Monarch butterfly on swamp milkweed
Last week, I was manning the booth at the Montgomery County Fairgrounds Demonstration Garden (yes, it’s a mouthful), when someone plopped a tall, spindly plant down onto the table. The plant looked pretty pitiful; the flowers were long gone and the paddle-shaped leaves had circular holes in them. But upon closer examination of the stems, I spotted a string of tiny, lantern-shaped pupae along with a company of black, yellow and white striped caterpillars. The plant was none other than milkweed and the chrysalises contained baby monarchs in the process of forming.
We placed the milkweed next to a grouping of Joe-Pye weed and sat back to see what would happen.
Things aren’t looking up for the monarch butterfly
Monarch butterflies are considered by many to be the ‘king’ of butterflies, with a wing-span of over 4 inches (hence the name, monarch.) But, according to the National Wildlife Federation, their population in North America is in steep decline. Over the past twenty years, monarch numbers have plummeted by an astonishing 90 percent, leading scientists to question what’s happening. They suspect the answer is tied up with milkweed.
Close-up of swamp milkweed, Asclepias incarnata
Why milkweed you might ask? Because milkweed is the host plant for monarchs, and monarch caterpillars will only eat plants in the family. But milkweed has been disappearing, too. Over the last couple decades, large-scale clearing of meadows and prairies for development coupled with heavy pesticide use has resulted in the plants becoming increasingly scarce, placing in jeopardy the tiny population that depends on it for survival.
The problem is so big that according to one National Public Radio (npr) report, monarch populations overwintering in Mexico that averaged around nine hectares from 1995 to 2002, in 2014 took up less than one.*
A migratory insect
Every spring, thousands of Eastern monarchs begin their annual migration across the Great Plains on their journey from Mexico to Canada, covering over 3,000 miles in the process. And every fall, they do the trip in reverse. The insects breed along the way, stopping three times to go through four stages of development: egg, larvae (caterpillar), chrysalis and adult butterfly. The new butterflies live for just four to eight weeks, long enough to fly further north and lay their eggs. Then the next butterfly continues the journey.
Millions of monarch butterflies flying in Mexico
This means that it takes three butterflies to make it all the way to Canada.
Incredibly, the fourth generation butterfly born in Canada lives a bit longer. This is the monarch that migrates back to warmer climates like Mexico. This butterfly lives for six to eight months, long enough for it to start the whole process over again in the spring. (To read more about the monarch butterfly cycle, click here.
A misunderstood plant
The milkweed family, Asclepias, is composed of more than 100 varieties of leafy plants. Tall and upright with long, elliptical-shaped leaves, milkweeds bear dense clusters of vanilla-scented rosy-pink or orange flowers. The plant owes its common name to the milky latex that oozes when a stem is snapped.
Milkweed provides all the nourishment the four generations of monarchs need to transform from larvae into butterflies. The baby caterpillars feed on the leaves until fully grown, and then attach themselves to a stem or leaf to start the process of metamorphosis. Once they hatch, the monarchs move on to other flowers to live out their short life.
Monarch chrysalis hanging from a milkweed stem
In addition to nourishment, milkweed provides other advantages to monarchs. As the caterpillars undergo transformation in chrysalis, they ingest toxic chemicals secreted in the plants’ sticky sap. These chemicals, called cardenolides, provide the caterpillars with a key defense against would-be predators such as birds and mice.
Monarch caterpillar munching on milkweed
Specifically, cardenolides are so toxic and bitter tasting to other vertebrate species that they have learned to associate bad taste with the butterflies’ distinctive orange and black markings. Although as adults, monarchs no longer eat milkweed, they are able to sequester the toxins that they ingested as larvae, providing them with protection against many predators during the remainder of their lifespan.
Monarchs’ distinctive colors help ward of predators
Monarch butterflies only lay one egg per leaf, but they lay eggs on lots of leaves and always on more than one plant. They are mini eating machines. Three days after it arrived to the fair, the caterpillars had devoured the plant they rode in on; in their place hung rows of tiny pupae.
Many of us are familiar with the roadside milkweed, but lesser known is that there are now many beautiful perennial varieties that can enhance your garden while helping you do your part to save the monarch species.
Common milkweed, Asclepias syriaca
Ready to save the monarchs? Here are some great new milkweed varieties to try, available at many local nurseries.
Butterfly Weed, Asclepias tuberosa
This bright orange beauty blooms from May to September. It just won Perennial of the Year for its brilliant flowers, hardy, upright stems and good drought-tolerance.
Butterfly weed, Asclepias tuberosa
Or, for a great yellow variety, try ‘Hello Yellow’, available through White Flower Farm.
Asclepias tuberosa ‘Hello Yellow’
Swamp Milkweed, Asclepias incarnata
Swamp milkweed ‘Cinderella’ available at Perennials.com
Or try a mix of hot colors, Asclepias Gay Butterflies Mixture, available at White Flower Farm.
Asclepias Gay Butterflies Mixture
Milkweed generally blooms from June to August. All varieties need full sun and well-drained soil. If you observe caterpillars or chrysalises on your plant, wait until the butterflies have flown away, then simply cut the plant to the ground.
* Monarch populations are measured in hectares, which roughly equal 2 1/2 acres.