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Deposing a Monarch from his Throne in the Sky

By Stephen Aitken


The Monarch Butterfly is recognized by the black and orange markings that pattern its 8cm wingspan

One of the world's most spectacular biological events, the migration and the over-wintering behavior of the Monarch Butterfly, Danaus plexippus, is under serious threat. The black and orange markings that pattern the Monarch's 8 cm wingspan are recognized the world over and no other butterfly is known to migrate distances up to 3,000 miles and over-winter in clusters with millions of individuals. The conservation of the Monarch migratory phenomenon has become a tri-national issue between Canada, Mexico and the USA. Though endemic to North and Central America, the Monarch has recently expanded its range to include most of Europe and Asia, thus its status has become an issue of international importance.

The Migration Phenomenon

Monarch butterflies migrate distances up to 3000 miles over five subsequent generations

There are two distinct migratory populations of Monarchs, one west of the Rocky Mountains and the other to the east. The former population over-winters in the Eucalyptus groves of coastal California, while the latter migration is much more spectacular in terms of density and length, spanning three nations.

Individual butterflies migrate up to 50 miles per day and the entire migration to their ancestral wintering grounds can be as far as 3,000 miles. Several characteristics make this migration a highly unique phenomenon. One is that the round trip is completed by as many as five generations before they return to eastern Canada. Another is the intense clustering that takes place in the over-wintering sites in the Oyamel Fir forests west of Mexico City. A living carpet of insects sweeps over the trees, rocks and bushes and often tree branches break under the collective weight of these 0.5-gram insects. There is no host plant in this area of Mexico and the Monarchs leave their roosts only to sip water from icy streams nearby. When the sun warms the resting butterflies, they start to flutter, rising to a crescendo and ending in a deafening roar. In the month of March, they start on their migration north, which is accomplished in steps by up to five subsequent generations. A Canadian entomologist, Fred Urquhart, discovered the spectacular over-wintering sites in 1976 and brought them to the attention of the world through an article in National Geographic Magazine1.

The Habitats

Tree branches often break under the collective weight of these 0.5-gram insects

North America - The Monarch habitat all along the migratory path through the US and Canada is dependent upon resident populations of milkweed (Asclepias) upon which the caterpillars feed. In eastern Canada, the primary larval host is Common Milkweed (A. syriaca), which accounts for 95% of the milkweed found there, while in western Canada it is Showy Milkweed (A. speciosa).

Wildflowers provide a nectar source for the adult butterflies, particularly during the fall migration. At this time, sugars from the nectar are converted to the fat that is essential for the Monarch to complete its migration and over-winter successfully. Nectar sources also include Goldenrods (Solidago), Asters (Aster) and Purple Loosestrife (Lythrum salicaria).

Recently abandoned farmland in eastern Canada has created suitable areas for Monarch breeding, since the host plant thrives in this type of habitat. As a result, there has been a shift in the overall range of Monarchs into eastern Canada. However, over the next several decades this habitat will decline as the farmland gives way to the growth of trees and shrubs. The migration is vulnerable to the loss of milkweed and nectar sources through landscaping, the growth of succession forests as well as larval and adult butterfly mortality due to the use of agricultural pesticides.

Mexico - Forested ridge-tops west of Mexico City, populated by Oyamel Fir trees (Abies religiosa), become the refuge for over 100 million Monarchs, escaping the cold winter weather of Canada and the northern USA.

Life Cycle

The caterpillar initially feeds upon its lost shell and later upon its milkweed host

The Monarch has four life stages: egg, larva (caterpillar), pupa (chrysalis) and adult (butterfly). After a 5 to 10 day incubation period (depending upon the temperature), the egg hatches into a caterpillar that initially feeds upon its lost shell and later upon its milkweed (Asclepias) host. When the pupa is formed, it hangs under a leaf for several weeks with the developing butterfly inside. Finally, with the legs positioned downwards, the butterfly splits the chrysalis and pumps fluid into its wings to harden them. The Monarch Butterfly is ready for the world.

In its summer territory, the Monarch mates three to seven times and the adult lives 2 to 6 weeks. When the days start to shorten, the hatching of non-reproductive butterflies (in breeding diapause) is triggered, and these become the migratory individuals that travel south to the over-wintering sites (though not all Monarchs are migratory as Florida has resident populations).

