My gerbils did have mites, it was confirmed by a vet and I did see them. Since they such the blood of animals they get pretty big and are brownish red, and when you squeeze them blood comes out. I saw them crawl up and down my wall and crawl around in the tanks. Perhaps there are different types of mites, but I saw them and that is why I brought them to the vet, and the vet did confirm it. Also, the last time Dora's tank had it, my boyfriend helped me clean out her tank, and my boyfriend got one on him, and he saw it too, and he squeezed it and blood came out of it.