If you've enjoyed watching monarch butterflies gleam orange in the fall sunlight as they head south for the winter, you have the humble milkweed to thank.
"There's a deep relationship between monarchs and milkweed," said Jamie Koehler, the assistant manager at the Missouri Department of Conservation's Cape Girardeau Nature Center. "You can't talk about one without talking about the other."
Last week, Koehler gave a virtual presentation on the many species of milkweed, their role in nature and the threats milkweed — and the monarch caterpillars the plants host — face.
There are 73 known species of milkweed, of which 18 are native to Missouri, she said.
"Some of these milkweeds I've never seen before," Koehler added. "One of the things I think is so cool about milkweed is that it has adapted itself to incredibly different array of habitats. There are aquatic milkweed that like wet feet and others that live in the desert."
Despite their varied habitats, milkweed species share a few key features.
One is the structure of the flowers. Each small flower (often clustered together into umbrella or ball-shaped masses) has a distinctive star shape. Some of the flower's structures are fused together to cover the area containing the flower's pollen. When a pollinator — a bee or butterfly, for example — visits the flower to sip its nectar, one of its legs might slip into a slit in the structure.
"They get stuck and they pick up this pollen," Koehler said. "Then they go to another plant and they might slip again and deposit that pollen."
Most milkweeds are full of a milky, toxic sap (though the sap of some milkweeds is clear).
"There's a chemical inside this sap that's called a cardiac glycoside," Koehler said. "What's happen is that some animals aren't harmed by cardiac glycoside, and to other animals it's toxic to and it'll make them sick."
The insects that can eat milkweed without being harmed evolve bright colors: for example, the monarch caterpillar and its distinctive stripes and the monarch butterfly's bright orange and black wings. As they munch on milkweed, they store up the toxin inside their bodies.
"If a bird was to eat the caterpillar or butterfly, because of the toxin, it makes them sick and they regurgitate," Koehler said. "They learn very quickly to pay attention to caterpillars and their colors to make sure they don't eat this particular monarch caterpillar because they know it's going to make them sick."
A third important feature is the milkweed seed pod. Though the seed pod's shape varies, they're generally rather large and pointed, and they're stuffed full of flat seeds with tufts of fluff. When the pod cracks open, the wind carries the seeds away.
Koehler offered a handy hint for people who want to collect milkweed seeds. It can be a bit tricky, she explained, because the seeds must be allowed to mature on the plant, but wait too long and the pods open and the wind whisks away the seeds. She suggested placing a little organza draw-string bag — the kind often used to hold wedding favors — over each pod, which allows the pod to mature but catches the seeds if it opens before you can harvest it.
Most of Missouri's milkweeds prefer prairies, fields and glades. Species of milkweed found in Callaway County include, but aren't limited to:
Common milkweed (Asclepias syriaca): Tall, sturdy plants with broad leaves, clusters of pink-lilac flowers and large spiny seed pods. This milkweed is widespread and common throughout the county.
Butterfly weed (Asclepias tuberosa): Bushy plants with multiple stems, narrow leaves and bright orange flowers. It's found in a wide variety of habitats and often grows on disturbed soil.
Fourleaf Milkweed (Asclepias quadrifolia): A delicate, single-stemmed milkweed 12-18 inches tall with small clusters of pink flowers. There are three or four sets of narrow lance-shaped leaves, of which one or two of the upper sets has four leaves in a whorl. Unlike most milkweed, they prefer woodland environments.
Honey vine milkweed (Cynanchum laeve): This vining milkweed has heart-shaped leaves, clear sap and small white clusters of sweet-smelling flowers. It tends to be weedy, with vines growing up to 33 feet long.
Climbing milkweed (Matelea decipiens): Another vining milkweed with heart-shaped leaves, this one has milky sap and distinctive maroon flowers with long lobes. It occurs in glades, savannas, tops of bluffs, rocky, open upland forests, and along streams and rivers.
Prairie milkweed (Asclepias hirtella): Standing 1-3 feet tall, this milkweed has long, narrow leaves and round clusters with many small greenish-white flowers speckled with purple. Its stems are hairy.
Swamp milkweed (Asclepias incarnata): Standing up to 6.5 feet tall, these milkweeds have vivid purple-pink flowers clustered at the very top of each plant. They live in moist bottomlands and other damp areas.
According to Koehler, there are plenty of benefits to adding milkweed to your landscape. One is the much-beloved monarch butterflies rely on milkweed to reproduce — though adult butterflies can drink nectar from many flowers, milkweed is the only thing monarch caterpillars eat. In fact, milkweed species provide food or shelter to some 357 species of insects, including monarchs.
"Now there's a lot of challenges and concerns about the population of monarchs," Koehler said. "Scientists are noticing significant drops. What they're saying is there's been an 80 percent drop from mid-90s."
One reason for the drop is logging and climate change in Mexico, where monarchs spend the winter, returning to the same forests each year. Missourians might not be able to do much about that, but they can help by planting milkweed, waiting to mow milkweed-filled fields until after the monarch butterflies emerge as adults in fall, and by limiting their use of herbicides and pesticides.
"If you have hayfields or farm property, if you can work your mowing schedule around the monarch's schedule, that would be superb," Koehler said. "Maybe not mowing along roadways would make a difference too. You can encourage your county and city not to mow."
According to Koehler, now's an excellent time to sow milkweed. The plant's seeds have a thick outer layer, which needs the repeated freezing and thawing it'll experience during a Missouri winter to weaken and allow the baby plant to emerge in spring.
"If you're going to sow common milkweed, do it in the fall and let nature take care of it," she suggested.
Koehler also advocated for clearing away dead milkweed plants after the first frosts. It's possible a certain parasite of monarchs, Ophryocystis elektroscirrha (known as OE), spends the winter on dead milkweeds and transfers to new growth in the spring, building up over time. Milkweeds are perennial, returning year after year. Koehler said the science is still inconclusive.
"Most of time I encourage people not to clean up their gardens, but for monarchs, I think it might be good idea to clean up milkweed to get rid of (OE) spores," she said.
To learn more about planting native plants, including milkweeds, visit grownative.org and the Missouri Botannical Garden's website (bit.ly/3cXNegE). Many groups, including the Xerces Society and Missourians for Monarchs, have information about protecting the butterflies.
To view and sign up for future MDC classes, visit mdc.mo.gov/events.