This was posted in the pig section too, but I thought it was interesting what it said about Michigan.
Even though they only estimate about 6,000 pigs there, they must be afraid of them getting a foothold there. They have instituted a "shoot on sight" order, meaning anyone with ANY type of license can shoot a wild pig if they see it.
http://www.foxnews.com/scitech/2011/02/07/oink-feral-pigs-growing-problem/
Pretty cool.