In Praise of Milkweed

Milkweed is a plant that stimulates very different emotions from the farmer and nature lover. It is poisonous to livestock and is thus a detrimental presence in hayfields and pastures. Yet it has beautiful flowers and provides a home and food for a community of insect specialists and generalists that feed on its nectar, leaves and seeds. Of course everyone’s favorite butterfly, the monarch, is completely dependent on milkweed for larval food. Wherever you live you will be familiar with one of the many milkweeds, perhaps the common milkweed, the swamp milkweed, the spectacular butterflyweed, or the white milkweed vine so widespread in southern Florida.

Insects that utilize milkweed fall into two general categories, specialists that can eat the poisonous parts of the plant and actually retain these toxins and use them to protect themselves, and generalists that feed on the non-toxic nectar or are carnivores. The monarch is the best known specialist and advertises its toxicity by bright colors. In this photo the monarch is feeding on nectar along with a generalist bumblebee. The protection gained by the monarch which retains toxins from the milkweed diet of the caterpillars is so potent that other butterflies mimic it; some of these mimics such as the Gulf fritillary are also toxic themselves from the passionvines eaten by their caterpillars.

Most of the insects seen feeding on nectar of milkweeds are generalists such as this tiger swallowtail on a common milkweed. A wide variety of species are seen gorging on milkweed nectar. For example I have shown here a yellow collared scape moth on the pink flowers of a swamp milkweed, and a metallic green native bee on the spectacular flowers of butterflyweed. There will also be species such as spiders and carnivorous assassin bugs that are feeding on the visitors to the flowers. In this sense the milkweed is a “keystone species” that supports an entire community of organisms by its mere presence. If you remove milkweed from the ecosystem, there is an enormous loss of other species.

Some of the specialists that feed on milkweed may not be so familiar since they are not as obvious as the monarchs, nor do they get the same amount of publicity. For example caterpillars of the milkweed tussock moth can be numerous in small groups and will defoliate an entire plant. The red milkweed beetle is common and is sometimes called the four-eyed beetle since its antennae divide each eye into two parts. Large milkweed bugs can also be found in family groups feeding on seed pods. Note again that these specialists are all brightly colored to advertise the toxicity they gain from eating milkweed.

No matter the size of your yard or farm, you have the opportunity to encourage the growth of milkweeds and thereby the amazing community of organisms that depend on it. In Florida we plant milkweeds in the yard and enjoy the parade of insects that utilize them. At our Virginia farm we cut our hay fields only once, in early to mid June, to allow the abundant common milkweed to re-grow and provide food for a multitude of insects in mid to late summer. Forgoing a second hay cut is a small price to pay for the wonderful natural show that revolves around the food provided by milkweeds to insects. In addition the summer grasses that regrow after the fields dominated by fescue are cut provides an abundance of seeds, insects and cover for birds during the rest of summer, and the upcoming fall and winter.

Bill Dunson, Englewood, FL & Galax, VA
wdunson@comcast.net