Accepted Answer

The ants should not be toxic to him even if he ate them but eating spoiled food can cause digestive upset in a dog.
This may be due to intestinal upset from a new food or treat, intestinal parasites such as worms, coccidia, or giardia.
This could also be due to a swallowed non food item, ingestion of something toxic including plants, mushrooms, chemicals etc.
With a small dog another issue may be pancreatic inflammation which you can read about here
http://www.peteducation.com/article.cfm?cls=2&cat=1580&articleid=335
So seeing the vet to find out what is going on should be a priority.
An over the counter med you might try would be Pepcid or Tagamet or Zantac.
Be sure to tell the vet when you see them if you use any of these.
You can read about dose amounts (and cautions) scrolling down on the pages here
http://www.petplace.com/drug-library/cimetidine-hcl-tagamet/page1.aspx
http://www.petplace.com/drug-library/famotidine-pepcid/page1.aspx
http://www.petplace.com/drug-library/ranitidine-hcl-zantac/page1.aspx
If that helps then you can see if some bland food and plain pedialyte added to the water bowl will help.
I would suggest trying boiled chicken meat or hamburger with the fat drained off, mixed with really well cooked rice in a ratio of 1/3 meat to 2/3 rice to see if that works. It's not a balanced diet but OK to use for a few meals while working on controlling digestive upset.
Hope this helps you!

Expert:	NancyH
Pos. Feedback:	99.5 %
Accepts:	19876
Answered:	5/27/2008

Dog Expert:Rescue, Train,Breed,Care

30+ yrs dog home vet care & nursing, rescue, behavior&training, responsible show breeding, genetics