According to my Stokes guide, the Pileated Woodpecker is the largest of the woodpeckers, crow sized 18". A while back I had a pair of them searching for grubs in the oaks in my front yard. they leave a pretty big hole after they are done. We have Acorn Woodpeckers too, they are the ones with the clown faces. They store acorns by making a hole just large enough to force an acorn into. There is one large oak that is half dead that has been turned into swisscheese by them, they also nest in it. They only use dead standing trees for this purpose. Eventually the dead trees fall and they have to find a new home. I have to make sure and leave the bird houses open otherwise they will fill them with acorns, then because the doors are too small for them they either try to open it bigger or they just abandon the acorns..
Gabby