In addition, areoles can produce spines of many different types to suit their needs. A typical areole may have one or a few long, sharp central spines, which serve as the primary defense. Beneath them are often numerous (10 or more) smaller, radial spines produced around the edge of the areole. These may serve as a secondary defense against small creatures that can get past the central spines. In some species, though, such as "Cephalocereus senilis", the tangle of hairy radial spines serves to shade the plant and retain a layer of cool, humid air next to it.