A large nutria feeds on aquatic plants in a pond in Roseburg, Ore., on Friday, Sept. 9, 2011. Nutria are semi-aquatic rodents originally from South America. In most cases they are considered an invasive pest species in North America. Feral population have been reported in 40 states. According to a report from Portland State University, research suggests that the highest population densities of nutria in the world may be in Oregon's freshwater marshes. Check out more or my nature pictures. Reprints are available from the gallery.