I can not think that ants and worms would be all a tiny duckling needs, but this may not even be related to what is going on now, Do you know of a rehabber in your area? I would suggest taking the little one to them.They know how best to deal with injured or sick wild birds. You could try some infant vitamins with out iron some have found that helps with some of the symptoms your seeing .
Agreed - this is why I am so quick to suggest that someone get in contact with a licensed animal rehabber on all the "I just *saved* a x, y or z" -- the fact of the matter is that they require special care from someone with the experience and knowledge not only to provide the physical needs of that species, but to do so in a way that respects the wild nature of the species and allows for the best chance of a successful rehabilitation and release - something most well-intentioned people are simply not in a position to provide.
Don't feel bad, he was probably sick when you found him. If you ever need to find an avian vet, try this link:
