Asclepias Curassavica (Neotropical Milkweed) - Pros and Cons

Yellow-flowered Asclepias curassavica

Here are some pictures of Asclepias curassavica (common names "tropical milkweed" or “neo-tropical milkweed”). This plant is very popular currently in the US and is the milkweed variety I see most often in stores here in Southern California. The monarchs certainly love it.

There are a couple of varieties: one has yellow flowers, and the other has yellow and red flowers. The plant originates from the tropical parts of the Americas, extending from tropical Mexico in the north to the tropical north of South America.

Red and Yellow-flowered Asclepias curassavica

Unlike many native milkweed varieties found in the United States which are deciduous (go dormant in the winter), "tropical milkweed" grows and flowers year-round. Because of this I actually had caterpillars right through this past winter here in Southern California, and yes, they made it safely to "butterflydom" since in the winter predators like wasps and praying mantises are dormant. The same thing happens in Florida where tropical milkweed is becoming established/invasive.

Asclepias curassavica seeds

There is a debate going on in “monarch butterfly land” as to the dangers of tropical milkweed becoming popular in the range of the eastern monarch migration. This is the migration followed by monarchs that winter over in northern Mexico and which then migrate north following a route east of the Rockies as far as Canada. It has been observed that because of the availability of tropical milkweed in the migration range that some butterflies are choosing to not migrate back south to Mexico in the fall.

Should we care about that or not? There are a couple of arguments put forward against asclepias curassavica. They are, first, that if monarchs do not migrate to Mexico for the winter, there is greater risk of them being killed by a winter freeze in the southern United States. Second, the parasite Ophryocystis elektroscirrha (OE) that debilitates monarchs can survive through the winter on tropical milkweed. Most milkweed varieties native to the United States die down completely to the ground during the winter which deprives OE of an environment on which to survive the winter.

I’m not sure what your take on this debate is. The first milkweed plants I bought were asclepias curassavica. This past winter I bought seeds for a couple of native California milkweeds and have managed to get a few of them established. Perhaps over time I will eliminate the tropical milkweed, but I certainly acknowledge the impulse within me to keep tropical milkweed in my lineup since that means I will have the joy of seeing caterpillars and butterflies through the winter. I am after all, “The Crazy Monarch Guy”, right? Where I live near the California coast frost is about a 1 in 10 years event so most years it would be fine, right? But shouldn't I be encouraging them to fly back to Pacific Grove or Santa Cruz and the other wintering locations along the central and northern coast of California where they will be safer? As always, we love to play god with nature, something that has brought our planet to a very sorry state. Which reminds me to ask, have you read “The 6^th Extinction” by Elizabeth Kolbert? I'm reading it at the moment. Both fascinating and scary. I thoroughly recommend it to you.