This butterfly is famous for its epic migration, but now it's endangered

On July 21, 2022, the World Conservation Union (IUCN) released the latest Red List of Endangered Species. Among them, the migratory monarch butterfly (Danaus plexippus plexippus) was included in the Red List of Endangered Species for the first time.

Monarch Butterfly｜Three Butterflies

Despite the best efforts of butterfly guardians over the past few decades, monarch butterfly populations have been declining at an alarming rate.

Among them, the monarch butterfly's western North American population is at the greatest risk of extinction. Its population has dropped from 10 million in the 1980s to 1,914 in 2021, a 99.9% decrease in just 40 years; the larger eastern North American population has also decreased by 84% from 1996 to 2014; the local population, which is known for migrating from Mexico and California in winter to its summer breeding grounds throughout the United States and Canada, has decreased by 22% to 72% in the past decade.

A cluster of monarch butterflies | Steve Corey / Wikimedia Commons

These butterflies use their short lives to stage an epic migration every year. However, this wonder is now under threat.

The life of a monarch butterfly

In North America, no butterfly is more famous than the monarch. This large butterfly, found across North America and northern South America, is instantly recognizable by its striking bright orange wings, which are accentuated by thick black wing veins.

Monarch butterfly | Rbreidbrown / Wikimedia Commons

As early as 1758, Linnaeus, the founder of taxonomy, described the monarch butterfly in Systema Naturae and named it Danaus plexippus. Its English name is monarch butterfly, which means monarch or king. It is said to be in memory of William I, Prince of Orange of the Netherlands. Therefore, they are also translated as monarch butterfly and emperor butterfly.

Like other butterflies, the life cycle of the monarch butterfly is divided into four stages: egg, larva, pupa, and adult. The female butterfly often lays eggs under the young leaves of the milkweed plant (Asclepias). Their eggs are creamy white and have a pointed oblong shape.

Monarch butterfly eggs | Lorie Shaull / Flickr

The eggs will hatch into larvae after 3 to 10 days, and the larvae will feed on the leaves of the milkweed plant. The whole plant of the milkweed genus contains highly toxic cardiac glycosides [gān]. If people accidentally eat it, it can cause dizziness, nausea, vomiting, diarrhea, breathing difficulties and even risk of death. However, the larvae of the monarch butterfly have evolved a unique ability. Not only will they not be poisoned by eating the leaves, but they can also store the toxins of the milkweed plants in their bodies as chemical weapons for self-defense.

The larvae of the monarch butterfly are yellow, white and black, with very eye-catching patterns. This is a warning color, telling predators "don't mess with me". The monarch butterfly is poisonous, so insect-eating animals are naturally in awe of it and dare not eat it at will.

Monarch butterfly larva | Victor Korniyenko / Wikimedia Commons

After four molts, the larvae become pupae. Their pupae are green and hang upside down under the plants. Over time, the color of the pupae gradually darkens. After a few weeks, the pupae's epidermis cracks, and the head and body of the adult gradually emerge from the old epidermis until the wings become engorged and hardened, allowing them to fly freely.

Monarch butterfly chrysalis | Kimberly Smith / Wikimedia Commons

The bright colors of the adult monarch butterfly also have the effect of showing that it is "toxic". Its strength and appearance have attracted "copycat products", such as the black-striped pseudo-monarch butterfly (Limenitis archippus), commonly known as the viceroy butterfly, and the tiger butterfly (Danaus genutia) distributed in Southeast Asia and Australia-New Guinea.

See the differences between the 3 types of butterflies:

Figure 1 is a black-striped butterfly, which looks very similar to the monarch butterfly, but is not poisonous and relies on its resemblance to the monarch butterfly to deceive its natural enemies; Figure 2 is a tiger butterfly, and Figure 3 is a monarch butterfly. The monarch butterfly has large white spots on the tips of its wings｜Three Butterflies; Armon / Wikimedia Commons

A thousand miles of pursuit, a lifetime of searching for butterflies

There are two subspecies of the monarch butterfly, the most famous of which is the nominate subspecies distributed in North America, which has long-distance migration behavior and is listed as endangered. The other subspecies of the monarch butterfly (Danaus plexippus plexippus) does not migrate and is not on the endangered list.

The migratory monarch butterfly is like the migratory birds of the insect world. Every autumn, it forms large flocks and flies to the warm south to overwinter, and then migrates back north in the spring.

Every October, 150 million monarch butterflies gather in Canada to start a five-week migration, with a maximum speed of 50 kilometers per hour and a journey of up to 5,000 kilometers. Eventually, they arrive in the Sierra Madre Mountains in Mexico, where they gather to overwinter, feed and breed. This is an extremely spectacular gathering, and what makes the forests full of color is not the red leaves, but the orange monarch butterflies. According to statistics, in the mountains where monarch butterflies gather, more than 3 million butterflies can gather on a few large trees.

