A few weeks ago, we had four adult milkweed bugs, Oncopeltus fasciatus, on our balcony terrarium milkweed plants. I pointed one out in a photo with its neighbors, a Chinese mantid and a crab spider.
One reason we grow milkweed is that it attracts interesting insects, such as Monarch butterflies, bright orange “dancing” aphids, and these milkweed bugs. All of them are bright colored because they are full of bad-tasting chemicals from the milkweed plant, so they stand out to predators, who learn quickly that they taste terrible and leave the others alone.
These nymphs will feed on the developing seeds of the milkweed.
Steven E. F. Brown 