I have a 1 year old male cairn terrier that will eat snails, bugs and whatever else he may find in the yard.  Yesterday he ate a snail from the yard (no pesticides or bait) was used here so the the snail was not poisoned.  However, my dog has vomited, and is been ill since.   He is drinking water, eating and going potty okay but is lethagic and overall not feeling well.   I understand that if snail bait was used he would be poisoned but it was not---can just eating a snail cause these symptoms? 

I would go to the vet as eating snails slugs etc can make them quite ill as this happened to one of mine a few years ago and I dont use slug pellets etc either better to be safe than sorry.

It could be you have neighbours who've used bait :(  I'd get him seen by a vet, and discourage him from doing it in future as snails can carry worms (I think it's lung or heart worm, but I can't remember.......)

its lungworm digger, my dog got it last year so I'm dreading the 'snail season' again :(  Guest take your dog to the vets asap, or it could be as suggested bait from your neighbours,

I always get confused with horses and dogs - I know heart worm is a problem in the States and lung worm can be a problem for horses kept with donkeys that aren't wormed - but then I am easily confused ;)

and me :) must be my age ;) and the fact I try to take in too much info and then muddle it all up!

And heartworm too.  Not normally found in the UK there appear to have been some cases thought to be linked to eating snails
http://www.parkvets.com/clientinformation-angiostrongylus.html