snail alert!

Recently I've seen a lot of large snails around the apartment complex where I'm house-sitting, but I usually only see one or two at a time. Well tonight I walked by -- for lack of a better word (this will be addressed later) -- a LOT of snails... there must have been about 40 of them, no joke, all in one small area. The picture above only shows a few because the darkness made it hard to capture the grand scale of the snail gathering that was going on. It looked as though someone had collected all the snails in the complex and put them together for a party or something... but who would collect snails, none-the-less throw them a party?
So here's my question: what is a group of snails called? My research has irrefutably shown that snails are social mollusks... but are they a herd? A flock? A school of snails?
Snail experts of the world: your help is urgently needed!