Budapest slug mating

It's the last day of October: damp, windy and mild. As I go out into the garden, pondering upon the impending winter lockdown, I find two Budapest slugs circling on a cherry leaf on the ground. Budapest slugs remind me of hedgehog poo, dark and shiny and all the right shape. If they had been on the path pebbles I would have easily missed them. I watch them for a few minutes. They keep slowly circling, head-to-tail for a while as they follow each other's mucus trails. This is slug courtship and it happens at slug pace. It's 10:40 and it doesn't look like much is happening any time soon. I regularly go out to check on them for the rest of morning and afternoon. As I'm typing this, I grab a torch and decide to check on them again. They are still there, exactly in the same position as 3 hours ago. 

10:42

11:06. The pair have moved onto the path pebbles now, the circling has stopped. They are now finding each others genital openings at the right side of their heads.

11:20. Copulation proper appears to start.

12:20

14:31

17:20. Very little change in the last few hours. The slugs are now entwined and practically immobile.

I pick the Slugs of Britain and Ireland and check the species account for info on their mating behaviour. Of note is that they are mainly subterranean and active year round.

This quote is fitting: 

"in winter adults are often found almost motionless, mating. Mating lasts many hours and involves the production of elaborate spermatophores"

I wonder if they'll be there tomorrow.

More information

Rowson, Ben, James Turner, Roy Andreson and Bill Symondson Slugs of Britain and Ireland. 2014. FSC Publications. AIDGAP.