The symptom of worms in cats is that the cat is very thin and does not gain weight no matter what he eats. The cat will often rub its butt on the ground, which may be the itching caused by tapeworms in the body. If you see this behavior, you should deworm the cat. Because the parasites stimulate the cat's gastrointestinal tract and cause symptoms such as vomiting and diarrhea, this indicates that the situation is serious and the parasites must be dewormed immediately.