It depends on what size they are and if they are leaking any fluids. They might be a sign of an allergic reaction to something your cat eats or touches. If they start to really bother your cat or you, I suggest you see a vet to find out for sure what they are.
Also it could be a flea mound. My cat has had one before. If you leave it alone it will go away. This happened when she got fleas, because she is an indoor cat but she got outside and i guess they just jumped on to her.
If the worms look like white rice, then they are probably tape worms. If they are longer, they are probably round or hook worms. Either way, your cat needs to be wormed. If the worms found in your cat's stool are tapeworms, your veterinarian will have to provide a prescription dewormer like Drontal or Droncit to kill the worms. Other types of worms can be killed with regular heartworm prevention or over the counter wormer.
You should take it to the vet ASAP and have him/her checked it could be something as simple as a food allergy but it could also be something more severe... all those symptoms could be indications of Kidney failure... which could be brought on by Feline Lukemia,FIV, FIP or a number of different other aliments as well. Age can also place a part in why these symptoms are occuring. Again consult you vet...