Butterflies are often polymorphic, and many species make use of camouflage, mimicry and aposematism to evade their predators. Some, like the monarch and the painted lady, migrate over long distances. Some butterflies have parasitoidal relationships with organisms including protozoans, flies, ants, and other invertebrates, and are predated by vertebrates. Some species are pests because in their larval stages they can damage domestic crops or trees; other species are agents of pollination of some plants, and caterpillars of a few butterflies (e.g., harvesters) eat harmful insects. Culturally, butterflies are a popular motif in the visual and literary arts.