Kate Morgan writes
My daughter put a dish containing dried cat food on to her garden path,
about half and hour later she looked out and saw that the dish was
covered in slugs of all sizes, not only were they enjoying the cat food
but there were at least another 20 advancing up the path towards the
dish, how do they communicate or is it just the smell of the cat food
that attracts them.

Just the smell I think. As far as I know they're not social beings.
--
Kay