The great migration

Monarchs' taxing journey links multiple generations

|  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.


A monarch caterpillar and milkweed.

The monarch lifecycle is dependent on milkweed. The butterflies lay eggs only on milkweed plants, and those eggs then hatch into caterpillars that feed on the milkweed, Bryerton said. The milkweed also has protective qualities for the butterflies, because the toxins they acquire from eating the plant make them poisonous to many of their potential predators.

Unfortunately, the milkweed population across the United States has dropped significantly, with more than 860 million stems lost nationwide in the past decade, according to the U.S. Geological Survey. This loss of monarch habitat has also caused the monarch population to drop.

This loss of monarch habitat is one of the main contributing factors to a significant and troubling drop in the monarch population, as much as 90 percent over the past 20 years, according to the Illinois Department of Natural Resources (IDNR).

Although monarchs are not listed as an endangered species, with such a devastating drop in the monarch population, efforts are underway nationwide to help address the decline. One of the primary efforts is to replenish the supply of milkweed in areas where the butterflies nest.

“Milkweed plants have become more scarce as we have gotten better at eliminating weeds in general from all types of areas, including farms and right of ways,” Bryerton said. “Also, as we convert more fields into development, there are fewer places for milkweed to grow.”

In some areas, garden clubs, ecological groups and government agencies having been giving away milkweed seeds in the hopes people will plant them to help boost the monarch population. In fact, visitors to the Forest Preserve District’s Plum Creek Nature Center can get free milkweed seeds for planting in their own yards.

Other efforts include attempting to restore milkweed along ditches and rights of way. Some states have also planted milkweed along highways where they do not mow to help increase milkweed stems, Bryerton said.

The U.S. Geological Study estimates as many as 1.8 billion additional milkweed plants may be necessary to return the monarch population to a sustainable size.

While a large-scale effort is needed, including restoring milkweed in agricultural areas, you can help at home too by planting milkweed in your own yard and garden.

“The cool part is if you plant milkweed in your yard, you may be able to watch the entire process of butterfly development,” Bryerton said. “The butterflies will lay eggs on the plants and you can watch the caterpillars develop into a pupa.”


Many species of milkweed are native to Will County and will grow well here with little extra care, he said. “They are designed to tolerate our weather and soil conditions and so grow well here.”

Among the milkweed species to plant in our area are common milkweed, prairie milkweed, swamp milkweed, purple milkweed, butterflyweed and whorled milkweed. The milkweed plants that are native to Illinois are not necessarily something people will find at local nurseries and garden centers, but you can order them online or purchase them at local plant sales.

“The butterflies can smell the plant from a bit of a way off and will be drawn to it,” Bryerton said. “Once they land on it, they will confirm that is indeed milkweed and lay eggs if it is a milkweed plant.”

He said the pollinator garden they maintain at Plum Creek Nature Center includes milkweed among other plants planted with the intention of attracting pollinating birds and insects. The garden was revamped last year, and they added a swamp milkweed plant in one corner.


“We had close to 30 caterpillars on this plant,” he said. “For some reason, the butterflies found this right away and liked it a lot. We were able to watch the adults lay eggs on this plant.”

In addition to planting milkweed to sustain monarchs during the summer, the University of Illinois Extension reports that planting more fall blooming perennials such as liatris, Joe Pye weed, black-eyed Susan, aster, coneflower and downy sunflower in gardens will also provide resources for the butterflies before their long journey back to Mexico.

A monarch butterfly and wildflowers.


Several groups and organizations track the annual migration of the monarchs each spring and fall, collecting reports from citizen scientists and mapping locations of their sightings over time. One such organization, Journey North, offers a real-time map of the migration both north and south each year so you can see when they are nearing your community.

Tracking the migration gives scientists data to help understand monarchs and how their population is affected by various factors. And this knowledge is more than just a vanity project, allowing us to continue to enjoy the beauty and splendor of monarchs.

Butterflies – including monarchs – play a key role in our ecosystem, helping pollinate native plants and crops. More than 150 agricultural plants in the United States require pollinators, according to the IDNR, and experts estimate that one-third of all the bites of food we take are dependent on pollinators, which, in addition to butterflies, include other insects, birds and bats.

Simply put, the arrival of the monarchs each spring is a sign that our ecosystem is working the way it must to allow many plant species to continue to exist. Beyond being a beautiful sight to behold and appreciate, they are vital to our environment.


Lead image via Shutterstock

Photo credits: Bob Bryerton, Glenn P. Knoblock, Suzy Lyttle, Lorenzo Pesce

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