prolegs. A change of form or metamorphosis occurs during the next two weeks finally resulting in the monarch butterfly.

Annual migration of monarchs is truly amazing and unique among butterflies, making a two-way trip like some birds. In North America, massive southward migrations of an estimated 300 million begin in August and last until the first frost. In the spring only about half that number returns north due to losses from high winds, storms, snow, fatigue, starvation, bird predation and human interference.

Two different populations of monarch butterflies inhabit the United States and Canada. When the fall migration commences, the monarch population east of the Rocky Mountains travels up to 3,100 miles (4,960 km), averaging of 12 miles (19 km) per hour and 50 miles (81 km) per day.  Their destinations are specific areas in the Transvolcanic Range of the Sierra Madre in Central Mexico.

The butterflies overwinter in the same 12 mountain spots every year at elevations of 8600 to 10,200 feet (2600 to 300 m). Millions concentrate there, hibernating in large clusters in the oyamel fir trees. These sites were first discovered only in 1976 and seven of the sites are now protected as important bioreserves.

The monarch population west of the Rockies spends winters at perhaps 300 minor sites in central coastal and southern California, from Monterey south. These monarchs hibernate in eucalyptus trees.

The lifespans of monarchs vary depending on the time of year. If born in the summer, a monarch only lives 2-5 weeks, during which it lays eggs for the next generation. The last generation of the year, however, enters into a non-reproductive phase called diapause before migrating south and it can live up to nine months.

In February and March, toward the end of their wintering over, these butterflies become reproductive and begin their northward migration, laying eggs on milkweeds as they go. Though only one generation migrates south, it takes 3-4 generations each year to return north by summer.

Scientists are trying to determine exactly how monarch butterflies manage to return to the same overwintering spots over a gap of several generations. It appears the butterflies inherit the flight patterns, based on a combination of circadian rhythm, the magnetic pull of the earth and the position of the sun in the sky. Whatever the exact causes, the journey of the monarch butterfly is an incredible geographic and biologic story.

The wintering grounds in Mexico this year had perhaps 59 percent fewer monarchs than last year, likely related to a disturbing decline in habitat for the butterflies. One particularly disturbing conclusion is the effect of the decline in milkweed along the migration paths owing to the use of herbicides and perhaps some genetically engineered corn in U.S. agriculture. Milkweed is particularly susceptible to pre-emergent and defoliant herbicides.

And that is Geography in the News.

Co-authors are Neal Lineback, Appalachian State University Professor Emeritus of Geography, and Geographer Mandy Lineback Gritzner. Dr. Daniel Stillwell of Puerto Vallarta, Mexico, provided valuable research assistance. University News Director Jane Nicholson serves as technical editor.

Sources: GITN 983 Monarch Butterflies Begin Journey North, Apr. 3, 2004; http://www.fs.fed.us/monarchbutterfly/migration/index.shtml; http://www.learner.org/jnorth/monarch/; http://whyfiles.org/006migration/; Urquhart, Fred A. The Monarch Butterfly, International Traveler (University of Toronto Press, 1987); and http://www.news.cornell.edu/releases/May99/Butterflies.bpf.html

This is an abbreviated Geography in the News article revised for David Braun’s National Geographic NewsWatch blog. Nearly 900 of the 1200, full-length weekly Geography in the News articles (with Spanish translations) are available in the K-12 online education resource Maps101.com, including maps and other supporting materials and critical thinking questions.



  1. Joyce Moody
    WPB FL
    March 22, 2014, 5:21 pm

    Paul Cherubini, you make it sound like a wasted effort for me to go out and supplement my milkweed whenever a generation wipes it out. I’m not even sure FL monarchs migrate. Surely we are benefitting the species by keeping our gardens plentiful? Do all monarchs migrate?

  2. Paul Cherubini
    March 28, 2013, 10:49 pm

    Home gardeners cannot increase the amount of available monarch breeding habitat. Why? Because there are billions of milkweed plants in the wild in USA that support hundreds of millions monarchs and millions of those milkweeds are permanently destroyed each year due to sprawl and more intensive weed control practices on hundred of thousands of square miles of farmlands, pastures
 and roadsides.  Therefore if home gardeners plant mere 1000’s of milkweed “waystations” each year, they will not offset even 1/10th of 1% of the amount of milkweed that is permanently lost each year.  So mathematically it is not valid for anyone to claim or infer than home gardeners or other types of hobbyists can increase the amount of milkweed.

