According to one calculation, the economic damage from invading alien species might be costing the global economy more than any other form of environmental disruption – $1.4 trillion a year. This episode of Nature Inc. is a keyhole into the price nations are paying for failing to stop species invasion. We feature a cast of leading villains: cane toads in Australia; zebra mussels and the Burmese python in the USA and love grass in Brazil.