Another possible pest

I have tiny black ants on my tomato plants. Should I do something about them or are they harmless?

By the way, thanks to those that identified my previous issue with aphids. The Safer's Soap worked like a charm and I also was able to get some white flies befor they caused too much damage.

I wouldn't worry so much about the ants as the aphids they might bring in. Be vigilent and keep an eye out for them.