This is a Yellow slug crawling through a wormery that I saw at the London Green Fair recently. I mistakenly called it a Leopard slug at the time, not being particularly familiar with slug species and assuming that this spotted thing must be one. But now I know better having looked it up.
However if you've never seen a video of Leopard slugs mating, I suggest you do so right now - but not if you're eating or otherwise easily repulsed. It's truly bizarre.