I saw quite a few worms and two small black slugs earlier today, but one worm that was clearly still alive appeared to be at least a decimetre long! Have you ever studied any worms or slugs for a while, meaning watching them move very slowly for at least quite a few seconds, let along while the sky was foggy if not drizzly or the ground still wet from the rain?
I actually saw a few huge worms yesterday too. One worm looked longer than my hand as it slithered or however worms move. They make this stuff called humus (I think it's pronounced with a long U?) which helps the soil be even better for plants.