Nancy’s  Final (I hope) Word on Tropical Milkweed


As co-founder with April of our Habitat Corridor Project, I mostly talk about how to make gardens more wildlife friendly, and the habitat value of native plants. Though I have written more than a few times this past year on monarch butterflies and milkweed, it seems important to highlight some concerns over recent efforts to ban the sale (and discourage the planting of) tropical milkweed. Asclepias curassavica (tropical milkweed) has been banned in several California counties, including Marin, Contra Costa, San Mateo, and Ventura. And I hope it doesn’t happen here. The downfall of the monarch butterfly is a complex issue that many experts believe involves climate change, loss of habitat, and pesticides. In a UC Davis Bug Squad blog (see link below), Professor Hugh Dingle (UC Davis), whose focus the last 20 years has been on monarch butterflies, says that “it is a wasted effort”.   Art Shapiro, expert on monarchs for the last six decades at UC Davis, agrees, calling the rationale behind the ban “hogwash”.  These two researchers and others believe that winter breeding by monarchs is influenced by warmer winters caused by climate change. Shapiro points out that this tropical milkweed has been planted in coastal southern California for a century, but winter breeding only began about a decade ago. Moreover, another entomology professor at Washington State University, David James, who has studied monarch migrations and breeding in the Bay Area, believes tropical milkweed may be a vital resource for monarchs in a changing climate.  The “parasite” question and current research is thoroughly evaluated in this article. I will add this from my own personal experience (and that of other habitat colleagues in Marin County):  Without the easy availability of tropical milkweed (at the time), I would not have been able to successfully rear caterpillars taken from a native milkweed that had been stripped.  No matter what milkweed a monarch caterpillar starts out on, it can be successfully transferred to tropical milkweed. To read all of the evidence, please follow the link below.

Tropical Milkweed