The monarch’s migration

The annual migration of the monarch butterfly from the north of the continent to the forests of Mexico is a unique event in the world. Follow the steps of these beautiful butterflies on their epic journey.
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Monarch butterflies have 16,866 gene pairs, with unique genetic mutations that allow them to get less tired when flying and to consume less oxygen.

Danaus Plexippus

A butterfly like no other

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The monarch butterfly weighs only half a gram, just like a paper clip.

The monarch butterfly is a lepidopteran of the Nymphalidae family. Its scientific name Danaus plexippus, which can be translated as "transformation" and "sleeper", makes reference to the butterfly’s metamorphosis and hibernation processes.

The monarch butterfly is one of the most widespread butterflies in the Americas, and it is the only species that annually migrates to the Mexican forests.

Its size ranges between the 9 and 10 centimeters, (the males are larger and have a spot on the wings that the females do not have). The black marks are more pronounced in the females. 

Danaus PlexippusDanaus Plexippus
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In Greek mythology, Danaus and his 50 daughters fled persecuted by Aegyptus and his 50 children, one of whom was called Plexippus. The butterflies, which migrate as a group, seem to emulate the protagonists of this legend.

Habitat

The monarch butterfly lives in great part of North America, although the ones that migrate to the Mexican forests are those that live east of the Rocky Mountains. Butterfly colonies from the Pacific coast live in the same place all year round or migrate to southern California in winter.

In their natural habitat, monarch butterflies are dependent on the asclepia plant, commonly called "milkweed". They lay their eggs in the milkweed, since it is the only plant that their caterpillars are able to eat since birth. This plant provides the butterflies with a very effective natural defense against predators, since it makes them toxic or, at least, taste awful. Adult butterflies do feed on the nectar of other flowers.

However, monarch butterflies are not free of predators. Ants, spiders and wasps eat their eggs and two species of birds find them tasty as adults: the black-headed grosbeak (Pheucticus melanocephalus) and the black-backed oriole (Icterus abeillei).

Monarch butterly lifecycle

Like all lepidoptera, the monarch butterfly undergoes an amazing transformation:

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The mating of the monarch butterfly can last between 20 minutes and many hours. Of the 400 eggs that the female lays, barely 30% survives, since ants, spiders and wasps eat them.

Monarch butterly lifecycle
  1. After mating, the female butterfly lays her eggs on the back of the milkweed or asclepia plant. A butterfly can lay up to 400 eggs. Once the eggs are deposited, the monarch dies. These eggs take 4 to 8 days to hatch.

  2. When the caterpillars hatch they eat the shell of their eggs and feed on the milkweed. After about two weeks, the caterpillar builds a chrysalis, which stays hanging from the plant. 

  3. The chrysalis or pupa phase lasts between 8 and 15 days. While inside the chrysalis, the caterpillar undergoes an extraordinary transformation until it becomes a butterfly. In the last stage, the chrysalis is transparent and the butterfly can already be perfectly seen from the outside.

  4. The butterfly leaves the chrysalis. The generations that do not migrate live from 3 to 6 weeks and the butterflies that actually migrate (the Methuselah generation) live between 8 and 9 months. Finally, the butterflies reach their sexual maturity and mate.

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The average life of a human is 75 years. If we had a Methuselah generation, it would live 525 years.

Migration

A migration unique in the insect world

The migration of the monarch butterfly is a unique phenomenon in the world of insects. The cold winters of the north of the USA and the south of Canada have forced the monarchs to adopt an unparalleled survival strategy: to emigrate through all the width of the continent until they arrive to a few hectares of land in the sacred fir (oyamel) forests of Mexico’s central area, where they gather by millions. This feat is carried out by every fourth generation of monarch butterflies. The first three generations live between one and two months, but the fourth generation, called Methuselah due to its longevity, lives 8 months. The amazing Methuselah generation undertakes the autumn migration to the south, a journey of almost 5,000 km to the forests of central Mexico, where they find their hibernation territory. After winter, the same butterflies begin their migration back north, starting their annual cycle once again.

Generation 1

Generation 1

These butterflies are born from the eggs deposited in the south of the USA in April and fly north during spring migration. In May they lay their eggs in the center and east of the continent. 

Generation 2

Generation 2

The butterflies reach their maturity between May and June, and they continue their migration from the center and east of the continent settling all through the north of the USA and the south of Canada.

Generation 3

Generation 3

The third generation of monarch butterflies is born and dies in its summer habitat, in the northern states of the USA and Canada, from the Rockies to the Atlantic, going through the Great Lakes.

