I just had an exterminator out to get rid of one of those that was about 2 foot around. They are called bald faced hornets and are a member of the wasp family. They are black and white and their stings are extremely painful. They will swarm to protect thier nests. If it is an area that you don't go near I would leave it alone as they will abandon it in the winter. Unfortunately my nest was in a bush right next to our garden. Mike