I have a few different milkweed plants (Asclepias spp.) growing on our property, and they’re among my favorite native perennials. I love common milkweed for the monarch butterflies it attracts and the swamp milkweed for its beautiful pink flowers.
One of the more unique features of these interesting plants are the fascinating relationships they have with the insects that feed on them. For the monarch, milkweed is the larva’s sole food source. The monarch caterpillar spends its life feeding on the leaves of milkweed until it’s ready to build its chrysalis and morph into an adult. The red milkweed beetle (Tetraopes tetrophthalmus) also uses members of the milkweed family as its primary food source. Neither of these insects causes significant damage to the plants, and both of them incorporate the toxins contained in the foliage of the plant into their bodies and use it as a form of chemical defense. Milkweed beetles and monarch caterpillars are extremely distasteful to birds and other insect predators.
Milkweed bugs are another host-specific insect that utilize various species of milkweed for food. They, too, absorb the toxins and are distasteful to predators. I’ll often find milkweed bugs on the seed pods of my butterfly weed (another member of the Asclepias genus) in autumn. They look a lot like box elder bugs with their reddish-orange and black coloration, and they don’t cause enough damage to warrant any treatment.
And still another insect that finds my milkweed particularly welcoming is the oleander aphid. This introduced aphid species is the one insect that can actually cause significant damage to milkweed plants. They literally suck the life out of my plants because their population builds far more quickly than the ladybugs and lacewings that keep them in check. I go out to my garden every few days and shoot these little yellow aphids off my milkweed plants with a sharp stream of water. I don’t want to use any pesticides—even organic ones—on the plants, as I don’t want to risk harming any monarch eggs or caterpillars there. Although my oleander aphid infestation gets pretty severe every year, it has never once killed the plant.
Despite the handful of insects that call milkweed lunch, this is an incredibly worthwhile garden plant that deserves a place in every yard.