The larvae of both butterflies and moths exhibit mimicry to deter potential predators. Some caterpillars have the ability to inflate parts of their heads to appear snake-like. Many have false eye-spots to enhance this effect. Some caterpillars have special structures called osmeteria (family Papilionidae), which are exposed to produce smelly chemicals used in defense. Host plants often have toxic substances in them and caterpillars are able to sequester these substances and retain them into the adult stage. This helps make them unpalatable to birds and other predators. Such unpalatability is advertised using bright red, orange, black, or white warning colors. The toxic chemicals in plants are often evolved specifically to prevent them from being eaten by insects. Insects, in turn, develop countermeasures or make use of these toxins for their own survival. This "arms race" has led to the coevolution of insects and their host plants.