Why Monarch Butterflies Make an Epic Journey Every Year

Butterflies are some of the most beautiful insects in the world. With so many different species and variations, butterflies are a marvel to behold. Now, imagine seeing a massive monarch butterfly swarm, creating a breathtaking spectacle! This video by Nature on PBS shows a stunning flutter of butterflies. Keep reading below to learn about why monarch butterflies swarm.

Why Do Monarch Butterflies Swarm?

Monarch butterflies, like other butterfly species and birds, must migrate to warmer climates during the cold winter months. Monarch butterflies are unique because they are unable to “overwinter.” Overwintering is the process of surviving the winter by either continuously moving or remaining in a dormant state. Instead of overwintering, monarch butterflies migrate by swarming together in roosts of hundreds or thousands. Swarming helps monarch butterflies stay warm and ward off any predators they might encounter.

Monarch butterflies typically migrate from the northeast United States and Canada all the way down to central Mexico, where they will find a warmer climate. They cluster on Oyamel trees, a fir tree native to Mexico, because these trees are strong enough to support the weight of thousands of butterflies. Migrating south during the winter months ensures that these butterflies do not freeze to death.

When Do They Leave?

Scientists categorize monarch butterflies by generations to better understand their migration patterns and life spans. The first generation consists of the offspring of butterflies that overwintered, or swarmed, in Mexico. This generation begins the journey north as winter ends. By the time they reach the northern United States and Canada, the weather will be warm again, and the butterflies will be in their third or fourth generation. As the last generation returns, the weather will start to get cold again, repeating the cycle for future generations.

Do Other Butterfly Species Swarm?

Monarch butterflies are unique among butterflies as they are the only known species to make a two-way migration both north and south, similar to the migrations of some birds. Other butterfly species can overwinter at all stages of life, meaning that while they may migrate in one direction, they do not need to make the return journey to a warmer climate. While monarchs may be distinctive in this regard, other butterfly species also experience swarms similar to those of monarch butterflies. The Painted Lady butterfly is also known for forming swarms similar to those of monarchs, showing that swarming behavior is not exclusive to a single species.