In the El Rosario Nature Reserve in Mexico, what look like yellow dead leaves on the trees are countless monarch butterflies resting on the branches | Zhang Chenliang

They hibernate here for the winter, and then start to return north in the next spring, breeding on the way. After the old generation of butterflies die, their children will take over their journey back home - no monarch butterfly can complete the entire round trip independently, this huge migration is completed by the joint efforts of several generations of butterflies.

The first scholar to study the migration of monarch butterflies was Canadian entomologist Frederick A. Urquhart, who had been interested in monarch butterflies since he was a child and wanted to find out where they went in the winter. In 1937, he began to study the migration routes of monarch butterflies and founded the Butterfly Migration Society, which mobilized thousands of citizen volunteers to participate in the marking and tracking of monarch butterflies. This is one of the largest and most widely participated scientific research activities in North America.

El Rosario Reserve, monarch butterflies flying in the sky｜Zhang Chenliang

After years of tracking, Fred and his volunteers roughly figured out the migration route of monarch butterflies: they migrate from Canada, the northeastern and midwestern United States to the southwest for wintering. But monarch butterflies disappeared in the area bordering Texas and Mexico. Where did these butterflies go?

In 1972, Fred's wife asked for help from Mexican volunteers. An American couple living in Mexico spent more than two years searching in Michoacán State in central Mexico, and finally found tens of millions of monarch butterflies in the high-altitude mountain forests of Mexico.

Monarch Butterfly｜Three Butterflies

Fred climbed the mountain forest the following year after learning the good news. He saw a group of monarch butterflies gathered in the valley, bending the branches. At that moment, the 65-year-old finally solved the puzzle of his life. Among the butterflies, Fred found a butterfly marked with "ps 397". It was marked by volunteers in Minnesota, USA, and took two months to fly more than 3,000 kilometers to reach Mexico.

Monarch butterflies feeding on nectar in El Rosario Nature Reserve｜Zhang Chenliang

Fred passed away in 2009. He dedicated his entire life to the study of monarch butterflies, leaving behind four books and a large number of papers. He also influenced a large number of young researchers to embark on the "butterfly chasing path."

Guardian Epic Journey

There are 14 main colonies of monarch butterflies in Mexico, covering an area of ​​5.62 million hectares. This world-shaking discovery has been highly valued by the Mexican government. In 2008, the monarch butterfly habitat was listed as a World Natural Heritage Site and has been strictly protected. Today, in the United States, Canada, and Mexico, the monarch butterfly colonies are popular local eco-tourism attractions every autumn and winter, attracting tourists from all over the world.

However, the migration is always full of surprises and obstacles, and many butterflies die as a result; butterflies that finally reach their wintering grounds also face environmental pressures, such as abnormal weather and changes in habitat. Studies have shown that with the deterioration of global habitats and the reduction of habitats, the population of monarch butterflies has been declining year by year, and there is also a risk of migration failure. Among them, illegal logging has the greatest impact on monarch butterflies. A large number of native coniferous forests have been destroyed, and the interference of human activities has dealt a heavy blow to monarch butterflies.

Monarch butterflies flying between buildings in El Rosario Reserve｜Zhang Chenliang

Intensive agricultural production is another major threat. The use of large amounts of pesticides and herbicides has reduced the number of milkweed plants that monarch butterflies rely on for survival, resulting in a decrease in the number of butterflies.

Other studies have shown that climate change has become an important factor in the decline of migratory monarch butterflies in recent years: droughts limit the growth of milkweed plants and increase the frequency of catastrophic wildfires; extreme temperatures trigger the premature migration of butterflies - before their food, milkweed plants, have time to grow; in addition, with global warming, increased carbon dioxide levels may cause milkweed plants to produce more toxic enol components, which monarch butterfly larvae cannot tolerate, and severe weather has killed millions of butterflies.

"Butterfly Garden" with Milkweed Plants｜Sandieji

Therefore, strengthening habitat protection, reducing the use of pesticides and herbicides, and planting more milkweed along roadsides or in small "butterfly gardens" can all do their part to continue this epic migration.

At risk of extinction

Although ecologists have been calling for stronger protection of monarch butterflies, the inclusion of the migratory monarch butterfly in the Red List of Endangered Species has sounded a wake-up call for us.

Dr Jon Paul Rodríguez, Chair of the IUCN Species Survival Commission, said: “It is sad to see the monarch butterfly, a butterfly renowned for its migration and cultural significance, facing extinction. Assessing the extinction risk of species provides the basis for conservation actions to try to protect such species and avoid further losses.”

Migratory monarch butterflies resting in a pine tree | C. Formanski / Wikimedia Commons

The latest IUCN Red List includes 147,517 species, of which 41,459 are at risk of extinction, 902 are already extinct, including our endemic white sturgeon, and 82 species have been declared extinct in the wild.

“Today’s Red List update highlights the fragility of natural wonders, such as the unique landscape of monarch butterflies that migrate thousands of kilometers,” IUCN Director-General Bruno Oberle said in a statement. “To protect this rich and diverse nature, we need effectively and equitably managed protected areas, while taking decisive action to combat climate change and restore ecosystems.”

Author: Sandie Ji

This article comes from the Species Calendar, welcome to forward

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