Plants & Animals

Swamp Milkweed

For years, I chased butterflies all over the state. It never occurred to me that I didn’t have to go any farther than my own garden. Last summer when I started converting my garden to native plants, including several species of milkweed, I began to see many insects and pollinators, such as bees, butterflies, and skippers. They seemed to be particularly attracted to the sweet scent of swamp milkweed flowers that I planted just a few months earlier.

Missouri is home to 18 different species of milkweed (Asclepias). Interest in milkweed has grown in recent years due to the rapid decline of monarch butterflies. The population of monarch butterflies has dropped dramatically over the past decade due in large part to the decline of its caterpillar host plants, milkweed, across its North American migratory route. Monarch caterpillars can only feed on milkweed, so monarch butterflies feed on the milkweed flowers and lay their eggs on the plants.

The emerging caterpillars then feed on the leaves. The sap from milkweed contains toxic chemicals that repel insects and other herbivorous animals, making monarch caterpillars poisonous to predators.

Swamp milkweed (Asclepias incarnata) is also known as pink milkweed. This perennial plant is shade tolerant and can grow 2–5 feet tall. The flowers have large blossoms composed of small, rose-purple flowers. The deep-pink flowers are clustered at the top of a tall, branching stem, producing a sweet vanilla scent that attract many butterflies, especially monarch butterflies.

Swamp milkweed prefers wet to damp soil in full sun to partial shade and typically is found growing wild near the edges of ponds, lakes, streams, and along ditches. Once blooming occurs in mid- to late-summer, long, relatively thin seed pods are produced that grow upright. The pods split open in late summer to late fall, releasing seeds that are attached to silky hairs, which act as parachutes to carry the seeds on the currents of the wind.

One morning my daughter spotted a monarch butterfly feeding on milkweed flowers, and a few weeks later we were very excited to find several monarch caterpillars crawling on the milkweed leaves.

By late summer, we encountered as many as 60 monarch caterpillars in our garden, and this was just from a handful of milkweed seeds we had planted. We were able to raise and release over 50 monarch butterflies by early fall.

As my daughter and I watched the last monarch butterfly fly away one cool morning, she looked at me with enthusiasm and suggested that we should plant more milkweeds next year. So we did, along with many other native flowers that provide nectar sources for monarch butterflies. Now we find a variety of insects and butterflies in our garden that intrigue and excite my daughter. What a great way to introduce kids to nature! —Story and photograph by Noppadol Paothong

We help people discover nature through our online Field Guide. Visit mdc.mo.gov/field-guide to learn more about Missouri’s plants and animals.