The Great Monarch Butterfly Migration: One of the Greatest Phenomena of the Natural World

With its brilliant bright orange, black, and white markings, the monarch butterfly is a beautiful insect and arguably one of the most recognizable butterfly species to inhabit North America.

Their life cycle begins with an egg laid on a milkweed plant. After 3-5 days, the egg hatches, a caterpillar emerges and begins its tireless phase of feeding. Monarch caterpillars feed exclusively on milkweed as they grow and molt over a two week period. After two weeks of feeding, they will form a chrysalis where they undergo metamorphosis. After roughly another two weeks, they emerge as an adult butterfly. The adult Monarch spends its life feeding on nectar from wild flowers, looking for mates, and laying eggs to continue their life cycle, but it is in the fall when one of the greatest phenomena in the natural world occurs: the migration of the Monarchs.

Unlike other butterfly species, Monarch butterflies can not survive the harsh cold winters of the north, and therefore, are the only butterfly species known to migrate two-ways. By minding environmental cues, monarchs know when it's time to head south for the winter. Using a combination of air currents and thermals (upward currents of warm air), some populations travel as far as 4,500 km to reach their winter home.

A monarch's winter home depends on the regional population it belongs to. Monarchs in Eastern North American overwinter in the Sierra Madre Mountains of Mexico, where Monarchs in Western North America make their second home in California. Between the months of October to late March, the Eastern population of North America’s Monarchs roost within the same 11 or 12 mountain ranges in the states of Mexico and Michoacan each year. They roost within oyamel fir forests at elevations of between 2,400 and 3,600 metres above sea level. This specific combination of hillside oyamel forest and elevation provides an ideal microclimate for these butterflies with temperatures ranging between 0-15°C. This is important because if the temperatures were any lower, the butterflies would be forced to use their fat reserves as energy. Additionally, the humidity in these oyamel forests ensures that the monarchs do not dry out. Similar to the Eastern populations, the Western population of North America overwinters in microclimates found within the Rocky Mountain Range along the Pacific coast in California near Santa Cruz and San Diego.

As if the great monarch migration wasn’t amazing enough, you may find it interesting that the journey back north in the spring consists of many generations of butterflies. A typical monarch butterfly only lives for a few weeks so it often takes 3-5 generations of offspring to complete their northbound journey in the summer months. Monarchs will stop along their journey, reproduce, where a new generation of butterflies is given time to grow and continue the next leg of the trip. Once the butterflies reach their final destination in the summer months the migration has ended, and towards the end of the summer a new, special generation is born. This final generation of Monarchs, often referred to as the super generation, delay sexual maturity and are the ones that make the return trip back south in the fall. This trip is done entirely by a single butterfly whose lifespan has changed from a few weeks to up to eight months. Once they spring returns in the overwintering sites, sexual maturity begins and the cycle continues. Researchers are still unsure as to how Monarch butterflies locate their winter homes without ever being there before. It is theorized that a magnetic pull of the earth and the position of the sun among other variables are used as directions aids during migration.

In Ontario, Monarchs are listed as a species of special concern, though they are federally classified as endangered. Loss of habitat and a change in weather conditions caused by both climate change and human development threaten the future of this species. Colder, wetter winters could be lethal to this species and hotter, drier summers could cause wintering locations to change. Deforestation of their winter homes in Mexico and the increasing loss of milkweed plants necessary for feeding and reproduction continuously threaten the survival of this beautiful creature, but there are ways you can help.

You can help provide the monarch butterfly with the plant native species they need to collect a source of energy for their long journey in the fall. Plant milkweed species such as Common Milkweed, Butterfly Milkweed, and Swamp Milkweed, as well as butterfly friendly flowers like Pale Purple Coneflower, Black-Eyed Susans, and New England Aster. With your help, Monarchs can be given the boost needed to make their remarkable migration each year. Due to people simply maintaining native vegetation in areas of their property, or deliberately planting these beautiful flowers, the “Monarch Movement” has already seen great gains in Canada and the USA.