Posted: 27/07/2013 at 16:32
Have the ants made a nest in the bottom of the pot, so you are seeing them coming in and out of the base, or are they crawling over the plant? I have terrible trouble with ants nesting in the roots of my plants and killing them by digging out all the soil and drying them out. If that is the trouble, just water a lot to persuade them to move.
If they are climbing over the plant, as nutcutlet says, look for aphids because the ants are feeding on the honeydew they produce and protecting them from preditors. The aphids will be the things damaging the plant.