Do they have a sense of smell?
Our rear patio is completely enclosed by a wall that's about 3 foot tall on our side, and as we are on the side of a hill the other side of the wall is about 10 foot.
I quite often put food out for visiting cats and we some times gets slugs eating it. But last night was horrible there were about 6/7 of them, about an inch wide and about 4/5 inches long. No idea where they come from, but we are out in the country. I just wondered if the smell attracted them.