Licking can be an habit. but excessive licking and scratching will cause skin rashes. The reason could be our dogs bore and needs more physical exercises, or could be food allergies or a sign of vitamin and mineral deficiencies. Like you say, could also be mites or ticks causing the scratch and licking. Excessive licking and scratching will causes infection to our dog.
my suggestions :
1) take him to the vet for complete check up
2) check on the contents of the dog food u feed him. most of the vet will suggest switch to lamb and rice, you may try to switch and see if that is the cause (food allergies) to him.
3) giving him supplement and vitamins suggested from the vet after the visit.
4) bring him out more often and give him more exercise or join in some course that available so that he will tired and forget about the licking.. haha
5) spray unpleasant liquid (non poison) on the spot he used to lick.
hope this help..