How Climate Change Could Reshape Monarch Butterfly Migration

The monarch butterfly makes an annual journey from Canada and the United States to the mountains of central Mexico.

Although this migration appears fragile and elegant, it relies on highly specific weather conditions and plant life. New research indicates that climate change may disrupt this balance in significant ways.

Scientists at the National Autonomous University of Mexico investigated how future climate conditions could affect monarch butterflies in Mexico.

Rather than concentrating solely on adult butterflies, the research closely examines eggs and caterpillars.

These early life stages are particularly vulnerable, depending heavily on temperature, rainfall and access to suitable plants.

A journey across countries

Every autumn, a distinct generation of monarchs starts its southward flight.

This group covers thousands of kilometres before spending the winter in high-altitude forests, including protected sites such as the Monarch Butterfly Biosphere Reserve.

Several months later, as temperatures increase, new generations begin travelling north once more. Gradually, monarchs spread throughout extensive areas of North America.

Fewer butterflies have arrived in Mexico in recent years. A number of factors are behind this decline.

Loss of forest reduces secure winter refuges, parasites weaken individual butterflies, and weather patterns have become more unpredictable. Rising temperatures add a further challenge.

Monarch migration requires milkweed

The researchers assessed 46 milkweed species found along Mexico’s migration routes. Milkweed plants in the genus Asclepias are essential to monarchs.

Females lay their eggs exclusively on milkweed leaves. Once caterpillars emerge, milkweed is their only source of food.

Milkweed offers monarchs protection as well. Its chemicals make caterpillars and adult butterflies unappealing to predators. This bitter flavour supports their survival.

To identify where monarchs currently breed, the team drew on data from Red Monarca and the citizen-science programme Journey North.

Combining plant records with butterfly observations provided a more detailed view of present-day breeding areas.

Predicting the monarch’s future

Rather than waiting decades to document change, the scientists used computer models. These models estimate where suitable habitat exists now and how those locations could change in the future.

Climate was assessed first, as temperature and rainfall patterns strongly affect butterfly survival. The researchers then considered milkweed distribution.

Land use was included last, covering forests, farmland, natural vegetation and locations close to water.

The projections covered 2030, 2050 and 2070, using two separate climate models. Both point towards a similar pattern of change.

As temperatures rise, suitable breeding habitat for eggs and caterpillars is expected to shift southwards within Mexico.

Climate is the main pressure

While the figures differ between the models, the overall trend is unmistakable. Under one scenario, suitable habitat may contract by around 40 percent by 2070.

Under the other scenario, the reduction may be nearer 8 percent. Even this lower projection represents a loss.

Warmer conditions influence both butterfly lifespan and the number of eggs laid by females. Temperature also affects the timing of migration.

If crucial areas become excessively warm, butterflies may not receive the appropriate cues to begin their northward journey.

Milkweed and land shifts

Future projections also show milkweed zones moving southwards. Certain new places may become suitable for milkweed to grow.

Yet where climate, plant availability and land conditions all coincide, these ideal areas often shrink or move further away from the Mexico–US border.

Land use remains comparatively stable across many Mexican regions, particularly where natural vegetation and rainfed farming are present.

This stability indicates that, in this case, increasing temperatures may pose a greater risk than expanding farmland.

The future of monarch migrations

The study highlights a serious concern for the 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 the projected climate scenarios, optimal monarch butterfly habitat is expected to move towards southern Mexico.

This may make the lengthy journey more difficult, causing some butterflies to cease migrating and remain in one place.

Should breeding areas shift further south, monarchs may no longer travel such great distances. Some populations may stay in north-eastern or central Mexico throughout the year.

Over time, non-migrating monarch butterflies could develop shorter wings. This may ultimately make long-distance flights more difficult.

Furthermore, some tropical milkweed species may increase parasite infections that weaken butterflies and reduce their flight strength.

Shared responsibility across borders

Monarch migration connects Canada, the United States and Mexico through one shared natural phenomenon, requiring coordinated conservation across national borders.

Climate change respects no political boundaries, and neither do butterflies.

As warmer temperatures and changing rainfall patterns redraw the map of suitable habitat, the areas supporting monarch eggs, caterpillars and milkweed may continue shifting southwards.

By the end of the century, this iconic migration may take different routes, demand more energy or occur in forms very different from the spectacle recognised by millions today.