Curiosities

The migration of the monarch butterfly

Without a doubt, the monarch butterfly ( Danaus plexippus ) is the most iconic butterfly in North America. It is a nymphalid lepidopteran insect that feeds on milkweed and is characterized by its striking orange wings with black stripes and white spots. It is well known for its extensive annual migration, which involves millions of butterflies that travel distances of up to 5,000 kilometers. In Mexico they are an ecotourism attraction and with increasing frequency, there is talk in the media about their beauty and vulnerability in the face of extinction.

Why the migration of the monarch butterfly occurs

Like salmon, wildebeest, and many species of birds, monarchs make massive annual migrations in search of favorable environmental conditions. Their migration is an amazing natural phenomenon in which millions of individuals travel from northern North America to the south , where temperatures are much warmer during winter.

Monarch butterflies can have two completely different life cycles . The time and place in which they are born greatly influences their longevity and behavior:

  • In Canada and the United States, up to five generations of monarch butterflies will hatch between spring and early summer, which will live between two and six weeks and will not require migrating. Monarch butterflies that are born and live in Mexico, Australia, Spain, Central and South America should never face temperatures below zero degrees Celsius and, therefore, they also live from two to six weeks and do not migrate.
  • Monarch butterflies that hatch in Canada and the United States in late summer and early fall typically live up to eight months and migrate annually. They are called “methuselah butterflies” or “methuselah generation” and travel south during the winter in search of higher temperatures , to return north again with the arrival of spring.

They are born, live and feed in the rocky mountains, grasslands, gardens and forests of the northern United States and southern Canada, where temperatures between spring and fall vary between 0 and 30 degrees Celsius. At the end of autumn and winter, temperatures can reach -34 ºC. Monarch butterflies do not survive in such cold climates and that is why they travel thousands of kilometers to the mountainous forests of Mexico, where winter temperatures remain between 3ºC and 25ºC.

When they arrive at their destination, they enter a period of hibernation that lasts approximately four or five months. We advise you to read about What animals hibernate and why .

With the end of winter, the monarch butterflies begin their return to the north, where they will reproduce and each female will deposit between 300 and 500 eggs on the milkweed plants (which will also serve as food for the larvae).

When is the migration of the monarch butterfly

During the months of August and September the monarch butterflies begin their long journey. They arrive at their destination between the end of October and the middle of November , which means that their journey lasts approximately 2 months .

In Mexico there is a myth that says that monarchs come to the country every year to visit their dead. This is based on the fact that their arrival in the territory often occurs on the first and second of November, dates on which the Day of the Dead is celebrated nationwide.

When they arrive in Mexico they hibernate for four or five months, from October or November to February, March or April. They remain in certain Mexican forests and sanctuaries, where they fly, feed and drink water during the day and crowd into trees at night to protect themselves. At the end of winter, they prepare to return to the north, where they can reproduce and die.

During the migration season of the monarch butterfly, it travels distances ranging from 2,000 to more than 5,000 kilometers . Its origin and destination can be summarized as follows:

  • Start of migration: in southern Canada and northern United States.
  • Migration destination: it is the state of California in the United States and the states of Michoacán and the State of Mexico in Mexico.

They go through almost every state in the United States and Mexico to reach their destination and form groups ranging from hundreds to thousands of individuals to take different routes depending on environmental factors , such as winds, rainfall and pollution.

The ability to instinctively orient and travel to a place they have never been and will never return to is one of the most extraordinary qualities of these butterflies. Remember that monarch butterflies are native to the United States and Canada, but their distribution has spread to other countries in America, such as Mexico, Costa Rica, Puerto Rico, Panama, Colombia, Brazil, Venezuela and Peru. In addition, it is an introduced species in Australia, New Zealand, Spain (including the Canary Islands), Portugal and also in some African and Asian countries. Despite being an invasive species , local scientists and biologists claim that it does not pose any risk to ecosystems.

In the 1990s, it was estimated that the number of monarch butterflies that carried out this mass migration was close to 1 billion copies. At present, and despite efforts to conserve the species, this figure barely reaches 35 million butterflies.

Monarch butterfly populations are declining at an alarming rate due to human impacts and climate change. Deforestation is killing the forests in which it lives and hibernates, and agriculture and pesticides are killing the milkweed that it feeds on and lays its eggs in. Let’s reduce our environmental impact and take care of our monarch butterflies!

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