The Lepidoptera, especially the butterflies, are known for the beautiful colors and patterns of their wings. Red, yellow, black, and white pigments are found in the scales; the blues and greens, and the metallic, iridescent hues found especially in tropical species, are caused chiefly by refraction. Some butterflies are protectively colored to match the environment. Many conspicuously colored species are distasteful to birds, which learn to avoid them, and others are protected by their resemblance to the distasteful species (see mimicry). Among the most beautiful butterflies are the swallowtails, found all over the world, the monarchs, and the peacock and tortoiseshell butterflies.