Monarch Butterfly Migration: 3,000 Miles to a Forest She's Never Seen
Monarch butterfly migration is one of the strangest journeys in nature. Every fall, eastern monarchs fly to the mountains of central Mexico, some covering more than 3,000 miles. None of them has ever been there before. Their great-great-grandparents were the last ones to make the trip.
Quick Facts
- Species: Monarch butterfly (Danaus plexippus)
- Distance: More than 3,000 miles for some, per the U.S. Fish and Wildlife Service
- Destination: Oyamel fir forests in central Mexico
- Super generation: Lives up to about eight months
- Navigation: A sun compass kept on time by clocks in the antennae
From Pinhead Egg to Butterfly
A monarch starts as a tiny egg on a milkweed leaf. The caterpillar eats only milkweed, and over five growth stages it grows to almost 2,000 times its original mass, according to the Monarch Joint Venture. Then it hangs upside down and forms a jade-green chrysalis dotted with gold, where its body is rebuilt into a butterfly.
Poison on Purpose
Milkweed contains toxins called cardenolides. Monarch caterpillars store them in their bodies, and the U.S. Fish and Wildlife Service notes that the butterfly's bright orange is a warning to predators that eating one can be toxic.
The Super Generation
Summer monarchs live only a few weeks. The generation born at the end of summer is different. The Fish and Wildlife Service calls it the super generation: these butterflies live up to eight months, about eight times longer than their parents and grandparents. They hold off breeding until spring and save their energy for the flight.
How Do Monarchs Know Where to Go?
No one shows them the way. Monarchs steer by the sun. A 2009 study in Science found that clocks in their antennae help them correct for the sun's movement across the sky, so they keep heading south all day.
A Forest Covered in Orange
In Mexico, millions of monarchs pack into oyamel fir forests close to two miles above sea level, according to the Cincinnati Zoo. They cluster so densely that branches sag. In spring they fly north, lay eggs on milkweed, and the cycle starts again.
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Frequently Asked Questions
How far do monarch butterflies migrate?
Eastern monarchs fly to central Mexico each fall. Many travel more than 2,000 miles, and some cover more than 3,000 miles.
How long do monarch butterflies live?
Summer monarchs live a few weeks. The fall migrating generation can live up to about eight months.
How do monarchs find their way to Mexico?
They use the sun as a compass, and clocks in their antennae help them adjust for the time of day.
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Sources
- U.S. Fish and Wildlife Service: The Phenomenal Monarch Migration: the super generation, 8-month lifespan, 3,000-mile flight
- U.S. Fish and Wildlife Service: Monarch: milkweed toxins and migration
- Monarch Joint Venture: Monarch Life Cycle: five instars and 2,000-fold growth
- Merlin, Gegear and Reppert (2009), Science: Antennal Circadian Clocks Coordinate Sun Compass Orientation in Migratory Monarch Butterflies: the antenna clock
- Cincinnati Zoo: Multiple Monarch Generations Make the Migration: oyamel fir forests and generations
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