Are earth worms poisonous to dogs?
According to AKC (American Kennel Club) the earthworms be avoided b/c they may carry parasites like roundworms:
'While bacteria could cause stomach upset in your pet your biggest worry should be roundworms. The eggs of the roundworm (Toxocara larvae) can be left behind in soil by other dogs or wildlife and then ingested by the earthworms. Then once the earthworms are eaten by your dog, he runs the risk of getting the common parasite. Puppies are quite susceptible to getting roundworms, especially from their mothers. But adults can get them too. Check your dog's stool for spaghetti-shaped worms for the main telltale sign of roundworm infection. If your dog does get roundworms, don't despair, working with your vet on a de-worming protocol will usually take care of the problem.'
No. If your dog ate one, don't worry about it.