The Downy Woodpecker is the smallest woodpecker in North America. He's maybe 6 inches long. It would probably take him a decade or so to do any real damage to an apple tree.
I see I'm getting some referrers from a site called INSPIKS. If you came from there, you should know that there is nothing very mysterious about the evolution of woodpeckers. Googling on "evolution of woodpeckers" will find a lot of useful material from actual ornithologists and biologists. I like this little snippet: scienceblogs.com/tetrapodzoology/2008/08/woodpeckers_barb... to start with, and there's also a nice discussion of the woodpecker's tongue at www.talkorigins.org/faqs/woodpecker/woodpecker.html .