At least that's what I think it is. See this

I came back from walking Bobby and found THIS hanging off a tree next to the garden shed! Looks like something out of a horror flick but it seems to be two slugs copulating. I went in to have breakfast and when I came out later it was all gone.
And here's a close up

A close-up of the intimate couple. I'm guessing here that the large sack underneath them is full of fertilised eggs or larvae, or some such.
This has really thrown me. For the first time ever here there's a slug problem. I see their trails everywhere. The sneak under the front door and crawl (slide?) around the loungeroom after midnight (how do they know). When I encountered the two slugs this morning I was taken aback but fascinated. When I looked around I could see lots of what looked like snail trains on the trees around the garden shed. So I have to ask -
DO SLUGS LIVE IN TREES?!