Climate change will disrupt the monarch butterfly’s famous migration

The monarch butterfly travels from Canada and the United States to the mountains of central Mexico every year.

This journey looks delicate and graceful, but it depends on very specific weather conditions and plants. New research suggests that climate change could disturb this balance in serious ways.

Scientists from the National Autonomous University of Mexico studied how future climate conditions may affect monarch butterflies in Mexico.

The research does not focus only on adult butterflies. Instead, it looks closely at eggs and caterpillars.

These early stages are more fragile and depend heavily on temperature, rainfall, and the availability of the right plants.

A journey that spans countries

Each fall, a special generation of monarchs begins flying south.

This group travels thousands of miles and spends winter in high mountain forests, including protected areas like the Monarch Butterfly Biosphere Reserve.

Months later, when temperatures rise, new generations start moving north again. Over time, monarchs spread across large parts of North America.

In recent years, fewer butterflies have reached Mexico. Several problems contribute to this decline.

Forest loss reduces safe winter shelters, parasites weaken individuals, and weather patterns have also become less predictable. Moreover, rising temperatures now add another layer of difficulty.

Monarch migration needs milkweed

Researchers examined 46 milkweed species growing along migration routes in Mexico. Milkweed plants from the genus Asclepias are not optional for monarchs.

A female lays eggs only on milkweed leaves. When caterpillars hatch, milkweed becomes the only food source.

Milkweed also gives monarchs protection. The plant contains chemicals that make both caterpillars and adult butterflies unpleasant to predators. That bitter taste helps survival.

To understand where monarchs reproduce today, the team used information from Red Monarca and the citizen science program Journey North.

This combination of plant data and butterfly observations helped build a clearer picture of current breeding areas.

Trying to see the future

Instead of waiting decades to observe change, scientists used computer models. These models estimate where suitable habitats exist today and where those areas may shift in the future.

The study considered climate first. Temperature and rainfall patterns strongly influence butterfly survival. Next came milkweed distribution.

Finally, land use was included, such as forests, farmland, natural vegetation, and areas near water.

Predictions were made for 2030, 2050, and 2070 using two different climate models. Both models show a similar direction of change.

Suitable breeding areas for eggs and caterpillars are likely to move southward within Mexico as temperatures rise.

Climate is the main pressure

The numbers vary between models, but the trend remains clear. In one scenario, suitable habitat could shrink by about 40 percent by 2070.

In the other, the reduction could be closer to 8 percent. Even the lower estimate still represents a loss.

Warmer conditions affect how long butterflies live and how many eggs females produce. Temperature also influences when migration begins.

If it becomes too warm in key areas, butterflies may not find the right signals to start their northward flight.

Milkweed and land shifts

Milkweed zones also shift south in future projections. Some new areas may become suitable for milkweed growth.

However, when climate, plant presence, and land conditions all align perfectly, those ideal zones often become smaller or move farther from the Mexico–U.S. border.

Land use in many Mexican regions remains relatively stable, especially in areas with natural vegetation and rainfed agriculture.

That stability suggests that rising temperatures pose a greater threat than farmland expansion in this case.

A future without monarch migrations?

The study raises a serious concern about migration itself.

“Although the monarch butterfly species itself may not be directly threatened under climate change scenarios, its migratory process is,” noted the researchers.

Under projected climate scenarios, optimal monarch butterfly habitat is likely to shift toward southern Mexico.

This could make their long journey harder and cause some butterflies to stop migrating and stay in one area.

If breeding areas move farther south, monarchs may stop traveling such long distances. Some populations could remain in northeastern or central Mexico year round.

Over time, non-migrating monarch butterflies may develop shorter wings. This may eventually make long flights harder.

In addition, certain tropical milkweed species can increase infection by parasites that weaken butterflies and reduce flight strength.

Shared responsibility across borders

Monarch migration links Canada, the United States, and Mexico through a single, shared natural phenomenon that depends on coordinated conservation across borders.

Climate change does not recognize political boundaries, and neither do butterflies.

As rising temperatures and shifting rainfall patterns redraw the map of suitable habitat, the areas that support monarch eggs, caterpillars, and milkweed may continue moving south.

By the end of the century, this iconic migration could follow new routes, require more energy, or unfold in ways that look very different from the spectacle millions recognize today.

The study is published in the journal PLOS Climate.

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