Beaver (Castor canadensis), have been kicking around in North America for 2 million years. Ecologically they do all sorts of great things: their ponds ease flooding downstream, and support large numbers of bird species, fish, amphibians, and otters. They're what's called a keystone species, as in the keystone to an entire eco-system. But they're also the world's second largest rodent and a nightmare for property owners. Humans and beavers have a long history together because they like to live in the same places, but the way we've built our infrastructure has almost guaranteed our two species will be locked in eternal conflict.