Butterfly Boom

Monarch butterflies spend summers in Canada and the northern U.S. But in the fall, many migrate as far as 4,800 kilometers (2,980 miles) south to Mexico to avoid the cold. Last year, scientists estimated that about 300 million monarchs spent the winter there. That’s the highest number in 12 years!

Storms can kill monarchs. But last year, the butterflies experienced mild weather in Mexico. Despite the population boom, monarchs are still under threat, says Craig Wilson, a researcher at Texas A&M University. One reason is that humans have killed off many milkweed plants to make room for crops and cities. Milkweed is the only food source for monarch caterpillars.

You can help the migrating butterflies by planting milkweed and other flowers in your yard.