Can someone tell me what these catepillars are?

I have a variety of lillies in my garden being eaten by caterpillars. These things only seem to eat lillies but they strip the leaves completely. These caterpillars don't look like caterpillars at all. They look like the poo that comes out of an earthworm. I actually thought they were poo from a slug or something but this morning I took a closer look when I thought I saw one move. Look like a 1/4" long black blob with a Caterpillar head. I sprayed soapy water on them and I think they must be dead as they're in the same spot as this morning. Does anyone know what they are and how to get rid of them?