Generation 4 (I)

Generation 4 (I)

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This small and strong butterfly can fly 120 km every day at an altitude of 100 meters.

The fourth generation, called Methuselah, begins the migration south in mid-August, and after flying more than 4,000 kilometers, reaches the sacred fir forests of Michoacán between October and November.

Generation 4 (II)

Generation 4 (II)

Millions of butterflies gather to hibernate and survive winter in the Mexican forests. In December and January they form clusters all over the trees and reduce their biological activity in order to withstand the winter cold.

Generation 4 (III)

Generation 4 (III)

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How butterflies are oriented in their migration is still a mystery. It is known that they use the position of the sun and the terrestrial magnetism. This article tells you more about it.

In February, when the temperatures rise, the monarchs come out of their lethargy and look for food and water. They must mate and begin the migration north. These are the butterflies which will lay their eggs in the southern United States.

What is the monarch butterfly doing? A year in the life of the monarch, month by month.

OCT
NOV
DEC
JAN
FEB
MAR
APR
MAY
JUN
JUL
AUG
SEP
October

The monarchs arrive in Mexico. After crossing the US from north to south, the swarms of butterflies continue their way to the sacred fir forests of central Mexico, their winter home.

Throughout the month of October, the butterflies take over the Mexican skies during the last stage of their autumnal migration. The first ones to arrive settle in the sacred fir forests of central Mexico, in a protected area. The laggards, perhaps those who travel from farther away, continue to arrive throughout the whole month, completing their journey of thousands of kilometers. It is now time for them to feed, as they will need energy reserves to survive the harsh winter before them.

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November

Butterfly colonies in the sanctuaries. The monarchs form large colonies that will remain together until spring. The sanctuaries open at the end of the month, allowing controlled visits into this natural wonder.

The butterflies settle in their winter home, the sacred fir forests of central Mexico located within the Biosphere Reserve, at more than 3,000 meters of altitude. Although the Reserve covers more than 50 thousand hectares, butterflies form their colonies in just a few hectares, gathering there by millions. The Reserve establishes the visiting routes depending on the location of the colonies and, at the end of the month, sets the sanctuaries opening date.

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December

The clusters. The monarchs are now settled into colonies and, as the days shorten and the temperatures decrease, they begin to form clusters in order to preserve the heat and stay alive during the winter harshness.

At lower elevations it is still possible to see some butterflies activity during this month. In the Reserve, where colonies are formed in the forests, at higher altitudes, once the butterflies begin to feel the rigors of the winter weather, they gather into huge clusters of up to a thousand specimens, their survival strategy for the winter. Butterflies cover trunks and branches, and clusters hang from the sacred firs. The forest is their sole protection from storms, snowfalls, frosts and strong winds. Therefore, it is vital to keep their ecosystem intact.

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Butterflies can withstand temperatures down to -14ºC without freezing, as long as they do not get wet.

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January

Hibernation. Butterflies create clusters to protect themselves from low temperatures. They remain in lethargy, with their biological activity to a minimum. Surviving the winter frosts is the most important thing now.

Monarch butterflies are adapted to cold climates and can withstand the subzero temperatures which are common to these forests. This month is critical for their survival. In order to withstand the cold, butterflies hibernate, that is, they reduce their vital functions to the minimum, and gather in clusters of up to a thousand specimens hanging from the sacred fir trees. A particularly strong frost, rain or wind can easily undo these clusters. The butterflies that fall, being in state of lethargy, are unable to take flight again and they die. There have been such harsh winters that millions of monarchs have died from the cold.

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In 2002 a frost killed over 40 million butterflies, the worst disaster ever recorded to happen to the species.

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February

The awakening. The first sun rays announce the imminent arrival of spring and awaken the butterflies from their lethargy. In sudden frenzy, the monarchs star moving and abandon their clusters to look for water and nectar.

In February the days become longer and in the middle of the day the temperature begins to rise. When the monarch butterflies start feeling the heat in their bodies, they begin to wake up and recover their vital functions. As the month moves forward, the butterflies leave their clusters and begin looking for water and food. In the warm hours of the day, when the sun still shines, the forests fill with swarms of fluttering butterflies, looking for streams and flowers in order to drink their nectar. It is time to regain strength to undertake the return trip.

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March

The departure towards the north. After mating, monarch butterflies begin their spring migration. The orange swarms of butterflies fly towards the south of the USA, where they will finally lay their eggs.

