It sounds like earwigs. Try this. Dampen a double sheet of newspaper and roll it into a tube. Lay the tube near the plant when the sun goes down. Check the tube in the morning by unrolling it. If there are earwigs in it that is the cause of the plant damage. The pattern you described does not truly relate to snails and slugs, but you could put a pie pan of beer out near the plant in the evening and see if there are any snails or slugs in it in the morning.