Ants in My Rosemary?

I live in Italy. I have a small herb garden on my balcony. I've noticed that there are red headed ants living in my rosemary. I don't mind as long as they are not harming the plant. The plant seems not to be suffering at the moment. If I am to get rid of them, any suggestions?

I am not familiar with ant species of Italy. They might be a carnivorous species and therefore useful by eating any other insects on your rosemary. Or they could be a farming species that carries aphids or scale insects onto your plant or onto the roots and protects them there in order to "milk" them for the plant sap they suck out of your plant. I would suggest you spend some time watching the nest and see what the ants bring into it to guess what type of ant they are.
To get rid of them, coat the soil and the bottom of the plant with the dust of diatomaceous earth. Repeat when the dust gets washed off by rain or watering.