Fly worry can cause more trouble in some pets than others. In dogs a traditional sign is crusting on the ear tips, which can be quite painful. Repellents should be used to prevent further fly bite or the dog should be kept inside in a screened environment. If your dog suffers from apparent fly worry, apart from instigating appropriate therapy it is important to check the lips, genital area and feet for any signs of disease, because a combination of disease in these areas can sometimes be a sign of more serious disease of other causes. In dogs, repellents containing a pyrethrin ingredient applied regularly (licenced for use on dogs) are usually the best. There are very limited options for cats as they do not tolerate most of the drugs which repel flies.