  3. Mona Miller
    Herndon, Virginia USA
    March 28, 2013, 7:12 pm

    In reply to M.Shamsul Haque, Pakistan

    You have a subspecies of the North American species Danaus plexippus.

    Your species may be:
    Danaus genutia

  4. Gail Morris
    Chandler, Arizona
    March 28, 2013, 6:00 pm

    Studies have shown that there is only population of monarch butterflies in the United States – there is not a separate East and West population, genetically they are nearly identical. Here is a clue as to why that might be the case. Monarch butterflies West of the Rockies may also fly to Mexico for the winter as we are learning by tagging monarchs in Arizona: http://www.swmonarchs.org/az-recoveries_wild.php
    Most monarchs here fly to Mexico, a few fly to the coast of California and a few spend the winter in Phoenix, Yuma and along the Colorado River. Monarchs in other western states may do the same.

    As Mona Miller points out well, the monarch population overwintering in Mexico plummeted this year. If you look at the population map over the years you can see this decline isn’t a one time event
    To get an idea of the size of the reduction, one hectare equals about 300 to 350 trees filled with monarch butterflies.

    The one thing we can all do here in the United States is plant milkweed. This is the monarch’s only host plant. There are native varieties with spectacular flowers attracting butterflies and pollinators that grow across the United States and southern Canada that can help increase the breeding areas this season. In Arizona we are working with nature centers, cities, and garden organizations to increase monarch friendly habitats.

    Monarch activity outside of GMO crops isn’t surprising since that is where the milkweed isn’t sprayed. GMO seed enables farmers to use glysophate sprays like Roundup on the crops themselves to destroy milkweed growing in the fields when plants are young.

    Gail Morris
    Southwest Monarch Study Coordinator

  5. Mona Miller
    Herndon, Virginia USA
    March 28, 2013, 5:24 pm

    I asked Dr. Chip Taylor at the University of Kansas, Monarch Watch about this paragraph in your recent article on Monarch butterflies:
    “Monarchs are also found in southern South America, Europe, Russia, Indonesia, Australia and New Zealand. They are migratory in Russia, the Azores, Sweden, Spain and Portugal, but have by far the longest routes in North America.”

    Dr. Taylor’s reply: Europe=only Spain, Portugal, Gibraltar –

    Russia, Indonesia, Sweden not at all and don’t migrate in the Azores and questionable migrations in Spain and Portugal where the pops are usually quite small.

  6. Mona Miller
    United States
    March 28, 2013, 2:22 pm

    I visited several Monarch Butterfly Sanctuaries in Mexico with a group from the Loudoun Wildlife Conservancy, which is from Loudoun, Virginia 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

    “Now, for the first time in its history, gardening has taken on a role that transcends the needs of the gardener. Like it or not, gardeners have become important players in the management of our nation’s wildlife. It is now within the power of individual gardeners to do something that we all dream of doing: to make a difference.”
    — Doug Tallamy, Bringing Nature Home

    Sources for milkweed:
    Monarch Watch Milkweed Market
    Monarch Watch

    Project Milkweed
    Returning Essential Wildflowers to America’s Landscapes

  7. M.Shamsul Haque
    March 27, 2013, 9:38 am

    Monarch Butterfly is the most common butterfly in Pakistan and India although it is not mentioned in this article. The host plant is a different variety of Milk weed than found in USA. A decorative variety of Milk weed that came from Mexico is also host to the butterfly and they like it so much that we call the plant a butterfly plant.

  8. Paul Cherubini
    March 26, 2013, 9:45 pm

    Monarch butterflies were actually spectacularly abundant in the GMO corn and soybean farmlands of the upper Midwest in 2011 and 2010: south-central Minnesota:

    2010 south-central Minnesota:

    So despite the widespread adoption of GMO crops, monarchs continue to be abundant on the GMO farmlands of the upper Midwest USA and are not hardly threatened.