The monarch butterfly is not only the state butterfly of Vermont, but it is also an iconic symbol of summer. Monarchs are seasonal residents here, and are now embarking upon a continent-spanning journey to their overwintering grounds in Mexico.
Monarch butterflies are the only butterfly species known to migrate two ways, much like migratory birds. Theirs is also the longest known migration of any insect! Since they cannot survive the harsh winters of the northeast, they take cues from diminishing daylight and cooler temperatures to start heading south. Monarchs migrate thousands of miles each fall, and amazingly, overwinter in a few distinct mountainous locations, the same locations (often even the same trees) from year to year.
The same monarchs that make the fall migration undergo “diapause”, delaying reproduction until their journey north in the spring. Then, they will look for milkweed plants to lay their eggs on. About four generations of butterflies are born each summer, and the fifth makes the big southern migration. This means that the butterflies migrating this year are probably the great-great-great-grandchildren of last year’s overwintering monarchs.
Since the monarch butterflies migrating this year have no way to learn or remember a migration route they have never experienced, researchers think that monarchs use light cues from the sun as a compass to guide their migration. There may also be specific genes that play a role in keeping their migration on course.
Monarch butterfly populations have been on the decline in recent decades. Their overwintering grounds are at risk of human disturbance, and their reproduction has been impacted by weather variability, pesticides, and diminished milkweed abundance. It is important for scientists and citizen scientists to continue to monitor monarch butterflies and manage habitats to promote their populations. You can become a member of the Fairbanks Museum Community of Observers, or check out our exhibit called “Cloaked in Color” to learn more about the amazing world of butterflies.