Read an Academic Passage

The Migration of Monarch Butterflies

The annual migration of the monarch butterfly is one of the most spectacular phenomena in the natural world. Every autumn, millions of these insects travel up to 3,000 miles from their summer breeding grounds in the northeastern United States and Canada to overwintering sites in central Mexico. What makes this journey particularly remarkable is that it is not a round trip for any single butterfly. It is a multi-generational relay, with successive generations completing different stages of the journey. The generation that flies south to Mexico has never been there before, yet it unerringly finds the same small forest area its ancestors inhabited.

Scientists have long studied how these butterflies navigate such a vast distance. Research indicates that they use a combination of cues. Their primary guide is a sun compass, located in their antennae, which allows them to orient themselves by the position of the sun in the sky. They also possess an internal biological clock that compensates for the sun's movement throughout the day. Some studies suggest that monarchs may also be sensitive to the Earth's magnetic field, using it as a supplemental navigation tool, especially on cloudy days when the sun is not visible.

Unfortunately, the monarch migration is now an endangered phenomenon. The survival of the butterflies depends on specific environmental conditions at every stage of their journey. A primary threat is the loss of milkweed, the only plant that monarch caterpillars eat, due to agriculture and land development in their summer breeding grounds. The use of pesticides is another major concern. Furthermore, deforestation and habitat degradation in their overwintering forests in Mexico threaten their survival during the vulnerable winter months, prompting urgent calls for international conservation efforts.