This is commonly called "fly strikes." It may look almost as though the dog is striking at flies that are not there.

This is often caused by vision loss, age and seizures.

It also could be a sign of liver shunt disease.

You can read about seizure problems and causes in dogs here

http://www.geocities.com/labsr4ulist/pawseizures.htm

If you can catch the behavior and video tape it, even if it's only for a few seconds, this will help your vet to help your dog.

Some dogs do it and it means nothing so I would not get too worried. However, I would try to document the behavior at your first opportunity.

There is not much that you can do at home except maybe try an herbal remedy called homeopet (www.homeopet.com). It's a natural anxiety reliever so it will help if this is an anxiety disorder or the dog is troubled and anxious.

Let me know if you still have questions.

It really doesn't sound like fly biting. If she's looking at her tail, she might be experiencing pain in that area. The most common cause of pain around the tail is anal glands that are overly full or infected. This can be pretty painful. In some situations, the glands can even get infected.

I would see the vet to have the glands expressed and then go from there.