Thanks for your comments and suggestions! After reading here on the forum about a trick to combat snails/slugs, I added a few slices of potatoes in the pot amongst the copper pennies and orange slices!! I hadn't seen any slimy snail tracks on the plants but thought I'd give it a try. It worked! Today I have caught several tiny tiny snails, barely visible to the naked eye. One was big enough (<2mm) to photograph. They are too small to leave any visible tracks behind but they sure have an appetite!!! Amey and others who suspected snails, you are absolutely right! My phals are going to have potatoes all over them for a little while and if need be, I use Ferric phosphate on them. Thanks Amey for naming the product to use.
Here is one of the culprits. Can you believe I flicked it outside and didn't even kill it....!