Each summer, we look forward to seeing Monarch butterflies dancing about the native prairie in the Children’s Garden, or perched atop the various species of milkweed throughout the Gardens. Their bright colors will often steal my attention, and I feel compelled to pause my work to admire them.

By now, many of us have heard the North American migratory Monarch butterfly (Danaus plexippus) has recently been added to the International Union for Conservation of Nature (IUCN) Red list of endangered species. What most people don’t know are the causes and changes we will have to make to slow and lessen the demise of not only the Monarch butterfly, but the beneficial insect population as a whole.

The North American Migratory Monarch is a subspecies of Monarch known for its bright orange color and annual migration. They travel nearly 3000 miles from the Northern United States and Southern Canada in the summer, to Mexico and California in the winter. Monarchs go through 4-5 generations each year, but the last is the only one that migrates. 

When discussion of their rapidly waning population begins, what inevitably follows is the familiar talking point, “plant more milkweed.” Milkweed of the genus Asclepias is crucial to the life cycle of Monarch butterflies, and an actionable cause to get behind. Monarchs and milkweed have a symbiotic relationship where the milkweed is the sole host plant and food source of Monarch caterpillars, and the adult butterflies pollinate the milkweed. Milkweed contains a chemical compound toxic to many species of birds and mammals. These “cardiac glycosides” can harm or negatively affect the heart muscles. As Monarch larvae ingest the plant, they too become toxic to animals that may see them as prey. Female Monarchs will lay eggs on several species of milkweed but have a preference for Swamp milkweed (Asclepias incarnata) and Common milkweed (Asclepias syriaca). The issue is, many discussions begin and end with milkweed, however, it is only one piece of the picture when it comes to what Monarchs need to thrive again. 

Monarch caterpillar perched on a Butterfly weed (Asclepias tuberosa)

Beyond host plants, Monarchs need nectar-producing plants, food and shelter sources for adult butterflies and native plant communities to flourish. Milkweed is crucial, but it is just one part of their life cycle. The growth of industrial agriculture and the cultivation of monocultures has contributed to the destruction of native prairies, a source of shelter and food for many Monarchs and many other animals and insects.  The deforestation of Fir trees in Mexico’s oyamel forest, the Monarchs’ overwintering grounds, has created further habitat and population loss. Additionally, the increasing use of herbicides and pesticides on food crops has coincided with the Monarchs’ decline. 

Another factor of decline for the Monarch, possibly the greatest one, has been climate change. Monarchs take their migration cues from temperature. With rising temperatures, their autumn migration south has been delayed. Unfortunately, this means that by the time temperatures are cool enough to trigger their migration, the Midwest is too cold, causing many to die on their journey. Climate change has also increased the frequency of severe weather events such as drought and wildfires, which has increased mortality rates in Monarchs.

Monarch Butterfly getting nectar from a New England Aster (Symphyotrichum)

Why should we care about any of this? Because Monarchs are a symbolic pollinator, and if their population is declining, it’s indicative the same is occurring with other pollinator species. Their vibrant color and extraordinary migration patterns are intriguing and make us want to learn more about the natural world. As the dominant species on this planet, we are not above it but a part of it. We depend on a balanced ecosystem too. When the dominoes of the ecosystem start falling, in large part due to us, it is up to us to learn, make changes, and do less harm. It is up to us to foster stewardship and compassion for the very ecosystem we rely on. So yes, at risk of being redundant, I’d encourage individuals to plant milkweed, but not to stop there. Become knowledgeable about the different types of milkweed and nectar sources for monarchs, and plant those too. Mow and spray a little less, and advocate in your city for the need for natural spaces and prairie restoration. Ultimately, we will need to make changes and shoulder inconveniences so we may hope to continue sharing the planet with species like the Monarch.

Kyle Strain
Lead Horticulturist