Roly poly or pillbug, Armadillium vulgare, on edge of thin, yellow sheet of paper. Pillbugs are common backyard inhabitants around the world. They are called Pillbugs because they can roll into a ball (like an old-fashioned pill) when they are disturbed. A close relative, the Sowbug, looks similar but is a little flatter and can't roll itself up. These animals are actually crustaceans, like crabs or lobsters, and just like these underwater crustaceans, they breathe through gills instead of lungs. The gills, located on the underside of the Pillbug, must be kept slightly moist -- that's why you usually find these animals in damp places. - information found on the internet.