… [N]utria are distinctly rat-like in appearance, with long naked tails and vivid orange buck teeth. And they are big – up to 20 pounds. They can consume 25% of their body weight in vegetation daily and despoil up to 10 times that quantity. They’re vectors for a variety of diseases and parasites, and they burrow incessantly, posing a significant risk to levees. … Agency [California Department of Fish and Wildlife] staffers have trapped thousands over the past seven years, but the doughty animals have maintained a steady, seemingly inexorable expansion in range: north to the Suisun Marsh and perhaps beyond, east up the drainages of at least two rivers that feed into the San Joaquin Valley.