English Diagnostic Assessment

Every year, millions of monarch butterflies fly south for the winter. They travel up to 3,000 miles from Canada and the United States to reach forests in central Mexico. This long journey is one of nature's most amazing events. Scientists have studied monarchs for decades to understand how these small insects make such a huge trip.

Monarch butterflies weigh less than a paperclip, yet they can fly 50 to 100 miles per day. They use the sun and Earth's magnetic field to find their way. No single butterfly makes the full round trip. Instead, it takes three or four generations to complete the cycle. The butterflies that fly south in the fall are a special generation. They live up to eight months, much longer than the two to six weeks most monarchs live.

When monarchs arrive in Mexico, they gather in forests high in the mountains. Millions of them cover the trees, making the branches look orange. The cool mountain air slows their bodies down so they use less energy. They stay in these forests from November until March. Then they begin flying north again, laying eggs on milkweed plants along the way. Milkweed is the only plant that monarch caterpillars can eat.

Today, monarch butterflies face serious problems. Farmers use chemicals that kill milkweed in their fields. Without milkweed, caterpillars cannot survive. Also, forests in Mexico are being cut down for farming and building. Climate change makes weather less predictable, which can confuse the butterflies or destroy their resting spots. Scientists and volunteers are working to help by planting milkweed gardens and protecting the forests in Mexico. If people take action now, future generations may still be able to watch this wonderful migration.