First, stephen, can I say it would have been best to add both your thanks and this response under your original question, as if you were answering yourself, beneath everyone else's answers - I saw this question today and had to go to your profile page and look at the earlier question to know what you were talking about.

Ants do not damage plants - they don't eat them and they don't strip bark from them. If there are ants on a plant, its usually because the plant is infested with, commonly, aphids, or sometimes scale insect, and the ants are after the honeydew produced by these insects. The other possibility to explain ants on potted plants is there's a nest in the pot - that needs dealing with or they'll chew through roots just to make more room if they need it.
I'd like to see a picture of the damage to the bark, but one possibility does spring to mind - we had a very warm March, and wasps had started to function - wasps look for cellulose rich plant material to bite off and chew up to make their nests with, so that's a possible explanation. Be better if you could post a photo though.

Just out of interest, I did once lose a rosemary bush when ants nested underneath it.

And I a rhododendron in a pot - the whole thing was one big ants' nest when I turned it out...

:((