Mexican Milkweed, Asclepias curassivica

Wednesday, October 7, 2009

Nature Notes
by Bob Thomas

True nature lovers plant Mexican milkweed, Asclepias curassivica, in their yards.

It has pretty red and orange flowers, but often grows tall and spindly. The plants typically produce copious amounts of seeds, each attached to thin bunches of hair-like threads that are dispersed by the slightest breeze. Because of this mode of distribution, milkweed tends to spread about yards and fields rather quickly.

Milkweeds are host to monarch butterflies. In fact, they are the only food monarchs use as caterpillars. You plant milkweed in spring or summer, and you are guaranteed to promptly have monarchs visiting.

Most milkweeds, and especially Mexican milkweed, have a milky white sap that contains toxins called cardenolide glycosides. The brightly colored yellow, black and cream-white Monarch caterpillars consume the milkweed leaves and isolate the toxin, thus gaining poisonous qualities that protect them from most predators. After they metamorphose, the adults retain the toxicity.

Monarch caterpillars are often so plentiful that they strip all the leaves off milkweed plants. No worries. When the caterpillars pupate, the plants grow new succulent leaves.

Another neat nature aspect of Mexican milkweed is that the plants often host hundreds of bright yellow and/or red aphids around the flowers and seed pods. They are the same species one finds on oleanders. The aphids appear to have little negative impact on the plant, and simply add to its beauty and interest. If they are numerous, however, their honeydew (clear liquid excrement) may stimulate the growth of sooty mold, which may at least somewhat inhibit photosynthetic activity.

Mexican milkweed also attracts another beautiful bonus for the avid naturalist, cool herbivorous lygaeid milkweed bugs. These orange and black insects have piercing, sucking mouthparts and feed on the milkweed seeds and other plant tissues.

Plant Mexican milkweed and the monarchs will arrive quickly and happily.

Also published in Delta Journal, The Times Picayune, September 21, 2008.


Mexican milkweed, Asclepias curassivica.                                      A slight color variant of Mexican milkweed.
Photo by Bob Thomas.                                                             It has less red, but is a very effective
                                                                                                 Monarch butterfly attractant.
                                                                                                   Photo by Bob Thomas.


Mexican milkweed aphids and a milkweed                                    Mexican milkweed seeds after being
bug. Note the black smudges on the leaves                                  released from the pod.
and stems. This is "sooty mold" that grows                                  Photo by Bob Thomas.
on the honeydew (clear excrement) produced
by the aphids.
Photo by Bob Thomas.