Hi! It is very possible that the centipede...or millipede that your dog consumed is making his tummy sick. If he will still drink water, that's great.....you can add 1 tsp of pancake syrup to his water bowl to encourage drinking and help keep the blood sugar up if he is not eating. If he IS eating, give him bland food, such as lamb & rice (dry or wet....whatever he is used to) or boild some chicken and mix it with some cooked rice to feed him. You can actually withhold food for about 12 hours to help the digestive system rest, as long as he is drinking. If he continues with the diarrhea and/or he begins to vomit, as well, he will need to be seen by the vet. He may become dehydrated and may need re-hydration.
Let me know if you need more information! Donna RN