The Long Journey of the Monarch

Every autumn, millions of orange and black monarch butterflies leave their summer homes in Canada and the United States and begin flying south. Their destination is a small area of forest in central Mexico, over four thousand kilometres away. (A) Scientists have studied this migration for decades, and it continues to surprise them.

Unlike birds, monarch butterflies cannot store enough energy to complete the journey in one go. They stop to feed on flowers along the way, refuelling on nectar before pressing on. (B) A single butterfly may travel up to one hundred kilometres on a warm, sunny day.

When the monarchs finally arrive in Mexico, they do something spectacular. Millions of butterflies settle in clusters on the branches of oyamel fir trees, their wings folded and overlapping like layers of autumn leaves. (C) Local communities have come to call this event the arrival of the monarchs, and it has been celebrated for generations.

What makes the monarch's journey even more remarkable is that no individual butterfly completes the full round trip. The butterflies that travel south in autumn will overwinter in Mexico, then begin flying north in spring. (D) In this way, it may take four or five generations to complete one full cycle.

In recent decades, the monarch population has declined sharply. Milkweed — the only plant on which monarchs lay their eggs and which their caterpillars eat — has been destroyed across much of its range. (E) Without milkweed, there can be no monarchs.

Conservation efforts are now underway across North America. Schools, farmers, and government agencies are planting milkweed corridors to restore the butterflies' pathway north. (F) Scientists hope that, with continued effort, the monarch's great migration will continue for generations to come.

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Choose from these sentences — one does not belong anywhere:

1. They use warm air currents, called thermals, to rise high into the sky before gliding southward, conserving energy for the journey ahead.

2. The forest becomes so dense with butterflies that the air itself trembles with the movement of their wings.

3. They will lay their eggs on milkweed plants as they move northward, and it is their offspring that continue the journey.

4. Herbicides used in modern farming have cleared the plant from millions of hectares of farmland and roadsides where it once flourished.

5. In some areas, early results suggest that the butterfly population is beginning to stabilise after years of decline.

6. Despite travelling such vast distances, they navigate to the same mountain forests — and sometimes even the same individual trees — as their ancestors the year before.

7. Tagged butterflies have helped researchers discover that the same family of trees in Mexico may have hosted monarchs for over a century.