I don't know much about gardening, as you may have noticed, but I do know that you should deadhead your flowing plants to make them have some more flower. Only, someone, or something got there before me. Not slugs, I reckon, unless they had cleared up their slime as they left.
I lifted up the planter, and a hundred million woodlice dropped out to join the wriggling mass that had been sheltering under the pot. Rather like a scene from "Men In Black", only that time they were cockroach sort of horrors.
extract from Wikipedia
Woodlice as pests