Monarch Butterfly

Recent news accounts about the drastic decline in my favorite butterfly, the monarch, have disturbed me greatly. The population that migrated to the Mariposa Monarcha Biosphere Reserve in Mexico once covered more than 50 acres, but now occupies less than 3. According to the December 2012 census, this represents a 59-percent drop from the previous year. Weather conditions and human activities affect the population of monarchs. And according to Dr. Chip Taylor, director of Monarch Watch, a continued decline could mean the migration of these butterflies could be lost. Immediate action by each of us could help slow, and hopefully reverse this frightening population decline.

In a recent telephone interview, I asked Dr. Taylor about what the average person could do about it. His organization is running a campaign called ‘Bring Back the Monarchs’ to generate interest and share information about the plight of these imperiled beauties.

Monarch Biology

Danaus plexippus is probably our best-known butterfly because of the distinctive orange and black wing patterns on the adults. It was called ‘the Monarch’ in honor of William, Prince of Orange, who later became King William III of England. The caterpillars have an equally striking look with a black, yellow and white striped body. While adults feed on a wide variety of nectar plants, the female monarchs only lay eggs on milkweed. Milkweed also is the sole plant source for newly hatched caterpillars, making it vital to their continued existence. The toxic cardiac glycosides found in the milkweeds are stored in all stages of the butterfly lifecycle, making it bitter and poisonous for most birds to eat. The brilliant colors of both caterpillar and adult say “do not eat me” to predators.

Another complicating factor in the life cycle of the monarchs comes with the magical migration of the adults each year. We see them arrive in St. Louis in the late spring and flutter in and out of our gardens until almost frost. What we cannot see is the butterflies that arrive and those that return south in the fall are not the same ones. There typically are five generations in one year. The adults that fly south are often the same ones that return northward in the spring, but also can be new generations from eggs laid in Texas on the way back. Several generations are hatched in the Midwest and Canada, with the summer generations lasting about one month each. The migratory generation lives much longer, to head back to Mexico, winter there and begin the trek back north. They are fun to follow!

Why Are Monarch Butterfly Populations Declining?

There are no simple answers for the steep decline in the monarch population. Because of the wide-ranging migration, all impacts are cumulative, whether they occur in the U.S., Canada or Mexico. Weather conditions can cause extreme pressures, and the drought years have likely taken a very hard toll. Extreme heat weakens the adults and kills both host and nectar plants.

Milkweeds are Essential to Monarchs

Monarch adults may feed on a wide variety of nectar plants and are particularly fond of liatris, Joe-pye-weed and many prairie species. Any plant included in a typical ‘butterfly garden’ planting list would attract monarchs. At the Sophia M. Sachs Butterfly House in Faust Park and at Shaw Nature Reserve, butterflies of all genera are encouraged.

Milkweeds are included in the plant list for every habitat restoration project at Shaw, where monarch populations are monitored by staff and volunteers. Tracking monarchs by tagging has helped scientists uncover many details about the exact migratory patterns and is a great opportunity for citizen science. The spring Missouri generation moves northward and is not the one to actually make the entire journey back to Mexico. Of the autumn adults tagged, at least one Shaw visitor has been recovered at the main reserve in Mexico with the Missouri name tag on-board. You can help the monarchs by being a volunteer monarch-tagger, too. To volunteer at Shaw, register online or email

In May, Shaw Nature Reserve holds its Wildflower Market. Many of these plants can serve as hosts for migrating monarchs. Several Asclepias species suitable for Missouri gardens are being grown at Shaw for the spring sale. These include: A. incarnata, the marsh milkweed, with pink flowers from July to October; and A. purpurascens, the purple milkweed, which flowers in May and June.

My garden includes the plain, common milkweed, Asclepias syriaca. It arrived there as a weedy volunteer, but it stays because it is an insect magnet, monarch caterpillar host and provides seedpods for dried arrangements. Scott Woodbury at Shaw Nature Reserve lists marsh milkweed, mountain mint and blazing star as his top three nectar plants for monarchs. Marsh milkweed is particularly important to the southward migrating generation. Flexible in growing conditions, marsh milkweed is an excellent rain garden plant.

Woodbury warns that butterfly weed can be fussy. It doesn’t divide well and demands well-drained soil. Two other native milkweeds that are not well-suited to St. Louis are: Asclepias verticillata (whorled milkweed), which is too weedy; and Asclepias meadii (Mead’s milkweed), which is listed as a threatened species and not well-suited to suburban gardens. 

Every Monarch Matters

With all that we know about the habits of monarch butterflies, citizen scientists, gardeners, garden-clubbers and government officials can mobilize and create a broad coalition for swift action. There needs to be more effort to preserve the acreage reserve for monarchs, milkweeds and the many other species that occur in these lands. All of us can do something to help save these magnificent creatures.


Shaw Nature Reserve Spring Wildflower Market

Saturday, May 11, 9 a.m. to 4 p.m. ($5 per person)

Members Pre-Sale: Friday, May 10, 4 to 7:30 p.m., free for members.

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