It would not be ants as they do not eat foliage. The most likely culprit is slugs on your Hostas. Can you take pics of the damage?

Thanks so much for the response - here are some pics of the hostas, as
well as campanula, lilies, hot pepper plant, basil plant and a few other
flowering plants. I should also mention that these plants are not in the same locations - some are in backyard and some in the front. BTW can someone tell me what kind of lily that is (red one) please?

Looks like slug damage, Go out after dark with a flashlight and look around.

Thank you. If they are slugs, what can I do?

Lay a board or shingle in the garden and they will congregate under it during the day and you can kill them. Or, put out a saucer of beer and they will crawl in and die. Also, there are commercial slug baits you can use but make sure they are safe around pets.