They are the ones that can carry lyme disease. If you get bit by a tick with lyme, you will usually get a red ring around the bite site. Beware doctors really don't know much about Lyme disease. If you think you have symptoms, read up and be specific with your doctor. Also, I understand that the test for Lyme Disease is unreliable.
Wood ticks can carry diseases, like any biting insects but are less of a threat.
They are also much bigger and have a bite that you can't feel. We are seeing more and more deers coming into our yard thus more ticks. I knew something had to be done. My husband went to Lowes and there is something made by Bayer and it has worked for us. We have not seem a tick since.