This cardiac glycoside acts as anti-predator chemical defence for the milkweed. Rather than being harmed by the glycosides, the larval form stores it in its body. The chemicals are retained in the adult Monarch. This chemical acts as defense for the butterfly, because birds find monarchs noxious, and avoid them. The viceroy butterfly is a mimic of the monarch, having the approximate markings of the Monarch, but none of the toxic glycosides.
Birds also avoid viceroy butterflys, although they are good to eat.
Protective coloration is much more easily observed in a zoo. Although the animals may be displayed in simplified zoo settings, think of the habitat from which they came. Ask the zoo personnel if you need information as to the background coloration of their natural habitat. The tremendous variation in snakes make them particularly useful in studying the evolution of body patterns to blend in with the surroundings. For example, the sandy colored sidewinder rattlesnake of the desert southwest has vagrant black spots that blend with the pebble and sand habitat in which it lives, while the much larger dark and white pattern on the African Gaboon viper matches the sunlight mottled leaf covered floor of the equatorial forest.