Adult monarch butterfly nectaring on a swamp milkweed (Asclepias incarnata) in Ramsey County, Minnesota. Photo by Steven Katovich, USDA Forest Service, Bugwood.org, http://www.forestryimages.org/browse/detail.cfm?imgnum=5524769, CC BY 3.0
The monarch butterfly is a beautiful sight, whether it’s fluttering through a garden or resting on a flower. Understandably admired, it’s the state insect of Alabama, Idaho, Illinois, Minnesota, and Texas. It’s also the state butterfly of Vermont and West Virginia.
Unfortunately, the monarch butterfly population has been dropping drastically over the past decades. The situation is explained in a recent article authored jointly by Daniel M. Ashe, Director, U.S. Fish and Wildlife Service, and Collin O’Mara, CEO, National Wildlife Federation:
As recently as 1996, the estimated monarch population wintering in Mexico was more than one billion butterflies, turning forests into seas of orange and black. Last year, however, the wintering population numbered only about 56 million butterflies, gathered on fewer than three acres of forest.
Monarch butterflies, as well as other butterfly species, bees, birds and bats help move pollen from one plant to another, fertilizing flowers and making it possible for plants to produce seeds, berries, fruits and nuts that feed people and wildlife. More than a third of the food that we eat requires pollinators to grow. Yet like the monarch, many of these pollinators are declining, with habitat loss, pesticides and climate change all contributing to their struggles.
We need to know more about exactly why monarch butterflies are disappearing. But we don’t need to wait to take the actions that scientists tell us are necessary to redirect the monarch’s future skyward.
What can we do? Well, for one thing, we can plant milkweed.
Many of us in North America and elsewhere know that monarch butterfly larvae need to feed on milkweed (genus Asclepias) in order to achieve their transformation into winged butterflies. (As a matter of fact, so do the larvae of the monarch butterfly’s closest relatives, the other “milkweed butterflies” of the genus Danaus.) The monarch’s fate hinges on the available supply of milkweed in its natural geographic distribution. Various factors, including well-intentioned weeding, have caused that milkweed supply to dwindle.
Practically anyone can grow a successful patch of milkweed, as long as the right kind of milkweed is chosen and the right conditions are provided. Texas Butterfly Ranch’s aptly named “Got Milkweed?” planting guide offers this caution:
Those of us who have attempted cultivation of native milkweeds from seed in our home gardens have often met frustration and failure. The very traits that make native plants so hardy also often make them extremely particular about their soil, drainage, moisture and available light. As George Cates, chief seed wrangler at Native American Seed Co. in Junction, Texas told me: “These milkweeds have a mind of their own.”
Another reason to plant a species that’s native to your geographic location is that the monarch migration is largely dependent on the timing of milkweed blooms. Tropical milkweed, in particular, when grown outside of extreme southern areas of Texas and Florida, can throw off migration patterns, leading to disease and other problems. Ironically, gardeners wanting to help the monarchs have been planting the more readily available non-native milkweeds. As explained in an article in the February 2015 issue of the Proceedings of the Royal Society B:
Each autumn, monarchs migrate from breeding grounds in the eastern US and Canada to wintering sites in central Mexico. However, some monarchs have become non-migratory and breed year-round on exotic milkweed in the southern US. We used field sampling, citizen science data and experimental inoculations to quantify infection prevalence and parasite virulence among migratory and sedentary populations. Infection prevalence was markedly higher among sedentary monarchs compared with migratory monarchs, indicating that diminished migration increases infection risk. Virulence differed among parasite strains but was similar between migratory and sedentary populations, potentially owing to high gene flow or insufficient time for evolutionary divergence. More broadly, our findings suggest that human activities that alter animal migrations can influence pathogen dynamics, with implications for wildlife conservation and future disease risks.
Gardens planted to accommodate monarch migration are sometimes referred to as waystations. In an article on butterfly gardening for monarchs (where the ubiquitous and irresistible “Got Milkweed?” pops up again), Carole Sevilla Brown recommends, “Plant a Monarch Waystation. Go to the USDA Plants database to determine which species of Asclepius are appropriate for your garden.” Chances are that the species appropriate for your garden is/are what’s native to your area. (Essentially, that’s what the USDA Database shows.)
Ah, species. A look at the Encyclopedia of Life’s Asclepias taxonomies shows the complexity. There are dozens of Asclepias species, viewable by traditional biological taxonomy structure (the NCBI Taxonomy or the Integrated Taxonomic Information System), as well as by Extant and Habitat resource, as well as a few other slice-and-dice approaches. It’s apparent from these resources that there are milkweeds for all kinds of different growing conditions, from wetlands to scrubland.
Wherever you live, you can use one of the various online taxonomic resources, or a database that’s correlated with a detailed taxonomy, to determine what kinds of milkweed to grow.
Got milkweed? No? Use a taxonomy, and get milkweed!
Barbara Gilles, Taxonomist
Access Innovations, Inc.