Feral pigs such as this one have come to southern Ohio. The problem: They root up crops, erode soil, and muddy streams through their wallowing. (An ODNR Web page calls them “living rototillers.”) Also: They eat the eggs and young of ground-nesting song- and game birds, the young of deer and livestock, and the acorns that deer, squirrels, and wild turkeys require. And they carry pseudorabies and swine brucellosis, diseases that livestock, wildlife, and pets can catch. Read more on Ohio’s invasive species. (Photo by Makro Freak via Wikimedia Commons.)