The usual summer nasties..slugs and snails..Laura..If you have overhanging rims on your pots,check underneath them..a favourite place to hide..You will have to resort to using a proprietary control..I only use pellets in my pots..or maybe plant something else,they don't like..Pelargoniums ,for instance? I know how disheartening it is,but it's the old saying,prevention is better than cure..or at least trying to control them....good luck..