intense itching

Question
i have three large mixed breed dogs.  recently, all three have started scratching, with two of them biting so much at their tails and that area that they have created bald spots as well as patches of scabby and bloody skin.  we have found no evidence of flea infestation and hesitate to treat them for fleas if they aren't present.  what else could their itching be caused by?  they are all inside dogs.

Answer
There may be something common to their problem like sarcoptic mange. There may be a fungus in the carpeting or they may be picking up something outside when they go out to eliminate.  There may also be allergies to certain things that are prevalent in the environment right now. Ask your vet to look at the dogs to see if this is an individual problem in each dog or something that might be contagious.