Hi everybody, i need you guys help on this one, my dog was a normal dog until today, today i noticed he was cleaning his butt with his tonge, so i check it to see if there was something wrong and

and Oh my god!! he got a small hole under his anus!! the hole is aproximate the size of this red face,

anybody know what could be the cause? please help me, Im really confused on this!! maybe a spider bite him?, or worms cand do this? im gonna take him to the vet tomorrow, but anyone have any idea?????