| Story by Meghan McMahon |
One of the most anticipated events each spring is the arrival of monarch butterflies. When you learn more about the journey the monarchs take to reach Will County, you start to appreciate these beautiful butterflies even more.
Monarchs – the state insect of Illinois – typically arrive in our area in late May or early June each year, said Bob Bryerton, an interpretive naturalist for the Forest Preserve District. Their journey, though, begins many months earlier, thousands of miles away, in the Sierra Madre Mountains in central Mexico.
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“The adult monarchs in Mexico were hatched here and migrated there to overwinter,” Bryerton said. Then, at the end of the winter, they begin to travel north. “They migrate north as far as they can, lay eggs and die,” with their descendants repeating the process as they continue the trip.
Although it takes just one generation of monarchs to make it south to Mexico for the winter, it takes multiple generations, typically three or four, of the butterflies to return to their nesting grounds each spring, according to the U.S. Forest Service.
The butterflies can travel 50-100 miles a day, moving along flyways (regularly used routes) and using air currents to help speed their flight, the Forest Service reports. They only fly during the day, stopping to roost overnight. Frequent roosting spots include cedar, fir and pine trees because they have large, thick canopies that help protect the monarchs from cool nighttime temperatures. Because the butterflies tend to roost in large groups to keep them warmer at night, it’s not uncommon to see hundreds or even thousands of butterflies on a single tree while they are roosting.
Monarch butterflies depart their nesting grounds in the northeastern United States and southern Canada in the fall, traveling up to 3,000 miles to reach their overwintering grounds in Mexico. However, the monarchs that migrate south never return to these northern locations. Instead, it’s a new generation – several generations removed from the ones here the previous summer – that finds its way here to nest the following spring, despite never having been here before.
Scientists do not fully understand how monarchs make their way back to the same nesting grounds year after year despite never having been there before, but they do know that one plant – milkweed – is essential for the monarch lifecycle and helps drive the migratory patterns.