As birds begin their flights back to their summer homes in the north, one species of butterfly also embarks on a remarkable migration.
Monarch butterflies cannot survive the cold winters of the northeastern U.S. and Canada. Each fall, these delicate insects embark on a journey of about 3,000 miles to their overwintering grounds in the Sierra Madre Mountains of Mexico.
Although researchers are unsure how Monarchs navigate such long distances, the magnetic pull of the earth and the position of the sun may play an important role. It is one of the greatest natural events on Earth. But unlike birds, these individual butterflies will never return to their summer home.
As the temperatures rise in early spring, the Monarchs leave their wintering grounds to move north. They make it as far as Texas and other southern states before they stop to mate and lay eggs on milkweed plants, and then their life cycle ends.
The eggs hatch after just a few days and grow into brilliantly striped caterpillars. They eat massive amounts of milkweed before forming a chrysalis where they transform into an adult butterfly.
This new generation of butterflies flies a few hundred miles north, find more milkweed, and repeat the process. It can take up to four or five generations to complete the full journey to their ancestral summer homes in the northeastern United States and Canada. Each of these life cycles lasts only 5-7 weeks, compared to the 8–9-month lifespan of the butterflies who make the epic journey in the fall.
Sadly, their numbers are in decline.
The greatest threat to Monarch populations is a dramatic decline in the presence of milkweed across their range. Research suggests the large-scale use of herbicides used on farms has destroyed much of the milkweed.
Why is this plant so important? Milkweed is the only plant on which Monarchs will lay their eggs and is the primary food source for the caterpillars. Scientists, conservationists, and butterfly enthusiasts are encouraging people to grow the plant on their own. It is poisonous to pets and people, so be sure to plant it in an area your pets and children cannot reach.
You can track the Monarch’s migrations and report sightings for research purposes at
JourneyNorth.org.
