Biting paws is most often a sign of allergies; it can also be a sign of mites, but that's less common. Bc he bites, his paws get moist - and yeast can then overgrow btwn the paw pads. It could be just dirt, but it could also be yeast. I'd bring him to the vet to both rule out yeast and to address allergies (which can have a domino effect if left unchecked).
