I am in the process of repainting my exterior window frames. In one, about four feet off the ground, I've found holes in both sides of the frame. The holes are about two inches high and half an inch wide, and the deep -- seems to be all the way through the wood. The wood for an eigth of an inch around the holes is dry and soft. Any ideas what could have caused them? I want to make sure nothing has burrowed into my walls before I seal them and paint over.