The chewed foliage reminded me of grasshopper damage but the frass/excrement definitely looks like that of a caterpillar, or possibly a slug. If you aren't seeing any pests on the porch in the daytime, it's most likely a caterpillar, or slug feeding at night. After dark, take a flashlight out onto the porch and shine it around your plant(s); closely check the potting soil and also lift a few leaves to check the undersides. I bet you will find the pest!