The Threats

Monarch chrysalis

Physical - The principal threat to this unique migratory phenomenon is the vulnerability of the over-wintering sites. This spectacular seasonal event has provided tourist income to local communities. As many as 300,000 tourists flock every year to the town of Angangueo, Mexico. However the off-season practices are often environmentally damaging and threaten the phenomenon itself. The impoverished local communities harvest trees for construction, fuel and trinkets thus impacting the very resource that provides the tourist-related income. The forests are getting thinner and less able to buffer the protected areas from inclement weather, the results of which became obvious in January 2002 when freezing rain and cold winds killed up to 270 million Monarchs, approximately 25% of the reserve's population2. Dead butterflies lay 30 cm deep on the forest floor like orange and black snowdrifts. The Monarch can survive under snow for several days but if the temperature stays below 0 ° Celsius for a prolonged period, the mortality can be severe.

Monarchs blocking the sun in the skies of Angangueo, Mexico

Cultural - The communal land system, organized into ejidos - plots of land run and inhabitated by the local people though still owned by the government - grants the poor rural population of Mexico fairly free access to any and all natural resources. While US laws such as the Endangered Species Act (ESA) and the Environmental Protection Act (EPA) can be enforced in this region, the limitation of property rights, particularly the prevention of logging and harvesting of other natural resources, are usually handled by economic incentives i.e. the community receives financial compensation from the government. For an impoverished country like Mexico, these incentives are an expensive commodity and are very limited in number.


The Monarch enjoys little protection under national or international regulations because of its broad distribution and large populations. However the World Conservation Union (IUCN) lists the over-wintering spectacle as an "endangered biological phenomenon". The Mexican government made two presidential decrees in the years 1986 and 2000, protecting forests around the over-wintering sites. These have proven to be insufficient and at times merely symbolic. The rate of forest degradation has tripled since the first decree3. Current protection measures are inadequate in the face of the larger physical and cultural threats to the Monarch habitat.

The Zoological Society of San Diego (ZSSD) has been involved in conservation efforts (habitat preservation) since 1999, working with the Bosque Modelo Mariposa Monarca (BMMM), a non-government organization (NGO) based in Zitacuaro, Michoacan, Mexico. They have been working to create income-generating industries to benefit all of the ejidos, not just those that harbor the Monarchs4.

Conservation Solutions

The progress toward protection of the Monarch forests has been slow compared with the rate of its destruction. Satellite images suggest that forest loss in Mexico is occurring at a rate of 2.78 million acres per year, second only to Brazil. The recent freezing incidences, due to the elimination of buffer zones, indicate that the over-wintering phenomenon will end prior to the loss of the forests on which the butterflies depend. This would be an international tragedy and the loss of a truly unique natural phenomenon. A coalition of NGOs is required to seek protection of the Monarch forest. A "Phenomenon Recovery Team" should be charged with the initiation of a plan that would have legal powers similar to the US Endangered Species Act model.

Global attention is needed to protect the Monarch migration phenomenon, applying international pressure with international funding to designate the over-wintering sites as UN Cultural Heritage Sites with special protected status. Concomitant action must be taken to improve the quality of life for the communities directly impacted by the management of these sites. Only through such a series of initiatives by international agencies can we ensure the survival of the reign of the Monarch. Through international involvement, the amazing migration of this beautiful species can become a symbol of international cooperation and harmony. We must work together as one body to save the treasured gifts of our planet.

* Stephen Aitken is the International Coordinator of Tropical Conservancy and the Managing Editor of Biodiversity, Journal of Life on Earth. Visit the Tropical Conservancy website at: http://www.tc-biodiversity.org. Your emails will be forwarded to him by contacting the editor at: ScienceTech@islam-online.net

1. Urquhart, F. 1976. National Geographic Magazine Vol. 150 No. 2, p.161.

2. Anderson, J. B. and L.P. Brower 1996. Ecological Entomology 21, 107-116

3. Bojorquez-Tapia et al. 2002. Conservation Biology 16:2, 346-360.

4. Toone, W. and T. Hanscom 2003. Conservation of Monarch Butterflies in Central Mexico: Protection of a biological phenomenon, ervation Of Monarch Butterflies in CBiodiversity Journal 4:4, 14-20.

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