As I walked through a local prairie last week, looking for content for Nature Net’s “Wildlife Wednesday” post, I kept a special eye on every milkweed, hoping to spot the unusually colored Monarch caterpillar. Whenever the end of August rolls around, I hope to spot these special creatures, remembering back to summer 2002 of my childhood when I first came across a Monarch caterpillar. I remember walking the hot sand of the Sleeping Bear Dunes National Lakeshore in northern Michigan in awe at the discovery of such beings and their yellow, black, and white stripes—easy to find on the leaves of most milkweeds. Last week, however, on my hour-long walk, I glanced over hundreds of common milkweed plants, spotting none. Could it just be the location or time of day? Maybe. If it was part of a larger trend, what could I do to help these insects thrive?

Monarch Counts this Summer

I soon learned my observations were validated by reports of decreased Monarch counts this year. Every year, citizen scientists play a huge role in monitoring and understanding Monarch butterfly populations and their migration. Each year, volunteers at 382 monitoring sights in the state track Monarchs in egg and larvae form. During most years, Monarch counts increase through the height of summer. This year, however, July saw a notable decrease in counts as time progressed. While these seasonal counts can be good indicators of the health of the Monarch species as a whole, it is still only a piece of the puzzle. The larger picture will be revealed when the insects complete their annual migration to Mexico this winter. Winter of 2023-2024 reported the second lowest Monarch counts since annual censusing began in 1993, representing an 80% decline in population. Although their populations can sustain large fluctuations from year to year, two low years in a row can prove difficult to rebound from.

Image Source: Courtney Celley, “Monarch caterpillar on common milkweed.” USFWS Midwest Region. Accessed through Wikimedia Commons.

The Monarch Journey

Aside from their beautiful coloring and affinity with the poisonous milkweed plant, Monarch butterflies are also remarkable for the  epic, multi-generational migration they complete each year. Starting from a small section of mountains in central Mexico, home to the oyamel fir forests, Monarchs produce four or five generations each year along their route to the northern US and Canada and back again. Each generation is responsible for a portion of the migration route, laying eggs as they go, carefully timed to hatch before the Milkweed flowers open. While the caterpillars need milkweed (and preferably Common Milkweed, Asclepias syriaca) to feed upon, adults rely on a variety of nectar rich flowers to fuel them along their arduous trek.

Image Source: S. Sparrhawk, “Monarch Migration Map.” NPS graphic. Accessed through the National Parks Service.

Possible Causes

What could have caused Wisconsin’s low Monarch count? Some researchers suspect the cold and wet spring followed by a hot summer could have impaired the butterflies’ transition from pupa to adult. Aside from weather, Monarchs must navigate a number of perils throughout their migration. Habitat loss, herbicide and pesticide use, absence of Milkweed, and even butterfly-car collisions all endanger a butterfly’s successful travel. What’s more, climate change is a huge threat to Monarch vitality. Heavy storms and harsh winters in their wintering grounds can impede the Monarch’s departure. Phenological disturbances can also put the butterflies out of sync with the flowering of necessary nectar plants along their route while high temperatures reduce the nutritional value of milkweed.

What You Can Do

With all that said, there is certainly hope and many actionable steps you can take to support Monarch butterflies. When I was back at my parents’ home in Michigan last weekend, I was struck by the abundance of buzzing insect life so alive in their backyard. Their yard, full of mature native plants they graciously allowed me to plant during my ecology-obsessed adolescence, is a clear reminder of the impact one person can have. According to the Xerces Society, one of the best ways to support Monarch populations is by creating more high quality foraging and breeding habitat. In addition to reducing or limiting pesticide and herbicide use, this means planting native milkweed and other native nectar plants these butterflies need. Signing up for a citizen science monitoring projects is another great way to support Monarch conservation, helping to advance critical understanding of their complex migration.

For More

• See the how small changes in legislation in Ohio might help conservationists create more Monarch habitat. 
• Learn about the link between insecticide use and Monarch butterfly decline.
• See how scientists tag and track Monarchs during their migration:

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News from Nature Net Members​​

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Interested in gardening with a purpose? Sign up for the UW Arboretum’s annual Native Gardening Conference on September 15th. This year’s “Gardening for a Sustainable Future” theme is welcoming of gardeners of all ages and skill levels.	This summer, Madison Parks has brought a herd of goats to help manage invasive plant species at the North Unit of Cherokee Marsh. These hard workers are part of a prescribed grazing program that helps support native plant communities and reduces the need for herbicides.	Have you ever been curious about the Waubesa Wetlands that surround Madison? Check out a free screening of the new film “An Invitation to Wonder: Waubesa Wetlands” by local filmmaker Ben Albert.​

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