Dogs with ear mite infestations often have black or brown crusty ear wax. Dogs with ear infections tend to have more reddish-brown or yellow wax build-up. Ear mite infestations are caused by parasites and result in ear wax build-up. Ear infections, on the other hand, can be triggered by bacteria, yeasts, or physical irritation. Vets can determine whether the dog ear wax contains ear mites by analyzing a was sample under a microscope. Namely, a dog with ear mites will have excessive ear wax build-up, while dogs with ear wax build-up may or may not have ear mites.