North America and Canada’s skies in August and fall often flutter and shimmer like confetti. But it’s not because of weddings. The monarch butterfly migrations begin at this time, one of nature’s most spectacular and heroic journeys.
It’s when hundreds of millions of monarch butterflies fly up to 2,500 miles from their summer breeding grounds to their overwintering sites in Mexico or California.
This jaw-dropping feat, and insect, is now under threat from climate change, deforestation, and modern farming methods. So let’s follow the migrating monarchs on their incredible trip and learn why our futures are linked to theirs.
What Are the Monarch Butterfly Migration Routes?
Monarch butterflies are among the largest butterflies in the United States, with a 3.5-inch wingspan and weighing 0.5 grams.
Monarchs have two principal fall migration routes. The migrations start mid-August, with the last butterflies arriving at their overwintering sites by the first week of December.
These insects fly an average of 25-30 miles every day during their migration, using thermals and tailwinds to propel them where possible. In ideal conditions, a monarch may flap its wings only once every 20-30 feet traveled, gliding the rest of the way.
The western monarch population, those living west of the Rocky Mountain range, overwinter in California. They also migrate to the Pacific Coast, San Diego, and Santa Cruz. The eastern population of monarchs leaves their homes in late summer to migrate to central Mexico.
The overwintering monarchs reverse their journey in spring, taking the first step so that their offspring can return to their North American breeding grounds.
What Is the Life Cycle of a Monarch Butterfly?
Incredibly, a monarch butterfly’s lifespan varies. Most monarchs live 2-5 weeks. However, those that migrate stay alive for up to eight months; the monarch butterfly migration is responsible for this dramatic variation.
In summer in North America and Canada, there may be 2-3 generations of monarchs from June to August. They breed, with females leaving their eggs on milkweed plants, the monarch’s natural habitat. The eggs hatch, releasing the larvae, also known as caterpillars.
These caterpillars only eat milkweed, meaning their mother chose her laying site well. Milkweed is toxic to most insects and animals, but not the monarch. This plant’s toxicity makes the caterpillars unattractive to many predators, offering protection.
Next comes the pupa stage, with the monarch in a chrysalis, from which the adult butterfly emerges. Butterflies are excellent pollinators, from wildflowers to garden plants.
It is the fourth generation of monarch butterflies that is long-lived, surviving the long migration for winter and living for up to eight months. This generation is known as Methuselah.
How Do Monarch Butterflies Survive Their Migrations?
Monarchs cannot survive the cold winters of North America and Canada. That’s why they undertake their epic migration south.
The fourth generation of monarch butterflies has the most prolonged and arduous lifespan. They leave the ever-dropping temperatures of North America and Canada in August to fly up to 2,500 miles to their overwintering sites.
En route, they look for wildflowers and other nectar sources. While hundreds of millions if not billions may start the journey, many do not finish it.
A typical eastern migration route, called a flyway, could start in Lake Michigan, pass Iowa’s prairies, and go through Oklahoma, then Texas and its arid regions before heading into Mexico.
However, climate change, pesticides, and mono-culture farming techniques mean there are ever-fewer feeding opportunities for migrating monarchs. These dangers reduce the numbers of butterflies that make it to Mexico or California, where further jeopardy lurks in their winter homes.
It’s worth noting that humans only discovered this amazing migration in 1975, thanks to Kenneth and Catalina Brugger, part of a team led by Fred Urquhart.
Where Do Monarch Butterflies Go for Winter?
Fourth-generation monarchs need up to three months to traverse their flyway from north to south. On arrival, they seek sheltered roosting sites close to water.
In California, monarchs usually choose eucalyptus trees, Monterey pines, and Monterey cypresses for roosting. Pismo State Beach has between 20,000-200,000 butterflies in winter, one of the state’s largest populations.
In central Mexico, the monarchs head to the mountainous areas of Michoacán. They roost here in the millions, some say close to a billion, in oyamel fir trees, covering them in what looks like vast branches of drying leaves. It is said you can hear the beating wings of the millions of monarchs flying in Mexico.
The close contact and trees provide protection from cold weather experienced at the high altitudes there, between 7,875-11,811 feet (2,400-3,600 meters). Freezing weather could kill the monarchs.
Occasionally, there are so many thousands of monarchs in a tree that branches collapse. A more prescient threat is deforestation; without the fir trees, the monarchs will be in great peril.
These now three-month-old monarch butterflies enjoy the clean water and food sources in these warmer winter climes. But their journey is not yet over.
Why Do Fourth-Generation Monarchs Live So Long?
Now safely nestled in their overwintering sites, the long-lived fourth-generation monarchs provide spectacular flying displays. The El Rosario Monarch Butterfly Biosphere Reserve in Michoacán is a UNESCO World Heritage. It protects about 70% of this Mexican region’s monarch population.
The forest’s silence and perfect microclimate sustain the monarchs until they start their return journey north in March. The butterflies don’t reproduce in winter entering a suspended reproductive cycle called diapause. They live off their fat reserves all winter.
The monarchs’ journey north in March activates a new breeding cycle. The insects fly north, retracing their flyway route, looking for nectar to sustain them.
The fourth-generation monarchs need to find milkweed crops to lay their eggs, sometimes across sites 1,000 miles apart. After ensuring there is a new generation of monarchs, the Methuselahs’ epic eight-month lives end.
The fourth generation, the Methuselahs, have to live so long to ensure the survival of the species. Their longevity helps make them the only butterfly to migrate two ways.
Newly born, shorter-lived monarchs will survive 25-50 days as they continue their journey north, laying eggs and dying off en route. The return to the summer sites may take two to three generations. Most northern summer sites expect their monarchs to arrive around the time of the summer solstice. Warmer weather may bring them earlier, while colder weather may delay them by a week or two.
How Do Monarch Butterflies Remember Their Migration Route?
The valiant fourth-generation monarchs fly north to south and then a short way north once more. But they don’t have the chance to pass on the migratory route knowledge to their offspring. Furthermore, monarchs in different regions all take different paths. So how do migrating monarchs know where to fly?
There are several theories about this great unanswered navigational question. What scientists do know is that a monarch’s antennae act like a compass. Their antennae are sensitive to the amount and direction of sunshine and can pick up ultraviolet wavelengths and blue light. Internal circadian clocks may help guide them, but we don’t know how.
Others suggest that antennae search out suitable food, providing an olfactory map.
Many organizations tag monarch butterflies to monitor numbers and better understand their behaviors. Volunteers place a small tag on the insect’s underwing and follow its route.
How Did Monarch Butterflies Do in 2022?
Monarch butterflies enjoyed a successful 2022, with numbers increasing by around 35%. But that uptick doesn’t reverse the overall negative trend and crisis the monarch butterflies face.
Overall, monarch populations are thought to have decreased by 80% in the last 30 years. Indeed, the International Union for Conservation of Nature has placed the monarch butterfly on its red list of threatened species.
How Can We Protect Monarch Butterflies?
There are thousands of people helping protect monarch butterfly numbers. Tagging schemes help us understand their numbers and behaviors. They also help pinpoint stopping points during the monarch migration, identifying food sources, plus any changes in their migratory flyways.
There are several protected areas for monarch butterflies, with sites in Mexico, Texas, Florida, Kansas, Ohio, Iowa, and Ontario. Other groups, like the Xerces Society, work with communities and farmers to manage and restore habitats for monarchs.
Gardeners on monarch flyways can plant native milkweeds and stop using pesticides that harm caterpillars, butterflies, and many other forms of wildlife.
Which Animals Eat Monarch Butterflies?
Only one in 10 monarch butterfly eggs will survive to become a caterpillar. Spiders, mantids, and fire ants eat both eggs and larvae, and birds and wasps will eat adults. Common predators include Black-headed Grosbeaks ad Black-backed Orioles.
Others who like to snack on monarchs include toads and lizards; mice may eat the chrysalis. Many monarchs also die after becoming a host to a wide range of parasites.
Where Do Monarch Butterflies Go at Night?
Monarch butterflies roost at night in trees or hedges. They don’t actually sleep in the way humans do. Instead, they enter a quiescent state, a period of inactivity or dormancy.
The butterfly is inactive and enters a low metabolic state to conserve energy. This allows them to rest sufficiently for the coming day’s activities. However, butterflies don’t actually close their eyes and snooze because they don’t have any eyelids.
Are Monarch Butterflies Important to Mexican Culture?
Monarch butterflies have been making their annual migrations for millennia. It’s no surprise to find references to them in Mexican cultures.
In central Mexico, monarchs were called Parákata, or “harvester butterfly,” by indigenous Purépecha communities. They believed the monarchs were their ancestor’s souls returning, thinking echoed in Día de Los Muertos celebrations. Many people dress as monarch butterflies to symbolize this relationship.
What Is the Collective Noun for Butterflies?
The English language contains wonderfully descriptive collective nouns, and butterflies have an entire collection.
They could be a flight or flutter of butterflies or perhaps the more colorful kaleidoscope of butterflies. If you don’t like these insects, try calling them a rabble or swarm of butterflies. Other collective nouns include a rainbow, shimmer, or wing of butterflies.
Awe-struck nature fans may use the more decorative collective nouns. Gardeners angry at losing plants to hungry caterpillars could relate to their designated collective noun — an army of caterpillars.
Monarch Butterfly Fact File
Species: Danaus plexippus
Size: 3.5-inch wingspan
Diet: Herbivore. Caterpillars eat milkweed, and adults live off nectar.
Range: North, Central, and South America, Australia, India, Western Europe, and some Pacific Islands.
Habitat: Farmland, gardens, parks.
Markings: Bright orange wings with a black border and white dots. Wings covered with black veins.
Lifespan: 25-50 days for most generations, six to eight months for those that migrate.
Help Protect the Migration of Monarch Butterflies
The monarch butterfly migration is one of nature’s most beautiful events. Hundreds of millions, if not billions, of butterflies, take wing from North America and Canada as autumn approaches. A unique generation of monarchs, called Methuselahs, live almost 10 times as long as their immediate ancestors to ensure the survival of their species.
The Methuselah monarchs fly south to California and Mexico to warmer climes, following established migratory flyways. Due to the monarch’s short lives, none have traveled the route before. We don’t understand how they successfully navigate their way every year.
After overwintering, the Methuselahs start the journey back to North America and Canada, knowing they will die en route and never see home again. But their journey is not in vain, for them or the natural world. Monarchs pollinate wildflowers and crops en route, forming a vital part of nature’s cycles. Countless ecosystems depend on monarchs to survive.
It’s not all good news, though. The sheer number of monarch butterflies, estimated at billions, belies its status as an endangered species. Climate change, deforestation, mono-agriculture, pesticides, and more all threaten the monarch butterfly.
Tagging systems and conservation agencies are trying to understand and protect monarch butterflies. If monarchs disappear, not only will the skies be less wondrous, but humans will risk losing a vital cog in the wheel of life, with consequences unknown.
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