Dr. James Hansen: The monarch butterflies return

  • Published on April 29th, 2020

Last summer the population of monarch butterflies in the Northeast United States seemed to be greater than it had been in the past decade. This was consistent with the fact that the number of butterflies making it to Mexico for the 2018-19 winter was the highest since 2006-07 (see graph). Unfortunately, only half as many made it to the overwintering forest this past winter, perhaps due to unfavorable weather on the return trip. [1 ha = 2.47 acres is about 50,000,000 monarch butterflies, so more than 100 million butterflies are heading north this year.]

Monarch butterflies return

By James Hansen and Makiko Sato

The monarch butterflies are now moving north as shown by the map below, with the long-lived overwintering generation Monarch butterflies returnproducing the next generation early in the trip. The annual circuit from Mexico to Canada and back takes 4-5 generations.

BTW, it has been found that breeding monarch butterflies indoors does not generally produce healthy monarchs who know where they should be headed. The best way to help monarchs and observe their marvelous transformation from larvae to butterfly is by planting milkweeds, their only food

A remarkable 3-minute film of a ‘hummingbird’ drone spying on the monarch population in Mexico is available. Be sure to watch to the spectacular conclusion at the end!

About the Author

Dr. James Hansen directs the Program on Climate Science, Awareness and Solutions of the Earth Institute at Columbia University. The Guardian calls him "The Father of Climate Science" - his 1988 Congressional testimony on climate change helped raise broad awareness of global warming. He is often in the news advocating for a price on carbon and other forms of climate action, divesting from fossil fuels, and helping his grandchildren sue the government over their future. He is the author of "Storms of my Grandchildren".