What kind of bug is this?
These are milkweed bugs. Typically found on milkweed plants. In general, they do not do much damage to milkweed plants. Treatment is not recommended as you can do more damage to the Monarchs that are using the plant. If objectionable, you can hand pick instead of relying on chemicals.
While they maybe on other plants in close proximity to milkweed, they do not feed on the other plants.
Remove leaf litter and spent stalks in the fall to eliminate overwintering sites.