Ants do not eat plants. Not any of them, never. Ants are mostly carnivorous, some eat seeds, and only few tropical and sub-tropical species like Atta or Acromyrmex feed on special fungus, and use leaves to feed this fungus. So, if you would say that aliens or fairies eat your plants it would be more likely truth. Large carpenter ant (Camponotus) colony can damage old trees (or wooden houses). Ants often tend aphids and defend them from predators, making them more numerous, so this is the only ant activity against other plants. But aphids would be there anyway also without ants. But, in other hand, very large quantity of ants in garden often indicate presence of numerous aphids (including root aphids! They're hard to spot) or other, unidentified insects, which may be real pests. Ants hunt for every insects except of their aphid flock, so they actually defend the plants from any other, often much more dangerous, pest (maybe they think you are going to damage THEIR plant, that's why they attack you

) and help controlling the number of other insects. There are gozillions of potential garden pests, many of them are hard to detect, but whatever is damaging your plants, it's not the ants.
We'd like to help you with ID of your guests, but I'm afraid most of us aren't familiar with American species. A good photo would be very helpful, though.