Plague threatens prairie dogs, endangered ferrets Under a hot sun, a crew of four buzzed across the prairie on all-terrain vehicles a few miles from the pinnacles and spires of Badlands National Park, pausing frequently to spray white insecticide dust into prairie dog holes. And when the sun went down on many summer days, another crew took over to shine spotlights across the grasslands, trap endangered black-footed ferrets and vaccinate them against the sylvatic plague, a killer spread by fleas that threatens the ferrets and their main food source, the black-tailed prairie dog. Officials from five federal agencies and a number of conservation groups hope the double-barreled approach will stop the spread of plague and save prairie dogs and ferrets in the 20-mile long Conata Basin, a portion of the Buffalo Gap National Grasslands that lies just south of the Badlands in southwestern South Dakota....