Some species use toxic chemicals to deter predators. The South American dendrobatid frog has very poisonous secretions on its skin and the monarch caterpillar picks up toxins from the milkweed plants it feeds on. Toxic species are often brightly colored which advertises their toxic nature. This is called warning coloration. Predators who try to eat toxic species have a bad experience and learn to avoid them. In some cases predators may have an innate aversion to certain color patterns.