I have a group of these beetles on my dill plants. They might be black lady bugs, but seem too small at only 5mm. A positive ID would help be know whether to let them be, or remove them.
After some more research, I believe they are Ebony bugs (thyreocoridea), which some people once called Negro bugs. They have the white lateral stripe which helps identify them, and are known for eating flowers in the carrot family turning to seed like the ones I found. Hope they cause minimal damage.