The Monarch butterfly is a wonder of the natural world. It is known for its long impressive flight of migration, a journey that still holds mystery about how its winter haven is passed down from generation to generation. The beautiful wings of the Monarch are bright orange with black veins and a thick black border with white dots. There is a larger space at the top of the wings with orange and white spots. The underside of the wings are similar in pattern, but are a lighter orange. This flashy insect is one of the most commonly recognized butterflies.

Sometimes called the “milkweed butterfly,” the Monarch is one of the largest butterflies in Canada, with a wingspan that can reach up to 105mm.1 The Monarch’s scientific name is Danaus plexippus, which in Greek translates to mean “sleepy transformation,” a fitting name for how the Monarch caterpillar is transformed into such a beauty. The Monarch mainly exists in North America. It is perhaps surprising, but it can also be found in Argentina, Bermuda, the Azores, the Canary Islands, Hawaii and even India, New Zealand, and Australia. The butterfly is occasionally found in Europe, but is not established because there is a lack of suitable food plants.2

As is the case with all butterflies, the Monarch has four life stages and undergoes complete metamorphosis. The eggs are laid on the leaves of the milkweed plant and are oval shaped, like a football. The resulting larvae, known as caterpillars, are patterned with black, white and yellow stripes around their bodies. They feed on milkweed leaves and shed their skins as they grow. During the last shedding of skin (moulting) the caterpillar forms a chrysalis or pupa around itself. The chrysalis hangs from the plant and its green colour eventually becomes transparent as the adult butterfly develops inside, for approximately nine to fifteen days.3 When the time comes, the butterfly breaks out of its chrysalis and waits for its soft wings to harden. Once this is complete the new butterfly is ready to fly, feed, mate, and lay eggs and so the life cycle continues.

Although Monarch butterflies are very bright in colour, they do not have to overly worry about camouflage from predators. As caterpillars they store up the milkweed’s poisonous compounds of cardiac glycosides in their bodies, which most vertebrate predators, such as frogs, lizards, mice, and birds, cannot handle.4 Experience teaches these predators to avoid the bright colours of the Monarch.

These butterflies only live for about four to five weeks. But the migration route they fly in the winter takes months, so how do they do it? A special generation of Monarchs is born in the autumn, before the butterflies start their migration. The “Methuselah Generation” surpasses its previous generation and lives for seven to eight months. These Monarchs are not reproductive, which allows more energy to be put into surviving, and the cool hibernation conditions cause their metabolism to slow down, allowing them to live longer.5 It is this group of butterflies that migrates to Mexico. Then in the spring the same group begins to make its way back to the United States and Canada, but stops in the Gulf Coast to lay eggs. The offspring then continue the flight back to their summer sites.6

When the weather starts to cool and the leaves start to fall, the Monarchs do what everyone wishes they could do: leave the country to spend the winter in a warmer climate. The winter weather is much too cold and extreme for the Monarchs to have a chance of survival. Monarchs west of the Rockies migrate to a few select areas in California. Pacific Grove, near Monterey, for example, is known for its wintering butterflies.7 The rest of the North American Monarchs, however, make a much longer and dangerous journey south, to central Mexico.

The butterflies migrating to Mexico begin to leave Canada and the United States in September and the beginning of October. They actively seek wildflowers for nectar to increase their strength and build up a fat store for the winter.8 The butterflies travel between 2,000 and 4,500 kilometers or more between their starting and finishing points, moving about 75 kilometers per day.9 It takes approximately two months for the fragile insects to arrive at their destination, and settle down to hibernate in the mountain forests of Mexico.

The butterflies’ trek south has been known about for a long time, however it was not known until recently where the butterflies went when they got to Mexico. The hibernation sites were discovered in 1975, due to the work for Dr. Fredrick Urquhart, of the University of Toronto, who developed a method of tagging and thereby tracking the butterflies on their migration route. This Monarch tracking continues with programs like Monarch Watch, Journey North and Texas Monarch watch, with volunteers playing a critical role alongside scientists.10

The butterflies flock to their hibernation sites, high in the temperate forests of the mountains of Mexico, in the Transverse Neovolcanic Belt. There are about twelve sites in this mountain range. The Monarchs closely cluster together on trees in small concentrated areas, as many as 14 million butterflies in a few acres,11 although it is extremely difficult to count an exact number. Sometimes the butterflies are so many that the branches buckle and break.12 The Oyamel fir forests, reaching 2,400 to 3,600 meters in altitude,13 maintain temperatures that are usually above freezing all winter. The right levels of humidity, wind, and sunlight inside the forests allow the Monarchs to hang on trees, looking like colourful leaves, without eating or mating all winter. The butterflies break up in March and early April and start their migration north.

Like all insects, the Monarchs also have natural predators, despite having the toxins from the milkweed in their bodies. Spiders, wasps, birds and mice, for example can be a threat to butterflies.14 In Canada and the United States, the butterflies face the elimination of their food source and habitat by development and pesticides. Milkweed, their larval food source, is often looked upon as a weed and is treated as such. In Mexico, illegal logging of the forests is placing growing pressure and threat on the butterflies’ precious hibernating sites. The Mexican government is finding that effective enforcement of its protection laws is difficult and poses a serious problem.15The Monarch Butterfly Conservation Program was created by the Mexican government, and is run to conserve the wintering sites, which are vital to the species’ continual survival.

  1. “monarch.” Canadian Biodiversity Information Facility. Government of Canada.
  2. “monarch.” Canadian Biodiversity Information Facility. Government of Canada.
  3. Oberhauser, Karen S and Michelle J. Sdensky, eds. The Monarch Butterfly Biology and Conservation. New York: Cornell University Press, 2004. 5.
  4. Oberhauser, Karen S and Michelle J. Sdensky, eds. The Monarch Butterfly Biology and Conservation. New York: Cornell University Press, 2004. 4.
  5. Oberhauser, Karen S and Michelle J. Sdensky, eds. The Monarch Butterfly Biology and Conservation. New York: Cornell University Press, 2004. 4.
  6. “Papalotzin: The Journey of the Monarch Butterfly.” Parks Canada
  7. “monarch.” Canadian Biodiversity Information Facility. Government of Canada.
  8. “Species Profile: Monarch.” Species at Risk Public Registry.
  9. “The Monarch of Migration.”
  10. Oberhauser, Karen S and Michelle J. Sdensky, eds. The Monarch Butterfly Biology and Conservation. New York: Cornell University Press, 2004. 11.
  11. “monarch.” Canadian Biodiversity Information Facility. Government of Canada.
  12. Ibid.
  13. “The Winter Palace.”
  14. “How many Monarch Butterflies Are There?”
  15. “monarch.” Canadian Biodiversity Information Facility. Government of Canada.