 These are the so called Methuselah generation of butterflies. Ever since they left their chrysalis in August they began an epic journey in the world of insects: they traveled almost 5,000 km., from the US and Canada to Michoacan, there, they hibernated for two months and now they must begin their return trip. Between February and March, their sexual organs will reach maturity and, before flying north, they must mate. The male butterflies die, and the females travel back, towards the south of the US. In March it is very common to find huge swarms of butterflies in the lower lands of the sacred fir forests, as they fly northwards, crossing the country.

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April

Final destination: southern USA. The spring migration begins in Mexico and reaches the south of the USA. These butterflies will lay their eggs here for a new generation of butterflies to continue their journey northward.

The Methuselah generation of butterflies is now fulfilling the last step of their life cycle. Eight months ago these same butterflies left the North of the continent in order to hibernate in Mexico and then began their journey back north, after mating. When they finally reach the south of the US, they look for milkweed plants to lay their eggs and die. The first generation of butterflies will be born from those very eggs and then continue its journey to the north.

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May

The first generation of butterflies. Born from the butterflies that hibernated in Mexico, the first generation of monarchs hatches in the south of the USA and continues its journey north, spreading through the center and east of the North American continent.

These monarchs, unlike their progenitors, live the normal life cycle of a butterfly, (between 3 and 5 weeks). The first generation of monarchs is born in Texas and other southern American states, and continues migrating north, extending all through the central plains and mountains of the eastern United States, where it lays its eggs before dying. The widespread use of pesticides in agriculture has significantly depleted the butterfly's natural habitat, since pesticides kill milkweed, the only plant where they can lay their eggs and that the larvae are able to eat.

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June

The second generation arrives north. Like their parents, these monarch butterflies migrate northward and settle in their summer territory, from the Rocky Mountains to the Atlantic coast.

The second generation of monarchs, born in the USA, is just like the first one, a traveling generation, with a life cycle of approximately one month. During this time, these butterflies reach maturity in the center and east of the country and continue their migration to their summer habitat, in the north of the US and in southern Canada. During their journey, these butterflies spread over a very extensive territory, searching through the meadows and forests for the best places to lay their eggs, those with an abundance of milkweed.

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July

The third generation in its summer habitat. The third generation of monarch butterflies lives in the north of the US and in southern Canada, where summers are relatively cool and provide a suitable habitat for them.

These monarchs are the great-granddaughters of the butterflies that migrated to Mexico and, when they finally reproduce, they will be the parents of the next migrating butterflies, the so-called Methuselah generation. Extended through the temperate regions of the North American continent, the monarchs find a suitable habitat with abundant sunlight (due to the latitude), with not very hot summers and enough humidity. These butterflies complete their life cycle of about a month in the meadows, valleys and wooded areas where they can find both the milkweed, necessary for their survival, and other flowers and plants to feed on. 

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August

The Methuselah generation. The fourth generation of monarchs ─the so-called Methuselah butterfly, due to its longevity─ is finally born. These is the generation which will complete the incredible migration to the south, as well as the hibernation and the beginning of the migration journey back to the north.

The Methuselah generation is born in the forests and fields of the North of the USA and Canada. This generation, which, extraordinarily, is able to live until April and achieve the feat of migrating south, spends the month of August feeding in order to create the food reserves needed by an insect of just a few grams to be able to face the long trip before him. With the arrival of the cold weathers, announcing the change of season, the butterflies living in the continent’s boreal regions begin their autumnal migration to the south.

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September

Autumnal migration. All throughout the North American continent the monarchs abandon their summer habitats and gather by millions to undertake the almost 5,000 km long journey awaiting for them, until they reach Mexico.

From the north of the continent down to Mexico, the monarch butterfly populations come together, flying silently south in enormous swarms. As they approach the Mexican border they gather into giant and beautiful orange clouds. Throughout their journey, many conservation organizations, schools and volunteers participate in the specimen tagging process, which helps monitor the butterfly populations in order to understand the dynamics of their incredible migration. Along the way, butterflies fly above lakes, storms and strong winds before reaching their destination.

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If butterflies find a strong storm or hurricane on their way, they might get lost. It is believed that the colonies of monarchs in the Atlantic islands such as Madeira, the Azores or the Canary Islands, arrived there dragged by the wind.

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Between April and October, south to north migration, north to south migration. In the spring, monarch butterfliess abandon their winter habitat in Mexico and migrate to the USA and Canada, where they will live for three generations. The fourth generation will make the autumnal migration back to Mexico, and arrive to our country in October. This generation will also undertake the first stretch of the spring migration to the north.

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