Which invasive species poses the biggest threat to California? The answer depends on who you ask. A desert ecologist might point to the Sahara mustard working its way north to fill the Colorado and Mojave deserts with tinder. Her counterpart in Sonoma County might say Scotch broom, or gorse. Urban birders might point at starlings or outdoor cats, anglers at giant reeds, foresters at the sudden oak death pathogen. A jaded environmental activist might say humans since we brought all the other stuff with us, ignoring the minor detail that humans are native to California.