|I think this is an Arion rufus|
I did buy a bait trap for slugs and snails from Amazon, which should arrive today, designed as a rather humane way to kill slugs and snails. It has three wells in which the gardener is supposed to pour some beer in order to drown the slugs. They are attracted to the smell, and the book I am reading from the library has some interesting tips about beer and gastropods: apparently they much prefer Budweiser to other beers. It's been awhile since I bought that beer, but I'll give it a try.
The book is called The Secret Lives of Slugs and Snails: Life in the Very Slow Lane. The author suggested that I go out into my garden early in the morning to see if I could find any of my unwanted pests, which I did, and the guy in the picture is, I believe, an Arion rufus variety. Yes, there he was, hanging out happily in my tattered plant, so I tapped him on the back and watched him curl into a ball. Then I picked him up and threw him over the fence. After having learned about these gastropods from the book, I just couldn't bring myself to kill him. At least he'll need to navigate over the hazelnut shells again. By then, hopefully, my plant will have recovered enough to survive.