Are the ants living in the soil media? There are several insecticides that will work against ants. You should be able to find one at any near by garden store. You can also use ant bait. This works well because the worker ants will bring the poison back to their nest, causing the whole ant population to injest it. You shouldn't see any more ants after that!
Thankyou for your response. I did not try an insecticide because I was affraid it would kill the plants, but I did put ant bait near and on each plant. I think Its working. I replaced the moss with new and I'm waiting to see if the ants come back.