A welcome visitor to gardens, and sure sign summer is coming to an end when seen in large groups, monarch butterflies are a staple of St. Louis scenery and landscapes across the country. But their numbers are dwindling, scientists say.
Shrinking Numbers and Endangered Status
In July 2022, the International Union for Conservation of Nature, or IUCN, classified the monarch as endangered. The IUCN Red List of Threatened Species, founded in 1964, is widely regarded as the world’s most comprehensive inventory of the global conservation status of biological species. The Garden became an official IUCN Red List partner in 2019.
Efforts have also been made to protect monarchs under the Endangered Species Act following findings that the eastern monarch butterfly population has dropped by about 80 percent in the last 40 years, and the western population, which is found west of the Rocky Mountains and has a different migration cycle, has dropped about 99 percent. The exact cause and extent of the decline, and the best path to help them recover, is still being debated amongst entomologists, conservationists, and regulatory agencies.
In 2020, U.S. Fish and Wildlife ruled that protection under the Endangered Species Act (ESA) is warranted, but precluded. Essentially, this means the government agrees that it qualifies under the law, but there were 161 other species that it deemed to be a higher priority that needed to be focused on first. Monarchs will be reevaluated for ESA protection yearly through 2024, and could receive protection in the future.
For many conservationists and groups that have been rallying for monarch butterfly support for years, this ruling was a disappointment. But the Butterfly House and Garden want to remind everyone that you, as an individual, have the power to help the monarch butterfly and create positive change.
What You Can Do
One of the easiest and most rewarding things you can do to help monarch butterflies is to plant native wildflowers for them. Avoid annuals or non-native perennials when possible, and instead choose native plants. We recommend asters, coneflowers, goldenrod, Golden Alexander, and of course, milkweed.
There are dozens of beautiful Missouri native wildflowers that bloom throughout the year whose flowers offer important food for butterflies. You can find a thorough list of beneficial species in this Butterfly Gardening Guide from the Kemper Center for Home Gardening. Also check out the Garden’s Native Landscaping Manual.
Butterfly House staff recommend choosing a mix of spring, summer, and fall blooming plants for any butterfly garden so there are always nectar sources available for butterflies. Spring and fall blooming plants are often the most overlooked, but are arguably the most important for monarch butterflies because they need energy for their migrations going north or south. Some entomologists point directly at reduced nectar sources during the fall migration as a leading cause in the population decline.
How This Helps Monarchs
Each year monarch butterflies complete an incredible, multi-generational migration that begins in the mountains of Central Mexico where cool temperatures, just above freezing, keep millions of butterflies in a hibernation like state for the winter months. As days lengthen and temperatures rise it signals spring- time to start their journey north in search of the two main things their species needs to survive: flower nectar and milkweed plants.
These plants fuel their journey north and serve as host plants for females to lay eggs on. Monarchs travel as far as they can before laying eggs. Once the eggs hatch, the caterpillars grow into adult butterflies who continue the journey north. This cycle continues for three to four generations every summer, and by early fall monarch butterflies can be found across the eastern half of North American from Canada south to Mexico.
In the fall, the subtle changing of the light from the sun tells monarch butterflies it’s time to go south. The same butterflies that emerged from their chrysalides in Ontario, Canada or St Louis, MO will eventually fly to central Mexico where they will spend the winter before beginning the cycle all over again in the spring.
More About Milkweed
In addition to offering nectar from their flowers, milkweed is incredibly important to the lifecycle of monarchs as it is the only plant the caterpillars can eat.
Missouri is home to 18 species of milkweed, many of which make great additions to gardens or landscapes.
Common milkweed is a staple, and most people are familiar with the tall plants with beautiful pink flowers. It’s wide spread, and monarchs love it.
For a smaller, or more unique variety of milkweed, try swamp, purple, green, or butterfly weed milkweeds. All of these plants will produce nectar for adult butterflies and food for the caterpillars.
Note: Although becoming more common in nurseries, planting tropical milkweed is generally not recommended anymore in the Midwest as it may interfere with the monarch’s migration. It may also harbor parasites and diseases.
Once you’ve planted your milkweed, think twice about reaching for that bottle of pesticide. Monarchs, and other beneficial insects like butterflies and bees, are usually susceptible to pesticides. Native plants have evolved along with native herbivores and as a result can sustain quite a bit of damage from insects munching on their leaves before it puts the plant in any danger. Many insects that people are concerned about, like the red and black large milkweed bug found commonly on native milkweed plants, actually pose no risk to the plant at all.
If you have milkweed already growing on your property, try not to mow or spray them when reasonable to do so. Milkweed doesn’t have to be part of a well-cared for garden to benefit monarchs.
Where to Buy Native Plants
The Butterfly House has an annual native plant sale every April that features dozens of species of wildflowers great for Monarchs, including multiple species of milkweed. Shaw Nature Reserve offers a Native Plant Sale every spring and fall.
Monarchs aren’t the only species of pollinators that need help. The Butterfly House launched Project Pollinator in 2016 and have partnered with 14 local conservation agencies to promote the appreciation of all pollinators through education and the creation of pollinator gardens. To learn more, visit butterflyhouse.org/projectpollinator.
Senior Entomologist, Sophia M. Sachs Butterfly House