Sunflower bugs - how can i get rid of them?

I've planted from seed those huge sunflowers. I have 3 that have grown loads they are about 3 foot now, although on one of them there seem to be hundreds of black bugs, tiny ones, maybe ants.. all in one area but hundreds.. and that particular sunflower is drooping and looking quite dry.. is there anything i can do to get rid of these bugs??