Photo by Jessica Walliser
Milkweed bugs, from nymph to adult, are distinguished by their black-and-red color pattern.
Last spring, I planted a handful of different types of milkweed in my garden. They hosted several monarch caterpillars this year, though I was never able to find any of the chrysalises. Now there are some different insects on the plants, and I thought you might be interested to learn about them, just in case your milkweed plays host to them, as well.
The red-and-black bugs I found on my milkweed pods are conveniently called milkweed bugs, and they are feeding on the seeds held within the pods. Milkweed is their primary food source, so it’s unlikely that they will harm any of the other plants in my landscape. These true insects hatch from eggs as tiny nymphs, then travel through five instars (or life phases) until they reach adulthood. They will shed their skin several times as they grow.
Sometimes it may seem like there are a few different kinds of insects on the plants because each of these instars looks a little bit different, though all milkweed bugs, despite their life stagew, have the distinctive red-and-black coloration. Milkweed bugs travel through this metamorphosis in about a month or so, staying attached to the seed pods during most of this time. They use a long, specialized mouth part to pierce through the pod and into the seeds.
Adult milkweed bugs have wings and can fly from plant to plant while the nymphs are wingless and remain fairly stationary. Milkweed bugs tend to group together on plants to feed, and sometimes several hundred individuals are found on a single plant. Neither adult milkweed bugs nor nymphs can bite or sting, so they are no danger to humans. They also have very few natural predators, as the sap of milkweed plants is extremely unpalatable and the insects take on this flavor as they feed.
The feeding of milkweed bugs does not harm the overall health of the plant and only reduces the viability of the seeds. They are a classic example of incomplete metamorphosis and watching them transform from nymphs to adults right before your eyes is kind of fun. (My monarchs, on the other hand, undergo complete metamorphosis where their larva—the caterpillar—look completely different from the adults. It’s a great lesson for both kids and adults and one we all need to understand and appreciate.