Q&A: They’re Orange and Black But Not Monarchs. What’s Eating My Milkweed Plant?

large milkweed bug nymphs

Photo: Beth Bukoski, University of Maryland Extension

Q: I found these orange bugs all over the milkweed I planted for Monarch caterpillars. What are they and what, if anything, should I do about them? I don’t want to harm other organisms.

A: What you have here are nymphs (juvenile stages) of Large Milkweed Bugs (Oncopeltus fasciatus). At this time of year, it is common to see these insects on different species of milkweeds throughout Maryland. The gray and black “insects” in your photo are actually cast skins of the young nymphs. Large Milkweed Bugs go through five instars (phases as nymphs) and shed their exoskeleton at each phase until they become fully developed adults.  

These bugs push their beak into developing seeds inside the milkweed seedpods, insert a digestive enzyme, and then suck out a liquefied meal. In doing so, the bugs consume toxic chemicals from the plant that render them distasteful to predators.

Unless you intend to save the milkweed seeds, no control is necessary. Large Milkweed Bugs are primarily a nuisance pest, and they are present on milkweed pods for just a short period of time. Like the Monarchs we hope to attract with milkweed plants in our gardens, these insects are migratory as well. The adults do not survive our cold winters. They will be on their way south as the daylight hours decrease and temperatures cool down.

By Christa K. Carignan, Coordinator, University of Maryland Extension Home & Garden Information Center

Have a plant or pest question? University of Maryland Extension’s experts have answers! Send your questions and photos to Ask an Expert.

References and Additional Resources

2 Comments on “Q&A: They’re Orange and Black But Not Monarchs. What’s Eating My Milkweed Plant?

  1. This article doesn’t answer the question where do butterflies go in the fall? Other than Monarch, who migrate? The swallowtail does not go back to the chrysalis stage, I am sure. Do the die?

    Like

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