Plant Profile: Milkweed

Some of our beloved summer flowers are those from the milkweed family. We like them for their pretty flowers and because they are the exclusive food for America’s most popular butterfly, the monarch. We grow a couple of native species and the tropical Asclepias curassavica, which dies in New York as soon as it gets cold, but can be easily grown from seeds.

Butterfly weed (Asclepias tuberosa) on the left and the tropical milkweed (A. curassavica) on the right.

Milkweed has its name from a white latex-containing sap that also contains toxic heart glycosides. This poison protects the plants against herbivores. Some insects, however, are adapted to eating milkweed and don’t get sick.

One of them is, of course, the monarch butterfly, whose larvae eat nothing but milkweed. But there are also aphids and the milkweed bugs (Oncopeltus fasciatus) who live on the sap of milkweed plants. These insects do not only thrive on the poisonous milkweed, they also store the toxin and are thus becoming poisonous themselves.

Aphids on our butterfly weed (left) and a monarch larva (right).

Large milkweed bugs are found on the seed pods of our tropical milkweed plant. The photo on the left shows nymphs of different sizes, the photo on the right an adult.

Different from many other insects that are green or brown and blend in with their environment, the milkweed specialists are quite conspicuous with their bright red or yellow colors and black patterns. These colors says clearly: “Don’t eat me! I will make you sick!” Birds that have tasted one of these insects remember the experience very well and do not make the same mistake again.

A honey bee enjoys the nectar of our tropical milkweed (left). The flowers are also visited by tiny wild bees (right).

The nectar of the milkweed plants is not poisonous and is collected by our honeybees and by several species of wild bees. Monarch butterflies like it, too.

LaGuardia Corner Gardens is currently visited by many monarchs who are migrating from Canada to Mexico. This is clear sign that summer is over and fall has arrived.

A migrating monarch had stopped in the garden to refuel for the long flight south.